FACTORS OF ORGANIC EVOLUTION
_Variation--Selection--Isolation--Spencer's Contribution--External
Factors--Internal Factors--Direct Equilibration--Indirect
Equilibration_
Darwin rendered three great services to evolution-doctrine, (1) By his
marshalling of the evidences which suggest the doctrine of descent, he
won the conviction of the biological world. (2) He applied the
evolution-idea to various sets of facts, not only to the origin of
species in general, but to the difficult case of Man; not only to the
origin of the countless adaptations with which organic nature is filled,
but to particular problems such as the expression of the emotions; and
in so doing he corroborated the evolution-formula by showing what a
powerful organon it is. (3) Along with Alfred Russel Wallace, he
elaborated the theory of natural selection, which disclosed one of the
factors in the evolution-process.
As we have seen, Herbert Spencer preceded Darwin in his championing of
the doctrine of descent, to which the natural mood of his mind, and the
influences of Lamarck and von Baer had led him to give his adhesion. He
also applied the evolution-formula to an even wider series of facts than
Darwin ventured to touch, viz., to the inorganic world and to
psychological and sociological facts. It remains to be seen what his
position was in regard to the Factors of Organic Evolution.
Spencer's position may be more clearly defined if we first sketch the
answer which most biologists would at present give to the question--What
are the factors of Organic Evolution?
_Variation._--Postulating the powers of growing and reproducing, of
acting on and reacting to the environment, postulating also heredity
without which no organic evolution is possible, biologists distinguish
two sets of factors in the evolution process. On the one hand there are
_originative factors_ which produce those changes in living creatures
which make them different from their fellows. These changes or observed
differences are of two kinds--(_a_) they may have their origin in the
arcana of the germ and be inborn _variations_ (germinal, constitutional,
endogenous, etc.), or (_b_) they may be acquired _modifications_ wrought
on the body of the individual by environmental influences or by use and
disuse (somatic, acquired, exogenous, etc.). Thus "modifications" or
"acquired characters" may be defined as structural changes in the body
of the individual organism, directly induced by changes in the
environment or in the function, and such that they transcend the limit
of organic elasticity and persist after the inducing causes have ceased
to operate. Merely transient changes which disappear soon after their
cause has ceased to operate may be conveniently called "adjustments."
Now when we subtract from the total of observed differences between
individuals of the same stock, all the modifications and adjustments
which we can distinguish as such by their being causally related to
some alteration in function or environment, we have a remainder which we
call "variations." We cannot causally relate them to differences in
habit or surroundings, they are often hinted at even before birth, and
they are not alike even among forms whose conditions of life seem
absolutely uniform. This distinction between _modifications_ and
_variations_, though clear in theory, is not always readily drawn in
practice, but it is of great importance, for while all innate
variations, except complete sterility, are transmissible, and thus may
form the raw materials of progress, there is no secure evidence that
acquired characters or somatic modifications are transmissible.
Therefore, the latter, though very important for the individual, and
indirectly important for the race, cannot be assumed (without further
proof) as directly important in the transmutation of species.
As to the nature and frequency of inborn variations, Biology has
recently begun to accumulate precise observations, and has renounced the
bad habit of simply postulating variability without statistically or
otherwise defining it. Life is so abundant and so Protean that
biologists have tended to draw cheques upon Nature as if they had
unlimited credit, scarce waiting in their impetuosity to see whether
these are honoured, but the very title--_Biometrika_--of a new journal
shows that the science is emerging from the slough of vagueness in
which, to the physicists' contempt, it has so long floundered. All
science begins with measurement, and one of the great steps that have
been made of recent years is in the tedious, but necessary task of
recording the variations which do actually occur. From these we can
argue with a clear intellectual conscience back to what may have been.
One result is plain, that variation is a very general fact of life;
whenever we settle down to measure we find that specific diagnoses are
averages, that specific characters require a curve of frequency for
their expression, that a living organism is usually like a Proteus.
