CONCLUSION 475
Summary of the argument and of the conclusions.
APPENDIX I 483
Summary of evidence as to restriction of increase amongst
Primitive Races.
APPENDIX II 488
LIST OF AUTHORITIES QUOTED 489
INDEX 509
LIST OF ABBREVIATIONS
_A. R. B. E._ = Annual Report. Bureau of Ethnology, Smithsonian
Institution.
_A. R. S. I._ = Annual Report of the Smithsonian Institution.
_Am. Anth._ = American Anthropologist.
_Am. Jour. Obstet._ = American Journal of Obstetrics.
_Am. Stat. Ass._ = Publications of the American Statistical
Association.
_Ann. de Pal._ = Annales de Paléontologie.
_Ann. Mus. Congo Belge_ = Annales du Musée du Congo Belge.
_Arch. für Anth._ = Archiv für Anthropologie.
_Aust. Med. Jour._ = Australian Medical Journal.
_Biol. Bull._ = Biological Bulletin.
_Bull. Soc. Anth._ = Bulletin de la Société d’Anthropologie.
_C. I. A._ = Congrès International d’Anthropologie.
_Cent. für Min., Geol. und Pal._ = Centralblatt für Mineralogie,
Geologie und Paläontologie.
_Coll. Mon. Eth._ = Collection de Monographies Ethnographiques.
_Eug. Lab. Mem._ = Eugenic Laboratory Memoirs.
_Eug. Rev._ = Eugenics Review.
_Geog. Jour._ = Geographical Journal.
_Int. Arch. Eth._ = Internationales Archiv für Ethnographie.
_J. A. I._ = Journal of the Anthropological Institute.
_Jour. Eth. Soc._ = Journal of the Ethnological Society.
_Jour. Pol. Soc._ = Journal of the Polynesian Society.
_Jour. Roy. Agric. Soc._ = Journal of the Royal Agricultural Society.
_J. R. S. S._ = Journal of the Royal Statistical Society.
_Mem. Am. Anth. Soc._ = Memoirs of the American Anthropological and
Ethnological Societies.
_Mem. Anth. Soc._ = Memoirs of the Anthropological Society.
_Mem. & Proc. Man. Lit. & Phil. Soc._ = Memoirs and Proceedings of the
Manchester Literary and Philosophical Society.
_Mém. Soc. Anth._ = Mémoires de la Société d’Anthropologie.
_Phil. Trans._ = Philosophical Transactions of the Royal Society.
_Quart. Jour. Geol. Soc._ = Quarterly Journal of the Geological
Society.
_Q. J. M. S._ = Quarterly Journal of Microscopical Science.
_Rev. Col. Inter._ = Revue Coloniale Internationale.
_Rev. d’Anth._ = Revue d’Anthropologie.
_Rev. d’Eth._ = Revue d’Ethnographie.
_S. I. B. E._ = Smithsonian Institute, Bureau of Ethnology.
_Soc. Rev._ = Sociological Review.
_Trans. Amer. Gyn. Soc._ = Transactions of the American Gynecological
Society.
_Trans. & Proc. N. Z. Inst._ = Transactions and Proceedings of the New
Zealand Institute.
_Trans. Edin. Obstet. Soc._ = Transactions of the Edinburgh
Obstetrical Society.
_Trans. Eth. Soc._ = Transactions of the Ethnological Society.
_U. S. Geog. & Geol. Survey_ = United States Geographical and
Geological Survey of the Rocky Mountain Region.
_Z. G. E._ = Zeitschrift der Gesellschaft für Erdkunde.
_Zeit. für all. Erd._ = Zeitschrift für allgemeine Erdkunde.
_Zeit. für Eth._ = Zeitschrift für Ethnologie.
_Zeit. für Morph. und Anth._ = Zeitschrift für Morphologie und
Anthropologie.
_Zeit. für Soc._ = Zeitschrift für Socialwissenschaft.
I
HISTORICAL
1. Problems of population fall into two main groups—those connected with
the quantity and those connected with the quality of the population.
Considerations of the population problem are commonly devoted to one of
these chief aspects to the exclusion of the other with the result that
the relation between them is seldom appreciated. It is one of the
objects of this book to show that all problems of population have the
same origin. The development of biological knowledge in the last
century, and in particular the discussion of evolution, have made it
clear that the whole population question and all the problems arising
therefrom have their origin in the fact that mankind has a definite
position in the animal kingdom. In the next two chapters an attempt is
made to set out the basis of the whole question in the light of modern
research, and in the fourth chapter are discussed the nature of the
various problems and their relation to one another; first those which
are connected with the quantity and then those that are connected with
the quality of the population.
This was not, however, the manner in which the question was first
approached. There was not, to begin with, an understanding of the
zoological position of man leading to a growing comprehension of the
problems to which it gave rise. From early days attention was
particularly directed to the question of numbers. Between the fifth
century b. c. and the eighteenth century a. d.—between, that is to say,
the time of Plato and that of Malthus—opinions were often expressed
regarding the desirability or otherwise of a dense population. The work
of Malthus focussed opinion upon this point. In a restricted sense this
problem can be solved without an understanding of the biological origin
of the whole question, and the discussion which followed the publication
of the _Essay on Population_ has resulted in the general acceptance of a
solution by students of political economy. In a wider sense the solution
of this problem depends upon a comprehension of its biological origin,
and it was not therefore until after the middle of the last century that
all the problems connected with quantity fell into their proper setting
owing to the work of Darwin and Wallace, both of whom acknowledged their
debt to Malthus. The latter, though he did not in any way realize the
fact, was discussing a point which is most intimately connected with
evolution, and both Darwin and Wallace were influenced by their
acquaintance with the work of Malthus in arriving at their explanation
of the process of evolution. Thus from the time of Darwin and Wallace it
has been possible to view the population problem as a whole, though the
discussions of the problems connected with quantity have been pursued
independently not only before but also after the publication of the
_Origin of Species_.
Problems of quality did not arouse the same early interest. It is, of
course, well known that Plato was occupied with this aspect of the whole
problem;[1] Roman authors also commented upon the eugenic bearing of
certain practices.[2] In later days in a remarkable book Campanella
dwelt upon the importance of good breeding.[3] But the interest in
quality was not, as was the interest in quantity, widespread or long
maintained; it was not until the origin of living species by evolution
had been generally accepted and some knowledge of inheritance had been
gained, that problems of quality came to occupy anything more than the
passing attention of mankind.[4] J. S. Mill and Buckle, for instance,
both of whose opinions were formed just before the time when the
importance of heredity came to be appreciated, deny that it is in any
way relevant to the study of social problems.[5]
2. In the preface to the greatly enlarged second edition of his famous
book Malthus stated that he had found many references to the subject of
which he had not been aware when he published the first volume.[6] He
acknowledged that several authors had shown themselves to have possessed
a grasp of the ‘principle’ which it was the object of his book to
demonstrate. Among these he mentions Plato and Aristotle. In these cases
Malthus was too anxious to attribute the first enunciation of the
‘principle’ to others. It was only owing to the very peculiar
circumstances of Greek life that the problem ever arose at all. A
consideration of the ideal city state involved the question as to what
was the most desirable number of citizens. This point occupied Plato’s
attention, and in one place he deals with it in detail. There should be,
he says, 5,040 citizens in the state.[7] In the _Republic_ he explained
that the number of citizens was to be kept about the same by a strict
regulation of unions.[8] In the _Laws_, however, no such system is
advocated, and he discusses the possibility of a failure to maintain the
number.[9] He appears to think that various checks such as infanticide
and ‘inundations’ will keep numbers close to the desirable level; if too
great an increase takes place, then recourse must be had to emigration.
It does not seem that the problem was ever approached more closely in
Greek literature.
References to this subject by Roman authors are confined for the most
part to laments over the infertility of the old Roman stock. That which
drew the attention of the Romans to the subject was thus a peculiar
phase of the problem, and the views expressed by them were in
consequence usually limited to the search for a remedy for a particular
weakness in national life. As we shall point out later, it is doubtful
how far infertility was characteristic of all classes; that it was not
widespread seems incidentally to be indicated in the following curious
passage from Tertullian in which he is led to express views reminiscent
of many modern contributions to the subject. Tertullian is confuting the
Pythagorean theory of the transmigration of souls, and argues that, if
it were true, the number of men must remain unchanged. But, he says,
this is obviously not so; population continually increases. This leads
him to refer to the state of contemporary civilization. ‘We find’, he
says, ‘in the records of the Antiquities of Man[10] that the human race
has progressed with a gradual growth of population.... Surely it is
obvious enough, if one looks at the whole world, that it is becoming
better cultivated and more fully peopled than anciently. All places are
now accessible, all are well known, all open to commerce; most pleasant
farms have obliterated all traces of what were once dreary and dangerous
wastes; cultivated fields have subdued forests; flocks and herds have
expelled wild beasts; sandy deserts are sown; rocks are planted; marshes
are drained; and where once were hardly solitary cottages are now large
cities. No longer are savage islands dreaded, nor their rocky shores
feared; everywhere are houses, and inhabitants, and settled government,
and civilized life. What most frequently meets our view is our teeming
population; our numbers are burdensome to the world, which can hardly
supply us from its natural elements; our wants grow more and more keen,
and our complaints more bitter in all mouths, whilst nature fails in
affording us her usual sustenance. In very deed, pestilence, and famine,
and wars, and earthquakes have to be regarded as a remedy for nations,
as a means of pruning the luxuriance of the human race.’[11]
3. It is not until we arrive at the sixteenth century that we discover
any considerable interest in the matter. From thence onwards references
are very frequent. In a general way it is not difficult to understand
how this comes about. The movement of thought at that time turned to
problems of practical importance. The interest in questions connected
with population was above all things due to the problems created by the
rise and consolidation of the great European states. In some measure
also the voyages of discovery and the foundation of colonies drew men’s
thoughts to these questions. It is, as we shall see, in the works of the
new class of political writers and theorists, and in the descriptions of
travel, that we find most references.[12]
These references take for the most part the form of discussions as to
the desirability or otherwise of a large population. There is, indeed,
often but little discussion; the benefits of a large population seemed
so obvious. Men were mostly of the same opinion as the author of the
book of Proverbs, ‘in the multitude of the people is the king’s glory;
but in the want of people is the destruction of the prince.’[13] The
reasons are not far to seek. A large population appeared to mean both
power and riches. The advantage of a large population in supplying a
large army proved most attractive and greatly influenced the authors of
the eighteenth century.[14] It has not altogether lost its attraction
for some people at the present day, as we shall have reason to notice in
a later chapter. This simple view of the benefits of a large population
coincided with the development of the mercantile theory of trade.
Authors of this school of thought also concluded that upon the whole the
larger the population the better. Protests against this point of view
are, however, met with from time to time. Those responsible for this
opposition to the prevailing opinion were influenced in some cases more
by observation than by theory and in other cases more by theory than by
observation. As instances of the former several English writers of the
end of the sixteenth and beginning of the seventeenth centuries may be
cited; as instances of the latter several authors chiefly belonging to
the later part of the eighteenth century. The views of the
last-mentioned authors are often influenced by a conception of the
relation between population and subsistence closely similar to that of
Malthus. But they are not alone in their anticipation of his position.
From the sixteenth century onwards we find in passages dealing with
population more or less clear statements of the Malthusian position.
These authors, however, are not always led to an unfavourable view of an
increase in population. Many of them, indeed, support the current view
as to the advantages of large numbers. Nevertheless on the whole a
consideration of the connexion between population and the food-supply is
usually associated with a fear of increase. We may now review in more
detail the trend of opinion sketched above. This will bring us to the
publication of the _Essay on Population_.[15]
4. Long before the sixteenth century men gave expression to the view
that large numbers are beneficial. ‘Quae familia plus multiplicatur in
prolem, amplius cedit ad firmamentum politiae,’ said Saint Thomas
Aquinas.[16] But it is only later that we meet with a marked insistence
on this view. ‘In my opinion’, says Bodin, ‘they erre much who doubt of
a scarcitie by the multitude of citizens and children, when as no cities
are more rich nor more famous in arts and discipline than those which
abound most with citizens.’[17] According to Botero ‘the greatness of a
citty is sayd not to be the largeness of the citty or the circuit of the
walls, but in the multitude and the number of the inhabitants and their
power’.[18] Machiavelli held very similar views, and Henry IV of France
is reported as saying that ‘the strength and riches of kings consist in
the number and opulence of their subjects’.[19] In accordance with the
views thus widely and strongly held, examples of which might be
multiplied almost to any extent, practical measures were taken to
encourage the increase of population. Of these the best known is the law
of Colbert passed in 1664. Like most of such laws it was modelled on the
laws of the later Roman Empire. Similar laws were at one time or another
in force in most European countries.
Towards the end of the seventeenth century there arose a school of
writers who might be classed as political economists, though the term
was not in use. In accordance with the mercantile theory of commerce
then predominant a large population was held to be advantageous. The
older and vaguer theory that a dense population was necessary if the
state was to be powerful was found to coincide with the newer theories
as to conditions of prosperous trade. Of these authors Petty and Graunt
are celebrated as among the pioneers of statistics. According to the
former: ‘fewness of people is real poverty; and a nation in which are
eight millions of people are more than twice as rich as the same scope
of land in which are but four.’[20] ‘Forasmuch as princes’, says Graunt,
‘are not only powerful but rich according to the number of their people
(hands being the father as lands are the mother and womb of wealth) it
is no wonder that states by encouraging marriage and hindering
licentiousness, advance their own interest, as well as preserve the laws
of God from contempt and violation.’[21] Sir Charles Davenant and Sir
Josiah Child are two of the foremost authors of this school. The former
writes as follows: ‘people are the real strength and riches of a
country; we see how impotent Spain is for want of inhabitants with their
mines of gold and silver and the best ports and soil in the world; and
we see how powerful their numbers make the United Provinces with bad
harbours and the worst climate upon earth. It is perhaps better that a
people should want country than that a country should want people. When
there are but few inhabitants and a large territory, there is nothing
but sloth and poverty; but when great numbers are confined to a narrow
compass of ground, necessity puts upon them invention, frugality, and
industry; which in a nation are always recompensed with power and
riches.’[22] The latter refers more than once to the subject. ‘Whatever
tends to the population of a country tends to the improvement of
it.’[23] ‘Most nations in the civilized parts of the world are more or
less rich or poor proportionable to the poverty or plenty of their
people and not to the sterility of their lands.’[24] To these quotations
we may add one from Sir William Temple: ‘I believe the true and original
ground of trade to be a great multitude of people crowded into a small
compass of land.’[25]
It would be possible to quote many similar remarks from authors who
wrote in the following century. Frederick the Great had very decided
opinions. In a letter to Voltaire he says: ‘Je regarde les hommes comme
une horde de cerfs dans le pare d’un grand seigneur et qui n’out pas
d’autre fonction que de peupler et remplir l’enclos.’[26] Hume speaks of
‘the general rule that the happiness of any society and its populousness
are necessary attendants’.[27] Adam Smith says ‘that the most decisive
mark of the prosperity of any country is the increase of the number of
its inhabitants’. Nevertheless that which interests us most in the
authors of this period is the growing interest in other aspects of the
subject.
