the present day. It is clear that some methods are necessary. Even if it
should be thought advisable that population should increase, it cannot
possibly be desirable that it should increase as fast as is possible. It
therefore falls to those who disapprove of certain methods to suggest
others. This problem is seldom faced by those who would dissuade men and
women from certain practices. The attempt to advise in these matters
without regarding the problem as a whole is strongly to be
deprecated.[1517]
Abortion is condemned on every hand, and we are thus left with
postponement of marriage, restriction of intercourse between married
persons, and the use of contraceptive methods as the means of bringing
about the limitation of families. There is much to be said for the
postponement of marriage for a certain period after the age of puberty.
That education should be completed, and that a certain experience of
life should be gained, before the choice of a partner is made and the
responsibilities of setting up a home are undertaken, are obviously
desirable. In order, however, that postponement of marriage should be
effective, it would require that the average age at marriage should be
so late as to produce many undesirable consequences. It seems certain
that, not only under present conditions, but under almost any conditions
of social life that we can picture, late marriage must be accompanied by
a system of prostitution and irregular sexual habits which nearly every
one agrees in deploring. Apart from this almost overwhelming argument
against late marriages, there are many other objections. It is not a
good thing on the whole for children that their parents, should be
beyond a certain age.[1518] Much can be urged with force against late
marriage on the lines that after a certain age the outlook and habits of
celibates so change as to render them less fitted to bring up a family.
As few will be found to advocate late marriage as the only method, we
may leave the matter at this point.
With regard to restriction of intercourse, the most important question
is whether it can possibly be effective. Very serious doubts arise on
this account when it is proposed to rely on this method alone. Late
marriage might be in practice effective because sexual desire would find
its satisfaction apart from marriage. Abstention from intercourse
implies that sexual desire will not find its satisfaction; on this
account it is likely that it can only be effective when accompanied by a
system of prostitution that we have already agreed to regard as
undesirable. Apart from this there are strong arguments against this
method founded on the undesirable psychological results of abstention.
It is in fact perhaps scarcely possible to think of a marriage system as
satisfactory in which what we must regard as the physical object of
marriage is not realized.
We are thus led to speak of the use of contraceptive methods and we may
glance at two sides of the matter—ethical and physiological. It is a
notable fact that all religious bodies, so far as their opinions can be
discovered, are strongly opposed to this method.[1519] This objection is
founded upon many considerations, of which the most striking is perhaps
that the method allows of, or rather that it encourages,
self-indulgence. Those whose attention has been drawn to the problem of
the causes of the progress and decay of civilization will not fail to
feel the force of any argument against the spread of habits which
encourage self-indulgence. But it may be suggested that the normal
exercise of any physical function can scarcely be called
self-indulgence. There is a mean in the satisfaction of physical
appetites, on the one side of which is self-indulgence and on the other
side asceticism. It is a question whether those who disapprove of these
methods because they encourage self-indulgence are not in fact demanding
an ascetic life. As a form of self-discipline there may be much to
recommend ascetic practices, but that is another matter. The fact is
that in the use of these methods there is nothing which necessarily
encourages self-indulgence. They make it possible to exercise a normal
function; they do not necessarily lead to its over-use. This would seem
to be without doubt the most tangible objection to these methods. The
other objections are on the whole rather of a religious than of an
ethical nature, and as such fall outside the scope of this book.[1520]
In addition to the ethical there is the physiological aspect of the
matter. There are several different methods employed to prevent
conception. It is a matter of great importance to know which of them can
be employed without causing ill health. With regard to this little is
known and opinions vary. More than this need not be said.
It is no part of the object of this book to advocate any particular
methods;[1521] it is only intended here to show what problems arise at
the present day from the quantitative aspect of the whole matter. It may
be suggested that upon the question of the methods of limiting
population it is desirable that there should be some consensus of
opinion. Man has not only to settle how far he is going to limit
population, but how he is going to do it.
6. We may now glance at certain questions which if they are to be
referred to at all in this part of the book are most easily introduced
here. These questions are not directly concerned with the quantitative
aspect of the problem; their importance lies chiefly in their bearing
upon the qualitative aspect.
It is a familiar fact that at the present day the birth-rate is higher
among certain sections of the population than among others. There is
reason to believe that this was also the case in some of the older
civilizations—notably in Rome. We may first look at the facts and
afterwards at the causes. Many investigations have shown that there is a
higher fertility among the lower social grades. Heron found that there
is a high average correlation between the birth-rate and conditions
which indicate a lower social grade, such as the number of pawnbrokers
per 1,000 inhabitants, the amount of child employment, pauperism,
overcrowding, and other indications of poverty and lack of
culture.[1522] Whether a differential birth-rate results or not in a
differential contribution to the next generation depends on whether
there is a differential survival rate, and if so, whether it compensates
for or not the differences in the birth-rate. The following extract from
the Report of the National Birth-Rate Commission throws light upon this
point. Using material provided by the Registrar-General for England and
Wales giving the births for 1911 classified according to the occupation
of the father, the following is the position:
‘Classifying into groups arranged in descending order of social grade we
have:
_Social Class._ _Births per 1,000 married males aged under 55
years._
Upper and middle classes 119
Intermediate 132
Skilled workmen 153
Intermediate 158
Unskilled workmen 213
‘The rate of mortality in the first year of life is also provided in
these groups, and follows the same order, viz. 76·4, 106·4, 112·7,
121·5, 152·5. If, however, we multiply the birth-rate by the difference
between unity and the proportion of deaths, i. e. the proportion of
survivals in the first year, the resulting effective birth-rates are
still in the same order, viz. 110, 118, 136, 139, 181, after the hazards
of the first twelve months have passed. We must conclude, therefore,
that the initially higher birth-rate of the lower classes is not so
reduced by heavier infant mortality that their effective birth-rates are
brought into approximate equality with those of the wealthier classes.
We have no material allowing us to extend the comparison to later years
of life; but equally we have no reason to suppose that such an extension
would change the order.’[1523]
All available evidence goes to support this conclusion, namely, that the
higher the social status the lower is the fertility, and that this
initial difference is not removed by subsequent differential mortality.
This is apparently true not only for England but also for other
countries in which the economic situation is similar, and is a
relatively recent phenomenon.[1524]
7. In looking for the causes of this differential increase as between
various sections of the population, we have to remember that, in
accordance with what has been said in the last chapter, we suppose the
position in regard to population in the nation as a whole to be ruled by
economic factors. If there is an increase, then we suppose that increase
to be somewhere about that which the economic situation demands in order
that the greatest income per head should be gained. It follows that
generally speaking the conditions we find among the mass of the
industrial population excluding the lowest class approximate to those
which are demanded; but it is possible that, just as the increase among
the lowest class is excessive, so the increase among the higher social
class may be too small judging from the economic standpoint. We have
here to ask what factors there are which bring about a lower fertility
among the upper classes, recollecting that this low fertility may not be
wholly due to an approximation to economic requirements, but may
represent a failure in adjusting increase to the economic situation.
Among the factors which bring about a low fertility in these classes,
those connected with differences in education and the age at which the
maximum income is obtained are the most important. Education is
continued in these classes up to an age at which men in the industrial
classes are earning almost the maximum wage to which they will ever
attain. Even when education in the ordinary sense of the word is
finished, there usually follows a period when the salary gained is low,
or when perhaps a premium has to be paid in order to obtain a start in
whatever profession is chosen. Doctors and barristers seldom begin to
earn until some years after their education is complete. Further, when
they do begin to earn, the income is often for many years low, and may
in some cases not reach the maximum until late in life. Among the
industrial population conditions are wholly different, and the maximum
rate of wages is soon reached. Whatever forces, therefore, may be
playing upon the industrial population, there are in addition the above
forces playing upon the professional classes which account for the lower
rate of increase among them.
There are also many other factors at work in the same direction. In the
life led by the upper social classes there are more numerous ways in
which the desire for relaxation, change, and pleasure may find
satisfaction than among the lower classes. Life is in many ways more
varied. This has an influence upon fertility in two ways. When a
marriage takes place among the upper social classes it involves to a far
more considerable extent than among the lower classes a renunciation of
much that has given pleasure hitherto. When a man marries and ‘settles
down’ he gives up, as a rule, many activities from which he had derived
pleasure before. Further, after marriage the possibility of indulging in
many of the pleasures which this varied life offers is often
incompatible with the bringing up of a family. Children are often in the
way. Again, though children are no longer the economic asset among the
lower classes which they were before the passing of the Factory Acts,
the possession of children is generally looked upon among those classes
as a support in old age when the power of earning has gone. Children, on
the other hand, among the upper classes have rather to be provided for,
and in any case are seldom regarded as a support.[1525]
Very many other factors might be mentioned, but enough has been said to
show how in the main the different fertilities may be explained. The
insufficient income of many of the less well-paid groups of the higher
classes is often alleged as a cause of low fertility. This view is well
founded when, as often occurs, social conventions force a so-called
higher standard of living upon them—a standard which merely involves the
expenditure of more money than among the industrial classes in
preserving appearances without adding to welfare. When, however, this is
extended to classes in which income has reached, say, between £600 and
£1,000 a year, it cannot be allowed that income is truly insufficient.
It is in such cases only insufficient when more than is reasonable is
expended in the way of material satisfaction. A man cannot be heard to
say that he cannot afford a large family as otherwise he will not be
able to keep a motor-car—so long, that is to say, as the motor-car is
not necessary to his profession.
7. This differential fertility occurs in countries where the population
is less homogeneous than in England, and thus assumes importance in
another aspect. For whether we assume the differences between the
elements in the population to be due to inherited characters or to
varying social traditions—a question to be discussed later—a change in
the proportion of the different elements will be of great importance.
According to Hill, who has investigated this matter in America, the
percentage of white women of native parentage under 45 years of age
bearing no children is 13·1, while the percentage of foreign women is
5·7. The average number of children for white married women of native
parentage is 2·7, and for similar women of foreign parentage 4·4. Among
the foreign women the average number of children for a married English
woman is 3·4, for a German 4·3, for an Italian 4·9, for a Pole
6·2.[1526] The above is only one example of conditions which obtain in
many countries raising difficult problems.
The same problem arises in an even more important form when there are in
the same country races as different as the white and the negro. In the
United States and in South Africa the problem assumes greater importance
than elsewhere. In the latter country the negroes are increasing faster
than the white element of the population. In America this has not been
the case in the last hundred years; but the fact that the white element
has maintained its relative position is due to the fact that in addition
to the increase in the native-born white population there has been an
increase due to immigration.[1527]
8. The question of the relative rate of increase of the population of
different countries is a somewhat different matter. It is due to many
factors, one of the less important of which is that the population of
various countries does not approach equally closely to the number
desirable in each country. The chief factor is the variation in the arts
of production in use in each country. It is only an extension of this
fact that the natural resources of different countries have been more
exploited in some cases than in others. In Russia the arts of production
in use are less advanced than in more western countries. The
introduction of western methods into such a country enables a rapid
increase of population to take place. During the same period the
increase can only be slow in countries which already use these methods,
and thus, so long as the knowledge of the arts of production is not
equal in all countries, different rates of increase are liable to arise
when knowledge spreads into a more backward country.[1528]
Such changes are altering the composition of the population of the
world. The following figures have been given for Europe. Out of 1,000
inhabitants there were in the years named the following proportion of
Teutonic, Romance, and Slav elements:
1801 1850 1905
Teutonic 375 369 273
Romance 355 321 251
Slav 268 310 375
XIII
THE QUALITATIVE PROBLEM
We now approach the second part of the problem, and turn from a
consideration of the quantity to a consideration of the quality of the
population. In the second and third chapters we found that reproduction
was a necessity, and that to the fact of reproduction can be traced the
origin of problems both of quantity and of quality. In the third chapter
we further found that the position of animals and plants in a state of
nature as regards problems of quality was in its broadest aspect simple.
The changes in the forms of organisms, which, when viewed as a whole, we
call evolution, are due to changes in the physical basis from which new
generations arise. The long procession of organisms, usually of
increasing complexity, from the simplest type to the immediate ancestor
of rational man, thus owes its being to a long procession of changes in
the germ-cells.
When treating of the quantitative problem among men, we considered a
large amount of evidence which bears also upon quality, and this
evidence, supplemented as and where necessary, will enable us to make
some estimate of the importance of qualitative changes among men. This
is the object of the remaining chapters. We have to try and estimate how
far human history is comparable with changes among species in a state of
nature—is due, in other words, to germinal changes. There are two other
possible causes of change among men—the direct influence of the
environment and the influence of tradition—and in order to estimate the
importance of germinal change, it will be necessary also to consider
what importance is attributable to these two factors. To one of
them—namely to tradition—we shall find reason to attribute great
importance. Tradition, in fact, comes ultimately to be of more
importance than germinal change among the underlying causes of history.
But tradition is profoundly influenced by the quantity of population
among other factors, and, therefore, to the extent to which this is so,
the determining factor in human history is still bound up with the
population problem. As history ceases to be strictly correlated with
changes in quality, it comes to be influenced by a factor the nature and
strength of which is largely determined by the quantity of population.
Thus the two aspects of the whole problem are linked together in the
case of man in a manner that does not obtain among species in a state of
nature.
The attempt to deal with this problem will be undertaken in the
following manner. In Chapter III reference was made to the influence of
the environment upon growth and upon the adult form. In Chapter XIV this
subject will be developed so far as species in a state of nature are
concerned, and the results of the inquiry will be applied to man in
Chapter XV. The subject-matter of Chapter XV will be confined to the
influence of the environment upon human bodily and mental characters.
The influence of the environment as a stimulus affecting the direction
in which mental characters are used will be left to a future chapter.
We next turn to inquire what influence changes in the germ-cells have
had. Before we can make any progress it is necessary to ask what
characters—physical and mental—have their basis in the germ-cells, and
an inquiry into this subject will occupy Chapter XVI. In Chapters XVII
and XVIII we ask what evidence there is of selection and other factors
throughout human history which we have reason to suppose have a bearing
on change in the average germinal constitution of the human species.
This will among other things necessitate an examination of the facts in
Chapters VII, VIII, and X in order to ascertain what bearing they have
upon selection. Having thus some knowledge of what is inherited, and
having discussed the occurrence of such factors as in human history may
have brought about changes from one generation to another in the
character inherited, we shall be in a position in Chapter XVII to
attempt an estimate of the results which the factors—selection and
others—have had upon physical characters. We shall find that as regards
these characters the position is more or less clear; we shall find, that
is to say, that the influence of selection and other factors, considered
in conjunction with the influence of the environment discussed in
Chapter XV, does enable us in the main to understand how the physical
evolution of man has come about. With regard to mental characters to be
discussed in Chapter XVIII, we shall find that the task cannot be
similarly completed. With a far less degree of certainty than in the
case of physical characters we shall arrive at some idea as to how
mental characters have evolved. This, however, still leaves unanswered
the problem as to how far the evolution of mental characters accounts
for what we call history. To attack this problem it is necessary to
consider how the environment acts as a stimulus upon the mind,
conditions the degree to which and the direction in which the mind is
used, and thus leads to the building up of tradition. In Chapter XIX we
consider the nature of human mental endowment and the manner in which
tradition is built up and handed on. In Chapter XX we consider the
nature of the environment under which human mental activities have been
exerted. This will enable us in Chapter XXI to survey the broad facts of
history and to come to some conclusion as to the parts played
respectively by the changes in human mental endowment, by the direct
influence of the environment upon the mental faculties, and by its
influence as a stimulus upon the exercise of these faculties. In a
concluding chapter the results of the whole inquiry will be summed up.