There are no doubt long-lived, non-plastic, conservative types, such as
Lingula, where no visible variability can be detected (even in untold
ages if we consider the hard parts preservable as fossils), but to judge
from these as to the rate of evolutionary change is like estimating the
rush of a river from the eddies of a sheltered pool. Another result is
that it becomes possible to distinguish between _continuous_ variations,
which are just like stages in continuous growth, in which the descendant
has a little more or a little less of a given character than its parents
had, and _discontinuous_ variations in which a new combination appears
suddenly without gradational stages, and with no small degree of
perfection. Although there is truth in Lamarck's dictum that "Nature is
never brusque," although Jack-in-the-box phenomena are rare, the
evidence, _e.g._ of Bateson and De Vries, as to the frequent occurrence
of discontinuous variations appears conclusive. Such words as "freaks"
and "sports" express a truth, suggested by Mr Galton's phrase
"transilient variations," that organisms may pass with seeming
abruptness from one form of equilibrium to another. There is evidence
that these sudden and discontinuous variations--"mutations" many of them
are called--are often very heritable, that when they appear they come to
stay; and it seems likely, especially from facts of breeding and
cultivation, that these mutations, rather than the minute "fluctuating"
variations, have supplied the raw material on which selection has
chiefly operated in the evolution of species.
It also becomes more and more evident that the living creature may vary
as a unity, so that if there is more of one character there is less of
another, and so that one change brings another in its train. It seems as
if the organism as a whole--through its germinal organisation, of
course--may suddenly pass from one position of organic equilibrium to
another. Thus we are not shut up to the assumption of the piecemeal
variation of minute parts; there is greater definiteness and less
fortuitousness in variation than was previously supposed. We begin, from
actual data, to see the truth of the view which Goethe and Naegeli
suggested, that the evolution of organisms is pre-eminently a story of
self-differentiating and self-integrating growth,--cumulative,
selective, definite, and harmonious--like crystallisation. As to the
_origin_ of variations, it must be admitted that until we know the
actual facts better, we cannot expect to know much in regard to their
antecedents. Many suggestions have been made, some of which may be
summarised.
There is something comparable to the First Law of Motion to be read out
of the persistence of characteristics from generation to generation.
Like tends to beget like. But while the relation of genetic continuity
which links generation to generation tends to ensure this persistence,
it presents no more than a curb to the occurrence of variation. While
complete and perfect inheritance and complete and perfect expression of
that inheritance in development would mean the absence of variation,
there are many reasons why this completeness of hereditary resemblance
is rare. For the inheritance seems to consist of sets of hereditary
qualities not in duplicate merely but in multiplicate; they are not all
of equal strength or of equal stability; there may be a struggle amongst
them; and they are subject to changes induced by the changes in the
complex nutritive supply which the parental body--their bearer--affords.
A variation, which makes its possessor different from the parents, is
often interpretable as due to some incompleteness of inheritance or in
the _expression_ of the inheritance. It seems as if the entail were
sometimes broken in regard to a particular characteristic. Oftener,
perhaps, as the third generation shows, the inheritance has been
complete enough potentially, but the young creature has been prevented
from realising its entire legacy. Contrariwise, it may be that the
novelty of the newborn is seen in an intensifying of the inheritance,
for the contributions from the two parents may, as it were, corroborate
one another.
But in many cases a variation turns up which we must call _novel_, some
peculiar mental pattern, it may be, which spells originality, some
structural change which suggests a new departure. We tentatively
interpret this as due to some fresh permutation or combination of the
complex substances which form the material basis of inheritance, and are
mingled from two sources at the outset of every life sexually
reproduced. It is not merely in an intermingling of maternal and
paternal contributions that a life begins, but of legacies through the
parents from remoter ancestors. The permutations and combinations may
be due to a struggle between the elements which are the bearers of the
heritable qualities, or they may be due to fluctuations in the nutritive
stream which the body supplies to its germ-cells. It must be remembered
that the hereditary material is very complex, and that it has a complex
environment within the parental body. In spite of its essential
architectural stability, it may have a tendency to instability as
regards minor details, and we may perhaps find the change-exciting
stimuli in the ceaseless nutritive oscillations within the body, while
the mode of restoring a disturbed equilibrium may be through a germinal
struggle among the different sets of minute elements which we may call
the heritage-bearers. The idea of germinal selection has been elaborated
with great subtlety by Prof. Weismann.