5. Before referring to the more or less close anticipations of the views
of Malthus we may note that these optimistic views were not everywhere
accepted. In England particularly, towards the end of the sixteenth
century, several writers expressed a dread of over-population. According
to Holinshed there were some men ‘affirming that we had already too
great a store of people in England; and that youth, by marrying too
soon, do nothing profit the countrie, but fill it full of beggars, to
the hurt and utter undoing (they saie) of the commonwealth’.[28] Later
we find Brückner speaking as follows: ‘there are some who believe that a
people can never be too numerous and who speak of increase as if it
always contributed to happiness, and who consequently continually urge
the sovereign to encourage multiplication. The truth of the matter is,
however, often far different, depending on the country and
circumstances. In a free and enlightened nation, which has great natural
advantages, and which is protected from the invasions of less fortunate
neighbours, increasing numbers are a good.... In countries not so
circumstanced increase is worse than useless; it is, as a matter of
fact, impossible, and attempts in this direction can but result in added
suffering and an increased number of deaths.’[29] Arthur Young said the
same in more emphatic terms. ‘Of all the subjects of political economy I
know not one that has given rise to such a crowd of errors as that of
population. It seems for centuries to have been considered as the only
test of national prosperity. The politicians of those times, and the
majority of them in the present, have been of the opinion that to
enumerate the people was the only step to be taken in order to ascertain
the degree in which a country was flourishing. In my tour through the
North of England, 1769, I entered my caveat against such a doctrine, and
presumed to assert “that no nation is rich or powerful by mere numbers
of people; it is the industrious class that constitutes a nation’s
strength”; that assertion I repeated in my _Political Arithmetic_ in
1774.’[30] About the same time Rousseau remarked that ‘il y a pire
disette pour un état que celle d’hommes’.[31]
6. In the eighteenth century the problem was often discussed with
reference to the connexion between the population and the food-supply.
The contrast between the vast possibilities of increase and the
smallness of the actual growth in population also often attracted
attention. ‘Through various causes’, says Wallace, ‘there has never been
such a number of inhabitants on the earth at any one point of time as
might have been raised by the prolific virtue of mankind. The causes of
this paucity of inhabitants and the irregularity of increase are
manifold. Some may be called physical, as they depend entirely on course
of nature, and are independent of mankind. Others are moral and depend
on the affections, passions, and institutions of men.... To this last we
may refer so many destructive wars which men have waged against one
another; great poverty, corrupt institutions, either of a civil or
religious kind, intemperance, debauchery, irregular amours, idleness,
luxury, and whatever prevents marriage, weakens the generating faculties
of men, or renders them negligent or incapable of educating their
children, and cultivating the earth to advantage. ’Tis to such
destructive causes that we must ascribe the small number of men.’[32]
Sir James Steuart devotes a considerable amount of space to this
subject. ‘The generative faculty’, he says, ‘resembles a spring loaded
with a weight, which always exerts itself in proportion to the
diminution of resistance; when food has remained for some time without
augmentation or diminution, generation will carry numbers as high as
possible; if then food come to be diminished, the spring is overpowered;
the force of it becomes less than nothing. Inhabitants will diminish, at
least in proportion to the overcharge. If, upon the other hand, food be
increased, the spring, which stood at 0, will begin to exert itself in
proportion as the resistance diminishes; people will begin to be better
fed; they will multiply, and in proportion as they increase in numbers,
the food will become scarce again.’[33]
Malthus tells us that when he wrote his first edition the only authors
‘from whose writings he had deduced the principle which formed the main
argument of the essay’ were Hume, Wallace, Adam Smith, and Price.[34] In
the interval between the publication of the first and second editions of
the Essay he found that he had been anticipated more or less by many
others. Subsequently many other similar passages have been brought to
light. It is not worth while to discuss how far Malthus had been
anticipated. It is enough to note some of the opinions that had been
expressed. In the eighteenth century the fact that there is a connexion
between the population and the food-supply had become a commonplace. ‘La
mesure de la subsistance est celle de la population,’[35] said Mirabeau,
and the remark could be paralleled many times over.[36] Frequent
references to the vast power of human increase may be found much
earlier. In his _History of the World_ Raleigh had remarked that were it
not for wars, famines, pestilences, and so on, a teeming population all
the world over would have resulted long ago.[37] Machiavelli refers more
than once to the existence of checks. He attributed the barbarian
invasions in the later days of Rome to an unusually rapid increase of
the tribes beyond the Rhine and the Danube.[38] One of the most
interesting references to the subject is to be found in the work of
Botero from which we have already quoted. ‘I say, then, that the
augmentation of Cities proceedeth partly out of the virtue generative of
men, and partly out of the virtue nutritive of Citties. The virtue
generative is without doubt to this day the very same, or at least such
as it was three thousand years past. So that if there were no other
impediment or let therein, the propagation of mankind would increase
without end and the augmentation of Citties would be without terme. And
if it do not increase in infinite, I must needs say, it proceedeth out
of the defect of nutriment and sustenance sufficient for it.’[39] Later
on he continues: ‘although men were as apt to generation in the height
and pride of the Roman Empire, as in the first beginning thereof; yet,
for all that, the people increased not proportionately. For the virtue
nutritive of Citties had no power to go further.... By the selfe same
reason, mankinde growne to a certain complete number, hath growne no
further. And it is three thousand years agone and more, that the world
was replenished as full with people as it is at present.’[40]
What are perhaps more remarkable than these references to the relation
of numbers to the food-supply, so far as anticipations of Malthus are
concerned, are discussions mentioning the ratios which are found from
time to time. In the _Primitive Origination of Mankind_, Sir Matthew
Hale endeavours to show that mankind must have had a beginning and must
have an end, and finds support for this thesis in the facts regarding
human fecundity. He calculated that the numbers of mankind must increase
in a geometrical ratio unless hindered by checks. Obviously it has not
done so chiefly because, owing to absence of sufficient food, large
numbers are always being removed by various agencies which he enumerates
as plagues, famines, wars, floods, and inundations.[41] Sir William
Petty deals with the geometrical ratio at some length. He drew up an
elaborate table which, assuming four thousand years to have passed since
the flood, shows how an estimated world population of 320,000,000 could
have been arrived at.[42] The ratios, however, never played a very
prominent part in the discussion until after the publication of
Malthus’s book. They reappear now and again, as for instance in a book
by Saxe.[43]
7. Malthus published his first edition in 1798. He was born in 1766 at
the ‘Rookery’, a country house of some size near Dorking. In 1784 he
went up to Cambridge. In early days he had shown signs of ability and at
the university fulfilled this promise; he gained some prizes and was
placed as ninth wrangler in the mathematical tripos of 1788. In 1793 he
was elected fellow of his college, but only resided occasionally. In
1798 he was curate at Albury, close to his birthplace; in 1799 he
travelled through Sweden, Norway, and Russia, to collect information for
his second edition; in 1802, owing to the Peace of Amiens, he was
enabled to travel through Switzerland and France. The second edition
appeared in 1803. It was virtually a new book. The four succeeding
editions that were published in his lifetime were mainly reprints of
this edition with some new matter added. In 1804 he married, and in 1805
became Professor of History and Political Economy at Haileybury College,
which post he held until his death in 1834.[44]
It would seem that Malthus and his father used often to discuss new
books and questions of the day. His father, Daniel Malthus, was inclined
to favour the revolutionary school; Robert Malthus thought that he saw
serious objections to Godwin’s views on the subject of ‘perfectibility’,
and was so much impressed by them that he decided to put his ideas in
writing. Whereas in the first edition Malthus was chiefly concerned with
controverting Godwin and his school, by the time of the second edition
he had lost interest in this side of the matter and his attention was
almost entirely devoted to the problem of population.
Such was the origin of the book which focused the attention of men on
the population question. In the sixth chapter we shall have to review
the position which it sets out and to trace the subsequent development
of the theory. It is sufficient to say here that according to Malthus,
whereas population tends to increase in a geometrical ratio, food tends
to increase in an arithmetical ratio. As a result population is checked
by the operation of vice and misery, to which factors he added, in the
second edition, moral restraint. Statistics showed, even in the lifetime
of Malthus, that the increase of food was not limited to an increase in
an arithmetical ratio, and thus in reality the theory fell to the
ground. It was, however, only gradually realized that this was so and
that the relation between population and the food-supply is connected
with the question of the return to industry, which may at any one time
be increasing or decreasing according to the operation of many factors,
of which the increase in skill is the chief. The points which are of
interest in this historical sketch are the strong feelings which the
book aroused among the adherents of the various schools of thought, the
practical movement to which it gave shape, and finally the influence
which it had upon Darwin and Wallace.
8. From what has been said, it is clear that the ground had been well
prepared for a favourable reception. Further the ‘populousness of
ancient nations’ was a famous theme for controversy in the eighteenth
century. There had also been much discussion as to whether the
population of England was increasing or decreasing.[45] Again, in part
owing to the industrial revolution, and in part owing to the war,
questions as to poverty had attracted much attention, and to them
Malthus’s book had direct reference. Thus it is not surprising that the
success of the first edition was great and immediate.[46] Godwin
admitted that it had ‘converted friends of progress by the hundred’.[47]
Pitt dropped his Poor Law Bill in 1800 partly because of the opposition
of those who had been influenced by the Essay. The earlier supporters of
Malthus belonged, for the most part, to the Whig and Utilitarian
schools. Pitt, Paley, Copleston, James Mill, Senior, Ricardo, Macintosh,
and Whitbread all adhered to Malthus. In 1819 Brougham referred to the
‘principle of population as one of the soundest principles of political
economy’.[48] Support for Malthus was especially strong among the
Utilitarians. Referring to about the year 1825 J. S. Mill says:
‘Malthus’s principle was quite as much a banner and a point of union
among us as any opinion especially belonging to Bentham.’[49]
Opposition was chiefly to be found among the Tories, Revolutionaries,
and Radicals. Godwin published a reply to Malthus in 1801, and several
years later, finding that the ‘principle’ still gained ground, made
another attempt to refute it, which met with as little success as the
earlier attempt. As an example of the attitude of the followers of
Godwin towards Malthus, the following remarks by Shelley may be quoted.
‘Metaphysics and inquiries into moral and political science have become
little else than vain attempts to revive exploded superstitions, or
sophisms like those of Mr. Malthus, calculated to lull the oppressors of
mankind into a security of everlasting triumph.’[50] The Tory element of
the opposition was influenced by the feeling that the ordering of human
affairs could not be so innately bad as the Essay seemed to suggest.[51]
Southey and Coleridge represent this view; the former attacked the Essay
more than once with considerable violence.[52] Cobbett made himself
prominent among the critics by inventing the sobriquet ‘Parson’ Malthus.
It occurs in the following passage.
‘Why,’ said I, ‘how many children do you reckon to have had at last?’
‘I do not care how many,’ said the man, ‘God never sends mouths without
sending meat.’
‘Did you never hear,’ said I, ‘of one Parson Malthus?’
‘No, sir.’
‘If he were to hear of your works, he would be outrageous, for he wants
an Act of Parliament to prevent poor people from marrying young, and
from having such lots of children.’
‘Oh, the brute,’ exclaimed the wife, while the husband laughed, thinking
I was joking.[53]
Hazlitt, who may be classed as a radical, was one of the most violent of
the opponents. Indeed, as Mr. Bonar says, ‘Malthus was the best abused
man of his age.’[54]
The Essay early became known on the Continent. As far as Germany was
concerned, this was attributable, according to von Mohl, to a work by
Luden.[55] During the lifetime of Malthus the violence of the opposition
gradually weakened and the principle was very generally accepted. For
many years such opposition as there was was based rather on religious
grounds than upon an understanding of true weaknesses of the theory.
Nevertheless Sumner, who was afterwards Archbishop of Canterbury, and
Thomas Chalmers in early days both proclaimed their adherence to the
principle.[56] In 1840 three books were published which each attacked
the principle on religious grounds. Of the authors, Sadler was a
Churchman without apparently any strong political feelings, Alison a
Tory, and Doubleday a Radical.[57] That the religious motive continued
to inspire opposition may be gathered from an essay by W. P. Greg which
appeared at a much later date.[58]
It may be noticed that strong opposition was nearly always exhibited to
the views of Malthus by socialistic authors.[59] According to Proudhon,
‘la théorie de Malthus, c’est la théorie de l’assassinat politique, de
l’assassinat par philanthropie, pour l’amour de Dieu.’[60] Karl Marx in
a well-known passage attacked Malthus in most violent and offensive
language.[61]
9. As a result of the Essay, there began within the lifetime of Malthus
the advocacy of Neomalthusianism. Malthus himself definitely disapproved
of this practical application of his ‘principle’.[62] The practical
application of which he approved was made by Miss Martineau in one of
her _Illustrations to Political Economy_, which reads so strangely at
the present day.[63] As regards Neomalthusianism it is very generally
supposed that active propaganda only began about the time of the famous
Bradlaugh-Besant trial in 1876. This, however, is a complete
mistake.[64] The first publication of importance in which these ideas
were put forward was an article by James Mill in the _Encyclopaedia
Britannica_. His language was very guarded but the drift of his remarks
unmistakable. Four years later, in 1822, Francis Place wrote a reply to
Godwin. He covered much other ground but openly and deliberately
advocated these practices. For the next ten years there followed an
active propaganda. The events which first brought the whole question
into public notice are somewhat curious. In 1823 a number of handbills
were sent to Mrs. Fildes, well known in the North for her work among the
poor; these bills contained descriptions of the methods which the new
school of writers wished to see adopted by the working classes; an
anonymous letter accompanied them asking her to help in distributing
them. Mrs. Fildes was very indignant, and the whole story was published
in the journal called the _Black Dwarf_. The bills attained a great
notoriety and became known as the ‘diabolical handbills’. Suspicion
seems to have rested upon Robert Owen; it was stated in the _Black
Dwarf_, and has often been repeated since, that Neomalthusian methods
were in use at New Lanark. It is far more probable that Francis Place
was the author both of the handbill and of the letter. Whether this is
so or not, Place was occupied for the next few years in doing all he
could to spread the new opinions, for the sake of which he was prepared
to sacrifice much popularity.[65] In 1834 the Society for Promoting
Useful Knowledge refused his help because of his opinions on the
subject. He was violently attacked by Cobbett and Richard Carlile; the
latter was afterwards converted and published in 1825 articles
advocating these practices. The articles were reprinted in 1826 as
_Every Woman’s Book_, which went through several editions. At this early
date it is clear that on the one hand these books and pamphlets were
widely read among the working classes; Carlile in the _Republican_, for
instance, asserted that they were ‘circulating by thousands in the
populous districts of the north’. On the other hand Neomalthusian ideas
were held by many eminent men of the day. The Utilitarian leaders, if
not actually concerned in the propagation of these views, made their
approval known. J. S. Mill in his youthful days got into trouble with
the police through distributing some of these pamphlets. Grote somewhat
later presented to London University a copy of the famous _Fruits of
Philosophy_, of which there will be more to be said below.
After a while the propaganda died down, and for some fifty years there
was little heard of it.[66] Some books were, however, published in the
interval which subsequent events made famous. R. D. Owen’s _Moral
Physiology_ appeared in 1830. Knowlton’s _Fruits of Philosophy_ and
Drysdale’s _Elements of Social Science_ appeared in 1833 and in 1854
respectively. It was many years, however, before they became well known.