XIV
THE INFLUENCE OF THE ENVIRONMENT AMONG ANIMALS AND PLANTS
1. A brief inquiry into the part played by the environment among animals
and plants forms a necessary introduction to a similar inquiry as
regards man such as we shall undertake in the next chapter.
In the second chapter something was said as to fertilization and as to
the development of the zygote or fertilized egg to the adult form. It
has been shown by Herbst that, if this process of development is to
result in a normal adult, all the factors comprising the normal
environment must be present. Herbst ascertained the exact composition of
sea-water at Naples.[1529] Using as his material the larvae of
sea-urchins, he changed slightly in many different ways the composition
of the water. The experiments were very exhaustive. At every stage in
the development he observed the results of abstracting one or more of
the constituents of sea-water—the normal environment of the larvae.
Commenting upon the results of these experiments, Jenkinson says:
‘Whatever may be the ultimate explanation of the facts, there can be no
doubt whatever that the most complete demonstration has been given of
the absolute necessity of many of the elements occurring in ordinary
sea-water, its normal environment, for the proper growth and
differentiation of the larva of the sea-urchin. Nor is this all. Some of
the substances are necessary for one part or phase of development, some
for another, some at the very beginning, others only later on. Thus
potassium, magnesium and some degree of alkalinity are essential for
fertilization, chlorine and sodium for segmentation, calcium for the
adequate cohesion of the blastomeres, potassium, calcium and the
hydroxyl-ion for securing the internal osmotic pressure necessary for
growth, while without the sulph-ion and magnesium the due
differentiation of the alimentary tract and the proper formation of the
skeleton cannot occur; the secretion of the skeleton depends on the
presence of some sulphate and alkalinity, the skeleton requires calcium
carbonate, cilia will only beat in an alkaline medium containing
potassium and magnesium, and muscle will only contract when potassium
and calcium are there.’[1530]
Summing up the results of these and other experiments, Jenkinson says:
‘Every factor, or nearly every factor [of the environment], is necessary
for this or that phase or part of the process, some for the whole. Light
of a certain wave length will accelerate development; light of another
kind, or, in some instances, darkness, will retard it, or will stop it
altogether; a certain degree of heat is indispensable; oxygen is
required for respiration, water for growth; some eggs demand constant
agitation, others complete rest; fertilization or segmentation or
gastrulation, or some one or other of the later phases of development
may depend absolutely on the presence of some particular chemical
element; remove the factor in question, whatever it may be, and that
particular process will not occur, and the specific typical end which is
reached in normal development will not be attained.’[1531]
Putting aside until later the question as to what is implied by the term
normal environment, we may now ask what the relation is between heredity
and environment. To regard a developing organism as subject to the
action of two forces, one tending to thrust it in one direction and the
other in another, is to view the matter in a wholly false light.
Heredity and environment are, as is clear from the evidence given above,
complementary one to the other; without a germinal constitution there
can be no organism; without appropriate stimuli an organism cannot
develop. Similarly it is misleading to speak of the relative importance
of the two factors unless the terms are very clearly defined. To see
that careful definition is necessary, we have only to remember that,
because, with the exception of the anaerobic bacteria, all organisms
require free oxygen, environment might be held to be all important.
Here, however, we are not concerned with the problem as to the
conditions under which we might speak of the relative importance of the
two factors; we have merely to note that they are essentially
complementary.
2. We may now observe that, just as a normal adult only develops under
normal stimuli, abnormal stimuli experimentally induced may be followed
by every kind of result from the most extreme to the most insignificant
changes both of form and of life-cycle. We may note the results of a few
of the vast number of experiments which have been made. With regard to
plants it has been shown that ‘each developmental stage depends upon
special external conditions, and in cases where our knowledge is
sufficient, a particular stage may be obtained at will. In the Green
Algae, as in the case of the Fungi, we may classify the stages of
development into purely vegetative growth (growth, cell-division,
branching), asexual reproduction (formation of zöospores, conidia), and
sexual process (formation of male and female sexual organs). By
modifying the external conditions, it is possible to induce algae or
fungi ... to grow continuously for several years, or, in the course of a
few days, to die after an enormous production of asexual or sexual
cells. In some instances even an almost complete stoppage of growth may
be caused, reproductive cells scarcely being formed before the organism
is again compelled to resort to reproduction. Then again the sequence of
different stages of development may be modified as we desire.’[1532]
Another kind of experiment shows that foliage shoots can be converted
into runners and vice versa; it is, for instance, possible to induce a
germinating tuber of the potato to form foliage shoots under the
influence of a higher temperature. The transfer of plants from one
environment to another is often followed by remarkable changes. MacLeod,
for instance, states that a species of Philodendron which has large
leaves pierced with round holes was cultivated for many years in the
Botanical Gardens at Ghent in a greenhouse which was rather cool and
dry. The holes were found to be rare; at times it was not possible to
observe a single perforation in any of the leaves of a specimen. In
every other respect the plants were healthy. The plants were later
transferred to a greenhouse that was warm and moist and after a few
months the new leaves were found to be abundantly perforated.[1533]
Bonnier made some very interesting observations on the dandelion. He
found that the plant, when sown at a high altitude in the Pyrenees,
produced very short stems with hairy, dark green leaves and a compact
flower. On the other hand, seeds gathered from such plants growing at a
high altitude and sown in the neighbourhood of Paris produced after
three years elongated stems with less hairy and brighter leaves, or, in
other words, plants very similar to those grown from seeds obtained in
the neighbourhood of Paris. The modifications acquired during a given
time by a lowland plant grown at a high altitude, or by a highland plant
grown at a low altitude, took about the same time to disappear on
returning the plants to their original climates.[1534] Similarly
‘Schubeler sowed seeds of various plants in different latitudes in
Norway and proved that the brilliancy of the flowers increased with the
latitude. So great was the difference that it was difficult to conceive
that they were produced from the same batch of seeds.’[1535]
Observations on European peach-trees transported to Réunion were made by
Bordage. Such trees lost their deciduous habit and became evergreen,
though in some cases it took twenty years before the change was
complete.[1536] Lastly the red primrose ‘reared at a temperature of
30°–35° C. (with moisture and shade) has pure white flowers, but the
same plants reared at 15°–20° C. have red flowers. If the white-bearing
plants are brought into a cooler place, the flowers that are already in
bloom remain white, but those that develop later in the cooler
temperature are red.’[1537]
We may also notice the results of some of the experiments upon
developing animals. Stockard experimented with the fish _Fundulus
heteroclitus_. He subjected the eggs both before cleavage began, and
after the two- and four-celled stages had been reached, to solutions of
magnesium salts in sea-water. The eyes of a large percentage of the
embryos were abnormal. In some cases there was a single median eye; in
other cases there was a median eye showing signs of a double
structure.[1538] ‘In a long series of experiments Féré has shown that
monstrosities can be produced by exposing the hen’s egg to the
unfavourable influence of a large variety of substances. Vapour of
ether, alcohol, essential oils, nicotine, mercury and phosphorus,
injection of alkaloids such as morphine, nicotine, strychnine and
others, of bacterial toxins (those of tubercle and diphtheria), of
peptone, dextrose, and glycerine, several alcohols, certain salts ...
are all harmful, retarding and distorting the embryo to a greater or
less extent.’[1539] Many experiments show the effect of differences in
food, temperature, and humidity upon developing organisms. Agar carried
out some experiments on a small water-flea, Simocephalus. This animal is
enclosed in a kind of shell composed of two valves, somewhat like a
mussel. Normally the edges of the valves nearly meet, so that if a
section is cut across the animal transversely the shape of the body
enclosed in the valves is oval. When the food was varied in a certain
way, Agar found that the edges of the valves were turned outwards so
that the shape of a transverse section was no longer oval but bell-like.
He also found that the length was reduced by exposure to a high
temperature.[1540] Experimenting with a beetle, Tower found that both
the colour and the colour pattern could be modified by changes in
temperature and humidity.[1541] Similarly Morgan showed that a species
of the fruit fly exhibited a peculiar formation of the abdomen in the
presence of moisture; when raised in dry conditions the abnormality
disappeared.[1542] Poulton obtained some remarkable results when working
with the larvae of moths. ‘Larvae surrounded by the leaves on which they
fed, became, in the majority of species, light brown or light grey in
colour. If, however, an abundance of twigs had been mixed with the
leaves of the food plant, they became dark in colour. The larvae of the
Peppered Moth afforded the most striking result of all, for when reared
among green leaves and shoots they became bright green without
exception, whilst in the presence of dark brown twigs they nearly all
assumed a corresponding colour.’[1543]
A Japanese experimenter exercised rats for 90 to 180 days; he found that
this long-continued exercise markedly increased the weight of the heart,
kidneys, and other organs on an average to about 20 per cent.[1544] A
thickening has been observed in the stomach of a gull fed on grain for a
year and this change is said to take place under natural conditions in
the herring gull, which feeds in winter on fish and in summer on grain.
Conversely if graminivorous birds are fed on a carnivorous diet, the
gizzard assumes the form of a carnivorous bird’s stomach. Cuvier found
the length of the intestine of the wild boar is as 9 to 1 and of the
domestic boar as 13·5 to 1, a difference which is in part probably due
to diet.[1545] The colour of birds’ plumage is affected by their diet.
Hempseed causes bullfinches and other birds to become black. Cayenne
pepper causes yellow to change to orange red. In the New York Zoological
Gardens it has been shown that some birds, such as the bobolink, may be
so dieted that they keep their breeding plumage throughout the year and
will sing their spring song in mid-winter.[1546] Warren produced marked
changes in the common water-flea, Daphnia, by keeping them in a confined
space for many generations. ‘Semper and de Varigny found that when
fresh-water snails were reared in vessels of a shape that allowed them
abundant water but very little surface in which to take exercise they
developed into dwarf forms. Every precaution was taken to procure
abundant food, perfect aeration and thorough removal of waste products.
De Varigny’s experiments were particularly careful and point
convincingly to the conclusion that the condition of dwarfing was the
restricted area for exercise.’[1547] Lastly it may be remembered that,
as is well known, parasites may induce remarkable changes in their
hosts.
3. From what was said in the third chapter it follows that the results
of artificial subjection to abnormal stimuli just described are to be
interpreted as examples of the fact that different responses are given
to different stimuli by the same or approximately the same germinal
constitution. But large and conspicuous changes of this nature are not
visible only as the result of artificial circumstances. Many species are
normally subject to more or less definite and sudden changes in the
surroundings, and some of them exhibit more or less definite responses
to such changes. This is especially obvious in the case of sessile
organisms the outward form of which is clearly modified by the
surroundings. Thus ‘the water ranunculus, when growing submerged beneath
the surface of a pond, produces leaves the blades of which are cut up
into a number of fine thread-like segments. As soon as the top of the
plant reaches the surface of the water, those leaf-rudiments which are
just commencing their existence, proceed to develop in a totally
different fashion. The leaves to which they give rise possess a wide and
unpointed blade, which floats upon the surface of the water. The two
sets of leaves are as utterly different in their appearance as it is
possible for leaves to be. Yet the effect of the external conditions
upon the young leaf-rudiment determines which of the kinds is to
appear.’[1548]
Examples may also be found in the life-history of free-living organisms.
One is afforded by the common honey-bee. As is well known, a queen bee
differs markedly from a worker bee in shape. Both queens and workers
arise from fertilized eggs; whether a queen or a worker develops from
any one egg appears to depend wholly on the environment—a larva that
gives rise to a queen receiving in the first place different and
presumably more nutritious food than that received by a larva giving
rise to a worker, and, in the second place, inhabiting a cell which
differs in size and shape from that inhabited by a worker larva. Another
is afforded by the life-history of the plant lice (Aphids). At certain
seasons of the year winged forms appear. It has long been suspected that
the appearance of winged forms depends on some environmental stimulus.
That this is so has been rendered practically certain by the work of
Shinji, who has shown that aphids reared on plants watered with certain
solutions are winged almost without exception.[1549]
Among mammals the assumption of a winter coat by the lemming, ptarmigan,
and variable hare is a similar phenomenon. Sir John Ross has told how a
Hudson Bay lemming was protected from the cold on board his ship by
keeping it in the cabin. It retained its normal summer coat during the
winter. On exposing it in a cage on deck to a temperature of 30° below
zero, the fur on the cheeks and a patch on each shoulder became
perfectly white during the first night. After another day’s exposure
‘the patches on each shoulder had extended considerably, and the
posterior part of the body and the flanks had turned a dirty white....
At the end of a week it was entirely white except in a dark band across
the shoulders prolonged posteriorly down the middle of the back.’[1550]
A curious example of the importance of the environment before birth is
afforded by the difference between the mule and the jennet. The former
is the product of a cross between a stallion and a she-ass, the latter
between a jackass and a mare. There is every reason to believe that it
is not the fact that horse-ancestry is in one case traced through the
father and in the other case through the mother that gives rise to the
difference; the difference can only be attributed to the fact that in
one case the period before birth is passed within a mother of one
species and in the other case is passed within a mother of another
species.
4. We are now in a position to discuss what is meant by the term ‘normal
environment’. There is a more or less definite range of variations of
the environmental stimuli to which species in a state of nature are
subject. The range may differ greatly from species to species, but
remains more or less constant for any species. So long as the variations
fall within this range, the environment may be described as normal. Such
variations will be followed by different responses on the part of
similar germinal constitutions, and the variations among the members of
any species under a normal environment are due to the combined influence
of differences in the environment and of differences in the germinal
constitutions. From time to time in a state of nature organisms are
subject to variations of the environmental stimuli which fall outside
the normal range, and there are thus produced extreme modifications
similar to those which can be experimentally induced. Thus Gemmill on
examining a large number of fish embryos found monsters with a single
eye very similar to those experimentally produced by Stockard.[1551]
It may next be observed that there is a marked difference in the degree
to which sessile organisms on the one hand and free-living organisms on
the other hand respond to differences in the normal environment. The
former are much more susceptible to differences—or at least to certain
differences. Sessile organisms, for instance, differ from one another
very greatly in form and such variations are known to be chiefly due to
differences in the environmental stimuli. Free-living organisms do not
vary in this manner. The reason is fairly clear. All species are adapted
to a particular niche in nature, and among the former the mode of
adaptation of necessity takes the form of susceptibility to surrounding
conditions; a tree or a sponge must be able to adapt itself to its
actual surroundings. A free-living organism is, on the other hand,
adapted by its specific form to its niche in nature and, in order that
it may reach and maintain this form, it must exhibit a relative lack of
susceptibility to surrounding conditions.