Nor does it seem to us legitimate to exclude the possibility that the
germ-cell, or the germ-plasm as the essential part of it, may _grow_
into a slightly more differentiated and integrated unity before it
begins its task of development. For the power of growth is
characteristic of everything living. Enough has been said, however, to
indicate how uncertain is the voice of biology in answering the
fundamental questions as to the nature and origin of variations.
_Selection._--The first and most important of the _directive factors_ is
natural selection, and the most distinctive contribution which Darwin
and Wallace made to aetiology was to show how selection works and what it
can effect. The process admits of brief statement.
Variability is a fact of life, the members of a family or species are
not born alike; some may have qualities which give an advantage both as
to hunger and love; others are relatively handicapped. But a struggle
for existence, as Malthus called it, is also a fact of life,
necessitated especially by two facts--first, that two parent organisms
usually produce many more than two children organisms, and that
population thus tends to outrun the means of subsistence; and, secondly,
that organisms are at the best only relatively well-adapted to the
complex and changeful conditions of their life. This struggle expresses
itself not merely as an elbowing and jostling around the platter of
subsistence, but at every point where the effectiveness of the response
which the living creature makes to the stimuli playing upon it, is of
critical moment. As Darwin said, though many seem to have forgotten, the
phrase "struggle for existence" must be used "in a wide and metaphorical
sense." It includes much more than an internecine scramble for the
necessities of life; it includes all endeavours for and all changes that
make towards preservation and welfare, not only of the individual, but
of the offspring as well. In many cases, indeed, the struggle for
existence both among men and beasts is fairly described as an endeavour
after well-being, and what may have been primarily self-regarding
impulses become replaced by others which are distinctively
species-maintaining, the self failing to find full realisation apart
from its kin and society.
Now, in this struggle for existence, which has so many expressions, the
relatively less fit to the present conditions tend to be eliminated.
Though the process may work out progress, as measured by degree of
differentiation and integration, by increasing freedom and fullness of
life, and has doubtless done so, yet until we come to its highest forms
in subjective and finally rational selection, it works not towards an
ideal but towards a relative fitness to present conditions. And this may
spell degeneration, as in parasites, when an extrinsic standard is used.
Tapeworms may be just as fit to survive as golden eagles. Again, the
process of elimination does not necessarily mean that the handicapped
variants come at once to a violent end, as when rat devours rat, or the
cold decimates a flock of birds in a single night; it often simply means
that the less fit die before the average time, and are less successful
than their neighbours as regards pairing and having offspring. Moreover,
although the selective process is primarily eliminative or destructive,
like thinning turnips or pruning fruit-trees, we cannot separate its
positive and negative aspects. That nothing succeeds like success is
continually verifiable in nature, the fit variant gets a start just as
surely as the unfit variant is handicapped; there is favouring and
fostering just because there is sifting and singling.
Given variations and given some mode of selection in the manifold
struggle for existence, the argument continues, then the result will be
in Spencer's phrase "the survival of the fittest." And since many
variations are transmitted from generation to generation, and may,
through the pairing of similar or suitable mates, be gradually increased
in amount and stability, the eliminative or selective process works
towards the establishment of new adaptations and the origin of new
species.
Darwin thought chiefly of the struggle between individuals--either
between fellows of the same kin or between fellow-kin and foreign
foes--and of the struggle between organisms and the inanimate
environment. He also emphasised the sexual selection which occurs (_a_)
when rival males fight or otherwise compete for the possession of a
desired mate or mates, and in so doing reduce the leet, and (_b_) when
the females appear to choose their mates from amid a crowd of suitors.
While many now doubt if the range and effectiveness of preferential
mating is so great as Darwin believed, there seems no reason to doubt
that this mode of selection has been a factor in evolution. There are
facts which warrant us in saying that _das ewig weibliche_ plays a part
in the upward march of life, that Cupid's darts as well as Death's
arrows have evolutionary significance.