For many years no objection was taken to the _Fruits of Philosophy_, or
any similar work; such books were allowed to circulate freely. In 1876 a
Bristol bookseller, Cook by name, was condemned to two years’
imprisonment for selling an illustrated edition of Knowlton’s work. Soon
after another bookseller was also fined. Thereupon Mr. Bradlaugh and
Mrs. Besant determined to take up the subject and fight for what they
considered to be the right of freedom of discussion in these matters.
They had an edition of the _Fruits of Philosophy_ printed, and took a
small shop where it was openly exposed for sale. A prosecution followed.
In 1877 they were tried before Sir Alexander Cockburn, the Lord Chief
Justice; the Attorney-General prosecuted. The summing-up was distinctly
in favour of the accused; the jury, however, returned a verdict of
guilty, adding a rider to the effect that they considered the defendants
to be innocent of any immoral intention. Judgement was reserved. But in
the interval Mr. Bradlaugh and Mrs. Besant continued to sell the book,
and the result was that, instead of merely being bound over, as had been
the intention of the judge, they were condemned to six months’
imprisonment and to a fine of six hundred pounds. The judgement was
subsequently quashed in a higher court.
The trial was a huge advertisement for Neomalthusianism. For some years
spasmodic efforts to punish the sale of Neomalthusian books only served
to encourage the propagandists. In 1877 the ‘Neomalthusian League’ was
founded and a vigorous propaganda was carried on. The activity of the
league in England gradually declined, but not before the movement had
spread to foreign countries. Propaganda in other countries followed a
very similar course; in 1888 there was a trial in Australia which is as
famous in that country as the Bradlaugh-Besant trial in England.
Prosecutions occurred in India and in America. In 1891 a remarkable
dispute took place in Norway, and a law was finally passed to prohibit
the sale of Neomalthusian books. As lately as 1908 a Belgian doctor was
condemned to imprisonment for spreading the knowledge of Neomalthusian
methods.[67]
10. With this notice of the history of the development of
Neomalthusianism we may leave this side of the subject. The history of
speculation regarding evolution has been so often described that there
is no need to go into the facts here.
It is well known that before Darwin and Wallace turned their attention
to the subject, the origin of organisms by evolution as opposed to
origin by separate acts of creation had often been suggested. There was
already at the beginning of the nineteenth century a considerable
accumulation of facts regarding the structure and relation of organisms
to one another and regarding the fossil remains of organisms. This
evidence was seen to point to evolution as against creation, but until
Darwin and Wallace produced their theories no one had been able to
formulate a satisfactory hypothesis as to how evolution could have come
about. It is of great interest to observe that it was after reading
Malthus that both Darwin and Wallace independently formulated their
theories. Malthus had, in fact, when taking up for consideration the
quantitative aspect of the problem, so far as man was concerned, been
dealing with that class of facts upon which, not only the quantitative,
but also the qualitative aspect of the problem is based. When Darwin and
Wallace, with the problem of evolution before them, which is essentially
the problem of quality—the problem of the manner in which one type of
organic form can be derived from another type—chanced to read Malthus,
their attention was called to the class of facts connected with the
birth-rate, the death-rate, and allied phenomena. They realized that
among species in a state of nature a somewhat similar state of things
existed to that which Malthus, with another aspect of the problem in
view, was investigating in the case of man, and from a consideration of
these facts they founded independently the hypothesis of natural
selection.
It is of interest to note what Darwin and Wallace themselves say as to
their indebtedness to Malthus. In a passage in the well-known
autobiographical sketch Darwin writes as follows: ‘in October 1838, that
is fifteen months after I had begun my systematic inquiry, I happened to
read for amusement Malthus’ ‘Population’, and being well prepared to
appreciate the struggle for existence which everywhere goes on from
long-continued observation of animals and plants it at once struck me
that under these circumstances favourable variations would tend to be
preserved, and unfavourable ones to be destroyed. The result of this
would be the formation of a new species. Here then I had at last got
hold of a theory by which to work.’[68] In two letters that have been
published—one to Haeckel[69] and one to Wallace[70]—Darwin also recorded
in very similar words his debt to Malthus, and in the _Origin of
Species_, after describing what is meant by the struggle for existence
and how it comes about, says, ‘it is the doctrine of Malthus applied
with manifold force to the animal and vegetable kingdoms.’[71] So too
Wallace, in his reply, after having been presented with the first
Darwin-Wallace medal by the Linnean Society in 1908, acknowledged his
debt to Malthus in the following words: ‘both Darwin and myself, at the
critical period when our minds were fully stored with a considerable
body of preserved information and reflection bearing upon the problem to
be solved, had our attention directed to the system of positive checks
as expounded by Malthus in his _Principle of Population_. It is an
unimportant detail that Darwin read this book two years after his return
from his voyage, while I read it before I went abroad and it was a
sudden recollection of its teachings that caused the solution to flash
upon me.’[72]
Since the publication of the _Origin of Species_ much attention has been
paid to the problem of quality as regards the human race. It was obvious
that if the human race had evolved from some lower type, it was probably
still in process of evolution, and that the direction of evolution was
by no means necessarily upwards. It was also obvious that the further
evolution of the race was to some extent at least within human control,
if and when men chose to use the means of control that lay within their
power. Great impetus was given to this side of the problem by the work
of Sir Francis Galton, who coined the word ‘eugenics’.[73] Societies for
the study of eugenics and for the advocacy of eugenic ideals have been
started in England, in many European countries, in America and
elsewhere, and at the present day the educated classes in every country
are at least aware of the existence of the problem of the quality, as
they have long been aware of the existence of the problem of the
quantity, of population.
The development of opinion on this subject has thus run a peculiar
course. Attention was drawn in early days to the existence of the
problem of numbers, but men were long satisfied with asserting on
comparatively simple grounds that a dense population was desirable or
undesirable, and they usually came to the conclusion that the more
inhabitants in a country, the better for the country. Long before the
time of Malthus, and by many different writers, attention was paid to
the connexion between numbers and the food-supply. It was Malthus,
however, who first aroused public interest in the subject. His book,
indeed, made an impression that few books have ever made. Since his time
every educated man has had the problem of numbers in mind, and current
opinion still often enough reflects the view put forward by Malthus if
not in detail—for it is difficult to say what exactly the views of
Malthus were—at least in the general and on the whole gloomy and
fatalistic manner of regarding the problem. It is owing to the fact that
those contributions which, after the time of Malthus, attracted most
attention, added little to the development of thought, and owing to the
influence of the writings of J. S. Mill, who himself never shook off the
profound impression made upon him early in life by the Essay, that the
views, or perhaps we should rather say the outlook, of Malthus so long
maintained their sway. The development of the modern view as expounded
by political economists was not set out in a form that attracted public
attention, and it was thus possible for the late Governor of South
Africa, when answering a question in the House of Commons a few years
ago, to refer to the problem as though no important contribution had
been made to the subject since the time of Malthus.
Of the development of opinion regarding the qualitative aspect of the
problem there is little to be said. Popular interest in this subject is
of comparatively recent birth. That which is interesting to observe is
that, as a result of the course which thought has taken, the population
problem is seldom seen as a whole, and that the relations one to another
of the very numerous questions arising therefrom are scarcely ever
appreciated.
II
THE BASIS OF THE POPULATION PROBLEM: (1) THE QUANTITATIVE ASPECT
1. In what follows the evolutionary position is taken for granted. It is
assumed, that is to say, that the higher forms of life have evolved from
lower forms. If we make this assumption, we must suppose that at one
time the ancestors of man were living under those conditions to which
species in a state of nature are now subject. By species in a state of
nature are meant all species of animals and plants with the exception of
man and those species which have been domesticated by him. It is the
object of this and the following chapter to show that among species in a
state of nature the population problem exists both in its quantitative
and qualitative aspects, and further that in certain particulars of
fundamental importance the position is the same for all such species.
Certain propositions may be laid down which hold good for any one of
them, and in these chapters it is proposed to show what it is that may
be affirmed with regard to all of them. It follows that, since among the
ancestors of man the population problem must at one time have taken this
form, we shall, as the result of the discussion, arrive at a basis from
which we can proceed to study the shape which the problem in its double
aspect has assumed in the case of man.
It is necessary to emphasize the fact that this argument does not take
the form of developing an analogy between the position of man and that
of species in a state of nature. What we are doing is merely to attempt
to ascertain the conditions under which the ancestors of man lived, in
order that we may follow the changes which have taken place. Further, it
may be well to point out that the argument in these chapters will follow
rather an unusual course. It may seem that certain facts of considerable
general importance are passed over and others of little obvious
importance emphasized. The justification for this course will be
apparent later when we come to deal with the position with regard to
man; for this sketch is not introduced primarily with the object of
throwing light upon the position of species in a state of nature, but in
order to prepare the way for a discussion of the shape which the problem
has assumed in the case of man.
2. At the basis of both aspects of the problem lies the fact of
reproduction. All organisms reproduce their kind. Reproduction is
clearly a necessity, because all living things are liable to meet death
by accident and, unless there was reproduction, every species would soon
be extinguished. It is worth while observing that among all higher forms
of life a more or less clearly defined limit to the duration of life has
been evolved. In other words, natural death after a certain period
ensues. It would seem that natural death has been evolved in the
following manner. All organisms are subject to the wear and tear of
daily life, to meet which there is a faculty of recuperation. Among the
lower forms this faculty is very pronounced. The whole animal can be
regenerated from a small fragment and, as a result, very serious
accidents are not fatal. Among the higher forms there goes, generally
speaking, with the advance in structure a loss of the power of
regeneration, until among the highest there is little or no power of
regeneration; for a certain average length of time the highest organisms
withstand the batterings of daily life, gradually fail to recuperate,
and finally die. Given the necessity of reproduction to provide for the
continuance of the species against accident to its members, this further
evolution is not difficult to understand. A power of recovery from all
but the most extreme forms of accident is present among the simpler
types; the retention of such a power of recovery tends to be
incompatible with increasing complexity of structure, and it has, so to
speak, been more economical to evolve organisms provided with a power of
recuperation only against normal wear and tear over the period during
which they remain capable of reproduction. The higher types therefore,
after reproducing their kind, die and thus the battle of life is always
being resumed by fresh generations.
3. That in some such fashion reproduction has to be explained seems
clear; but we are concerned here with the facts of reproduction. It will
be necessary later to go into the nature of reproduction in greater
detail; all that needs to be said here can be stated quite shortly.
There are two forms of reproduction, known respectively as the sexual
and asexual; the latter type of reproduction occurs only among plants
and the lower animals. As sexual reproduction occurs among all groups of
animals and plants, whether asexual reproduction occurs or not (except
among the bacteria where the latter type alone is known) and as it is
the only type which occurs among the higher groups, asexual reproduction
may be disregarded here. The asexual type of reproduction, it may be
remarked, introduces no new principle, and those groups among whom it is
found are not on that account to be set apart from other groups as
though the general conclusions at which we shall arrive were not
applicable to them.
To make the process of sexual reproduction clear it is necessary to say
something regarding the structure of organisms. Excluding the Protista
for the moment, all organisms exhibit a cellular structure. Upon
examination under a microscope the living tissues are found to consist
of a number of compartments or cells. Among plants the typical cell is
in the nature of a small box with thick sides; among animals the sides
or cell-walls are very thin. Within the cell-walls there are to be
distinguished two chief elements, a central body, the nucleus, and the
surrounding cytoplasm. This cytoplasm consists of ordinary granular
protoplasm and the nucleus of a special kind of protoplasm. Only
protoplasm can properly be spoken of as alive. Those elements in the
body which are not protoplasm are either in the course of being turned
into protoplasm or are the products of protoplasmic activity. Examples
of the latter in man are the hair and the nails, and in the case of
other animals, feathers, shells, and so on. As a general rule, each cell
contains a single nucleus, but there are cells without a nucleus and
cells with more than one nucleus. The name Protista, mentioned above, is
given to the lowest animals and plants which are commonly said to
consist of a single cell. They may be thus thought of; but the group
includes forms with many nuclei of which it can only be said that cell
structure has not yet been differentiated. It is therefore possible that
the term cell should not be used at all in respect of this group.
Among the Protista sexual reproduction takes very different forms.
Essentially, however, it consists in the fusion of two individuals, and
if we regard each individual as a cell, it may be said to consist in the
fusion of two cells. Among the higher forms the essential feature of
sexual reproduction is the same; it consists, that is to say, in the
fusion of two cells. It no longer consists in the fusion of two
individuals, but in the fusion of two cells, one given off by one
individual, and one by the other.
The manner in which these cells, known as gametes, are given off by the
male and the female and the manner in which they fuse require some
further explanation. What happens in plants is in all important features
similar to that which happens among animals, and we may confine our
attention to the latter. In every normal member of every species there
is a generative organ.[74] It consists of a surrounding wall within
which is a mass of developing germ-cells. In the female the fully
developed gamete, called the egg or ovum, is, relative to the male
gamete, of large size. It is typically a motionless cell containing a
varying quantity of food substance which may, as in the case of the
bird’s egg, reach a large amount. The male gamete is a much smaller
cell. With a few exceptions it consists of a small oval-shaped head, to
which is attached, by means of an intervening neck or middle-piece, a
long vibratile tail. The head is the nucleus of the cell; if there is
any cytoplasm, it is reduced to a very small amount and its presence
cannot be readily demonstrated.[75] In strong contrast to the ovum the
spermatozoon is typically motile and can swim in those fluids in which
fertilization usually takes place.
Fertilization consists in the penetration of an ovum by a spermatozoon.
The tail does not always enter the egg; as soon as the head has entered,
a change takes place in the egg which sometimes prevents the tail, and
usually other spermatozoa, from entering the egg. The head or nucleus of
the spermatozoon approaches the nucleus of the egg and fuses with it. At
this point, therefore, we have a single cell, known as the zygote,
formed by the fusion of two cells, one derived from the male and one
from the female. The zygote grows and divides and ultimately gives rise
to an adult; into this process of growth it is not necessary to go for
the moment. The zygote is to be regarded as a new member of the species
the existence of which dates from the fusion of the two nuclei. Whether
the zygote lives an independent existence from the beginning, or is
retained within the body of the mother for a longer or shorter period,
is immaterial so far as the dating of the beginning of the existence of
a new individual is concerned. Every man and woman is thus in reality
some nine months older than his or her nominal age.
4. Such are the essential features of the process of sexual reproduction
through which new members of the species arise. We have now to consider
the outward features of the process, which vary very considerably. So
various are they, that at first sight it may scarcely seem likely that
there is any fundamental generalization that can be made regarding the
process as a whole among all species in a state of nature. When we have
glanced at the facts and at their interpretation we shall be in a
position to discuss what it is that holds good for all such species.
Among all multicellular animals and plants the number of spermatozoa
produced is infinitely greater than the number of ova. A single normal
sexual emission in man is said to contain about 226,000,000 spermatozoa.
This immense production of male gametes makes it likely that a male
gamete will meet and fuse with each female gamete. Among the higher
animals there are certain instincts which further ensure that the male
cells will be brought into the proximity of the female cells. Among
other multicellular animals and plants there are no such instincts.