5. The broad features of the situation among species in a state of
nature are now fairly clear. By outward inspection it cannot be
ascertained whether any particular characteristic is of the nature of a
modification or of a mutation. But we know that among sessile organisms
outward form is largely of the nature of modification, whereas among
free-living organisms, which interest us more closely because conditions
are more nearly comparable to those obtaining among men, modifications
play a much smaller part. A large number of measurements has been made
of certain features of particular species in a state of nature as, for
instance, by Allen for the squirrel and Weldon for the common shrimp.
Though on general grounds we may have reason to suspect how far the
variations recorded are of the nature of modifications, we can arrive at
no certain answer. Observations made on members of a species in a state
of nature, some of which are subject to conditions that differ from
those to which the rest of the members are subject, are of more
assistance for our present purpose. Thus the tiger ranges from tropical
to temperate regions. Tigers from the former regions exhibit certain
differences from those from the latter regions in respect of the
condition of the coat. It is possible that these differences are purely
environmental. Again certain marine molluscs from cold waters exhibit
differences when compared with members of the same species from warmer
waters; these differences may again be purely environmental. In those
cases in which a species has within recent years spread to a new
environment, it is often found the degree of variation has increased.
Thus Bumpus found that the egg of the common sparrow is more variable in
the United States than in England;[1552] it has also been noticed that
the variation of the common periwinkle is greater in America than in
England—both these species having been recently introduced into
America.[1553] It is also of interest to observe that Montgomery found
greater variations among migratory than among non-migratory species of
birds and the greatest variation among those that had the widest
range.[1554] Though, until the matter has been put to the test of
experiment, nothing can be affirmed as to the nature of these
differences, it is probable that in part at least these differences are
environmental. Such observations help to exhibit the degree of
importance that we are led to attribute to modifications among
free-living animals in a state of nature. It must also be borne in mind
that departures from the normal range of variations of the environmental
stimuli are not so very infrequent and that more or less extreme
modifications, as result, for instance, from the attacks of parasites,
do occur.
Lastly we may go a step farther and ask what happens when the
environment changes. This inquiry, if pursued, would lead us beyond the
scope of this chapter. A reference, however, to this problem may assist
to render the relation of a species under natural conditions to its
environment rather more clear. Change of environment may be due either
to the migration of some or all the members of a species to a locality
where the environment is different, or to an actual change in the
environment in the same locality. If the change is at all marked, then
there will be a different response on the part of the germinal
constitution to the new conditions. Let us suppose that the diet is
changed and that some members of a species of bird take to a diet of
grain having previously existed on a diet of fish. There will be a
different response in that the stomach will assume a different form. But
it is most unlikely that the old germinal constitution will be that
which gives the best response to the new conditions. Almost certainly a
somewhat different type of germinal constitution will be that which will
give the best response to the new conditions, will be that, in other
words, from which there will arise the form of stomach most suited to
dealing with grain. If and when, therefore, a mutation arises exhibiting
this changed type of germinal constitution, it will be favoured, and in
this manner a new variety and ultimately a new species may be formed. It
has thus to be remembered that, although the germinal constitution to
some extent responds differently to different stimuli, it is very
unlikely that any average type of germinal constitution will give the
best response to any other environment than that to which the species is
now subject. It does not therefore follow that, because the responses of
the germinal constitution are various, there are not factors making for
a change in the germinal constitution when the environment changes.
Summing up what we have said, we have to think of every species as
living under a more or less clearly defined environment into which very
many elements enter; whether the variations in these elements are great
or small, there is an average condition, and to that average condition a
certain type of germinal constitution gives the best response. In the
case of a free-living animal in the adult form the germinal constitution
does not respond readily to ordinary variations from the normal, though
it has to be remembered that extreme influences such as those caused by
parasites may cause marked reactions. Further, it has always to be borne
in mind that during development all animals and plants are particularly
susceptible to environmental changes. It is not possible to make any
precise statement as to how far the differences we see under natural
conditions are modifications and how far mutations. All that we can say
is that the part played by the environment in producing modifications is
on the whole smaller in the case of free-living animals than in the case
of sessile animals and of plants.
XV
THE INFLUENCE OF THE ENVIRONMENT UPON MAN
1. The way has now been cleared for a consideration of the influence of
the environment upon man. The relation of the ancestors of man to the
environment must have been the same as that between any wild species and
its environment. In the course of his history man has moved away from
this position until his relation to the environment has become so
different from that described for other animals and plants that we can
no longer speak of a normal environment. This has not come about because
man is not subject to the same laws as are other organisms. It has come
about because his relation to the environment has been modified in many
ways.
The conception of the normal environment involved the idea that, much as
the different elements composing the environment might vary, there was
some more or less clearly defined limit to their variations. In one
sense this remains true for man; but the variations are so much greater
in degree and in kind that there is a clear distinction between the
conditions obtaining among civilized races and those obtaining among any
wild species. Let us glance for a moment at what has happened. It is
obvious that man has varied his surroundings in every respect, not only
with regard to what we may call external circumstances, but also with
regard to nutrition and to customs and habits that we sum up under the
name of use. The most obvious changes in external circumstances are
those connected with the spread of man to every corner of every
continent. Man has become subject to every extreme of heat and cold,
humidity and aridity, of barometric pressure and all that goes to make
up climate. There is in addition a vast mass of artificial influences,
due in the first place to various methods of protection adopted against
climate. Every description of house is known, involving all degrees of
access to fresh air. Dress again varies almost infinitely—the variations
all being of possible influence upon the development of mental and
physical characters. The aggregation of men into towns involves exposure
to smoke, noise, and vibration among other factors. Modern industrial
conditions in particular expose workers to varied surroundings. Human
diet has become equally varied. The cooking of food was an innovation
involving great changes in the factors which play upon the digestive
organs. Innumerable animals and plants have been drawn upon by man as
food. Perhaps more important than the variations in what man eats are
the variations in what he drinks. Under the heading of use come all
those habits such as reading, washing, smoking, and shaving. Various
occupations bring with them various degrees of muscular activity or
involve its reduction to next to nothing. There are various modes of
riding and various ways of sitting. Lastly the prevalence of disease has
introduced another factor which has a profound influence upon mental and
physical characters.
This varying of the environment has come about gradually, slowly at
first and with increasing speed latterly, until at the present day, of
four men having their homes in the same town one may do clerical work
involving no exercise, another may labour in a cotton mill where it is
warm and moist, a third may perform hard physical labour in a mine in
semi-darkness where the air is full of a particular kind of dust, and a
fourth may work on board ship exposed to all the rigours of the
Atlantic. To such differences may be added all the differences between
meat-eaters and vegetarians, smokers and non-smokers, alcoholic drinkers
and abstainers, and so on. Contrast the variations in the environment of
modern man with the variations in the environment of any species in a
state of nature and it will be apparent why it was said above that the
relation of man to his environment was clearly distinguishable from that
of any species in a state of nature to its environment.
We are about to consider in this chapter the influence of the
environment upon the physical basis of life; we shall be concerned, in
other words, with its function as the complement of the germinal
constitution. The discussion will be limited to the notice of such
factors as are in operation; of the possible effects of the environment
there is no need to speak. From two other points of view also the
environment is of importance; as a factor in selection it will be
considered in Chapters XVII and XVIII; as the subject-matter, so to
speak, upon which mental processes work, it will be considered in
Chapters XIX and XX. It is important to distinguish the influence of the
environment in this latter respect from the sense in which it is
considered in this chapter. The failure to do so has vitiated many
contributions to the subject. It is felt that the environment is somehow
of great influence in social life and it is not realized that, if in the
respect in which it is considered in this chapter we find reason to
conclude that its influence is not great, there is another field in
which its influence may be established.
When considering the influence of the environment on man, it is
convenient to distinguish between physical and mental characters. Mental
characters may be considered under the head of the intellect, the
disposition, and the temperament. It must, however, be clearly
understood that this is merely a distinction convenient for our present
purpose which is not based upon, and does not imply, any fundamental
distinction. Mental characters, such as the instinct of gregariousness,
and physical characters, such as head form, are for our purpose merely
characters resulting from the play of certain stimuli upon a certain
germinal constitution.
2. It is remarkable how little on the whole is known with regard to the
influence of the environment on man. For the most part we have to depend
upon observations as distinguished from experiments. Though a few
experiments have been made, some deliberately but others accidentally,
we are for the most part in the position with regard to man that we
should be with regard to other animals, had we only such observations to
go on as those quoted respecting the size of marine molluscs, the
variation in the coat of the tiger, and the changes in the sparrow and
the periwinkle when introduced into America. Though such observations
may strongly suggest certain conclusions as to the part played by the
environment, no definite or precise results can be reached.
We may first consider some evidence bearing upon the influence of
particular factors such as exercise and climate. We may disregard those
rare cases of extreme modifications deliberately induced, such as the
distortion of the shape of the head or of the feet by pressure. These
extreme modifications approximate to mutilations such as amputation of
the finger-joints or the knocking out of the incisor teeth.
It is well known that exercise has considerable effect upon the
development of the muscles. It is also well known that there is a
clearly defined point for each individual beyond which exercise will
produce no further effect. Though exercise has a considerable effect
upon other organs, especially certain internal organs, it is probable,
not only that it has more effect upon the muscles than upon any other
system of organs, but that the effect upon the muscles is relatively at
least as great as, if not greater than, the effect upon any organ of any
other factor that we shall consider except disease. Owing to differences
in the amount of exercise the bodily development of man in a modern
community varies very considerably; owing to such modifications clerical
workers differ from blacksmiths, whether or not there are also germinal
differences. So too owing to differences in habits men of one race
differ from men of another race. Darwin, for instance, refers to the
thin legs and thick arms of the Payagua Indians who spend a large part
of their lives in canoes.[1555] It is certain that all such physical
differences are not due to germinal differences and that environment in
the shape of use is in part the cause. The position is similar with
regard to certain peculiarities observable among races that have adopted
unusual modes of squatting.
Little is known as to the effects of use upon mental characters. To some
degree no doubt the intellect is developed by use, though, perhaps, the
degree to which this is so is apt to be exaggerated in popular
estimation owing to the fact that modes of thinking acquired through
education add to the efficiency of the faculty, which result is mistaken
for the effects of use. That the effects of exercise are not great is
shown by the experience of the Workers’ Education Association. This
institution gives advanced courses to men often of middle age who have
received but little intellectual training in early life. It does not
appear that the strength of their intellects is much less than it would
have been had they received a university training. It seems at any rate
certain that the differences in the amount of use now obtaining between
the various professions and classes in England have less effect
generally upon mental than upon physical characters. Given, for example,
two men of equal intellect, one of whom received the best educational
training of the day, and the other of whom received the training given
to the working classes, it does not seem that at the end of the training
there would be anything like the same difference as regards strength of
intellect between them as there would be between two men, one of whom
received an athletic training and the other of whom did not.
3. Physical changes are not infrequently observed to follow upon changes
in the environment, though, when these changes are complex, it is often
impossible to say with which features of the environment the changes are
connected. Thus ‘the Anthropological Committee of the British
Association long ago showed the beneficent effects of the Factory Acts,
which rescued young children from the hardships of daily toil. Boys of
nine years in 1873 had a height and weight equivalent to the height and
weight of boys of ten years old in 1833.’[1556]
It is known that stature has increased in certain European countries
during the last century. Soren Hansen gives the following figures for
Denmark:[1557]
1852 to 1856 165·42 cm. average height.
1879 „ 1888 167·78 „ „ „
1891 „ 1900 168·43 „ „ „
1904 „ 1905 169·11 „ „ „
Similarly the stature of the Dutch has increased from 165·5 cm. in 1866
to 167 cm. in 1883 and to 168 cm. in 1899. A number of reasons has been
suggested to account for this marked increase, the higher standard of
living, the decrease in the incidence of disease which is known to
inhibit growth, and the smaller number of children in a family. This
last factor is certainly of importance at the present day. From some
observations made in an English manufacturing town Ewart concludes that
when children are born at a longer interval than two years they are on
an average three inches taller and three pounds heavier than children
born at a shorter interval.[1558] It is a fair assumption that in
families, where the income is small, the fewer the children the more
favourable would be the environmental conditions.
The physical inferiority of people living in poorly endowed surroundings
is often thought to be at least in part due to modifications induced by
hard conditions. Thus physical inferiority is noticeable in districts in
Europe that are markedly poorly endowed, as for instance in the area
between Limoges and Périgueux in France. So far as this is so, the
causes may have to be sought in climatic differences as well as in other
differences more directly comparable with those which exist between
well- and ill-treated children in the same country.
4. The influence of climate upon man has long attracted attention.
Statistical evidence has been produced showing that the shape of the
head—a characteristic usually considered not to be in any way
susceptible to such differences in the environment as occur between one
climate and another—is modified by climate. Boas produced figures
showing that the cephalic index (a measure obtained by calculating the
relation of breadth of the head to the length which is put at 100) of
Sicilians born in America to be 80, while that of Sicilians born in
Sicily is 78, and of Hebrews born in America to be 81, while that of
Hebrews born in Eastern Europe, whence the immigrants came, is 83. It
would appear that the Hebrews who are broad-headed in Europe become
narrower-headed in America, and that the Sicilians who are narrow-headed
in Europe become broader-headed in America. There would thus seem to be
an approximation in America to a cephalic index the mean of which lies
between 80 and 81.[1559] These results have been severely criticized
from many points of view. Sergi claims to have shown that the results
are the ‘pure effect of illusion due to the statistical methods employed
by the author’.[1560] It has also been suggested that the results are
due to selection. In this connexion it is interesting to note that both
Ammon and Levi obtained somewhat similar results and that they both
attributed them to selection. The former, working with figures from
Baden, found that the inhabitants of cities tended to become
longer-headed and concluded that the short-headed type tended to die out
under the conditions of city life.[1561] Levi, working on Italian
figures, came to the same conclusion and attributed it to the same
cause.[1562] Others have suggested that the methods of nursing children
may affect the shape of the head and that the changed habits of the
immigrants in America may account for the changes in the shape of the
head. Though it has certainly not been proved that the environment can
in the manner suggested change the shape of the head, the question
cannot be regarded as settled.
Observations have been made on the cephalic index of Jews which may
perhaps be held to lend support to the views of Boas. Huntington gives
the following table:[1563]
_Country._ _Cephalic Index of _Cephalic Index of _Difference_
Jews._ other Races._
Caucasus 87·5 87·4 0·1
Galicia 83·6 84·4 0·8
Baden 83·5 84·1 0·6
Little Russia 82·9 83·2 0·3
Turin 82·4 84·9 2·5
Lithuania 81·7 80·6 1·1
Russian Poland 81·9 80·9 1·0
White Russia 80·9 82·5 1·6
It would appear that there is a tendency for the cephalic index of Jews
to vary as does that of the surrounding types. Fishberg has attributed
this fact to intermarriage[1564] and this may be in part at least the
explanation, though in the present state of our knowledge the possible
influence of the environment cannot be altogether excluded.