Even more important, however, are other extensions of the
selection-idea. There may be struggle between groups as well as between
individuals, as when one ant-colony goes to war with another, and there
may be struggle of the parts within the organism just as there is
struggle between organisms. There is struggle when one ovum survives in
an ovary by devouring all its sister-cells, as in the case of _Hydra_
and _Tubularia_, and, after allowing a wide margin for chance, there may
be some form of selection among the crowd of spermatozoa encompassing
the egg which only one will fertilise, just as there is some form of
selection among the many drones which pursue the queen-bee in her
nuptial flight. Weismann has carried the selection-idea to a logical
finesse in his theory that there may be a struggle between the different
sets of hereditary qualities in the germ-cell, or that there is a
process of "germinal selection" at the very beginning of the individual
life. There are, we admit, great differences between the struggle of
hereditary items and the struggle of large parts within the organism;
between intra-organismal and inter-organismal struggle; between the
competition of individuals and the struggle against physical nature;
between personal selection and the conflict of races; between objective
and subjective selection; but, as it seems to us, they may be all
expressed in the same formula if it is useful so to do.
_Isolation._--In organic evolution variation supplies the materials
which some form of selection sifts. But besides selection another
directive factor has been indicated in what is called the theory of
isolation. A formidable objection to the Darwinian doctrine, first
clearly stated by Professor Fleeming Jenkin, is that variations of small
amount and sparse occurrence would tend to be swamped out by
inter-crossing before they had time to accumulate and gain stability. In
artificial selection, the breeder takes measures to prevent this
swamping-out by deliberately pairing similar or suitable forms together,
or by deliberately removing unsuitable mateable forms; but what in
Nature corresponds to the breeder?
It may be that similar variations occur in many individuals at once and
many times over; it may be that many variations are not at first small
in amount, but express big steps in organisation, as in Bateson's
instances of Discontinuous Variation or in De Vries's instances of
Mutation; it may be that many variations are not from the first
unstable, but express changes of organic equilibrium which have come to
stay if they get a chance at all; and it may be that the supposed
swamping effects of inter-crossing are in part illusory, as is strongly
suggested by some of the facts summed up in Mendel's Law; but there
seems to be still room and need for the theory of Isolation worked out
by Romanes, Gulick, and others.
They point out the great variety of ways in which, in the course of
nature, the range of inter-crossing is restricted--_e.g._ by
geographical barriers, by differences in habit, by psychical likes and
dislikes, by reproductive variation causing mutual sterility between two
sections of a species living on a common area, and so on. According to
Romanes, "without isolation, or the prevention of free inter-crossing,
organic evolution is in no case possible." The supporting body of
illustrative facts is still unsatisfactorily small, but there seems
sound sense in the idea.
An interesting corollary has been recently indicated by Professor Cossar
Ewart. Breeding within a narrow range often occurs in nature, and often
in human kind, being necessitated by geographical and other barriers. In
artificial conditions, this in-breeding often results in the development
of what is called prepotency. This means that certain forms have an
unusual power of transmitting their peculiarities, even when mated with
dissimilar forms, or, in other words, that some variations have a strong
power of persistence. Therefore, wherever through in-breeding (which
implies some form of isolation) prepotency has developed, there is no
difficulty in understanding how even a small idiosyncrasy may come to
stay, even although the bridegroom does not meet a bride endowed with a
peculiarity like his own. Similarly, Dr A. Reibmayr has argued that the
establishment of a successful human tribe or race involves periods of
in-breeding (_i.e._, marriage within a limited range of relationship),
with the effect of "fixing" constitutional characteristics, and periods
of cross-breeding (_i.e._ marriage between members of distinct stocks),
with the effect of promoting a new crop of variations or initiatives.
_Spencer's contribution._--Spencer was led to become an evolutionist by
the workings of his own mind, influenced by Laplace's Nebular
Hypothesis, by the transformist theory of Lamarck, by von Baer's law of
individual development, and by Malthus's recognition of the struggle for
existence in mankind. On the whole, it may be said that he came to the
theory of organic evolution from above, rather than from below, from his
studies on the intellectual and social evolution of man rather than from
acquaintance with the biological data. Not unnaturally, therefore, he
was to begin with a Lamarckian, believing in the cumulative transmission
of the transforming results of use and disuse and of environmental
influences.