Generally speaking, among the latter types fertilization may be thought
of as fortuitous. In anemophilous plants, for example, such as the
Pines, the male cells or pollen-grains are specially adapted so that
they are caught and carried by the wind for long distances. Many million
times more male cells than female cells are formed in these plants, and
some of them, wafted by the wind, eventually light upon the ovule. So
too among such lowly animals as the sea-urchin the male and female cells
are extruded into the surrounding sea-water; as these animals live close
together, and as the male and female cells ripen and are extruded at the
same time, the chance that any egg will remain unfertilized is small,
the number of the active spermatozoa being so many times greater than
the number of eggs. This simple form of fertilization is characteristic
of most plants and of many animals. In plants there are certain
complications, in particular those connected with fertilization with the
help of insects, into which it is not necessary to go.
The increasing complexity of animal structure is only roughly correlated
with increasing complexity in the processes connected with
fertilization. Though the most complex form of the process is found
among the highest animals, yet some animals, which stand relatively high
in the scale, exhibit a simple method of fertilization. Of this the fish
are an example, and, further, the more highly developed or bony fish
exhibit a simpler form than some of the more lowly-organized
cartilaginous fish. In fact, the stage next above that of which the
sea-urchin was given as an example can be illustrated from the bony
fish. The process in this group consists in the approach of the male to
the female alongside of whom he swims, led by a rudimentary development
of the sexual instinct. When the female ejects her gametes into the
water, the male does the same and the vastly greater number of the male
gametes ensures that all or nearly all of the eggs are penetrated by a
spermatozoon.[76]
The next stage is that characterized by external copulation. The male
clasps the female and when the latter ejects her eggs, he extrudes his
spermatozoa at the same time. The meeting of the gametes thus still
takes place outside the body of the female. This form of fertilization
is found among the Amphibia; the male frog, for example, has specially
developed pads on his front feet with which he embraces the female.
Internal copulation, though it is to be regarded as the most complex
form of the process, is found among such low forms as flat worms,[77] of
which the common tapeworm is a member, among many higher Invertebrates
such as snails and insects, as well as among cartilaginous fish, birds,
and mammals. The essential feature of internal copulation is that the
male is provided with a special copulatory organ or penis which he
inserts into the female. The male gametes pass through the penis, which
takes the form of a tube, directly into the body of the female, and
fertilization thus takes place within the body of the female.
5. When fertilization takes place without copulation it might be thought
that a small proportion of eggs only would be fertilized, that, so long
as fertilization, for instance, depends on the wafting by the wind of a
pollen-grain over a considerable distance until it alights on one small
spot, or upon the chance meeting of a spermatozoon and an egg in the
water, there would be but a small proportion of eggs fertilized. This,
however, is not so; observation shows that in a state of nature failure
is comparatively rare, and that the majority of female gametes are
fertilized. This is in the main due to the vast number of male cells
compared with the number of eggs. Among those forms in which copulation
takes place, fertilization is clearly dependent upon the strength of the
sexual instinct, which impels the male to seek the female. That this
instinct is very powerful is well known. It may for the time overcome
all other instincts. There is a frenzy of desire among many animals.
Male frogs and toads will remain clasping the female for many days
waiting for the extrusion of the eggs. Female toads have been discovered
smothered by the male in the sexual embrace.[78] It has been noticed
that birds, which under usual circumstances are frightened by the sound
of a gun, will take no notice when in pursuit of a female.[79] All the
evidence points to the fact that, owing to the strength of the sexual
instincts, females are rarely left undiscovered by a male in the sexual
season. Jenner records that one of a pair of magpies was killed and that
on the following day the survivor appeared with another mate. One of
this pair was killed and on the next day the survivor again appeared
with another mate. This was repeated for seven days and on each occasion
the survivor always appeared with a new mate.[80] In this connexion the
great development of those forms of secondary sexual characters may be
referred to which enable the two sexes to find and recognize one
another. Such are recognition marks, call-notes of many insects, birds,
and mammals, and the strong odours given off by many animals during the
sexual period.
Generally speaking, the male is always prepared for the act of
copulation and the act takes place when the female is ready to receive
the male. This is so among mammals whether the male experiences a sexual
season known as the ‘rut’, as among stags, or whether he does not, as
among dogs; for the period of ‘rut’ lasts longer than the period during
which the female is ready to receive the male. The facts, however,
regarding the sexual season in mammals are somewhat complicated owing to
the nature of the sexual season experienced by the female. A number of
different types of mammalian sexual season have been distinguished; it
is not necessary, however, to go into these distinctions. It is
sufficient to say that each sexual season consists of one or more sexual
cycles, known as oestrous cycles. An oestrous cycle may be divided into
four periods; the first, known as the pro-oestrous, is the period of
preparation which ends in the rupture of the blood-vessels in the mucous
membrane of the uterus. When the blood passes to the exterior, it is
known as the menstrual flow. The second period or oestrous is the period
of desire. This period is always short; in the sheep it lasts about
twelve hours and often in other species does not last as long. Only
during this latter period will the female receive the male;[81]
copulation never takes place at any other period, and yet in spite of
the fact that the opportunity for copulation is narrowly restricted, so
strong is the sexual instinct in the male, that it is very rare for a
female, so far as observation goes, not to engage in copulation at each
oestrous. The period of oestrous is followed by the period of
metoestrous during which the activity of generation subsides, and the
metoestrous is followed by the anoestrous or period of rest, after which
another pro-oestrous period begins a new cycle.
The period of oestrous, during which copulation takes place, is usually
marked by the presence of ripe female gametes which are therefore at
once fertilized. Ripe ova are, however, not always present at oestrous;
in the rabbit ovulation takes place an hour and a half after copulation.
In the bat there is a very marked want of coincidence between oestrous
and ovulation; copulation takes place in the autumn, but ovulation does
not take place until the following spring. In such cases the spermatozoa
remain alive in the uterus until the female gametes are ripe, when
fertilization is achieved; thus in the bat the spermatozoa remain alive
for several months. When such cases occur, therefore, it does not mean
that the ova are not fertilized. In the monkeys, however, ovulation may
occur independently of oestrous and in such a manner that the ova then
liberated may not be fertilized.
What has so far been said all goes to show that the majority of ripe ova
are always fertilized among species in a state of nature. There must be
a certain number of failures among those species which copulate, as when
a mammalian female, as must now and again happen, does not engage in
copulation during oestrous. Among species which do not copulate,
failures are doubtless more frequent. There is probably a greater
wastage of eggs when they are adhesive and fixed to some object than
when they are pelagic, as is most often the case among marine animals;
for when eggs are adhesive the seminal fluid may drift away.
We are now approaching a point at which it is possible to establish the
first generalization regarding the process of reproduction among species
in a state of nature. It is, however, not possible to make clear what it
is intended to convey until something has been said regarding animal
behaviour. Some of the most striking differences between one class of
animal and another as regards the process of reproduction are connected
with the evolution of animal behaviour. So far we have spoken of
instinct without defining what is meant, and until something has been
said regarding the course and limit of mental evolution among animals,
the nature of the common element in all forms of reproduction among all
species in a state of nature and the manner in which it differs from
what is found among men cannot be set out. It may seem that the
following review is taking us somewhat out of our path. It so happens,
however, that in view of the questions that will come up later for
discussion, such a sketch will be necessary and it may therefore be now
undertaken so as to render further amplification unnecessary.
6. Putting aside the behaviour of plants, we find among the lower
animals a type of behaviour which, though simple in a certain sense,
cannot be adequately explained without a prolonged discussion. Some idea
can be obtained of its nature if we consider in what a reflex action
consists. When a definite and simple stimulus is followed directly by a
definite and simple reaction we have what is called a reflex action.
This term, it may be noticed, is usually restricted to cases where a
nervous system is present. When similar reactions occur among organisms
in which the nervous system has not been differentiated, it has been
suggested that the term ‘autotype’ should be used.[82]
Reactions, however, probably never follow invariably upon the repetition
of the same stimulus. Among the lowest class of animals, the Protozoa, a
free-swimming ciliate Infusorian, will, if it comes into contact with
something in the medium which is abnormal, it may be, for example, an
alkaline solution, stop and go backwards. This is an example of a reflex
action. An analysis of its subsequent movements shows that, if it again
and again meets the alkaline solution, some modification of the reaction
takes place. The animal may show increased activity until either it is
overcome by the disturbing medium or it has freed itself from it. So
again after the digestion of food, such an organism shows a different
response to the presence of food.
More definite instances of different reactions following upon the same
stimulus are provided by experiments of changing the nature of the
medium. An Infusorian will react violently against certain new elements
in the medium to which after a time it becomes habituated, when the
reaction no longer follows. Very interesting experiments have shown that
even among the simplest class of organisms there is a certain learning
from experience. ‘A Stentor (one of the ciliate Infusorians) if gently
touched upon one side will contract upon its stalk, but will soon open
out again. Touched once more, it will perhaps bend to one side, and if
continually molested in this manner, it will uproot itself in pardonable
dudgeon and swim away. That is to say it has several ways of reacting to
the stimulus and seeking equilibrium, and, if one fails, it tries
another. But now when it anchors itself again, it seems to have learnt
something, for if again touched it does not go through the stages of
contracting and of bending aside. It keeps to its more radical remedy
and moves off again.’[83] It is doubtful whether there is any further
complication of this type of behaviour among organisms which do not
attain to the kind of behaviour that we have now to describe.
7. Herbert Spencer, as is well known, defined instinct as compound
reflex action. Though this definition cannot, for various reasons, be
accepted as adequate, it does suggest the essential nature of instinct,
which consists in the response to a given but often vague stimulus of a
more or less complicated series of reactions. Instinct is more than
compound reflex action because it involves the organism as a whole, and
is accompanied by, or is the outcome of, a mental process. All mental
process is said to involve three aspects—the cognitive or the knowing of
an object, the affective or feeling in regard to an object, and the
conative or striving to or from an object—and these three aspects are to
be found in all instinctive actions. The instinctive action is initiated
by a sense-impression and is followed by results so important because
the nervous system is innately organized to respond to certain
sense-impressions. It is presumed that some kind of emotional
excitement, however faint, always follows and that it gives rise to the
striving that we see in the form of movement. Instinct has been defined
as ‘an inherited or innate psychophysical disposition which determines
its possessor to perceive and to pay attention to objects of a certain
class, to experience an emotional excitement of a particular quality
upon perceiving such an object, and to act in regard to it in a
particular manner, or, at least, to experience an impulse to such
action’.[84]
Every one is acquainted with many examples of instinctive action. ‘There
are many instances of insects that invariably lay their eggs in the only
place where the grubs, when hatched, will find the food they need and
can eat, or where the larvae will be able to attach themselves as
parasites to some host in a way that is necessary to their survival. In
such cases it is clear that the behaviour of the parent is determined by
the impression made on its senses by the appropriate objects or places:
e. g. the smell of decaying fish leads the Carrion fly to deposit its
eggs upon it; the sight or odour of some particular flower leads another
to lay its eggs among the ovules of the flower, which serve as food to
the grubs. Others go through more elaborate traits of action, as when
the Mason-wasp lays its eggs in a mud nest, fills up the space with
caterpillars, which it paralyses by means of well-directed stings, and
seals it up; so that the caterpillars remain as a supply of fresh animal
food for the young which the parent will never see and of whose needs it
can have no knowledge or idea.’[85] To take some examples from among the
Vertebrates, ‘pheasants, plovers, moor-hen, domestic chicks and
ducklings, with many others, are active soon after birth, and exhibit
powers of complex co-ordination, with little or no practice of the
necessary limb movements. They walk and balance the body so soon and so
well as to show that this mode of procedure is congenital, and has not
to be gradually acquired through the guidance of experience. Young water
birds swim with neat orderly strokes the first time they are gently
placed in the water. Even little chicks a day or two old can swim
well.’[86]
Enough has been said in the way of illustration, as numerous examples
are familiar to every one. It is possible that instinctive behaviour may
have to be attributed to so lowly a group of organisms as the flat
worms. Instinct reaches its greatest development among the insects, and
some examples have been given above of the amazingly intricate series of
actions which are performed by insects, under the guidance of instinct.
There have been two lines of mental evolution among animals, one
culminating in the insects and the other in the Vertebrates. Among the
former instincts have become very specialized; among the latter they
have remained far more generalized. Among the latter again there has
been a far higher development of intelligence than among the former,
thus further distinguishing the two lines of mental evolution. It is
probable, however, that intelligence, though certainly at times in a
very primitive form, always accompanies instinct, and to the discussion
of intelligence we must now turn.
8. We saw how as lowly an animal as an Infusorian can in a sense learn
from experience. It is only when learning from experience reaches a more
advanced stage that we speak of intelligent action. If we watch one of
the higher animals which, under the influence of desire, is striving to
satisfy this desire, we find that it behaves in the following manner. An
animal, for instance, is shut up in a box with food outside. It is led
by instinct to all kinds of sporadic activities; it will clutch and claw
and make every kind of effort to extricate itself. If some simple catch
has been contrived which opens the door and offers a way of escape, the
animal will probably sooner or later accidentally operate the catch and
escape. If the animal is replaced in the box many times, it is found to
escape on the average sooner. It learns in fact in some degree to
operate the catch and thus to gain freedom and food. The question which
arises is what degree of mental development we have to assume in order
to account for these facts.
The stage in learning from experience which follows next upon that
present among some protozoa is exemplified by the chick which at first
instinctively pecks at various objects. If it pecks at a yellow
caterpillar with an unpleasant taste it will drop it. The next time, or
after a series of such experiences, it will avoid the caterpillar. The
explanation seems to be that a modified response arises directly from
the sight of the caterpillar. The sense-impression has become charged
with feeling that first arose as the result of experience. This simple
explanation is to be preferred to that which would assume the
realization by the chick of the relation between the position when it
again finds itself with a yellow caterpillar before it and the nastiness
which it previously experienced. The process is thus one of the revival
of acquired meaning, and we have now to ask if a higher stage of mental
process is ever to be attributed to animals or whether the behaviour of
the animal in the cage is to be explained on the same lines as the
behaviour of the chick.
‘Let us suppose’, says Professor Hobhouse, ‘revival to operate in a mind
capable of perceiving three objects A B C in definite space and time
relations, C being something desirable, e. g. food. If the three objects
are present to the senses, the first two leading up to the third (e. g.
as intervening objects in space), conation will be definitely directed
to C via A and B. Let this have happened and then let A alone be given.
If the animal is hungry, i.e. if there is a conational basis to go upon,
A will, according to the law of revival, excite a conation corresponding
to the previous one, but this was a conation definitely directed to B
and C in succession as things standing in a definite relation to A. The
animal then directs its efforts to a point where, in accordance with the
first experience, B and C should be. It looks for them, or if B is some
change which brings C about, sets itself to perform B and so obtain C.
Its action is directed to something not given, and this appears to be
the germ of a conation or practical idea.’[87] It is thus possible that
in the behaviour of the animal in the box we may have to recognize the
first step towards a higher mental process. Effort may be directed to
something not given and thus there may be the first sign of the
emergence of an idea. Whether this is so or not, such an idea is
certainly not a general idea; it is merely a reference to something to
come, and that is all. This is the highest degree of mental development
that we can attribute to animals and it may be noticed that, this being
so, there can probably be no true memory among animals. Explicit ideas,
therefore, among animals, so far as they exist at all, do not give rise
to other ideas following one another in sequence. They are isolated and
serve merely to guide action.