The uncertainty surrounding the matter is in fact a good example of the
state of our knowledge regarding many similar problems affecting
man.[1565] Boas himself, it may be noticed, only believes in a ‘strictly
limited plasticity’[1566] of head form; it is indeed evident that this
and other physical characters which distinguish the races of man are for
the most part of the nature of mutations and not of modifications.
Europeans who migrate to tropical climates and the inhabitants of
tropical climates who come to live in Europe retain the greater part of
their distinguishing physical characters.
The manner and degree in which tropical climates influence Europeans is
a matter of considerable interest. There is as yet but little known on
the subject. Sir Patrick Manson, writing in 1907, said that ‘although
many attempts have been made to trace and explain the effect of
temperature on the physiological processes of the human body, more
especially in reference to the pathological proclivities to which
atmospheric heat and cold may conduce, it cannot be said that any
important conclusions have been attained.... But though we may not be
able to indicate precisely the way in which our bodies are
physiologically affected by extremes of atmospheric temperature,
especially prolonged high temperature, our sensations, the loss of
physical and mental energy, the modification of physical characteristics
undergone by white races when placed for several generations in tropical
conditions, and the dark skins of all tropical races indicate that the
white races on first arrival are not in all respects adapted for
tropical conditions, that they are somehow prejudicially affected
thereby, and that while living in tropical countries they are more open
to certain pathological risks than are the natives of those
countries.’[1567] Since the year in which Sir Patrick Manson wrote
further information has been obtained on this subject. Our knowledge is,
however, still scanty. With regard to actual facts it is known that the
pulse, rate of breathing, and temperature of the body do not vary when
measured in Europe and when measured among white men under tropical
conditions. The number of red blood-corpuscles and the amount of
haemoglobin in the blood is the same and metabolism is not less intense.
On the other hand the rate by which a nervous impulse travels along a
nerve decreases in Europeans the longer they live in the tropics. The
muscles and the connective tissue become more elastic. The well-known
pallor of Europeans living in the tropics is due to a thickening and
softening of the epidermis, which becomes opaque.[1568]
It is very difficult to arrive at any conclusions as to what the effects
of a tropical climate upon Europeans really are. It is necessary to
discount the effect of tropical diseases and of the habits and customs
of Europeans living in the tropics. On the whole it is probable that the
popular notion of the considerable and generally injurious nature of the
modifications undergone by Europeans living in the tropics is
exaggerated. It is said that, for example, in Java, when sanitary
conditions are good and reasonable habits adopted, the death-rate among
European children is less than in Europe. Nevertheless a tropical
climate does have an injurious effect upon Europeans. There is no doubt
that Europeans in the tropics are more irritable and in general more
highly strung than in their native land. Clearly in some fashion the
nervous tone is injuriously affected by residence in tropical climates.
In a similar manner nervous tone is affected by many elements in the
environment in civilized countries, such as vibration, noise, and so on,
leaving aside the effect of food, drink, and disease. To the importance
of disease in this respect we shall return later. As regards noise,
vibration, and so on, but little is known—their influence being possibly
considerably greater than is usually suspected.
5. Ellsworth Huntingdon has in recent years in a number of publications
elaborated a theory according to which climate has been one of the main
factors in determining where civilization shall develop and flourish. As
this theory depends upon the supposed direct influence of the
environment on man, it may be noticed here. He has made observations
which are interpreted as showing that there are optimum climatic
conditions under which the maximum energy is exhibited. These conditions
arise when the average temperature of day and night together lies
between 58° F. and 71° F. and when there is a certain degree of
moisture. His observations, made in America, were based on the output in
piece-work factories and on similar data and tend to show that not only
do all European races, including the Finns, display most energy under
these optimum conditions, but also the Japanese and the negroes. He then
proceeds to show that where these optimum conditions prevail in the
world, there to-day are to be found the highest forms of civilization.
Upon these data he raises a very far-reaching theory to the effect that
throughout history civilization has arisen and flourished only where
there has been an approximation to these climatic conditions. To the
obvious difficulty that former civilizations have often flourished in
countries the climate of which at the present day is far from these
optimum conditions, he replies that climate has changed, a theory which
he has for some years strongly advocated.[1569]
It may be said that there is nothing novel in the idea of optimum
climatic conditions.[1570] In the previous section it was pointed out
that Europeans in tropical climates suffer from injurious mental
disturbances. What is remarkable is that the optimum conditions for
negroes should be the same as for Europeans. It will require more proof
than has yet been advanced before this can be accepted. Further, the
changes in climate which the theory demands have not been proved.
Professor Gregory has reviewed the question and his conclusions do not
support those of Huntingdon—at any rate not in such a manner as to
render the theory tenable.[1571] Nevertheless, whatever the fate of the
theory in its present form may be, its enunciation has raised many
interesting questions and has incidentally helped to show how little we
know at present regarding the effect of the surroundings on man.
6. When men move from one climate to another they come under the
influence not only of changes in temperature and moisture but also of
food and sometimes of altitude and other factors about the effects of
which there is a considerable amount of information. A vegetarian diet
is said to produce changes in the gut; but changes in beverages are
probably of far greater importance than changes in food. The effects of
alcohol have been closely studied, chiefly with regard to its influence
upon nervous tone. Nervous tone is affected in an important manner by
many drugs, as for instance by opium, and in a lesser degree by tea and
coffee. Changes in nervous tone are of such importance that its
susceptibility to various influences has to be borne in mind. It is
quite possible that the introduction of a new form of beverage into a
country might have a perceptible effect upon the average condition of
nervous tone and thus have a bearing upon the course of history.
Altitude is known to have various effects upon physical characters. The
fact that the larger lung capacity of those who live at high altitudes
diminishes on descent to the plains, as recorded by Darwin of the Quicha
Indians, is evidence that this character is in part at least
environmental.[1572] The effect of high altitudes has lately been
studied in much detail. It is known that there is among other changes an
increase in the number of red blood-corpuscles in the blood.[1573]
7. Attempts have been made to obtain more precise information by the use
of statistical methods. Thus the correlations have been measured between
the state of children’s eyesight and fifteen environmental conditions.
The mean of the correlations was found to be 0·04—only one reaching
0·1.[1574] Again the association between various intellectual and
physical characters and conditions, which were taken as representing a
good or bad environment, has been measured. A slight association was
found between intelligence in boys and few people per room and no
association between eyesight, condition of glands and hearing, and bad
economic and moral surroundings.[1575] Somewhat different results have
been reached by American workers, who find that by employing
psychological tests a fairly well-marked difference can be detected
between children in the same school whose parents belong to different
social classes and who would therefore be subject to different home
conditions.[1576]
The interpretation of these results is difficult. Before any definite
conclusion could be reached with regard to any one character, it would
be necessary to measure the effect of every factor in the environment
upon that character. As the matter stands there is strong but not
conclusive evidence of the small influence of the surroundings, so long
as we suppose that innate differences do not exist between the subjects
measured. But if innate differences exist, then the interpretation of
the absence of any marked degree of correlation must be that the common
elements of the environment supplied by the community are of greater
importance than the innate differences. We shall find reason to conclude
in later chapters that small innate differences do exist, and, if this
is so, then the interpretation of these results is not at variance with
the general, though necessarily vague, conclusions derived from the
evidence previously given, i.e. that the influence of the environment as
represented by the variations actually occurring in the elements of the
surroundings hitherto mentioned is small.
8. There is another class of factors which may be summed up under the
heading of disease. It was remarked that disease may produce notable
results among species in a state of nature. Compared, however, with the
state of things among men, and especially in the later stages of
history, disease is rare among such species. Among men it comes to
assume a peculiar importance.
Disease results both from the attacks of parasites and from other
causes. The various classes of disease will be referred to in the next
chapter. We are here concerned only with the results, and we may think
of the disease as affecting particular organs in the body and as
affecting the general functioning of the organs. Every organ in the body
is liable to be attacked by disease and the modifications produced are
in many cases familiar. Thus all physical and mental characters may be
directly and to almost any degree modified by disease. Again it is known
that the result of disease in children is to inhibit growth, and that
the growth thus lost is not subsequently made up. Disease may thus be
said to draw upon the capital and not upon the income of children.[1577]
We may here confine ourselves to some notice of the effect of disease on
the general functioning of the bodily organs which though not so
familiar is more important from our point of view.
The functioning of the bodily organs has been found in late years
largely to depend upon certain glands—known as the endocrinous or
ductless glands—in a manner and to a degree altogether unsuspected. The
thyroid gland, for example, manufactures a secretion which is essential
to the proper growth and normal metabolic functions of the whole body.
If it is removed from a child, the whole body is stunted and mental
deficiency results. Certain maladies, such as goitre, cretinism, and
others are known to be connected with a diseased condition of the
thyroid. Profound modifications of both physical and mental characters
may thus follow when these glands cease to function normally, which is
known to be the case in certain specific diseases and may arise in other
ways which are not fully understood.
Temperament depends upon the general functioning of the bodily organs
and upon the actual condition of the nervous system. Disease, whether it
takes the form of a failure of the ductless glands to function as they
should, or some other form, always affects the general functioning of
the body and thus has a direct bearing upon temperament. Thus ‘we know
now’, says Mr. McDougall, ‘that defect of the functions of this organ
(thyroid) may reduce any one of us to a state of mental apathy bordering
upon idiocy, and that its excessive activity produces the opposite
effect and may throw the mind into an over-excitable condition verging
upon maniacal excitement. Again we know that certain diseases tend to
produce specific changes of temperament, that phthisis often gives it a
bright and hopeful turn, diabetes a dissatisfied and cantankerous turn.
It is clear that in some such cases of profound alteration of
temperament by bodily disorder the effects are produced by means of the
chemical products of metabolism, which, being thrown out of the diseased
tissues into the blood and reaching the nervous system by way of the
blood-stream, chemically modify its processes. It is probable that every
organ in the body exerts in this way some influence upon our mental
life, and that temperament is in large measure the balance or resultant
of all these many contributory influences.’[1578]
Thus in addition to the more obvious direct effects of disease upon
mental and physical characters, there are the more subtle and profound
effects upon temperament, and in our general summing-up we shall find
reason to attribute no small importance to temperament in its influence
upon progress. It thus becomes of importance to observe that in
particular regions of the world certain chronic and non-lethal diseases
are very common. Clearly the result of disease upon temperament is
greatest when it takes the form, not of kill or cure—which is on the
whole the case in temperate climates—but of chronic non-lethal maladies
which are common in tropical climates, especially in Africa. The
hook-worm disease is an African disease which has been introduced into
America. The hook-worm (Ancylostomum duodenale) is an internal parasite
which attaches itself to the lining of the intestine and causes bleeding
and anaemia. Death may ensue, but the patient usually lives a long time.
It is a most debilitating disease; it is said to affect some 50 per
cent. of the inhabitants of some tropical and sub-tropical countries.
Even as a mild infection it is the cause of much invalidity and heavy
economic loss. The laziness and degeneracy of the ‘poor white trash’,
who are said to belong to the purest-blooded English stock in the United
States, are due not so much to the environment[1579] and heredity as to
the ravages of these parasites. In a public lecture, delivered before
the University of Pennsylvania, in 1915, Allan Smith, citing the factors
which have caused the Southern States to lag in American progress,
mentioned that the hook-worm disease ‘stands with malaria as worse than
wars and the devastations of battles and worse than all other pathogenic
agencies in combination’. Through the influence of these diseases ‘the
men and women of the South, bred from the best colonial stock, offspring
of pioneers, with the blood of English gentry and of continental
cavaliers in their veins, sank lower and lower in physical degeneration
and squalor, were derided and denounced as lazy and shiftless and
condemned in popular opinion as worthless and a disgrace’.[1580]
There are many other tropical and sub-tropical diseases of a somewhat
similar nature. Among them may be mentioned the ‘yaws’—marked by various
eruptions probably due to a spirochaete—the guinea-worm, which lives
buried in connective tissue; bilharzia, a trematode worm which lives in
the bladder and infects nearly 50 per cent. of the inhabitants of Egypt;
and elephantiasis, due to a worm related to the guinea-worm. The manner
and degree in which these various diseases affect the nervous tone
varies very much. In general the result is debility and a lowering of
the nervous tone. So too malaria is a cause of debility, and the main
reason for the decadence of Ancient Greece has been sought in this
disease.[1581]
9. The results of the inquiry so far, though illuminating, are
indefinite. This is largely because we are ignorant regarding innate
differences. The consideration of the evidence as to identical twins
offers a way out of this difficulty. It is known that there are two
kinds of twins. There are the so-called identical twins, between whom
there is a very close resemblance, and other twins between whom there is
no greater resemblance than between any two children of the same
parents. It was formerly thought that there was a sharp distinction
between the two kinds of twins—identical twins arising from a single
ovum, which completely separated into two halves during early
development, each half giving rise to one child, ordinary twins arising
from the simultaneous fertilization of two ova. If this was so, then
identical twins would always have approximately the same germinal
constitution, whereas other twins would have germinal constitutions as
different as on the average are those of the offspring of the same
parents. That identical twins do thus at times arise is practically
certain, but it has recently been shown that the supposed sharp
distinction between identical and other twins does not exist.[1582] This
may be explained by various assumptions. It may be supposed that some
ova are binucleate or that some ova are penetrated by two spermatozoa;
again the earlier or later separation of the blastomeres may have a
bearing upon the position. Under any of these circumstances twins
intermediate between identical twins and ordinary twins would
arise—twins, that is to say, not having approximately similar germinal
constitutions, but germinal constitutions more nearly alike than those
of ordinary twins. However this may be, it is sufficient for our purpose
to note that so-called identical twins are always more alike in their
germinal constitutions than are ordinary twins and may quite frequently
have practically similar germinal constitutions. It, therefore, follows
that differences between identical twins must be very largely of the
nature of modifications. It is thus of great interest to ask in what
these differences consist.