In the essay on "a theory of Population" (1852) Spencer was within
sight of one of the great doctrines of Darwinism. "From the
beginning," he said, "pressure of population has been the proximate
cause of progress." "The effect of pressure of population, in
increasing the ability to maintain life, and decreasing the ability
to multiply, is not a uniform effect, but an average one.... All
mankind in turn subject themselves more or less to the discipline
described; they either may or may not advance under it; but, in the
nature of things, only those who _do_ advance under it eventually
survive.... For as those prematurely carried off must, in the
average of cases, be those in whom the power of self-preservation
is the least, it unavoidably follows that those left behind to
continue the race, are those in whom the power of self-preservation
is the greatest--are the select of their generation."
Here Spencer recognised the eliminative and selective effect of
struggle in mankind. Why was he "blind to the fact," as he
afterwards said, "that here was a universally-operative factor in
the development of species"? In his _Autobiography_ he gives two
reasons for his oversight, one was his Lamarckian preconception
that the inheritance of functionally-produced modifications
sufficed to explain the facts of evolution. The other was, that he
"knew little or nothing about the phenomena of variation," that "he
had failed to recognise the universal tendency to vary."
Similarly, in his essay on "Progress: its Law and Cause" (1857), he
still "ascribed all modifications to direct adaptations to changing
conditions; and was unconscious that in the absence of that
indirect adaptation effected by the natural selection of favourable
variations, the explanation left the larger part of the facts
unaccounted for" (_Autobiography_, i. p. 502).
In his article "Transcendental Physiology" (1857), Spencer advanced
a step beyond the position occupied in his essay on "Progress." He
showed that with advance in the forms of life there is an
increasing differentiation of them from their environments, that
integration as well as differentiation is part of the developmental
process, but the leading conception of the essay was "the
instability of the homogeneous." This was recognised, like "the
multiplication of effects," as a cause of progress, as "a principle
holding not among organic phenomena only, but among inorganic and
super-organic phenomena." It was in this essay also that he began
to use the word "evolution" in place of the more teleological word
"progress."
In the same year (1857) Spencer again approached the idea of
selection as a directive factor in evolution. In an essay on "State
Tamperings with Money and Banks" he gave among other reasons for
reprobating grandmotherly legislation, that "such a policy
interferes with that normal process which brings benefit to the
sagacious and disaster to the stupid." "The ultimate result of
shielding men from the effects of folly, is to fill the world with
fools." "This was a tacit assertion, recalling like assertions
previously made, that the survival of the fittest operates
beneficially in society."
Darwin's _Origin of Species_ appeared in 1859, and marked another
step in Spencer's evolutionism. Hitherto, though he had several
times approached the idea of Natural Selection, he had "held that
the sole cause of organic evolution is the inheritance of
functionally-produced modifications"; now it became clear to him
that he was wrong, and that the larger part of the facts cannot be
due to any such cause (_Autobiography_, ii. 50).
In 1864 Spencer definitely sought to assimilate the Darwinian idea
of Natural Selection into his system. He had become convinced that
the hereditary accumulation of functional modifications could not
be the sole factor in organic evolution; he had recognised the
importance and efficacy of Natural Selection as a directive agency
thinning and "singling" the crop of variations which is always
abundant; but he had not seen how to absorb "Natural Selection"
into his general physical theory of evolution. It seemed "to stand
apart as an unrelated process."
"The search for congruity led first of all to perception of the
fact that what Mr Darwin called 'natural selection,' might more
literally be called survival of the fittest. But what is survival
of the fittest, considered as an outcome of physical actions?"
Spencer's answer was that the changes constituting evolution tend
ever towards a state of equilibrium; on the way to this there are
stages of "moving equilibrium"; some organisms have their moving
equilibrium less easily overthrown than others; these are the
fittest which survive; they are, in Darwin's language, the select
which nature preserves; and thus "the survival and multiplication
of the select becomes conceivable in purely physical terms, as an
indirect outcome of a complex form of the universal redistribution
of matter and motion" (_Autobiography_, ii. pp. 100-1). In short,
natural selection is part of the universal process towards more
stable equilibrium.