9. The highest form of mental process attributable to animals reaches a
fuller development among men. This stage of mental development has been
called the stage of perceptual correlation. How far the apprehensions of
direct relationships in consciousness are developed among animals is
doubtful; there is no doubt that among men such relations are
apprehended. Action, therefore, is not merely connected indirectly with
the result, as in the example of the chick; action is undertaken with an
end in view. If the chick came to apprehend the relation between the
caterpillar and the unpleasant taste, it would have reached the fully
developed stage of perceptual correlation; we have seen that we have to
assume in this case a simpler state of mental process, though in certain
cases a study of animal behaviour does suggest some approach to the
higher stage. At this stage, which is fully developed only in man, the
world ceases to be presented merely as sense-impressions charged with
feeling and takes the shape of a mass of objects of perception related
together and underlying the sense-impressions and the feelings evoked by
them.
In man there is developed a still higher stage of mental process which
is his peculiar possession and chief distinguishing characteristic. This
is the stage of conceptual thought. In the perceptual stage activity is
guided solely by the presence of the objects perceived. If there is any
anticipation of the end, the action from moment to moment is still
always guided by what is actually given. In the conceptual stage action
is guided by an ideal anticipation of the end. What underlies mental
process at this stage is generalization. The situation as given is
broken up and analysed; elements common to it and to previous situations
are recognized and synthesized. These two processes of analysis and
synthesis go on side by side and concepts are formed which are outside
the world of perception. Common elements in the perceptual order are
recognized and there is thus made possible a grasp of the continuity
running through experience.
Man is thus no longer guided by what is immediately given in experience;
he can make plans and shape his actions with an ideal end in view. With
the development of conceptual thought goes the development of language,
whereby man learns from others and passes on to others what is in his
mind. Of the stage of conceptual thought there will be more to say in a
later chapter. This further development is only mentioned here in order
to contrast mental process in its highest form in man with the process
in animals.
10. We have now to consider the bearing of mental development upon the
process of reproduction. All animals are endowed with a certain power of
reproduction which we shall call fecundity. Fecundity is measured by the
number of ripe ova produced, the number of spermatozoa having no direct
bearing on fecundity. We have seen that the highest animals—those most
nearly related to man—are gifted with instinct and intelligence. The
value of intelligence lies in the fact that it enables instinct to adapt
itself to the special circumstances of the moment and thus to bring
about its end more surely. The sexual instinct is in this manner
assisted by intelligence, and among animals which copulate the power of
reproduction is thus able to realize itself to the full or almost to the
full. There may be certain failures to achieve reproduction and certain
cases of perverted instinct; to some of these cases we have already
referred. Broadly speaking, however, it is true that the highest
development in animals of instinct and intelligence works towards the
fulfilment of that degree of fecundity which is innately given. It
follows, therefore, that in this sense mental development among animals
has not in any fashion changed the position of the higher animals when
compared with that of the lower animals. Reproduction in the sea-urchin
and reproduction among the mammals—vastly as the mental processes
differ—is still similar in this respect. The power of reproduction is
realized to the full or almost to the full. All that instinct and
intelligence do is to ensure that in this more complex process of
fertilization the full power of reproduction is as nearly as possible
realized—that is to say, that nearly all ova are fertilized.
Among men, even in the lowest stage in which they have been studied, the
position is entirely different. Owing to the development of conceptual
thought men act with some ideal object in view. Customs grow up which in
their origin must be traced to some process of reasoning, however
obscure, and action deliberately undertaken, as well as custom, may
affect the realization of the power of reproduction. Thus among the
lowest of primitive races we find that men abstain from intercourse for
various motives which we must regard as due to the presence of reason.
Or again, they may practise certain forms of mutilation of the sexual
organs which may affect the power of reproduction. The origin of such a
custom may be hidden; it may be almost certain that it was not
originated with any understanding of its effect upon reproduction and
even that its effect has never been recognized; nevertheless originally
such a custom could only have arisen if reason was present. Similarly,
among the lowest races there are abundant examples of the practices of
abortion and infanticide which, though they do not affect fecundity,
have an important bearing upon the quantitative aspect of the population
problem and are again the products of reason.
Among men, therefore, owing to the development of a higher stage of
mental power, fecundity is not realized to the full, and we have to
distinguish between the power of reproduction, which we have called
fecundity, and the actual degree of reproduction, which we shall call
fertility. It may, perhaps, assist to emphasize what is meant if for a
moment we think of the reproductive process among animals as
‘mechanical’. The introduction of this term should not be taken to have
any ultimate significance—any reference whatever to the true nature of
mental process. It is only used as a convenient term to illustrate the
difference between reproduction among animals and among men. Among all
species in a state of nature reproduction may be thought of as
‘mechanical’, whereas reproduction among men is never ‘mechanical’. The
number of young produced in the case of the human species is far from
being completely correlated with the fecundity. There may be all degrees
of difference between fecundity and fertility. Among species in a state
of nature fecundity and fertility are for all practical purposes one and
the same thing because reproduction is ‘mechanical’ whatever may be the
stage which mental development has reached. Further, such differences as
exist among species in a state of nature between fecundity—the number of
ripe ova—and fertility—the number of fertilized ova—are due to failures
of the gametes to meet and may be called, just as the whole process may
be called, ‘mechanical’. Such ‘mechanical’ differences between fecundity
and fertility may also be found in man but the chief cause of the
differences in the case of man is altogether of another kind and is due,
as we have seen, directly to the development of conceptual thought.
It was said above that it was proposed to show that certain
generalizations can be made regarding the process of reproduction among
species in a state of nature. This then is the first generalization.
(Fecundity and fertility are closely correlated and, compared with the
position among men, reproduction may be thought of as ‘mechanical’ and
even the failures to realize the full power of fecundity may be thought
of as ‘mechanical’.)
11. It has been mentioned that fecundity is very large among all species
in a state of nature and we have now to ask what it is that determines
how large it shall be. As we have seen, the fecundity is roughly
measured by the number of ova produced, and this number clearly depends
upon many factors, such as the beginning and duration of the mature
period, the number of eggs produced at any one time, and the length of
the period between the epochs of egg production. Into details of the
proximate causes of the differences in fecundity it is not necessary to
go. What it is desired to know is what factor or factors in general
ultimately determine the strength of fecundity in each species. We may
first take some examples of the degree of fecundity drawn from various
groups.
The common whelk lays its eggs in capsules of which a great number are
produced. It has been calculated that a small clump of such capsules of
about two cubic inches in size contains about 200,000 eggs. Another
mollusc, Aplysia, may lay from 2,000,000 to 3,000,000 at a time. ‘An
oyster may have sixty million eggs and the average American yield is
sixteen millions.’[88] The number of eggs found attached to the edible
crab in the breeding season varies between half a million and three
millions. A single pair of flies may produce 20,000 larvae. The number
of eggs produced by parasites may very largely exceed these numbers.
Among the vertebrates the fish are the most prolific class. ‘In a Ling
61 inches long and weighing 54 pounds the ovaries contained 28,361,000
eggs; a cod of 21½ pounds 6,652,000. The least prolific of British food
fishes is the herring, in which the number of ovarian eggs varied from
21,000 to 47,000 in four specimens examined.’[89]
These vast numbers of eggs produced at any one time make theoretically
possible a prodigious rate of increase. It has been calculated that a
single cholera bacillus can give rise to sixteen hundred trillion of
bacilli in a day, forming a solid mass weighing a hundred tons. ‘Wallace
quotes Kerner to the effect that a common British weed (_Sisymbrium
sophia_) often has three-quarters of a million seeds; if all grew to
maturity for only three years the whole of the land surface of the globe
would not hold them. An annual plant with only two seeds would be
represented by 1,048,576 in the twenty-first year.... If all the progeny
of one oyster survived and multiplied, its great-great-grand-children
would number thirty-six with thirty-three noughts after it, and the heap
of the shells would be eight times the size of the world. Huxley
calculated that if the descendants of a single green-fly all survived
and multiplied they would, at the end of summer, weigh down the
population of China. The common house-fly lays eggs in batches of 120 to
150 at a time, and may lay five or six of these batches during its life
of about three weeks in very hot weather. At the end of summer, if all
developed, and if there were six generations, the progeny of a single
pair, pressed together into a solid mass, would occupy a space of
something like a quarter of a million cubic feet, allowing 200,000 flies
to a cubic foot.’[90] ‘There is no exception’, says Darwin, in a
well-known passage, ‘to the rule that every organic being naturally
increases at so high a rate, that, if not destroyed, the earth would
soon be covered by the progeny of a single pair. Even slow-breeding man
has doubled in twenty years, and at this rate in less than a thousand
years there would literally not be standing room for his progeny.
Linnaeus has calculated that if an annual plant produced only two
seeds—and there is no plant so unproductive as this—and their seedlings
next year produced two, and so on, then in twenty years there would be a
million plants. The elephant is reckoned the slowest breeder of all
known animals, and I have taken some pains to estimate its probable
minimum rate of natural increase; it will be safest to assume that it
begins breeding when thirty years old, and goes on breeding until ninety
years old, bringing forth six young in the interval, and surviving till
100 years old; if this be so, after a period of 740 to 750 years there
would be nearly ninety million elephants alive, descended from the first
pair.’[91]
12. These examples show that the power of fecundity, which is always
huge, is in many instances much greater than in others. Were it not for
the fact that normally all but a small proportion of eggs are always
fertilized, it might be suggested that in those cases in which there was
no copulation a much larger number of eggs was necessary than among the
higher forms, in order that a sufficient number should be fertilized.
This, however, can only be a partial explanation of the larger number of
eggs among those lower forms where there is no copulation.
In order to obtain an answer to the question as to what it is which
determines the fecundity of any species, it is necessary to look into
certain features of the life of animals and plants in a state of nature.
Observation and deduction bring one remarkable fact to light. The number
of adults of any species at any one season of the year, when compared
with the number in the corresponding period in other years, remains upon
the whole constant. This fact cannot be based upon statistics, for we
cannot take anything approaching to a census. Nevertheless, it is an
unavoidable deduction from the known facts. The more emphasis that is
laid upon variations in numbers from season to season, the more apparent
does it become that such differences are trivial when compared with the
possible rate of increase. But we know that all but a small proportion
of eggs are fertilized, and as we date the existence of a new member of
the species from the moment of fertilization, it is clear that the
numbers composing every new generation greatly exceed the number of
adults to which the new generation owes its existence. It follows,
therefore, that all but a small proportion of the young of each
generation perish before the adult stage is reached. The most remarkable
increases in the adults of any species ever recorded are negligible
compared with the possible increase, and observation shows that as a
general rule there is no increase at all.
Fecundity is, therefore, in some manner connected with this fact that
the great majority of fertilized eggs do not give rise to adults, and in
order to throw further light upon this connexion we must ask how it is
that the young perish.
13. To make clear how it is that the young of every species perish on so
large a scale, it is necessary to refer to the interdependence of all
living organisms. This can perhaps best be illustrated by reference to
the chief distinction between animals and plants. A difference in the
mode of nutrition is that which chiefly distinguishes animals from
plants. There are other differences but their importance is small
compared with that we may now describe. The need of food is common to
all living things and is due to the nature of the living substance
called protoplasm—the physical basis of all life. Protoplasm is of a
very complex constitution. It is for ever wasting away and if life is to
be preserved food must be supplied to compensate for the loss. The need
is as great among plants as it is among animals, but the means of
supplying it are fundamentally different.
Plants feed upon very simple substances—salts of nitric acid, salts of
ammonia, and carbonic acid. Among green plants carbonic acid is taken in
from the air through small apertures in the leaves known as stomata; the
salts of nitric acid and ammonia are absorbed from solution in the water
of the soil. Carbonic acid and water are synthesized within the cells of
the plant into starch; starch is converted into sugar and the sugar is
combined with the salts of nitric acid and ammonia to form amino-acids
which are eventually transformed into proteids. Thus the plant makes
good the unavoidable waste of its living substance by elaborating the
highly complex protoplasm from the simplest elements.
The method pursued by animals is entirely different. They feed upon
complicated substances, which may be divided into proteids, fats, and
carbo-hydrates. These substances do not take their places directly in
the living cells of the body; they first undergo a process of digestion,
after which they are assimilated. Digestion involves the breaking down
of these complex foods to a certain stage; proteids, for example, are
reduced to amino-acids, and starches to sugars. In these forms they are
soluble and are taken up by the walls of the alimentary canal and are
afterwards resynthesized into proteids and starches.
The importance of this distinction lies in the fact that the only method
of obtaining the highly complex substances necessary for animals is to
feed upon the tissues of other animals or plants. It is obvious that
every animal species cannot feed upon some other animal species; in the
end animals as a whole must depend upon plants because plants alone are
able to elaborate the substances which animals need. In a sense,
therefore, animals are parasitic upon plants; in any case the existence
of animals is bound up with the continued existence of plants. This
interdependence of living organisms runs all through the conditions
under which species in a state of nature live and takes a variety of
shapes. The dependence of one organism upon another is largely connected
with the question of the provision of appropriate surroundings which are
often only found in the proximity of certain other species. Many species
can only flourish in the neighbourhood of trees. The interdependence
between certain species is very intimate. There are many examples of
what is known as symbiosis, as when a certain species of sea anemone
lives on the back of a particular species of crab. Again, parasites,
which alternate between one host and another, are dependent upon finding
a member of a particular species at a certain time in their
life-history, as otherwise they perish. Many examples of interdependence
are within common knowledge, and, bearing this feature of organic life
in mind, we may go on to ask how it is that, through the elimination of
a great proportion of the young of every species, the number of adults
remains upon the whole constant.
14. Taking animals first, it is probable that the most common cause of
elimination lies in the fact that the young of all species are consumed
by members of other species. It is difficult to estimate even roughly
the relative importance of the various causes of elimination; ‘the
causes’, says Darwin, ‘which check the natural tendency of each species
to increase are most obscure’.[92] The particular factor mentioned,
however, certainly takes a very prominent place. The young of marine and
fresh-water animals almost all form food for other species and are
obviously exposed to attack. So too, though perhaps not to so great a
degree, are the young of terrestrial animals; whether we think of the
larvae of insects or the eggs of birds, we find that they are in most
cases liable to be consumed by enemies. Even where copulation is
internal, the developing embryo is, except among mammals, seldom long
retained within the body of the mother, and once exposed to the outside
world it almost invariably becomes an object of prey to many enemies. In
fact, wherever we look, this cause of elimination plays a very great
part, arising immediately from that aspect of the interdependence of
species which is derived from the mode among animals of making up for
the wastage of protoplasm.
Elimination again is largely due to failure to find those conditions
under which alone life can continue. These conditions may be connected
with the nature of the organic or of the inorganic surroundings. When
the young of the flat worm, known as the Liver Fluke, which infects
sheep and causes a serious disease, passes from the sheep to the
exterior, it can only maintain itself for a certain time in the
free-living form. Unless within this time it meets with a certain
species of snail into which it penetrates, it will die. Besides such
failures to find suitable organic surroundings, there may be failures to
find suitable inorganic surroundings. The larvae of such species as the
mussel, which require suitable surroundings to which to attach
themselves in order that the adult form may develop, will perish if such
surroundings are not available. There is a further class of factors
connected with the inorganic surroundings which bring about elimination.