Galton collected data regarding thirty-five cases of identical twins. He
summarizes the information about them up to the time at which they left
the family circle as follows. ‘In a few of these not a single point of
difference could be specified. In the remainder, the colour of the hair
and eyes were almost always identical; the height, weight, and strength
were nearly always so. Nevertheless I have a few cases of a notable
difference in height, weight, and strength, although the resemblance was
otherwise very near. The manner and personal address of the thirty-five
pairs of twins are usually described as very similar, but are
accompanied by slight differences of expression, familiar to near
relatives though unperceived by strangers. The intonation of the voice
when speaking is commonly the same, but it frequently happens that the
twins sing in different keys.’[1583] He goes on to say that ‘both twins
are apt to sicken at the same time in no less than nine out of the
thirty-five cases. Either the illnesses, to which I refer, were
non-contagious, or, if contagious, the twins caught them simultaneously;
they did not catch them the one from the other. This implies so intimate
a constitutional resemblance, that it is proper to give some quotations
in evidence,’[1584] and he proceeds to give detailed evidence. Later he
remarks on the ‘similarity in the association of ideas. No less than 11
out of the 35 cases testify to this. They make the same remarks on the
same occasions, begin singing the same song at the same moment and so
on.’[1585] With regard to tastes and dispositions Galton says that ‘in
16 cases—that is in nearly one-half of them—these were described as
closely similar; in the remaining 19 they were much alike, but subject
to certain named differences. These differences belonged almost wholly
to such groups of qualities as these: the one was more vigorous,
fearless, energetic, the other was gentle, clinging, and timid; or the
one was more ardent, the other more calm and placid; or again the one
was the more independent, original, and self-contained; the other the
more generous, hearty, and vivacious. In short the difference was that
of intensity or energy in one or other of its protean forms; it did not
extend more deeply into the structures of the characters. The more
vivacious might be subdued by ill health, until he assumed the character
of the other; or the latter might be raised by excellent health to that
of the former. The difference was in the key-note, not in the
melody.’[1586] Galton sums up the evidence as follows: ‘It follows from
what has been said concerning the similar dispositions of the twins, the
similarity in the association of their ideas, of their special ailments,
and of their illnesses generally, that the resemblances are not
superficial, but extremely intimate. I have only two cases of a strong
bodily resemblance being accompanied by mental diversity, and one case
only of the converse kind.’[1587]
It has to be remembered that up to this period the twins had been reared
under very similar conditions indeed; Galton in fact says that they had
been reared ‘exactly alike’.[1588] He goes on to ask what changes were
produced when they left the family and went out into the world. He sums
up the result of his inquiries into this point as follows: ‘Here are 35
cases of twins who were “closely alike” in body and mind when they were
young, and who have been reared exactly alike up to their early manhood
and womanhood. Since then the condition of their lives has changed; what
change of nurture has produced the most variation?... They (the 35
cases) showed me that in some cases the resemblance of body and mind had
continued unaltered up to old age, notwithstanding very different
conditions of life; they showed me that in other cases the parents
ascribed such dissimilarity as there was, wholly or almost wholly to
some form of illness.’[1589] ‘We may, therefore, broadly conclude that
the only circumstance, within the range of those by which persons of
similar conditions of life are affected, that is capable of producing a
marked effect on the character of adults, is illness or some accident
which causes physical infirmity.’[1590] Galton then turns to consider
the details regarding twenty cases of unlike twins and he finds that in
spite of similar surroundings no growing resemblance can be
traced.[1591]
10. In attempting to sum up our conclusions on this subject, we may
first ask what influence is to be attributed to the environment and then
ask what bearing such influence has upon the main problem under review
in these later chapters. It has always to be recollected that changes in
the environment may have the most extreme results. Some examples were
given of experiments upon developing animals, and it was shown that in
the case of fish, for example, monsters of various kinds can be
produced. So too doubtless extreme modifications could be produced in
the case of man and are occasionally produced by untoward surroundings
and by such customs as those of the distortion of the head and of the
feet. What we want to know, however, is not what modifications can be
produced, nor what exceptional modifications sometimes arise, but what
changes are induced by the variations in the environment which usually
occur.
The answer is that, putting aside disease among the factors and leaving
out for the moment temperament among the characters, such variations as
occur are of little importance. This applies to both physical and mental
predispositions and includes the effect of not only such factors as
climate and so on but also of such factors as are summed up in a good or
bad home environment. It is probable that physical predispositions are
on the whole more susceptible to such changes as occur than are mental
predispositions. There is no reason, for instance, to think that the
normal variation of any factor which influences mental predispositions
produces as much effect as does use upon muscular development. But it is
also further clear that, though we must, keeping aside for the moment
questions connected with disease and with temperament, think of such
modifications as occur as not of much importance, nevertheless these
modifications are of greater importance than among species in a state of
nature closely related to man. Consider for a moment muscular
development. Side by side in the same street may live a man whose daily
work is wholly sedentary and whose muscles are in consequence
undeveloped, and a man who works in a mine or engineering shop and
develops his muscles accordingly. Nowhere among vertebrate animals in a
state of nature are such differences found.
Though but little is definitely known on the subject, it seems that
temperament is more susceptible to changes in the environment than are
other mental or physical characters. Changes of climate, for example,
appear to produce more marked changes in temperament than in any other
character. Temperament is certainly very susceptible to the influence of
disease, which may also profoundly affect all characters both mental and
physical. It is probably in its effects upon temperament that disease
has its chief importance. We may even have to recognize in the effects
produced by certain tropical diseases a serious hindrance to progress in
tropical countries. It is difficult, however, to disentangle from the
effects of disease in this sense the effects which it produces in the
sense awaiting consideration in later chapters. Clearly the wide
prevalence of disease, where such is the case, must form an important
factor in the surroundings which the mind has for the subject-matter of
its activities—but on this and on allied subjects there will be more to
say later.
We have already in what has just been said referred to one kind of
modification in its effect upon progress. Upon this subject in general
it may in the first place again be emphasized that, so far as is at
present known, there are no grounds for believing that modifications of
the kind considered in this chapter give rise to mutations. From this it
follows that the results of modifications are not cumulative. Unless in
every successive generation the modification is induced, it will not
reappear. Secondly these modifications on the whole tend, as in the case
of the effect of disease upon temperament, to be connected with a
condition of things that acts as a drag upon progress rather than as a
spur to progress. The reason for this is clear in the light of what has
been said in the last chapter. It was there shown that the germinal
constitution among species in a state of nature has come to be through
the action of selection of such a kind that under certain stimuli it
gives rise to a certain form. This form is that which is best adapted to
meet the normal features which characterize the niche in the organic
world which the species occupies. Large modifications only become
apparent when the species or certain members of it are no longer subject
to their normal environment. To meet the new surroundings a somewhat
different germinal constitution would give a better response. In other
words the most satisfactory conditions are those under which
considerable modifications do not arise.
Lastly we may again refer to a point that has already been alluded to.
Great stress has been laid by certain authors, for instance by Professor
Ridgeway, upon the influence of the environment upon man. Ridgeway in
one passage speaks as follows: ‘My argument was, and is, that as the ice
sheet receded, man passed upwards from the south or south-east into
Europe, and settled in the three southern peninsulas, gradually
spreading northwards over the Alps and extending eventually up to the
Baltic. As they gradually spread upwards, under the influence of the
environment (and in the environment I, of course, include food), they
grew less dark, those of them who settled permanently along the axis of
the Alps tending to have shorter skulls, while those who had passed
upwards earliest became the most blonde and tallest people in the
world.’[1592] It is clear from other passages that Ridgeway is including
two very different things under the phrase—the influence of the
environment. He is thinking of the production of modifications such as
have been studied here, and also of the elimination of certain types
under the influence of the environment. He does not make it as clear, as
is perhaps desirable, to which of these two factors he attributes most
importance. But what is more relevant to our argument is that to include
the results of selection under the heading of the influence of the
environment is somewhat misleading. Selection is a wholly different
matter and, unless it is carefully distinguished from other factors,
confusion of thought results. The effects which follow from elimination
owing to climate and food should not be summed up under the heading of
the influence of the environment; in this book they are considered in
Chapters XVII and XVIII.
XVI
HEREDITY IN MAN
1. Having touched upon the influence of the environment in producing
modifications, we have now to approach the subject of the selection of
characters, both mental and physical. It is proposed to consider in this
chapter what it is that is inherited, and in the two following chapters
to consider the results of selection.
What is meant by saying that any character is inherited is clear from
former chapters. There are certain predispositions in the germinal
constitution of every individual—predispositions to give rise to certain
characters under certain conditions and to other characters under other
conditions. There is a predisposition, for instance, in the species of
primrose referred to in Chapter XIV to give rise to red flowers at a
certain temperature and to white flowers at a different temperature, the
colour of the flower being equally inherited in both cases. We may
therefore take as our starting-point the fact that there are in the
constitution of every individual many such predispositions.
From the results of breeding experiments upon Mendelian lines certain
conclusions have been reached which carry us farther. These experiments
have shown that certain unit-characters can be isolated which behave in
a certain manner when crossed, and from the manner in which they behave
it is deduced that they depend upon unit-factors in the germinal
constitution which are invariable. The number of unit-characters which
have been detected in any one species is not large; it is true that in
one species of insect about two hundred unit-factors have been found,
but even this number can only form a small proportion of the total
number if it is the case that the germinal constitution consists
entirely of unit-factors which on crossing give the Mendelian ratio.
This is the working hypothesis which is put forward as the explanation
of inheritance, and which it is the object of investigators now to test.
We may consider for a moment what it is that this hypothesis implies.
We have to think of the germinal constitution as containing a very large
number of factors—predispositions in other words. The characters to
which these factors give rise may be the characters which we see when we
examine any individual, but more often they are not. There are, for
instance, cases in which the colour of a flower or of the coat of a
mammal are unit-characters but more often such visible characters are
the product of two or more unit-factors. There are many cases now known
in which the visible character is in this fashion due to the presence of
several unit-factors. With regard to this hypothesis in general all that
can be said is that at present no facts are known which are definitely
in contradiction to it. It is the only hypothesis which holds the
field.[1593]
Up to the present very few unit-factors have been distinguished in man.
It has been found that brachydactyly—a peculiar malformation of the
hand—presenile cataract, tylosis—a thickening of the hands and of the
soles of the feet—epidermolysis bullosa—a blistering of the skin—and
night blindness behave as simple Mendelian characters. So too does eye
colour, pigment in front of the iris being dominant to its absence—in
other words, brown, green, and hazel being dominant to pure grey and
blue. There is also some reason for thinking that musical ability is a
recessive character. On the hypothesis outlined above it must be
supposed that most of the visible characters of man are the product of
several unit-factors which have not yet been identified. What appears to
happen when matings take place between people of different colour,
stature, and so on is that there is a blending of characters in the
offspring. Such appearances are not incompatible with the hypothesis—the
assumption being that many unit-characters are concerned.
This question as to the ultimate nature of inheritance has been
introduced here because of its inherent interest. It is not as a matter
of fact strictly relevant. What we require to know is rather what
predispositions are present in the germinal constitution. It is this
which is essential; the precise manner in which the predispositions are
represented in the gametes, whether by unit-factors or not, is not
essential to the present inquiry. We require to be able to give some
answer to such questions as whether disease, intellect, and temperament
are represented in the germinal constitution or not, and we can find an
answer to these questions without concerning ourselves with the ultimate
nature of inheritance.
2. Since studies of inheritance on Mendelian lines do not at present
enable us to say what human characters are inherited, we are dependent
for our knowledge of this subject chiefly upon biometry. The method
pursued by biometricians is as follows. The particulars with respect to
any character—say stature—are noted both for the parents and for the
children. The average degree of resemblance between parents and children
can thus be measured and expressed numerically. If the resemblance was
complete, if, that is to say, in respect of any character children
exactly resembled their parents, the fact would be expressed by saying
that the correlation was equal to unity. When the resemblance is less,
the fact is expressed by representing the degree of resemblance as a
fraction. It must be emphasized that this method merely measures the
average degree of resemblance; it does not without further inquiry tell
us how far that resemblance is due to inheritance. So far as such
degrees of resemblance are found, it is quite possible, supposing that
we had no further knowledge of the subject at all, that they might arise
as follows. It might be that all men had the same germinal constitution,
and that the degree of resemblance was due to the fact that fathers and
their children were brought up under more or less similar surroundings.
Though this fact should be borne in mind, such an explanation of the
resemblances found in the cases that will be quoted in what follows is
as a matter of fact shut out, and we may accept the correlations as a
measure of the degree of likeness due to inheritance.
The correlations between parents and children and between children of
the same parents have been determined in respect of many characters—both
mental and physical—and found to be about 0·5. Thus, in respect of
height the correlation between father and son was found to be 0·514,
between father and daughter 0·510, between mother and son 0·494, between
mother and daughter 0·507, between brother and brother 0·511, between
sister and sister 0·537, between brother and sister 0·553. So too the
average parental correlation in respect to eye colour is 0·495, and the
average fraternal correlation is 0·475. With regard to ability the
fraternal correlation is 0·46, the correlation between sisters 0·47, and
that between brother and sister 0·44.
All that has been said with regard to the nature of fertilization and
development lead to a similar conclusion. In the processes of maturation
and fertilization we can detect a mechanism whereby the bearers of
inherited qualities are transmitted from parent to child. In development
we see how, when the appropriate stimulus plays upon the fertilized egg,
an adult member of the species grows up. It is only when we suppose that
within the fertilized egg there are certain predispositions in respect
of every character which are derived from the parents that we can in any
way understand how adult individuals come into being.[1594] And it must
be emphasized that, however much opinions may differ regarding the
precise nature of the mechanism of inheritance, there is no difference
regarding the fact of inheritance. All biologists are agreed on this
subject up to a point; the matters in debate are not strictly relevant
here.
3. There are certain points, however, which, in view of the form which
the discussion in the following chapters will take, require further
treatment. As regards physical characters, it is sufficient to think of
all such characters whether great or small as inherited. But with regard
to disease it may be as well to consider further to what degree it can
be said to be inherited.
What we call disease falls under two headings: disease due to the
attacks of parasites and disease due to structural defects or
weaknesses. Parasitic infections are of post-conceptional acquirement;
they may be acquired, it is true, before birth, but such an acquirement
is strictly analogous to the ‘catching’ of a disease after birth. In the
sense, therefore, that parasites are not transmitted from the parent to
the ovum, as the germinal constitution is transmitted, disease is never
inherited.
It has been shown, however, that in the case of certain diseases, such
as tuberculosis, a definite susceptibility to contract the disease is
inherited. In other words, given an equal exposure to infection, some
men do not ‘catch’ the disease, some only experience a mild form, and
others die rapidly of it. It is probable that there are innately given
degrees of susceptibility to all diseases which are caused by the
invasion of the body by small, chiefly unicellular, parasites, which
produce their harmful effects by the secretion of toxins. The same does
not apply to the diseases caused by the attacks of the larger
multicellular parasites, such as tapeworms, which, at any rate to a
large extent, produce their harmful effects directly by causing lesions
of the tissues. As to how far we have to think of different kinds of
susceptibility to different diseases, or how far diseases go in classes,
so that susceptibility to one disease goes with susceptibility to
another disease and vice versa, little is known, but it is probable that
in some cases at least there is a linkage of susceptibilities, that, for
instance, susceptibility to scarlet fever is to some extent linked with
susceptibility to measles. We must suppose that there are structural
peculiarities which underlie these different susceptibilities. Though
various hypotheses have been put forward, we are still ignorant as to
their nature. But whatever the exact nature of these structural
differences, it is clear that they are inherited like any other physical
character.