When formulating his views on the classification of the sciences
and his reasons for dissenting from the philosophy of Comte,
Spencer pointed out that all the concrete sciences under their most
general aspects give accounts of the redistributions of matter and
motion; and he asked the question, What is the universal trait of
all such redistributions? His answer was that "increasing
integration of matter necessitates a concomitant dissipation of
motion, and that increasing amount of motion implies a concomitant
disintegration of matter." Thus Evolution and Dissolution appeared
"under their primordial aspects," and differentiations, with
resulting increase of heterogeneity, were seen to be secondary not
primary traits of evolution. So he arrived at his famous definition
of evolution:--"_Evolution is an integration of matter and
concomitant dissipation of motion, during which the matter passes
from an indefinite, incoherent homogeneity to a definite, coherent
heterogeneity; and during which the retained motion undergoes a
parallel transformation_" (_First Principles_, p. 396).
Having illustrated the evolution of the evolution-theory in Spencer's
mind, we pass to his final statement of the factors of organic
evolution.
(1) _External Factors._--He begins by pointing out that living creatures
are in the grip of a complex environment, which acts on them and to
which they react. And whether we think of the seasons or the climate,
the soil or the sea, we find that this environment is intricately
variable. Every kind of plant and animal may be regarded as for ever
passing into a new environment, and with increasing fullness of life
there is additional complexity in the incidence of external forces.
Every increase of locomotive power, for instance, increases the
multiplicity and multiformity of action and reaction between organism
and environment. There are chemical, mechanical, dynamic, and animate
influences which modify organisms, and as the actions of these several
orders of factors are compounded, there is produced a geometric
progression of changes increasing with immense rapidity. All through the
ages living creatures have as it were been passing over a series of
anvils on which the hammers of external forces play, with tunes of
ever-increasing complexity.
(2) _Internal Factors._--Passing to internal factors, Spencer started
from the fact that organic matter is built up of very unstable complex
molecules. "But a substance which is beyond all others changeable by the
actions and reactions of the forces liberated from instant to instant
within its own mass, must be a substance which is beyond all others
changeable by the forces acting on it from without." In any aggregate
"the relations of outside and inside, and of comparative nearness to
neighbouring sources of influences, imply the reception of influences
that are unlike in quantity, or quality, or both; and it follows that
unlike changes will be produced in the parts thus dissimilarly acted
on." Thus arise differentiations of structure, a transition from a
uniform to a multiform state, a passage from homogeneity to
heterogeneity, and this must go on cumulatively. For "the more strongly
contrasted the parts of an aggregate become, the more different must be
their reactions on incident forces, and the more unlike must be the
secondary effects which these initiate. This multiplication of effects
conspires, with the instability of the homogeneous, to work an
increasing multiformity of structure in an organism." Thus, if the head
of a bison becomes much heavier, what a multiplication of
effects--mechanical and physiological--must ensue on muscles and bones
and blood-vessels. One modification brings another in its train; there
are secondary and tertiary effects. And as the increasing assemblage of
individuals arising from a common stock is thus liable to lose its
original uniformity and to grow more pronounced in its multiformity,
indirect effects follow from inter-crossing and from altered competitive
conditions. Moreover, as times and seasons and ages pass, the
environment goes on changing, and on previous complications wrought by
incident forces, new complications are continually superimposed by new
incident forces. Thus there is an almost continuous movement towards
heterogeneity. But how is that kind of heterogeneity insured which is
required to carry on life? How is the evolution directed?
(3) _Direct Equilibration._--How is it that action and reaction between
the organism and its environment bring about _effective adaptations_?
Spencer's answer is that every change is towards a balance of forces,
and can never cease until a balance of forces is reached. "Any
unequilibrated force to which an aggregate is subject, if not of a kind
to overthrow it altogether, must continue modifying its state until an
equilibrium is brought about." Thus "there go on in all organisms,
certain changes of function and structure that are directly consequent
on changes in the incident forces--inner changes by which the outer
changes are balanced, and the equilibrium restored." "That a new
external action may be met by a new internal action, it is needful that
it shall either continuously or frequently be borne by the individuals
of the species, without killing or seriously injuring them; and shall
act in such a way as to affect their functions." But as many of the
environing agencies to which organisms have to be adjusted, either do
not immediately affect the functions at all, or else affect them in ways
that prove fatal, there must be at work some other process which
equilibrates the actions of organisms with the actions they are exposed
to.