They may be summed up under the heading of external circumstances.
Variations in temperature, moisture and so on, when they pass beyond a
certain limit, which is more or less clearly marked for each species,
are followed by death. Under this heading comes also death from
accident, as when animals perish from the violence of storms and in any
similar fashion. It is of interest to note that starvation is seldom the
primary cause of death. It may be a secondary result of abnormal
external circumstances; extreme cold, though not affecting directly the
members of one species, may be fatal to members of another species upon
which the former feed. But when circumstances are normal, so far as
observation goes, starvation is rare.
15. Among plants the same three groups of factors can be traced, though
their relative importance is not the same as among animals. Elimination
through consumption as food, for instance, by other species is not so
important. To a large extent plants can serve as food for animals and
survive. Nevertheless the young, especially in the form of seeds, are
very subject to attack by animals; seeds are one of the principal forms
of food for many animal species, and this form of elimination plays a
large part among plants. Dependence upon suitable organic and inorganic
surroundings plays much the same rôle as it does among animals. Some
species can only flourish in the shade of trees and others in the open.
Some species require one kind of soil and others another. The importance
of external circumstances again is very similar.
There is another factor of a somewhat different nature which is of great
importance. ‘With plants’, says Darwin, ‘there is a vast destruction of
seeds, but, from some observations which I have made, it appears that
the seedlings suffer most from germinating in ground already thickly
stocked with other plants.’[93] In order that a seed may germinate, it
must not only fall upon suitable soil but must find enough suitable soil
unoccupied. Otherwise it will not germinate or will not develop into an
adult. This is different from anything which happens among animals, and
is clearly an approach to starvation. It is, however, better thought of
as the result of the inability of any given area to support more than a
given amount of life. The endowment of any area may be such as to render
it incapable of supporting life at all, or it may be such as to render
it capable of supporting any degree of life up to and beyond that for
which there is space. In the sea the amount of nitrogen is the limiting
factor, and the deficiency of nitrogen is such that the question of
space does not arise.[94] In many parts of the world’s surface, however,
the endowment is such that more plants could be supported than there is
space for.
In this connexion it may be noted that the limitation of the surface of
the earth is not a cause of elimination in the true sense. This is best
seen if we imagine the surface to be extended. If to a continent already
inhabited there is added an unoccupied area, there will, if the new area
is generally of the same nature as that alone formerly existing, be a
spreading of organic life over the new area. It will only be at the
fringe of the occupied area that there will be any difference in the
amount of elimination of plant life. Unless the occupied area is of very
small extent, there will be no difference except within this narrow
fringe. In the fringe there will be a lessening of elimination, other
things being equal, because there will not be the same number of seeds
which fail to grow into plants owing to the previous occupation of
suitable soil, as in the more central parts of the area. When the new
area has been entirely occupied, the same conditions as existed in the
smaller area will exist throughout the larger area. Further, if the
surface available for occupation were indefinite in extent, there would,
except at the fringe, which would in this case be permanent, be no
difference as regards the amount of elimination. All that has been said
applies equally well if, instead of imagining these additions to take
place after evolution had reached its present stage, we imagine
evolution to have taken place from the beginning on an area of
indefinite extent.
16. We have, therefore, some idea of the manner in which the young of
animals and plants perish. Let us consider any animal species; we find
that the young are faced with a large number of dangers. The new members
of the species may be consumed by some enemy before they have developed
beyond the stage of the fertilized egg or at any stage in their
development. They may in general not meet with favourable organic and
inorganic surroundings, or at some particular stage they may not meet
with the environment necessary. At any time they may perish from
unfavourable external circumstances. The position of young plants is
similar, and in addition they may fail to find sufficient space in which
to live.
The dangers which any species encounters remain both in kind and in
degree fairly constant over a considerable period of time, and, unless
in each generation a number of young survives at least equal to the
number of adults in the generation to which it owes its birth, the
species will decline. It follows that the power of reproduction must be
such as to ensure that at least this number of young will survive. The
power of reproduction in any species is therefore connected with the sum
of all the dangers which the young of the species encounter. But it is
not true that the greater the fecundity the better for the species.
Reproduction over and above this degree would place the young in a less
favourable position. Competition bringing no corresponding advantages
would be increased, and starvation or injurious semi-starvation would
result. Any considerable increase in the strength of fecundity beyond
that which is essential could not therefore be beneficial.[95]
The facts regarding the conditions of life and the dangers to which the
young of different species are exposed coincide with the view that the
strength of reproduction is in the main determined by the sum of these
dangers. The greater strength of fecundity among those species which
shed their eggs into the water cannot be attributed, as we have seen, to
any failure of fertilization on a large scale; it may be attributed,
however, to the numerous dangers which the young of such species must
encounter. The chance that any single fertilized egg will grow into an
adult is far less in these cases than when the eggs are retained in the
body of the mother and when the young are guarded by the parent, and,
unless fecundity was on a large scale, a sufficient number would not
survive. Among plants reproduction must always be on a large scale
because it is necessary to ensure that a sufficient number of seeds will
fall, not only on suitable ground, but on suitable ground that is not so
occupied as to prevent growth to the adult stage, in addition to the
necessity of providing such numbers as will ensure a sufficient number
passing through all the other dangers. Eggs and young abandoned by the
parents may be variously exposed to danger. The development of instincts
common among insects which lead to the hiding of eggs in places where
danger of destruction at the hand of enemies is decreased, and to the
provision of food for the young when they develop from the eggs, is
accompanied by a decrease in fecundity. Further developments of the
parental instinct are accompanied by decreases in fecundity as the
degree of danger lessens. Parental care for the young is not uncommon
among the invertebrates. There are a number of cases in which the young
are retained in brood-pouches, as for instance by the common water-flea.
The fresh-water leech, Clepsine, broods over its young. Among the
vertebrates the fish for the most part take no care of their young. Some
fish, however, such as Gasterosteus, the Stickleback, make nests. No
great advance is found among the Amphibia or among the reptiles. One
reptilian group, however, the Chelonia, shows a remarkable advance; they
live in pairs and guard their young with care. If marriage be defined as
‘a more or less durable connexion between male and female lasting beyond
the mere act of propagation till after the birth of the offspring’,[96]
then the beginning of marriage is discernable in this group. This more
or less durable connexion between male and female is a well-known
characteristic of birds, as is also care for the young. ‘Most birds when
they pair do so for good and all until one or the other dies.’[97] The
connexion is not so durable, and the parental instinct is not so highly
developed, among mammals as among birds. The retention of the young
within the body of the mammalian mother, however, greatly decreases the
dangers to which the young are exposed. It is also worthy of note that
those species both of birds and mammals which prey upon others are on
the whole less fecund than other species, a fact which is to be
connected with the lower degree of danger to which their offspring are
exposed.
The lower degree of danger to which the young are exposed, the less the
fecundity; and the less the fecundity, provided that it reaches the
strength necessary to preserve the species, the better on the whole for
the species. In this manner we reach the second generalization regarding
the quantitative aspect of the population problem among species in a
state of nature, which may be stated by saying that the strength of
fecundity in any species is determined by the sum of all the dangers to
which the young of that species are exposed. This must be qualified, in
so far as fecundity and fertility are not the same, by adding to the
dangers to which the young are exposed the danger that a certain
proportion of eggs will not be fertilized. It follows that among men,
since fecundity and fertility are not the same for quite other than
‘mechanical’ reasons, fecundity is not directly related to the dangers
to which the young are exposed. It is clear that, when men, as is now
the case on a large scale, both abstain from intercourse and interfere
with the natural result of intercourse, and at the same time increase in
number, the strength of fecundity is considerably greater than that
which would enable a sufficient number of young to escape the
unavoidable dangers. But the ancestors of man must once have been
subject to the same conditions as those to which species in a state of
nature are now subject, and it will be into the causes and results of
this progressive divergence from the former conditions that we shall
look in the first part of this book.
III
THE BASIS OF THE POPULATION PROBLEM: (2) THE QUALITATIVE ASPECT
1. We have now to consider the qualitative aspect of the population
problem. There are two questions to which an answer is required. First
we ask: What is the nature of the changes which occur? In other words,
if we may speak of history among animals and plants, we want to know
what kind of changes underlie the facts which go to make up that
history. The second question is: How have these changes come about?
There is no doubt about the answer to the first question, and it can be
given very shortly. Though there is a certain consensus of agreement
regarding the answer to the second question, there are considerable
differences, of opinion over points which are not unimportant, and in
order to deal adequately with these points a long discussion would be
required for which there is no space. All that can be done here is to
set out the most important facts; they will provide a satisfactory
answer to the first question and enable some indication to be given of
the lines which the answer to the second must follow.
However slight the treatment of the problem, it must begin with a
reference to the physical basis of inheritance. Some description has
been given of the process of fertilization. It was said that only the
head and middle-piece of the spermatozoon penetrate the egg, and that no
cytoplasm or ordinary granular protoplasm can be demonstrated in these
parts of the spermatozoon. The head is the nucleus of the cell, while
the middle-piece contains the centrosome, a body which is attached to
the nucleus and plays an important part when the nucleus divides. From
these facts a very important conclusion follows. It is known that both
parents contribute equally to the offspring; therefore as the male
parent contributes only a nucleus and its appanage the centrosome, the
basis of the inherited qualities must be sought in the nucleus.
Attention is thus directed to the nucleus, which can sometimes be seen
in the living cell. Its detailed structure can, however, only be made
out in specimens which have been preserved and stained. The nucleus is
then seen to consist of a thin wall within which is contained a
colourless sap. In the sap are a number of beads of a darkly staining
substance known as chromatin suspended on delicate threads of a
substance known as linin. The division of a cell is always preceded by
the division of the nucleus and, when the nucleus divides, the chromatin
undergoes certain remarkable changes. The beads of chromatin become
aggregated together into rods—the number of rods which appear being
invariably constant in the same species, though varying from species to
species. These rods are known as chromosomes. Beyond saying that the
rods divide into two and that each daughter nucleus, and therefore each
daughter cell, is provided with that number of chromosomes which is
typical for the species, it is not necessary to follow the details of
the process of division any farther. Stated in the briefest possible
form, this is what happens during ordinary cell-division, such as that
which takes place when a fertilized egg is growing from a single cell
into a multicellular adult.
There is one remarkable exception to this type of nuclear division. In
the last division but one of those series of divisions which lead to the
formation of both male and female gametes, half, and not the full number
of chromosomes, is transmitted to each daughter nucleus. If therefore
the typical number of chromosomes in the nucleus of one species is eight
and in another four, the number of chromosomes in the gametes will be
four and two respectively. In the former species the nucleus of the egg
will have four chromosomes, and that of the spermatozoon also four, and
the full number typical of the species will only be restored when the
nucleus of the spermatozoon fuses with the nucleus of the egg in
fertilization.
The invariable reappearance of the same number of chromosomes in
ordinary cell-division, their reduction to half that number in the last
division but one which precedes the formation of the gametes, the
complicated mechanism which is employed and other evidence all lead to
the conclusion that the location of the basis of the hereditary
qualities can be further narrowed and sought in the chromatin—in one
element, that is to say, of the nucleus.[98]
2. The nucleus must not be thought of as isolated from the rest of the
cell; there is a constant and active interchange between the nucleus and
the cytoplasm. It has actually been demonstrated that at times particles
stream out from the nucleus into the cytoplasm. The nucleus is the
centre of activity; without the nucleus the cell cannot live. This being
so, how are we to view the process of development from the fertilized
egg to the adult? The process can be studied in detail. The egg divides
into two cells, then into four, eight, sixteen, thirty-two cells, and so
on. The gradual differentiation of the organs can be watched and their
lineage to certain cells in earlier stages traced. At every stage the
developing organism comes under the influence of certain stimuli
provided by the surrounding conditions. Very many elements in the
environment act as stimuli; among them are light, temperature,
gravitation, food, and so on. Provided that the environment is normal,
provided, that is to say, that the variations in the stimuli do not
exceed certain limits, an adult member of the species will be formed.
What is implied in the term ‘normal environment’ will be more fully
discussed in Chapter XIV, where the results of subjection to an abnormal
environment will also be studied. That a large number of stimuli varying
within only narrow limits are necessary, will there also be shown to
have been proved.
The process of development, therefore, takes the shape of the growth of
a particular organic form through the play of certain stimuli upon the
germinal constitution. The germinal constitution has, as we have seen,
apparently to be identified with the constitution of the chromosomes of
the fertilized egg, of which half are derived from the father and half
from the mother. It is known that the characters, which the organism
exhibits, in some manner have a basis in the germinal constitution. The
number of these separate characters is very large. What view then are we
to take of the nature of the germinal constitution? In the first place
every character as seen in the organism is the result of the play of
certain stimuli upon something in the germinal constitution. This
something can only be thought of as predispositions to the development
of certain characters under certain stimuli and to the development of
characters differing in degree or in kind from the former characters
under other stimuli. It is altogether misleading to speak of anything
but predispositions as present in the germinal constitution, though, of
course, for the sake of brevity other phraseology may be employed once
this point is understood. When, therefore, we speak of the inheritance
of any character, we mean that there is a predisposition in the germinal
constitutions both of the parent and of the offspring to develop this
character under certain stimuli, which stimuli must play both upon the
parent and upon the offspring if the character is to be manifested in
both of them.
If we have to regard the germinal constitution as somehow containing
very many separate predispositions or, as they are often called,
factors, is it in the second place possible to say in what these factors
consist? No definite answer to this question can as yet be given.
Certain hypotheses have been put forward. Weismann, for instance,
suggested that the factors were to be sought in groups of molecules of
chromatin. It is not necessary, however, to postulate definite and
separate particles as the physical basis of the predispositions. The
protoplasmic molecule is a very complex structure consisting of a very
large number of atoms. Similar atoms may be differently grouped within a
molecule, and different predispositions may well be functions of
different groupings.
3. In order that we may answer the first of the two problems set out at
the beginning of the chapter we must consider in rather more detail in
what the development of an organism consists.[99] Every character is, as
we have seen, the result of the influence of the environment upon what
is innately given. If two individuals were endowed with precisely
similar germinal constitutions, and if precisely similar stimuli played
upon each of them, then the adult forms would be similar in respect of
all their characters. But if the stimuli are not similar, if, for
instance, more food is provided in one case than in another, then,
though the germinal constitutions are similar, one adult may be larger
than the other. Again, let us suppose that the germinal constitutions
differ, that, for instance, there is in one case a predisposition to the
development of greater size than in the other, then, even if the stimuli
are similar, the adult forms will differ. The larger members of each of
these pairs may thus resemble one another very closely in outward
characters; but this close resemblance will not be due to similar
germinal constitutions. It follows that by mere outward inspection no
conclusion can be reached as to the germinal constitution. There are,
therefore, two classes of influences at work, and alterations in either
class of influence will bring about alterations in the resulting
organism; similar characters may be the product of one kind of
predisposition and one kind of stimulus, or of a different
predisposition and a different stimulus. It also follows that we cannot
speak of certain characters as inherited and of others as acquired. Let
us suppose that some departure from the normal structure occurs. It may
be due to a change in the environment, that is to say, to a new stimulus
acting upon an unchanged germinal constitution, or it may be due to a
change in the germinal constitution when no change in the environment
takes place. It should not be said that in the former case the new
departure is acquired and in the latter case that it is inherited. What
has happened is that in the former case a new stimulus acting upon the
old factors has brought forth a new character, and in the latter case
that the old stimulus has brought forth a new character because it has
acted upon a different factor.