We have therefore to note that (_a_) susceptibility to specific
infections is inherited. If gross anomalies, such as polydactyly and
syndactyly (malformations of the hand) are to be accounted as diseases,
then we may note that (_b_) gross anomalies are inherited. (_c_) Minor
anomalies are also inherited. Under this head come haemophilia, due to
some peculiarity in the blood-vessels, which results in their not
contracting as they should and to the absence of coagulating power in
the blood, albuminuria, due to some defect in the filtering apparatus in
the kidney, albinism, myopia, icthyosis, and others, all of which are
clearly due to structural peculiarities. Further, we may note that (_d_)
‘other conditions due, it would seem, to disturbances of metabolism,
underlying which may very possibly be finer anatomical variations, have
for long been noted as tending to be inherited; such as obesity,
diabetes, gout, and chronic rheumatism’.[1595] Lastly (_e_) certain
nervous diseases are inherited. We may distinguish two classes of
nervous disease—the homeomorphic and the heteromorphic. ‘In the former
the offspring show the same lesions and symptoms as the parents. These
are cases more particularly of lack of development or of premature
atrophy of certain groups of nerve cells.’[1596] In the latter the
parent may suffer from one kind of disease, while the offspring may
exhibit one or more of a group of other diseases. This is attributed to
a lack of development of the highest nerve-centres as a whole. There is
a lack of ‘perfect stability and co-ordination of various parts so that
according to the strains to which the individual members of family are
subjected, now one, now the other series of centres may show itself
unable to respond adequately, and one or the other form of mental
disturbance and nervous disease may result. Here are to be included the
condition of insanity, familial epilepsy and the neuroses.’[1597] In
other words, we sometimes find stocks in which there is a nervous
weakness, which may manifest itself in very various ways, including
hysteria, epilepsy, inability to control impulse, delusion, and so on.
Alcoholism is sometimes spoken of as though it was to be regarded as an
irresistible impulse to drink. Probably we should rather imagine that a
condition of general nervous weakness may at times manifest itself in
the form of a loss of control with regard to the use of alcohol.
According to Mott ‘there can be no doubt that neurasthenics, epileptics,
imbeciles, degenerates, eccentrics, and potential lunatics—all those
indeed with an inherent narrow margin of highest control—possess a
marked intolerance to the effects of alcohol’.[1598] Certain facts are,
however, very puzzling. Suicide, for example, would seem to be a manner
in which general nervous weakness may manifest itself. Nevertheless, the
tendency to suicide appears sometimes as a very definite and peculiar
disease which manifests itself generation after generation at a certain
age. Perhaps in these cases we should rather see an example of how the
same outward circumstances—here the knowledge of the family
history—tends to cause a general nervous weakness to manifest itself in
the same way, rather than an example of a specific nervous
weakness.[1599]
4. What we know as temperament stands half-way between physical and
mental characters. As we have seen, temperament depends upon influences
exerted by the functioning of the bodily organs on the nervous system
and upon the peculiarities of the nervous system itself. Though on this
account temperament or nervous tone is peculiarly susceptible to
environmental influences, a certain condition of nervous tone is
innately given. We must suppose the actual structure of the nervous
system to be largely inherited, and we must suppose that the manner in
which the bodily organs function is largely due to their innate
organization. We have thus to think of a certain temperament as always
given in the germinal constitution. An extreme example is an innate
defect of the thyroid gland which can produce any degree of mental
apathy. Again, such characters as excitability, rapidity of response,
and differences in respect of fatiguability and recuperation are largely
inherited.
Habit is best considered under this heading. The essential fact about
habit is that, if the nervous system is stimulated in a certain fashion,
so that a stimulus passes along certain paths, the next stimulus of the
same kind will produce an impulse which passes more easily along those
paths. Thus in time the same result, whatever it may be, is achieved by
the application of a weaker stimulus. This fact, which is of great
importance, suggests an actual modification of structure—an actual
fashioning of a path. Whether this is so or not, we do not know. What is
noticeable here is that the ease with which habits are formed
undoubtedly differs from man to man, and we have again to postulate
predispositions in the germinal constitution which tend towards a
definite degree of development of the power of the formation of habits.
5. The greatest difficulties arise when dealing with the purely mental
characters. There is a general agreement among biologists that mental
characters are inherited just as physical characters are inherited. As
we have pointed out, there is evidence to this effect derived from
studies on biometric lines. The difficulties arise when we attempt to
give more precision to the statement that mental characters are
inherited. One method of approaching this problem is to analyse mental
behaviour, and to ascertain if possible what faculties there are which
cannot be explained in terms of other faculties. Such faculties are the
least that we must suppose to be given in the germinal constitution. It
does not, of course, follow that irreducible characters are Mendelian
characters. In all probability they are due to the presence of many
Mendelian factors. This analysis is a matter of great difficulty, and
there is at present no agreement among psychologists as to what ultimate
faculties of the mind are given out of which the characters we observe
are compounded. Modern analysis leads to the idea of mental process as
the activity of a subject. But though we may not think of the mind
merely as a bundle of faculties, we have to attribute certain faculties
to the subject, and the question arises as to what these faculties are.
There is less difficulty with regard to the affective and conative
faculties, that is to say, those that are connected with feeling and
striving, than with regard to the cognitive faculties. Psychologists are
to some extent agreed as to what instincts can be recognized. McDougall,
for instance, gives the following list, associating in each case with
the impulse an emotion representing the conative or affective
aspect.[1600] (1) Instinct of flight and emotion of fear. (2) Instinct
of repulsion and emotion of disgust. (3) Instinct of curiosity and
emotion of wonder. (4) Instinct of pugnacity and the combative emotion.
(5) Instinct of self-assertion and the emotion of elation. (6) Instinct
of self-abasement and the emotion of subjection. (7) Parental instinct
and the tender emotion. To the remaining instincts which he names a
special emotion is less definitely attached. These instincts are those
of reproduction, sexual jealousy, female coyness, gregariousness,
acquisition, and construction. This list is not exhaustive; there are
other instincts of less importance, such as the instinct which tends to
make a boy at a certain age leave his home. The list, however, includes
all the more important instincts.
There are a number of other emotions often described as primary which
McDougall describes as complex. Thus, according to his view admiration
is a combination of wonder and self-abasement. When fear is added, we
have the emotion of awe, and when gratitude is added we have the emotion
of reverence. Gratitude is itself a combination of tender emotion and
self-abasement. In a similar fashion loathing, fascination, and envy can
be explained. According to this view, therefore, we should not think of
separate predispositions towards these complex emotions as existing in
the germinal constitution; we should think of them as determined by the
predispositions towards the simpler emotions.
McDougall further describes three general or non-specific tendencies
which have sometimes been classed as instincts.[1601] Sympathy, or the
sympathetic induction of the emotions, describes the fact that
instinctive behaviour incites similar behaviour in the observer.
Suggestion is defined as a process of communication resulting in the
acceptation with conviction of the communicated proposition in the
absence of logically adequate grounds for its acceptance. Imitation,
which has often been used to include sympathy and suggestion, is in the
limited sense adopted by McDougall, the tendency to copy the bodily
actions of some one else. Finally there is the tendency to play.
Apart, therefore, from temperament and the faculties connected with
cognition, we have to recognize predispositions towards certain
instincts and certain general tendencies. Without question they differ
in strength from man to man; without question such differences are in
large part attributable to varying predispositions in the germinal
constitution, and we must presume that such differences are in some way
connected with differences in nervous structure or organization. The
subject is one of great difficulty, and nothing can be affirmed
regarding it with any certainty. The ultimate modes of feeling seem to
be those of pleasure and displeasure, and of excitement and depression.
It is scarcely possible to stop at this point, and it seems that we have
to go on and attribute the more specific forms of feeling or emotions to
primary faculties incapable of further analysis. So, too, conation or
striving seems to be distinguishable into striving towards and into
striving away from an object. Again as with feeling it appears that we
have to go farther and presume certain more clearly-defined faculties as
indicated above.
6. The difficulties are still greater with regard to cognition. Analysis
seems to bring us to three ultimate faculties—those of judgement, of
comparison, and of association.[1602] Judgement consists in affirming or
denying, and upon this faculty all higher reasoning is built. Memory
should perhaps be considered as a special aspect of this faculty—as the
power to think of an object over again, and to affirm or deny it to be
the same object. This faculty, together with the faculty of comparing,
enables that process of distinction and systematization to be performed
upon which all the higher developments are based. To these faculties of
analysis and synthesis are to be added the faculty of association,
whereby objects come to be thought of in groups according to the
sequence in which they came to be presented to the mind quite apart from
their intrinsic affinities or distinctions. Thus, in addition to the
faculties whereby the mind attains some grasp of the constitution of the
world of objects, there is a faculty which in some degree mirrors the
history of the world.
It is probable that in addition to these ultimate faculties, there may
be many other faculties which cannot be reduced to aspects of the
former, and have therefore to be considered also as primary. However
that may be, what is important for our present purpose is that the
faculty commonly known as ability is undoubtedly innate. It may be very
variously composed of specialized forms of these three primary
faculties, and perhaps of other faculties combined in very many ways.
Every degree of ability is known and there are many forms in which it is
specialized, such as in musical, artistic, and other directions. It has
been shown that a high development of general ability is correlated with
a high development of any special ability. In other words, we have to
think of a genius with some marked talent as possessing on an average a
high general level of ability. There is ample evidence of the
inheritance of ability, both derived from the examination of large
numbers of cases and from the analysis of family histories. This
evidence also shows that musical and other forms of special ability are
inherited. We have therefore to think of predispositions in the germinal
constitution, which give rise to abilities of all kinds, although a more
correct analysis may refer them to some combination of the ultimate
faculties enumerated above, much as certain complex emotions are to be
referred to the combination of certain primary emotions, and not thought
of as given as such in the germinal constitution.
There are other characters which do not appear to be covered by any
extension of the term ability. Such, for instance, are will and
self-control. In its essence will seems to be the rising up of some
dominating impulse which controls or harmonizes the feelings. The weaker
impulse somehow overcomes the stronger. The will is variously explained,
and in modern psychological writings often in such a manner as to
exclude the idea of a special faculty. It is not necessary here to go
into these explanations of the origin of will. It is clear that, if it
has to be referred to the working of complex faculties which are
themselves explicable in the terms of more ultimate faculties, it is in
a sense innately given. Undoubtedly will is in a sense inherited.
However much will may be a product of the environment in the second
sense, there is clearly an innate tendency towards the development of a
will of a certain form and strength. Whether therefore it is an ultimate
faculty or not, it is due in some measure either to a definite innate
predisposition or to such a combination of other innate predispositions
as give rise to the manifestation of a will of a certain nature.
Finally, we may look at the whole problem of the inheritance of mental
characters from another point of view. It is known that certain areas in
the brain associated with particular functions are differently developed
in different individuals, and that there are differences in the speed at
which the nervous impulse travels which are doubtless due to anatomical
peculiarities and so on—that there are, in fact, differences in the
physical basis which underlies the manifestation of mental characters.
It is thus easy to understand in a general way how mental characters
which are based upon the nervous organization are inherited. A man may
inherit a brain in which certain regions are of relatively large size,
or a nervous organization by which impulses are swiftly conducted, and
thus we can understand how quickness of response, power of
concentration, readiness of association, type of mind (whether emotional
or intellectual) are inherited.
7. This brief inquiry into what is given in the germinal constitution
leads to the conception of large numbers of predispositions which under
the stimulus of the environment develop into the characters that we
observe. This is true at least of physical characters. In physical
characters we observe the result of the play of the environment upon
certain predispositions. With regard to mental characters the position
is somewhat different. Into mental characters, as presented to us—into
ability, for instance—there enters the influence of the environment in
the second sense. When we are judging the ability of a man from a
practical point of view, we are judging a character into the make-up of
which has entered not only certain predispositions and a certain
environment—using environment in the sense of the complement to
inheritance—but also the results of the influence of the environment in
the second sense, such as habit and what may be regarded as tools,
namely, modes of thought and so on. In order to get at the characters we
must disentangle or allow for these tools. This difficulty does not
arise in the case of physical characters. When measuring the physical
strength of two men we are not likely to allow one man to throw an
object with a throwing-stick and another to use his own unaided
strength. But we are apt when comparing ability to forget that one man
may have learnt to distinguish between the categories when another may
not have done so. To this difficulty we shall refer again later.
These predispositions have their basis in the germinal constitution and
are therefore inherited. It is probable that we should regard the
germinal constitution as consisting of unit-factors. However that may
be, it is clear that either a differential birth-rate (reproductive
selection) or a differential death-rate (lethal selection), will change
the average germinal constitution of the race among which they are
operative. Bearing this in mind, we may inquire when and where in human
history we can detect reproductive and lethal selection at work. And we
must remember that in the first place not merely obvious factors such as
war have been and are at work, but also that subtle changes in social
life and social organization may have profound effects, and that in the
second place not merely obvious characters may be favoured or
eliminated, but the least striking and most minute (though not
necessarily the least important) characters both mental and physical may
be similarly affected.
XVII
THE EVOLUTION OF PHYSICAL CHARACTERS
1. Having discussed what is given in the germinal constitution, we are
now in a position to inquire into the question of changes in the
germinal constitution. Such changes may affect physical or mental
characters. In this chapter we are concerned with physical characters
alone. Compared with the evolution of mental characters the evolution of
physical characters is a subsidiary matter; as this evolution, however,
has gone hand in hand with the evolution of mental characters and
furthermore possesses an importance of its own, all reference to it
cannot be omitted though the subject will be treated very briefly. As a
preliminary to this inquiry we may note certain facts about the
selection of physical characters in general.
We know practically nothing as to the cause of mutations. We have,
therefore, to take mutations for granted, and to inquire how certain
stocks with particular predispositions are favoured and others
eliminated. In this process both lethal selection and reproductive
selection play a part. Among species in a state of nature lethal
selection is more important than reproductive selection; among men the
importance of reproductive selection tends to increase until in the
latest period it assumes an importance approaching that of lethal
selection.
Hitherto we have only referred in passing to the existence of tradition
among men. Tradition will be found to form a serious complication when
we come to deal with the selection of mental characters. With regard to
physical characters it also complicates the position, but only to a
relatively unimportant degree. In the first place it makes the
environment very varied, especially in industrial societies where men
living next door to one another may be subject to very different
conditions in their daily occupations. Secondly, the fact that men
protect themselves against external conditions—for instance, against
cold—may lead to a group of men who are protected surviving, where a
less well-protected group perishes, though the former may conceivably be
naturally less resistent to cold than the latter. In the broad and rapid
survey that we shall make these complications can be disregarded; the
existence of tradition does not introduce, so far as physical characters
are concerned, that peculiar complication which is the cause of much
difficulty when we come to deal with mental characters—namely, the
combination of what is acquired through tradition with the underlying
character itself in such a way that the manifestation of the character
is connected in a varying degree with its innate strength. We shall
thus, when dealing with mental characters, have to attempt to strip off
the acquirements. When dealing with physical characters we can always
get down to the character at once. There is no difficulty in separating
the arm from the tool which it employs, and we thus get directly at the
character which has developed as the result of the influence of certain
stimuli upon a given predisposition. It is, on the other hand, difficult
to separate the intellectual characters from all those traditional
elements which combine with them in their outward manifestations—to
measure, for example, the strength of the instinct of curiosity, which
involves discounting all those elements in the tradition which may
inhibit or emphasize its expression.