Though the popular distinction between characters which are acquired and
characters which are inherited is misleading, there are, nevertheless,
two kinds of variation. A new departure may be due to a change in the
germinal constitution. In this case the new character will reappear in
future generations, provided that the changed germinal constitution
remains and provided that the complex of stimuli which composed the
environment does not change. Such a variation may be called a
‘mutation’. A new departure may also be due to a new stimulus acting
upon an unchanged germinal constitution. In this case the new character
will only reappear in future generations provided that the new stimulus
remains. Such a variation may be called a ‘modification’. Mutations,
therefore, are transmitted in the germinal constitution, while
modifications are not so transmitted.
4. Already we have reached the answer to the first problem. Permanent
change in organic form is due to germinal change. But before we go on
and ask how germinal changes, that have arisen, become established, we
must consider further the difficult problem of the manner in which
germinal changes arise. A reference first to what are known as ‘pure
line’ investigations and afterwards to Mendelian phenomena will
illustrate what is known as to the nature of existing germinal
differences; for until we have some such information, we cannot
profitably ask how existing germinal differences arise. The best known
‘pure line’ experiments are those carried out by Johannsen with beans.
The flowers of beans fertilize themselves; the offspring, therefore,
have approximately the same germinal constitution. The offspring
constitute a ‘pure line’, for by a ‘pure line’ is meant a group of
children which are the offspring of a single parent. The character
selected for investigation was weight and it was found that, if beans
were collected from a bean-field and weighed, every gradation occurred
between a minimum of about 20 centigrams and a maximum of about 90
centigrams. When the beans were separated into three classes—heavy,
medium, and light—sown and plants raised from them, the average weight
of the beans produced by the plants derived from the heavier seed was
greater, though not proportionately greater, than the mean weight of all
the beans, and that the average weight produced by the plants derived
from the lighter seed was less, though not proportionately less, than
the mean weight of all the beans. There was, in fact, a certain
regression on the part of the heavy and light classes to the mean
weight. A similar tendency to regression to the mean can be observed
when other characters are similarly studied. The average stature, for
example, of the offspring of tall parents is slightly nearer the mean
stature of the race than the average stature of the parents.
This tendency to regression to the mean has long been known, but it was
not until Johannsen proceeded farther and investigated inheritance
within a ‘pure line’ that it was understood. In the experiment
described, no attention was paid to the ‘pure line’. When Johannsen
separated the beans produced by the self-fertilization of a single
plant, divided them into heavier, medium, and lighter classes, sowed
them and weighed their progeny, he discovered a very interesting fact.
The average weight of the progeny of a heavy bean and of a light bean
belonging to the same ‘pure line’ was the same. The conclusion to be
drawn from this result is that the differences in weight between the
offspring of a single self-fertilized plant are due to differences in
the stimuli which play upon them. Obviously the stimuli do differ; the
weight is affected by differences in light, shade, number, and position
of the beans in a pod and so on. But since the offspring of a single
plant have approximately the same germinal constitution, the average
weight of the offspring of light beans, which are light because of
subjection to less favourable stimuli than the average, will not be on
that account lighter than the mean weight of the strain, and similarly
_mutatis mutandis_ with regard to the offspring of the heavy beans.
It follows, therefore, with regard to this particular character that
there are a number of different strains in the population. The beans
arising from any one strain are not of the same weight because they have
been subjected to different stimuli. If each strain was pure and if
differences in environmental stimuli could be removed, then beans
gathered from a bean-field would not exhibit a simple gradation in
weight: there would be a number of steps and as many steps as there were
strains. In actual fact, the modifications produce the gradation which
is observed. The fact that the nature of the germinal constitution
cannot, as stated above, be determined by a mere inspection of the
characters is exemplified by this experiment. If we take a bean
weighing, say, 55 centigrams, it may belong to a strain which varies,
say, between 20 and 65 centigrams, or to a strain which varies between
40 and 90 centigrams. It is only when this bean is sown, and the weight
of the offspring calculated, that the strain to which it belongs can be
ascertained. The experiment further shows why regression towards the
mean is observed, when, instead of limiting investigation to a ‘pure
line’, beans differing in a certain respect from the average, by, for
instance, greater weight, are selected and sown. Such beans will belong
to several different strains; they will, however, include more which
have been favourably than unfavourably influenced by the surroundings.
The average of the weight of all their offspring will therefore be less
than the average weight of the parents. At this point we touch upon the
problem of selection, but before we go on to deal with this question, it
is necessary to say something more about variation and the origin of
variations.
5. Self-fertilization is very exceptional, and what happens in the case
of the beans, though illuminating, is not typical. As a general rule in
reproduction, two parents contribute to the germinal constitution of the
offspring. Strains, therefore, do not remain pure, as in the case of the
bean, because they are continually crossed; we require to know what
happens when crossing takes place. This study, first successfully
undertaken by Mendel, has been greatly extended in late years. We may
first illustrate in the simplest form what it was that Mendel discovered
and then go on to inquire what deductions bearing upon the question we
have to answer are to be drawn from it.
A large number of experiments of the following kind has been made. Two
strains in any species are chosen; these strains exhibit opposed
characters. Such characters may be tallness and dwarfness, colour of the
flower, shape of the comb in fowls, condition of the seed, whether
smooth or wrinkled, and so on. We may call one character A and the other
_a_. The two strains are crossed, and in the first generation the
offspring are all alike and exhibit a character, A′. This character may
be the same as either A or _a_, a blend between them or something wholly
new. Whatever form it may take, it is produced by the interaction of A
and _a_. The members of this first generation are then interbred, and of
the second generation one quarter exhibit the character A, one quarter
the character _a_, and the remaining half the character A′. If the
quarter exhibiting the character A are interbred, all the offspring
exhibit the character A, and the same holds good regarding the quarter
exhibiting the character _a_; but if the half exhibiting A′ are
interbred, the offspring will split up in the same proportion as in the
previous generation, one quarter exhibiting A, one quarter _a_, and
one-half A′. This result holds good for any number of generations so
long as interbreeding is continued.
Into the very numerous complications which occur it is not necessary to
go. They are all interpreted by extensions of the simple explanation
which is applied in the elementary case given above. It is supposed that
all characters which behave on crossing as above are represented in the
germinal constitution by factors which behave as separate units; such
characters are called ‘unit-characters’, and such factors
‘unit-factors’. It is further supposed that each gamete bears one
unit-factor only in respect of each unit-character. If the strain is
pure, as in the case of the two strains exhibiting characters A and _a_,
then all the gametes will bear the unit-factors for A and _a_
respectively, and the fertilized eggs resulting from the crosses between
them will therefore contain both unit-factors. The hybrids, which, as we
have seen, exhibit the character A′, will produce gametes, half of which
bear the unit-factor for A and half the unit-factor for _a_. When the
hybrids interbreed, on the average of chances one quarter of the
fertilized eggs will have two factors for A, one quarter two factors for
_a_, and one-half both a factor for A′ and a factor for _a_. In this
manner the splitting up of the second generation is explained.
What is important in this explanation is the conception of unit-factors.
The extension of the explanation to cover the more complicated cases
does not involve any modification of principle. It follows that the
germinal constitution contains a very large number of unit-factors; what
therefore is innately given in the germinal constitution is a collection
of such unit-factors. Each unit-character based upon a unit-factor can
theoretically be separately distinguished and isolated. The
complications to which references have been made are in part due to the
difficulty of distinguishing unit-characters. What is apparently a
simple character may not be a unit-character, but a combination of
unit-characters. This apparently simple character cannot appear unless
all the unit-factors, upon which these unit-characters are based, are
present in the germinal constitution.
It may next be asked whether all unit-factors behave in this manner when
crossed. To this no definite answer can yet be given. The successful
analysis of apparently contradictory cases and the continual discovery
of characters which do behave in this fashion seem to point to an
affirmative answer. The suggestion is that, when this mode of behaviour
cannot be demonstrated, it is because the unit-characters have not yet
been distinguished and isolated.
This brief reference to ‘pure line’ investigations and to the Mendelian
analysis of crossing leads therefore to the following conclusions. When,
as in the case of the self-fertilizing bean, the strains are kept pure,
existing germinal differences in respect of any character are found to
be of the nature of steps which are usually small—though in outward
manifestation the differences are smoothed over by the influence of
environmental stimuli. This is the nature of the germinal differences,
and they remain what they are—apart from the origin of new factors or of
the loss of old factors, and apart from the effects of a differential
death-rate. When, as is usually the case, biparental reproduction takes
place, the position is more complicated: strains are being continually
crossed, and, as the result of the chance mixture of factors in the
germinal constitution of the children, the offspring of the same parents
differ in their germinal constitution one from the other. Therefore, in
any species in which biparental reproduction takes place, new
combinations are constantly arising; but, though in this manner the
germinal constitution may in a sense change, the change is due simply to
a shuffling of factors. What we require now to ask is what is known as
regards the manner in which new factors arise and are added to the
germinal constitution, and the manner in which old factors drop out and
are lost from the germinal constitution; for it is only owing to such
additions and to such losses that true germinal change occurs, and that
shuffling is rendered possible.
6. The interpretation of the results of the crossing of different
strains has shown what kind of changes underlie the appearance of
certain mutations. It has been shown that many of the varieties of
domesticated species have originated by the apparent loss of one or more
unit-factors.[100] Thus the numerous varieties of domestic rabbits and
of sweet-peas are all descended from a single wild species of rabbit and
of pea, and differ from the wild stock not by an addition to, but by an
apparent subtraction from, the total number of factors in the germinal
composition of the wild stock. The reasoning which has led to this
conclusion need not be followed here; one proof is that when certain
varieties are crossed, characters of the original stock reappear, due to
the fact that, one variety having apparently lost one factor and the
other another, crossing results in the re-combination of the factors
necessary to the manifestation of the original character.
This is a strange conclusion, but it seems nevertheless to be true that
in this manner many domestic varieties have arisen. If this was the only
manner in which mutations could come about, then we should be driven to
imagine that the most elementary form of life contained within it
innumerable factors, and that evolution has merely consisted in the
apparent dropping out of factors. This conclusion has indeed been
tentatively suggested. But until it has been definitely shown that this
is the only manner in which mutations originate, it must be supposed
that changes in and additions to the complex of factors can and do
occur. And we may note that certain distinguishing characters of
domestic varieties of fowls and of pigeons appear to have arisen by the
addition of factors; thus the ‘single comb’ of fowls is the original
character of the wild stock which has been modified by the apparent
addition of other factors and not by the dropping out of one or more
existing factors. It is again not necessary to go into the reasons which
have led to this conclusion. The conclusion is a deduction from the
analysis of crosses between different breeds of fowls.
7. For the most part we are quite ignorant as to the causes which have
led to the apparent losses and apparent additions of factors, though a
few observations seem to indicate certain circumstances under which the
dropping out of factors may take place. In this connexion some reference
must be made to the problem as to the inheritance of acquired
characters, though it follows from what has been said above regarding
terminology, that we should more correctly speak of this problem as the
question whether modifications in any one direction tend to be followed
by mutations in the same direction. As the result of prolonged
discussion and controversy it is now generally held that nothing of the
kind takes place. It is almost universally agreed, for instance, that
such modifications as are induced among men at the present day do not
lead to mutations in the same direction. Therefore we may for the
purposes of this book, so far as man is concerned, take it that acquired
characters are not inherited. But looking at the problem as a whole it
cannot be regarded as settled. There is, for example, some evidence of
the parallel induction of modifications and of mutations; but the
question may be raised whether such cases if substantiated fall under
the heading of the inheritance of acquired characters. Again, some
biologists regarding the problems of evolution generally find difficulty
in arriving at an explanation unless under certain circumstances
adaptive variations are followed by mutations.
We are thus left with the fact that mutations arise, and may be either
large or small. Outwardly, variations in characters are usually
continuous, because the environmental stimuli vary continuously, smooth
over and obscure the differences due to mutation, as in the case of the
beans mentioned above. But, discounting the influence of the
environment, the mutations themselves may form a series separated by
steps that are so small as to be scarcely measurable or which may be
very large. The weight of the beans is an example of the former kind of
mutation; the so-called ‘meristic’ variations, when another member is
added to a series, the addition, for instance, of a vertebra to the
vertebral column, is an example of the latter kind.
Whenever a mutation occurs, we have to think of it as founded upon some
change in the germinal constitution. Such changes are of the nature of
modifications of factors—and may be positive (leading to the apparent
addition of factors), negative (leading to the apparent loss of
factors), or qualitative. But of the nature of these changes we know
little, and of their causes less. What is important, however, is that
these changes do occur. Further, they occur in all directions. The
direction is, of course, in a sense determined by the starting-point—by
what is already given in the germinal constitution—but, given the
starting-point, mutations apparently occur in all directions. It is a
matter of importance to know whether mutations ever tend to occur more
in one direction than in another. Nothing definite has been ascertained
as to this particular problem, though, as we shall note later, certain
facts with regard to the evolution of animals suggest that there have
been tendencies to change along certain lines. It may also be asked
whether the continued selection of a character in any way affects the
direction of the variation of the germinal constitution. To this again
there is as yet no definite answer. On the whole it is not probable that
selection has any such effect.
8. So far, therefore, as we have at present gone, we have found that
permanent change is of the nature of germinal change. We have also
discussed the nature of germinal differences as they exist between
different individuals, and we have discussed the nature and causes of
germinal change. With regard to variation there is much which is
doubtful and obscure, but bearing in mind the essential features of what
is certainly known, we may turn to consider what passes in the organic
world. Upon this subject there is much less uncertainty. We have seen
how huge is fecundity. Of the young in any generation, only about that
number survives which equals the number of adults in the generation from
which they are derived. For normally in the organic world the total
number of adults of any species at corresponding periods in succeeding
years remains much the same. The instances of a marked increase in the
number of any species are rare, and are usually traceable to the
intervention of man, as the result of which certain of the dangers which
normally confront the young have been removed. It follows, therefore,
that normally of the many thousands of fertilized eggs of a fish, for
example, all but two perish. Even when the most rapid increase ever
observed is taking place, the great majority of young perish. From a
consideration of the circumstances it is evident that upon the whole
those individuals which present certain characters will have a better
chance of surviving than others which do not present these characters.
This point demands further consideration, because upon it turns the
whole question of natural selection. What is involved in this theory is
that the death-rate is selective, that those individuals which are best
adapted to the surroundings which confront the species do, on the whole,
have a better chance of survival. It is adaptation which determines
fitness, but the concept of adaptation does not of necessity include any
idea of progress. Given any complex of surroundings such as that which
confronts any species, there may be a more or less close fitting of the
organisms to this complex. The closeness of this fitting may have been
obtained by a simplification of structure, a complication of structure,
or it may be that for long ages the closeness of the fitting has been
attained by the elimination of departures from the mean of the species
in any direction and the preservation of the average type.