With regard to the strength of selection there is no exact knowledge,
with the exception of some work which has been done upon statistics for
modern communities. The occurrence of selection in the past is in fact
merely a deduction from what we know regarding innate predispositions
and regarding elimination and differential fertility. It has been shown,
however, that lethal selection does occur at the present day. Professor
Karl Pearson has calculated that selection accounts for a very large
percentage—perhaps 60 per cent.—of the deaths at the present day,[1603]
and Mr. Snow, summing up the results of an inquiry into this subject,
states that ‘natural selection in the form of a selective death-rate, is
strongly operative in man in the early years of life’.[1604] As it is
universally agreed that, if anything, the intensity of natural selection
has decreased with civilization, we may take it as certain that it was
operative to as great, or to a greater, extent during the emergence of
man and during what we have called the first and second periods of his
history.
2. During the intermediate period, which was of relatively immense
length, the greater part of human bodily evolution was accomplished.
Only two or three worn and fragmentary remains have as yet been
discovered from this period. It is at least apparent from them that the
amount of physical evolution which has been accomplished since the end
of that period is slight compared with what was accomplished within that
period. We may assume that lethal selection was strongly at work.
Changes in mode of life—the assumption, for instance, of a terrestrial
for an arboreal existence and the adoption of an upright posture—must
have involved lethal selection. These changes of habit must also have
brought ancestral man into contact with new enemies. The spreading of
man into new climatic zones was doubtless followed by selection, and
must again have involved contact with new enemies. So, too, selection
followed upon the first great steps in the acquirement of skill—the
making of clothes, the use of fire, and so on. In addition to lethal
selection, differential fertility acting through polygamy must have been
at work. In part no doubt differential fertility merely reinforced
lethal selection; but in part also it may have taken the form of sexual
selection and have favoured other types.
But when we come to details we find that we are ignorant regarding the
causes of even the largest changes. Some guesses have been hazarded. The
increase in the capacity of the skull is connected with the evolution of
the intellect and may be left for consideration in the next chapter. The
decrease in the size of the jaw and the corresponding decrease in the
size of the teeth were perhaps connected with a change in diet. The loss
of the hairy covering may have been connected with sexual selection or
it may have been favoured because it removed a lodging-place for
parasites.
3. As we pass from the intermediate to the first period of human history
we reach a region of less uncertainty. We are ignorant as to the
physical characters of man at the close of the intermediate period, but
we know that in the earlier part of the Upper Palaeolithic there was
existing one variety—the Grimaldi race—which bears certain resemblances
to the negroid type, and that in the latter part of the same period
there were existing several varieties closely resembling types of modern
European man. It seems, therefore, that, so far as this period is
concerned, we have to account not merely for the evolution of the main
types but also for the evolution of the less easily distinguishable
varieties of man. The splitting up may have begun in the former period
but it probably did not go far. As to how this evolution took place
certain conclusions may first be drawn from what we know must have been
the general conditions of life. Secondly, from what we know as to the
position among races of the first group, rather more definite
conclusions may be added concerning the nature and direction of
selection.
It has already been remarked that in all probability man spread into
various climatic zones before the beginning of the first period of
history. The consequences of this spreading of man must have been
twofold. Mankind became segregated into groups, the surroundings of
which differed, first in that they were subject to different climatic
environments, and secondly in that they were forced to pursue different
modes of life. It is clear that, whereas in some tropical regions man
would be supporting himself by hunting and collecting in such a way as
to require a certain type of bodily exertion, in a temperate region he
would be supporting himself by a very different form of exertion. This
difference between the needs of daily life would result in the favouring
of different types in the two regions. The type best adapted to gain a
living in one region would be different to that best adapted to gain a
living in another region.[1605]
Of far more importance in the production of varieties of men than the
factors already noted are differences in climate to which man has become
exposed. How great these differences are is familiar and need not be
laboured. We know little with regard to the manner in which different
types of man are suited to different types of climatic zones. But it is
clear that in general the races of men are innately adapted to different
climates. There is no historical reason why in all parts of North and
South America the European races should not have ousted the American
Indian as they have done in the United States. In Mexico and other
regions, however, where the climate differs most markedly from that in
Europe, Europeans have not succeeded in establishing themselves as they
have elsewhere in the Continent. In Mexico Indian blood largely
predominates over European, and the explanation must be that Europeans
are not so well physically adapted to the climate as are the original
inhabitants. In this there is nothing surprising. We can understand how
certain types of respiratory, excretory, and circulatory organs might be
better adapted than others to certain conditions of temperature,
moisture, actinic rays, and so on, though we may be ignorant as to what
types of circulatory and other organs are best fitted to any particular
climatic zone. It would be very remarkable if it were not so, if, that
is to say, any type of constitution was equally well fitted to any kind
of climate. In this manner to differences in habits and in climate we
may attribute the origin of the varieties of mankind.
Nevertheless, differences between races are far from being wholly due to
selection on these grounds. Sexual selection is of importance. There
grows up within each race a more or less clearly defined type of
physical beauty, and differential fertility working through polygamy
would evidently favour such types. That differences in colour to some
extent represent adaptations to climate is clear; in part such
differences are probably to be explained as due to varying ideals of
beauty, but there are probably yet other factors entering into the
evolution of racial types.
Recently Professor Keith has made an interesting contribution to the
problem of racial differences. Reference has already been made to the
ductless glands. It is now known that variations in the functioning of
these glands have a profound influence upon the bodily organs. Keith has
remarked that, if the peculiarities characteristic of the chief racial
types of man are considered together, it appears that they are
attributable to different degrees of development of these glands in
different races. It should be observed that this suggestion does not
involve the conclusion that racial differences are of the nature of
modifications. It is merely supposed that the innate development of
these glands is different in different races—that there is a
predisposition in one race to the peculiar development of one gland and
in another race to the peculiar development of another gland. The value
of the suggestion lies in the fact that it shows how many racial
peculiarities, for which there are at least no obvious explanations, may
be merely the accompaniments of a difference in the development of one
or more of these glands. It must be supposed that one or more of the
results of the developments of a gland are of direct value in facing the
peculiar conditions, whether climatic or otherwise, to which the race is
subject, and that the other consequences of the development of the gland
are in any case not prejudicial. These other consequences may possibly
take the form of noticeable peculiarities of colour or of bodily
structure which thus turn out in themselves not to be of survival value
but merely to be, so to speak, accidental peculiarities.
Some quotations from Professor Keith’s exposition of this suggestion may
make the matter more clear. ‘When we compare’, he says, ‘the three chief
racial types of humanity—the Negro, the Mongol, and the Caucasian or
European—we can recognize in the last named a greater predominance of
the pituitary than in the other two. The sharp pronounced nasalization
of the face, the tendency to strong eyebrow ridges, the prominent chin,
the tendency to bulk of body and height of stature in the majority of
Europeans, is best explained, so far as the present state of our
knowledge goes, in terms of pituitary functions.’[1606] After remarking
that the interstitial glands are largely the cause of secondary sexual
differences he goes on to say: ‘I am of opinion that the sexual
differentiation—the robust manifestation of the male characters—is more
emphatic in the Caucasian than in either the Mongol or Negroid racial
types. In both Mongol and Negro, in their most representative form, we
find a beardless face and an almost hairless body, and in certain negro
types, especially in Nilotic tribes, with their long, stork-like legs,
we seem to have a manifestation of the abeyance in the action of the
interstitial glands. At the close of sexual life we often see the
features of a woman assume a coarser and more masculine
appearance.’[1607] Later he remarks that the evidence points to the
original human colouring as black. Now, the supra-renal bodies cause a
clearing away of pigment and ‘there can be no doubt that the supra-renal
bodies constitute an important part of the mechanism which regulates the
development and growth of the human body and helps in determining the
racial characters of mankind. We know that certain races come more
quickly to sexual maturity than others, and that races vary in
development of hair and of pigment, and it is therefore reasonable to
expect a satisfactory explanation of these characters when we have come
by a more or less complete knowledge of the supra-renal
mechanism.’[1608] The thyroid acts directly upon the skin and the hair
and also upon the skeleton. ‘This is particularly the case as regards
the base of the skull and the nose, the arrest of growth falls mainly
upon the basal parts of the skull with the result that the root of the
nose appears to be flattened and drawn backwards between the eyes, the
upper forehead appears projecting or bulging, the face appears
flattened, and the bony scaffolding of the nose particularly when
compared with the prominence of the jaw is greatly reduced. Now these
facial features which I have enumerated give the Mongolian face its
characteristic aspect, and, to a lesser degree, they are also to be
traced in the features of the negro. Indeed, in one aberrant branch of
the negro race—the Bushman of South Africa—the thyroid facies is even
more emphatically brought out than in the most typical Mongol. You will
observe that, in my opinion, the thyroid—or a reduction or alteration in
the activity of the thyroid—has been a factor in determining some of the
racial characteristics of the Mongol and Negro races. I know of a
telling piece of evidence which supports this thesis. Some years ago
there died in the East End of London a Chinese giant—the subject one
must suppose of an excessive action of the pituitary glands—the gland
which I regard as playing a predominant part in shaping the face and
bodily form of the European. The skeleton of this giant was prepared and
placed in the museum of the London Hospital Medical College by Col. T.
H. Openshaw, and any one inspecting that skeleton can see that, although
certain Chinese features are still recognizable, the nasal region and
the supraorbital ridges of the face have assumed the more prominent
European type.’[1609]
4. If we turn now and look at the conditions of life among primitive
races, we find that natural selection and differential fertility tend to
work towards the preservation of existing types rather than towards
further evolution. The Australians may have existed in their present
home for many thousands of years without undergoing any considerable
change of type, and we have every reason to suppose that, if they had
been left untouched by white or other races, the racial type would have
remained substantially the same for thousands of years to come. The same
holds good if we consider any primitive race in its normal surroundings.
That this is so is clear if we glance at the chief causes of
elimination. The heavy child mortality recorded of all these races is
put down to neglect and exposure; it must on the whole result in the
elimination of the physically weak. Such customs as the bathing of
new-born babies in cold water seem designed to ensure this result. Among
the adults who on the whole are but little protected against climate
there must always be a certain tendency towards the elimination of those
less able to withstand the relatively harder seasons. There are also
many factors making for the cutting-off of the malformed and the
congenitally deficient. Among those races which normally practise
infanticide, deformed children are always killed, and among those races,
such as the Bantu races of Africa, who never regularly practise
infanticide as a custom, abnormal children are nearly always done away
with. Similarly the destruction of witches tends towards the same end
though they are more often marked by mental than by physical
peculiarities. Again the fact that abortion and infanticide are
practised to a greater degree among the less fortunate and the lower
social classes of the races in the second group has the same result, as
in general the stronger and more successful members of the race are
those who do not need to practise these customs to the same extent.
Finally, the general conditions of life among these races—more
particularly among the races of the first group—is such as to bring
about a continual elimination of the less physically fit. Speaking of
the Seri Indians McGee remarks upon the ‘elimination of the weak and
helpless’, and says further that ‘a parallel eliminative process is
common among American aborigines; the wandering bands frequently undergo
hard marches under the leadership of athletic warriors with whom all are
expected to keep pace, which leads both to the desertion of the aged and
the feeble’. He calls it ‘a merciless mechanism for improving the fit
and eliminating the unfit’.[1610]
As remarked above, the effect of polygamy must be to intensify the
action of selection. In this particular case the general result of
polygamy must be to preserve the average features of the race; for it
will be, so to speak, the all-round man, the man best adapted to the
climate, to the peculiar conditions of life and so on who will leave
most descendants. It is thus of interest to investigate the frequency of
polygamy among the races of the first two groups. This point has been
inquired into by Professor Hobhouse and his fellow authors. Polygamy was
distinguished by them into general and occasional polygamy, and though
it is very difficult to arrive at any exact figures their general
conclusions may be summed up as showing that, in all the subdivisions
considered by them, general and occasional polygamy was found in from
80–95 per cent. of the cases. General polygamy increases among the races
here placed in the second group, though there is no strong correlation
between the degree of polygamy and the economic stage. We observe in
fact a wide prevalence of polygamy among all races of any economic
stage, and upon the basis of these figures we must regard the
differential fertility arising from polygamy as a factor of great
importance.
It seems, therefore, that within the first and second periods there were
two tendencies at work—towards the evolution of varieties and towards
the maintenance of the various types. The evolution of varieties was due
in the first place to the spreading of man. As soon as spreading was
complete, a tendency towards a cessation of progress must have set in.
That further evolution took place was due chiefly to migration, with the
results of which we have yet to deal. Once varieties had been evolved,
apart from migration, and apart from changes in climate and progress in
skill, which only slightly and at long intervals modified the
surroundings, there was little basis for further evolution. Man had
mastered his surroundings up to a point and had made his position secure
in the circumstances under which he lived and the tendency was towards
the preservation of the types which had achieved these results in
different places.
5. In the third of our three periods there has been a remarkable change.
We find that there has been a gradual moving away from the conditions
under which in normal times there is in the races of the first and
second groups a rigorous elimination of those types which depart from
the mean. Lethal selection has come largely to take the form of
selection through disease.[1611] Though polygamy gradually ceases to be
a factor of importance, other forms of differential fertility become
prominent.
We may glance at the chief features of these changes. In the last
section we mentioned various factors—infanticide of the deformed,
customs with regard to the treatment of children, the neglect and
exposure of children, the general conditions of life, and so on—all of
which have as their result the cutting-off not merely of the deformed
and the monstrosities but also of all departures from the type best
fitted to contend with the climatic environment and the conditions of
daily life. Some of these factors—such as infanticide—disappear; the
action of others becomes, if anything, reversed; not only do the less
well-fitted types have a better chance of survival than before, because
the conditions are less rigorous, but they suffer little or no
disadvantage owing to the fact that the conditions have been
artificially rendered almost as favourable for the less fitted as for
the better-fitted. To take two examples, not only are men with defective
eyesight not eliminated, but they are by the invention of spectacles
placed in as good a position as those with perfect eyesight. Similarly a
woman with a narrow pelvis is, owing to the advance in surgical skill,
enabled to bear children and to transmit her peculiarity to her
daughters.
It should not be forgotten that, in spite of the gradual lessening of
the rigour of selection, selection owing to climate and the general
conditions of life still continues. But another factor has within this
period come to assume a preponderating importance, and that is selection
through disease. It was pointed out that diseases may be roughly
distinguished into those due to the attacks of parasites and those due
to structural defects. It is to diseases of the first kind that the
greater part of selection, which occurs in the third period, is due.
Some figures were given in an earlier chapter showing how large a
proportion of deaths at the present day is due to one or other of these
diseases. In the last chapter it was shown that men differ in their
susceptibility to these diseases, and selection has thus very largely
come to take the form of the elimination of the more susceptible, and of
the favouring of the naturally immune and of those who have a power of
resisting disease and of acquiring immunity. There has therefore come to
be an increasingly heavy premium upon the type of constitution which can
resist disease, and a strong constitution in this sense is not
necessarily the same as a strong constitution among primitive races
where the premium is rather upon muscular strength, perfect development
of the senses of seeing and hearing, and upon resistance to climatic
conditions. We have thus to think of the whole course of bodily
evolution as changing in the third period so as to meet a new danger
rather than as continuing on the former lines so as better to contend
with the old difficulties.