In this connexion it has often been pointed out that the death-rate in
certain cases is not selective, and does not therefore involve the
survival of the more fit and the elimination of the less fit. When the
whale opens its mouth and engulfs vast numbers of small organisms upon
which it feeds, there is apparently no escaping of certain types of
these organisms accompanied by a greater elimination of other types. But
these cases are not on the whole common, and further there is nothing in
such cases which counteracts selection; it merely means that sometimes
selection is not operative. A consideration of the mode of operation of
the factors of elimination, the general nature of which has been
indicated, leads without any doubt to the conclusion that in the vast
majority of cases, when any organism meets its death, either that
organism does not possess some character which other organisms possess
and which have enabled them to survive, or it possesses some character
which other organisms do not possess, and which at some crucial moment
has told against it. This subject could be considered at great length,
but it must suffice to say here that the more experienced naturalists
are, and the greater the knowledge they have of the conditions of
organic life, the more it is borne in upon them that the death-rate is
upon the whole selective, and that the best adapted types have a better
chance of survival than other types.
From the nature of the case it must be difficult to obtain statistical
evidence of natural selection. There are, however, certain cases known
which are of great interest. Bumpus, for instance, after a storm in
America collected 136 sparrows, all of which had been injured. Of these
72 recovered, while the remainder died. He weighed and measured all the
specimens and compared the figures for the survivors with the figures
for those which had perished. It was found that the average type of the
latter was larger and heavier than the average type of the former. It
was also observed that there was a less wide range of variability among
the survivors than among the dead, showing that the favoured type
approximated more closely than the others to the average type of the
species. This favouring of the average type has been shown to occur by
other observations, and it may be supposed that normally it is the
average type of any species which is best fitted to the particular niche
in nature occupied by the species, and that therefore adaptation will be
measured by the nearness of approach to this type. When, on the other
hand, circumstances are changing, some deviation from the average type
will be favoured.
9. This leads us to ask in more detail what it is that happens in the
process of selection. Selection has been likened in its action to a
sieve separating the fit from the unfit. But fitness is measured by the
characters exhibited, and these characters may be either of the nature
of mutations or of modifications. What is exhibited is selected quite
apart from the underlying nature of the character; but it is only when
variations of the nature of mutations are selected that there results
any change in the composition of the germinal constitution of the
species. So far as selection is merely that of modifications within a
strain, there will be no change in the average germinal constitution of
the progeny. It is only in so far as selection is a selection of strains
that there will be any change. If the strains among the beans referred
to above can be isolated, then the strain with the predisposition
towards the greatest weight can be isolated, the other strains
eliminated, and the average weight brought up to that found in this
strain. If the strains cannot be isolated, then an approximation only to
this result can be made by the continued selection of strains of the
greatest weight, and this is what occurs in nature.
This leads to the most important conclusion of all. Selection can only
act upon what is given. We may put aside the possible but quite unproved
influence of selection upon the direction of mutation. Apart from this,
selection can have no other effect than to eliminate certain strains and
to favour others. Supposing that under changing circumstances a certain
character is favoured, all that can happen through selection is that the
strain exhibiting this character will be favoured and all other strains
gradually eliminated. Further than this change cannot proceed until
mutations have occurred in the direction of further increase in this
character. As has been said, selection is no more than a sieve; as a
rule it is occupied in separating out the extreme types and favouring
the mean, but at times under certain circumstances it will favour some
type that deviates from the mean, but it can do no more than favour what
types are at any given moment in existence.[101]
10. We set out to answer two questions regarding quality. We asked in
what change among species in a state of nature consisted. The answer to
this is clear; it consists in changes in the germinal constitution. If
we can speak of history in connexion with species in a state of nature,
then their history is based solely upon germinal change. We also asked
how change came about. It is less easy to answer in a few words. Obscure
as are many of the details connected with the process, there is a
sufficient measure of agreement regarding the main facts to enable an
answer shortly to be formulated. The answer rests upon two series of
facts. The observed characters of organisms are based upon certain
predispositions in the germinal constitution. These predispositions or
factors under the stimuli of the environment give rise to the various
characters. These factors are derived from both parents through the
fusion of the gametes, and the complex of factors in the offspring is
the result of a chance mixture of factors. There may further at times be
a dropping out, an addition to, and perhaps a modification of the
factors. Secondly, the death-rate is selective. Although the result of
selection is confused by the effect of modifications which smooth over
the differences due to differences in the germinal constitution, the
effect is that individuals with certain factors are favoured and others
with different factors are eliminated. Therefore the average nature of
the factors may be changed should any type, other than that
approximating to the normal type, be favoured.
It is possible in this manner to understand how change has come about.
There are many difficulties, but they are all capable of fairly
satisfactory explanation. None at least is insuperable. There is one
problem which is perhaps somewhat difficult to solve unless a particular
supposition is introduced. This problem is connected with the evolution
of organs along certain lines, as, for instance, the evolution of horns
and teeth in the vertebrates. This class of evidence has chiefly
impressed itself upon palaeontologists, and one of the most
distinguished of them has stated that from this class of evidence he
concludes that ‘there are fundamental predispositions to vary in certain
directions’.[102] This is the supposition which it may be necessary to
introduce, but which does not in any way conflict with what has been
said.
IV
THE POPULATION PROBLEM AMONG MEN
1. It has been shown in the last two chapters in what the population
problem among species in a state of nature consists. With regard to the
quantitative aspect in particular it has been shown that among such
species mental evolution, greatly as the stage reached differs between
the lowest and the highest forms, has not attained a point at which the
essential features of the position have in consequence been affected.
Enough has been said to show that in the case of the most primitive
races of man now living mental evolution has reached a point in
consequence of which the quantitative problem has assumed a totally
different aspect.
With regard to the qualitative problem the question also arises as to
how far mental evolution in man has affected the position. In one very
important respect mental evolution has wholly altered the position of
man as regards this aspect of the problem, as it has regarding the
quantitative aspect. How this has come about may be considered after it
has been observed that mental evolution has also been the cause of other
changes which, while they do not alter the fundamental position of man
as regards the qualitative aspect, yet are of great importance.
As we have seen among species in a state of nature change is founded
upon germinal change. So, too, among men there is germinal change, and
so far as history (using the term in the widest sense to include what is
often rather meaninglessly called ‘pre-history’) is connected with
germinal change, so far it is of essentially the same nature as change
among other species. But both the direction and intensity of germinal
change among men have been greatly influenced by mental evolution.
Certain causes of elimination have been removed wholly or in part,
others have been introduced. The facts are familiar; there is no need to
labour the point. It is also worth noting that, should it be found that
mutation frequently arises owing to alterations in the environment
during the formation of the germ-cells, such a discovery might have
considerable bearing upon the position in man. Owing to human activity
under the guidance of reason, the environment has been profoundly
changed in many directions, and without question in consequence of such
changes the germ-cells of human beings are subject during their
development to far more varied stimuli than are those of other species.
This, however, is only a possibility. Nothing is known with certainty
upon the subject. It may be that the great variety of foods, the
absorption of alcohol and nicotine, the various occupations and customs,
and many other factors, all ultimately traceable to reason, may, some of
them in some way, tend to bring about mutation in man.
It is by making possible the development of tradition that the evolution
of reason has fundamentally changed the nature of the qualitative
problem among men. Into the nature and origin of tradition it will be
necessary to go in another chapter. Here all that is required is an
indication of its main features in order that its connexion with the
problem of change may be understood. In the stage of conceptual thought
reached by man, the formation of free ideas is the outstanding feature.
With the development of conceptual thought went the development of
language. By language ideas can be passed from one man to another and
also from one generation to another. There are other ways in which the
results of reasoning can be handed on, but they need not be considered
at present. What is important is that they can be and are handed on. Let
us consider for a moment the question of skill. Some improvement may be
made in the methods of hunting or of fishing. It may, of course, be
lost, but it may be, and perhaps usually is, transmitted to other men by
the inventor and afterwards to succeeding generations. Tradition is, in
fact, cumulative. Even among the most primitive races now existing there
is a huge mass of tradition. Succeeding generations do not necessarily
start at the beginning again. They start with the experience of the race
behind them, so far as it has been preserved.
Among the higher animals there is a certain handing on of what has been
learnt by experience; to this extent there is tradition also among them.
We shall return to this point later. So relatively unimportant, however,
is tradition among other animals, that we may for the moment regard
tradition as something which is found among men only. It is clear that
tradition has played some part in any case in producing the changes
which we call history. We have only to think of the rise of Japan to the
position of a great power in the last half of the nineteenth century.
The rise of Japan was an outstanding fact in the history of that period
and it was clearly in the main, if not wholly, a traditional and not a
germinal change. It took the form of a rapid absorption of European
tradition. The evolution of reason has thus introduced into the problem
of the causes of human history a factor which is not present in the case
of other species; it has also modified the course of selection, but
this, as we have seen, has not made a fundamental difference between the
position of man and that of species in a state of nature.
The problem before us is therefore as follows. Owing to the fact of
reproduction the population problem in both its aspects exists for all
species in a state of nature and further presents fundamentally the same
features for all such species. The ancestors of man were at one time
subject to the same conditions from which they have, step by step, moved
away owing to the development of the faculty of reason. We have to trace
the causes and results of this moving away—of the progressive
modifications of the conditions existing among species in a state of
nature.
Though the problem has two aspects, they are closely interwoven. Changes
which affect numbers also influence the quality of population. The
discussion has hitherto taken the form of an introduction to the problem
as a whole, and the two next chapters, the subject-matter of which will
be indicated in what follows, will also be devoted to certain problems
which equally bear upon both aspects of the question. From the seventh
chapter onwards the two aspects are treated independently; we deal first
with the quantitative and then with the qualitative aspect. Nevertheless
we shall, when dealing with the quantitative problem, present evidence
which we shall consider again later when treating of the qualitative
problem. The book thus falls into three parts; the first six chapters
are introductory to the problem as a whole, the next six chapters are
concerned with problems of quantity (though many of the facts brought
forward will be found also to bear later upon quality), and the
following nine chapters with problems of quality. The last chapter sums
up our conclusions as to the whole problem.
2. We may next ask what data are required in order that we may look into
the changes away from the conditions under which the pre-human ancestor
lived towards the conditions which now exist. In order that we may
consider the quantitative aspect of the problem, it is evident that we
require some knowledge regarding fecundity and as full details as
possible regarding the factors which bear upon fertility and
elimination. It is only when we are provided with such information that
we can hope to be able to determine how it is that numbers are regulated
among men.
In addition to such information, it will be desirable to have
information regarding various social customs and the general conditions
of life. As regards the inquiry into the qualitative part of the
problem, it is clear that facts regarding fertility and elimination are
again of value inasmuch as they throw light upon the nature and
intensity of selection. For the second part of the problem it is also
necessary to have in mind the main facts regarding the changes which are
summed up as history into the causes of which we have to inquire; and in
addition it will be necessary, in order that we may attempt some
estimate of the relative importance of change in the germinal
constitution on the one hand and of the other factor or factors of the
nature indicated above on the other hand, to make some inquiry into the
conditions which determine the nature of these latter factors. This will
involve a reference to certain elementary facts of psychology together
with some discussion of the origin, formation, preservation, and so on,
of tradition.
If we first ask how far the data desired are available, we may
afterwards go on to discuss how the facts are best presented. Our
information is obviously very incomplete as regards the history of
social habits and customs. Historical records do not take us farther
back than at the most six thousand years, and the information available
with respect to social customs, except for the latter part of the
period, is very inadequate. If we take a broad view of history, written
records have reference only to relatively modern times. There are two
other sources of evidence upon which we have to rely and they are as
follows.
Some indication of the bare outline of the course which history has
taken can be gathered from a study of the fossil and cultural remains of
man. The fossil remains are in the form of skeletons or portions of
skeletons and the cultural remains in the shape of tools, weapons, and
other traces of his mode of life that man has left behind him. It is
interesting to observe that an attempt can be made to date these
remains. They occur in certain strata, and estimates can be made of the
length of time which has elapsed since these strata were deposited.
Though a very large measure of doubt must surround any such estimates,
nevertheless there is a certain measure of agreement concerning the
facts which is of great interest. It is, therefore, possible to draw up
a table showing these strata, together with what we should perhaps call
guesses at the dates at which they began to be laid down. It can also be
shown in the table what fossil and cultural remains are found in the
respective strata.
The information, however, which we thus gain is very meagre. A study of
fossil remains can only provide us with an outline of the facts
connected with the evolution of the skeleton. More can be gathered from
a study of the cultural remains, and certain deductions of considerable
interest can be made especially in connexion with our present purpose so
far as the evolution of skill is concerned. But, of course, we can in
this manner gather nothing as to the nature of the social customs and
institutions belonging to the races which practised these skilled
methods. The question we have to face is whether this very bare outline
of the facts of history can in any manner be filled in.
3. There is a further source of evidence which we have to consider.
There has come under the observation of civilized man a large number of
races in a low stage of culture. The evolution of culture or of control
over the surroundings took place more quickly among certain races than
among others. Some races got left out of the main stream of evolution,
and finally in relatively recent years the more advanced races arrived
at a stage where they were in a position completely to dominate the
latter. The more primitive races were unable to offer any serious
resistance to the civilized races. It was, therefore, possible to regard
these primitive races dispassionately and scientifically; this study has
led to the collection of a vast amount of information regarding these
primitive races. These data are for many reasons often of a very
unsatisfactory nature; of this the chief cause is that, before an
accurate study was begun, contact with civilized races had often had a
considerable influence upon the former mode of life of the primitive
races. What we require and what is difficult to obtain is information as
to the conditions under which these races lived before they came into
contact with Europeans. With regard to the unsatisfactory nature of the
evidence there will be more to say later.
It is of primary importance to observe that these races are not to be
regarded as actual representatives of certain stages through which
civilized races have passed. We know that in the evolution of control
over nature civilized races have passed through certain stages of
culture; the first stage was marked by the use of unpolished stone
implements and the obtaining of food by hunting and fishing only; the
second stage was marked by the use of polished stone implements and the
obtaining of food by agriculture and the domestication of animals.[103]
These two broad divisions—the Palaeolithic and the Neolithic—may be
subdivided. But no primitive race can be regarded as representing any
definite stage in exact detail, whether in the first or in the second of
the two broad divisions through which civilized races have passed. While
the culture of the ancestors of civilized man was evolving from that of
the Palaeolithic stage to that of the present day, the culture of
certain other races did not progress as far even as the Neolithic stage.
But the culture of these races did not remain unmodified; it followed in
each case a line of evolution of its own. These races are therefore to
be regarded as specialized representatives of the earlier stages of
culture through which the civilized races passed. Nevertheless,
specialized though their culture may be, the general conditions of their
existence are certainly similar to the general conditions which must
have characterized the corresponding stage in the evolution of the
culture of civilized races. That is to say, the broad features which
characterize the conditions found among hunting and fishing races must
also have characterized the conditions under which our Palaeolithic
ancestors lived.