It is noteworthy that selection in this period has not been on account
of diseases of the second type due directly to structural defects. These
diseases are seldom lethal until after maturity has been reached, and
the tendency has rather been, as in the case of eyesight, towards the
increased chance of survival of those suffering from these defects.
Thus, though selection has turned in this period towards the weeding-out
of those susceptible to the attacks of parasites, it has come to
tolerate those who exhibit defects in structure as distinguished from
the peculiarities of structure which must be presumed to constitute the
physical basis of susceptibility.
All this is familiar enough. It is not so often realized that the
disappearance of polygamy in what we have called the mediaeval and the
modern sections of the third period works in precisely the same manner.
But the disappearance of polygamy does not mean that reproductive
selection ceases to be of importance. In mediaeval and modern times
celibacy, postponement of marriage, and restriction of families have
come to be practised in varying degrees by different stocks. There is
some trace of differential fertility in the earlier periods owing to
causes other than polygamy, but it is only in the mediaeval and modern
periods that they become important. It is doubtful how far, if at all,
the religious celibate class of the mediaeval period differed in
physical characters from the average. It would appear that during this
period postponement of marriage led to the producing of less children by
the lower social classes than by the upper. Therefore, so far as this
epoch is concerned, it is not apparent that differential fertility had
any considerable effect upon bodily characters one way or the other.
Possibly the net result of postponement may have been to favour the
better stocks.
Within the latter part of the modern period restriction of families has
assumed very great importance. It has been calculated that, as a
consequence of the fact that restriction is more practised by certain
sections of the population than by others, 50 per cent. of the married
population provide 75 per cent. of the next generation. It thus becomes
most important to determine whether the various sections of the
population are innately different as regards their physical characters.
Largely owing to our ignorance respecting the direct influence of the
environment, it is not possible to arrive at present at any precise
answer. But there can be little doubt that on the whole the most fertile
sections of the population are the less physically fit sections.
It is necessary, however, to view these facts in their proper
perspective. Though differential fertility of this kind may have been at
work among some of the ancient empires in their later years, it is
chiefly a very modern phenomenon characteristic of modern European
countries and their derivatives only within the last fifty years.
Therefore, however important a problem it may be for modern communities,
it is a factor which has had but little effect on human history as a
whole. It may be noticed that restriction of increase is not the only
form of reproductive selection in modern communities. Sexual selection
is also at work.[1612]
6. Such has been the direction in which, through selection and
differential fertility within races, changes have taken place. But
changes also take place through the conflict of races, and the nature of
these changes demands some notice. Warfare plays a part in the normal
existence of nearly all primitive races. It is sometimes, as among the
American Indians, a bloodthirsty affair, but more often than not it is a
relatively unimportant cause of elimination. It is not easy to arrive at
any conclusion regarding the results of warfare as an agent of
selection. Upon the whole, among primitive races, so far as physical
characters are concerned, there is probably a tendency towards the
preservation of the physically strong and fit. But it has to be
remembered that missile weapons were early introduced, and that, as
Thucydides remarked, missile weapons kill the strong man in the prime of
life as well as the weak. Again, success in warfare very largely depends
upon characters other than physical—such as the possession of skill. All
that can be said with certainty is that in the first and second periods
warfare was not a cause of elimination of the fit which it has come to
be in the third period. This latter fact has been lately brought home to
the civilized nations of the world in so obvious a manner that it need
not be further discussed.[1613]
Warfare following upon migration may exterminate whole races. The
Bushmen were apparently on the verge of extinction at the hands of the
invading Bantu peoples. In this manner a peculiar physical type may be
lost and another may become of relatively greater prevalence. Migration
may also be followed by any degree of racial mixture. Many rash
statements have been made by historians as to the biological results of
crossing. The consequences actually observed to follow upon a mixture of
races are to so large a degree the result of a conflict of traditions—a
subject with which we shall deal in a later chapter—that the purely
biological effects of crossing may be very largely obscured. Bearing
this in mind we may briefly refer to the conclusions to be derived from
recent biological work which bear on the problem. Roughly speaking there
are two possible kinds of crosses between races. First there are crosses
between the most clearly distinguished varieties such as white and
black. Heterosis, or hybrid vigour, will be exhibited in a marked
fashion in the first generation. Heterosis, the underlying cause of
which has only recently become apparent, is always at its height in the
first cross. The increase of vigour, however, is not long maintained in
subsequent generations. Further, each type, such as those which we are
considering, has a series of character complexes, built up through ages
of selection and compatible with one another, and by crossing such
complexes are broken apart. The chance of gain, on the other hand,
through the favourable re-combination of characters is small. On the
average, therefore, the result of such a cross is unfavourable. There
may also be crosses between races exhibiting less differences. Again,
heterosis will be visible on crossing. But in distinction to the results
of the former kind of cross, the other results may not be unfavourable.
Great variability may follow such a cross and this is on the whole
advantageous. Valuable character re-combinations may also come to light.
Thus we may say that, so long as there is not too great a difference
between the races which cross, the results are usually genetically
favourable; there will be the advantage of hybrid vigour, though this is
always temporary, and there may very possibly be the advantage of
valuable character re-combinations.[1614]
Migration is important not only because it is connected with war and
racial crossing but also because of the selection which follows upon
transfer to new climatic conditions. To the nature of these changes
allusion has already been made; it has been pointed out that races
adapted to maintain themselves in one environment cannot as a general
rule maintain themselves in a very different environment. To new
surroundings, which only differ slightly from the old, they may become
adapted by selection, and much selection on these lines must have taken
place as a result of racial movements in Europe. It is probably now
taking place among Europeans who have migrated to America. Dublin and
Baker, for instance, have shown that the death-rate varies considerably
among the different racial elements who have immigrated, some elements
being probably better adapted to the new environment than others.[1615]
Similarly selection may be going on within modern races owing to the
rapid urbanization of industrial countries. Urban conditions may be more
favourable to some types than to others. But it has not yet been shown
in what direction these changes, if they are in progress, are taking.
Summing up our conclusions we may say that the great changes in human
bodily form were accomplished in the intermediate period when the
splitting up into varieties may also have begun. This splitting was
continued in the first period and the modern types were formed before
the end of that period. The chief characteristic, however, of the first
and second periods was the maintenance of the types evolved, though this
was interfered with by migration which brought about elimination of
certain types, racial mixture, and further climatic adaptation. Finally,
in modern times there has been a lessening of the stringency of
selection, which previously tended to maintain the existing varieties,
and a turning of lethal selection to the building up of immunity against
disease.
7. There are one or two other points connected with germinal change
about which a word may be said. Of the origin of mutations we know
nothing, but since in all probability the ultimate cause of mutations
may have to be sought in some kind of environmental change, it should be
borne in mind that, as man is subject to an immense variety of
environmental stimuli, mutations may be more frequent in man than in any
species in a state of nature. It has been suggested that the germinal
constitution may be adversely affected by certain factors, especially by
the use of alcohol. Of this there is no certain evidence.[1616] It has
been supposed that there may be some connexion between the difference in
age of the parents on the one hand and the germinal constitution of the
offspring on the other. It has been supposed, for instance, that the
offspring are innately more vigorous when the parents are at a certain
age. So far as investigation has gone at present, it has not been
established that there is any such connexion—of sufficient importance at
least to deserve consideration here. In other words, the fact that among
certain races young men have wives of considerably greater age than
themselves and older men young wives, does not to any noteworthy extent
affect the germinal constitution of the race. Again it has been stated
that the first-born are innately inferior to the later-born
children.[1617] This conclusion has been criticized.[1618] As, however,
the preponderance of first-born children among the offspring as a whole
would not appear to be markedly greater at any one period of history
than at another, the inferiority of the first-born, if it exists, would
make no difference between men of different races at the same or at
different times.
The correlation of characters one with another should not be forgotten.
The favouring of one character may involve the favouring of quite other
characters. Of this what was said regarding the ductless glands is an
example. It has been supposed that liability to disease is correlated
with pigmentation and that, owing to selection through disease, a change
in the average pigmentation is taking place. Attempts to establish this
correlation have, however, failed. It is of particular interest to
notice that no correlations have been found between physical and mental
characters; this is so even as regards intellect and size of head.
8. A survey of the facts regarding the bodily evolution of man, and of
the conditions under which it has taken place, shows that there is at
least no more difficulty in understanding how it has come about than in
understanding how the varieties of any other species have come into
existence. Given mutations, the action of selection and of differential
fertility provides an explanation which is in general satisfactory,
though we may be a very long way from understanding how any one
particular change came about. There are in fact greater difficulties met
with from time to time in trying to reach a satisfactory explanation of
evolution among other animals than when dealing with man. The evolution
along particular lines of organization, the evolution of teeth and horns
among mammals, for instance, raises a difficulty which seems in the
present state of our knowledge perhaps to require the assumption that at
times there is a tendency for the continual occurrence of mutations in
the same direction. Such a difficulty does not occur in the case of
human bodily evolution.
It has been suggested that the facts regarding the course which the
evolution of living organisms has taken requires the assumption that
large mutations have occurred from time to time and have established
themselves as varieties. There is no doubt that large mutations do occur
and have established themselves in the course of the evolution of the
varieties of animal types known to us, and they may have done so in the
case of man. There is, however, no reason to imagine that the origin of
any particular change in man was due to a large mutation. It has been
stated that the number of chromosomes is different in the white man and
in the negro, and upon the basis of this statement it has been suggested
that one variety had arisen as a mutation from the other. This
statement, however, was apparently based upon erroneous observation.
Again, it has been suggested that the Pygmy type arose as a mutation.
But it has been observed that some Ba Twa pygmies of the Congo who three
generations ago left their forests, settled near the Bushongo, and took
to agriculture have become markedly taller. Intermarriage is said to be
out of the question and therefore we are led to suppose in the new
environment a taller type has been favoured.[1619] If this is so, if a
taller type can be selected by degrees in one environment, the shorter
type may equally well have been selected in another environment.
So far, therefore, as the history of man outlined in the fifth chapter
is the history of the development of his bodily structure, so far the
explanation of history is to be sought in changes in the germinal
constitution, and the changes undergone are strictly comparable with the
changes among species in a state of nature, though owing to the more
varied environment outward differences in the case of man may be rather
more often due to environmental influences than in the case of species
closely related to man.
XVIII
THE EVOLUTION OF MENTAL CHARACTERS
1. When we originally asked how far changes in the quality of the
population accounted for the facts given in the sixth chapter, it was at
once obvious that the interest centred in mental changes. Now that we
have gained some idea as to what is given in the germinal constitution
and as to the influence of the environment in general, we are in a
position to come more closely to the main problem. Three questions
present themselves. We have to inquire into the facts regarding the
stage of mental evolution reached at any one time. This involves making
both an estimate as to the extent of the gap between the pre-human
ancestor and Palaeolithic man and an examination of the differences in
the mental characteristics of the chief living types of man which may be
taken roughly to represent stages reached in the three chief periods. We
have next to ask if we can account for these facts, and this involves an
inquiry into selection, differential fertility, and such other factors
as may assist to explain changes in the germinal constitution. Lastly we
have to ask how far such changes as have taken place are correlated with
the main features of human history.
To make an estimate of the stage of mental evolution reached by one race
as compared with that reached by other races is not an easy matter. To
begin with there is the difficulty of discounting the direct influence
of the environment. Temperament we found to be peculiarly susceptible to
environmental influence. Temperament affects the functioning of other
mental characters in a very important manner. ‘Effective mental
ability’, says Professor Punnett, ‘is largely a matter of temperament,
and this in turn is quite possibly dependent upon the various secretions
produced by the different tissues of the body. Similar nervous systems
associated with different livers might conceivably result in different
individuals upon whose mental ability the world would pass a very
different judgment.’[1620] Apart, however, from this difficulty and
apart from the influence of disease, it is not probable that other
factors in the environment have any marked direct effect upon either
disposition or intellect.
There is a far more serious difficulty to which allusion has already
been made. It arises from the fact that mental faculties as exhibited in
daily life are overlaid by tradition and shaped by habit. There is no
difficulty in getting down to any physical character. It is always
possible to separate the limb from the tool which it uses. It is
frequently very difficult to effect the corresponding separation between
the faculty and the tool in the case of mental characters. Human mental
characteristics, as manifested in daily life, represent the combination
of acquirements with a certain basis. By the basis is meant that which
develops as the result of environmental stimuli acting upon the
predispositions. The basis of all mental faculties is, therefore, that
which strictly speaking is comparable with physical characters. Mental
characters as manifested in daily life represent this basis combined
with tradition. This applies not only to the intellectual but also to
the instinctive faculties. The manifestation of instinct is dependent
upon the channels into which it has been led by tradition and upon the
outlets which tradition provides for it.
In attempting to estimate the stage of evolution of mental characters
reached at any one time, we must, as far as we can, allow for all that
obscures their manifestation. There are several different ways in which
this may be attempted and it will be found possible to reach a fairly
definite conclusion with regard to the degree of development of mental
characters as exhibited by two races as different as the white and
black. But the inquiry into the differences between the more nearly
related varieties, such as the different branches of the white race,
present far more difficult problems, and by these methods we shall not
be able to approach them with much hope of success. Further, these
difficulties will be more strongly felt when we go on to inquire into
the causes of the changes which have led to the evolution of the
different types. Therefore, though in this chapter we shall reach
certain conclusions as to the nature, causes, and results of mental
changes in the earlier periods, we shall find that, owing to the
difficulties mentioned, we are unable to reach any conclusion as to the
later periods until we have inquired into the importance of tradition.
It will thus be necessary to cut short this inquiry and turn to consider
tradition in the following two chapters. Only when this subsidiary
inquiry has been made shall we be able to complete our estimate as to
the part played by changes in the germinal constitution so far as they
affect mental characters.
2. The indications as regards mental development obtainable from a study
of fossil remains are, of course, very vague. Such as they are, however,
considerable interest attaches to them. In the later part of the first
period, in the Upper Palaeolithic, that is to say, we meet with types of
men whose cranial capacity and the formation of whose brain, so far as
it can be judged from skulls, do not indicate any difference in mental
capacity as compared with modern man. It must be emphasized that this is
a very rough method of comparing intellectual capacity. Something,
however, may be deduced from such observations, and it is probable that,
though there may have been noteworthy differences between Cro-Magnon and
modern European intellectual capacity, as we judge differences to-day,
nevertheless looking at human evolution as a whole, we cannot escape the
conclusion that by the end of the first period, before man had learnt to
support himself otherwise than by hunting and fishing, by far the
greater part of the journey from the condition of our pre-human ancestor
to that of European man had been accomplished. This is a very important
deduction, because, inasmuch as the greater part of the progress in
skill had still to come, it means that progress in intellectual capacity
and progress in skill did not go hand in hand.