(4) _Indirect Equilibration._--There are many very precise adaptations,
_e.g._ in the not-living hard parts of many animals, which no ingenuity
can interpret as the directly equilibrated results of incident forces.
To interpret mimicry as due to direct equilibration is hopeless.
Therefore, Spencer passed to what he called "indirect equilibration."
"Besides those perturbations produced in any organism by special
disturbing forces there are ever going on many others--the reverberating
effects of disturbing forces previously experienced by the individual,
or by ancestors; and the multiplied deviations of function so caused
implied multiplied deviations of structure." A directly induced
modification induces correlated secondary and tertiary perturbations,
and when two differently endowed parents are mated they will bequeath to
their joint offspring "compound perturbations of function and compound
deviations of structure, endlessly varied in their kinds and amounts."
In short, Spencer postulated variations as indirect results of the
action of incident forces.
As the individuals of a species are thus necessarily made unlike in
countless ways and degrees, then amongst them "some will be less liable
than others to have their equilibria overthrown by a particular incident
force previously unexperienced... Inevitably, some will be more stable
than others when exposed to this new or altered factor. That is to say,
those individuals whose functions are most out of equilibrium with the
modified aggregate of external forces, will be those to die; and those
will survive whose functions happen to be most nearly in equilibrium
with the modified aggregate of external forces. But this survival of the
fittest implies the multiplication of the fittest. Out of the fittest
thus multiplied there will, as before, be an overthrowing of the moving
equilibrium wherever it presents the least opposing force to the new
incident force. And by the continual destruction of the individuals
least capable of maintaining their equilibria in presence of this new
incident force, there must eventually be reached an altered type
completely in equilibrium with the altered conditions." In short,
Spencer incorporated the characteristic Darwinian idea of Natural
Selection operating upon a crop of variations, and thus securing by the
survival of the fittest an indirect equilibration.
In an ingenious way, to which we have already alluded, Spencer
assimilated the theory of Natural Selection with his own formula of
evolution. Let us recapitulate his argument. All the processes by which
organisms are refitted to their ever-changing environments must be
equilibrations of one kind or another, for change of every order is
towards equilibrium, and life itself is a moving equilibrium between
inner and outer actions--a continual adjustment of internal relations to
external relations. The process called Natural Selection is literally a
survival of the fittest; and "that is a maintenance of the moving
equilibrium of the functions in presence of outer actions; implying the
possession of an equilibrium which is relatively stable in contrast with
the unstable equilibria of those which do not survive." ... "The
conception of Natural Selection is manifestly one not known to physical
science: its terms are not of a kind physical science can take
cognisance of. But here we have found in what manner it may be brought
within the realm of physical science."
It is to be feared that Spencer deluded himself as to the success of his
_tour de force_. For he did not show that there is in inanimate nature
anything corresponding to the struggle for existence, nor did he give
any instances where the degree of effectiveness of response is of
critical value in determining the survival of competing inanimate
systems.
After pointing out that the various factors in organic evolution must be
thought of as co-operating, Spencer considered their respective shares
in producing the total result. Briefly stated, his conclusions were the
following:--
At first, the direct action of the physical environment was the
only cause of change. "But as, through the diffusion of organisms
and consequent differential actions of inorganic forces, there
arose unlikenesses among them, producing varieties, species,
genera, orders, classes, the actions of organisms on one another
became new sources of organic modifications." The mutual actions of
organisms became more and more influential, and eventually became
the chief factors.
"Always there must have been, and always there must continue to be,
a survival of the fittest: natural selection must have been in
operation at the outset, and can never cease to operate! While
organisms had small abilities of co-ordinating their actions and
actively adjusting themselves, natural selection worked almost
alone in moulding and remoulding organisms into fitness for their
changing environments, but as activity increased and brains grew,
the power of varying actions to fit varying requirements became
considerable." "As fast as essential faculties multiply, and as
fast as the number of organs which co-operate in any given function
increases, indirect equilibration through natural selection becomes
less and less capable of producing specific adaptations; and
remains capable only of maintaining the general fitness of
constitution to conditions. The production of adaptations by direct
equilibration then takes the first place: indirect equilibration
serving to facilitate it. Until at length, among the civilised
human races, the equilibration becomes mainly direct: the action of
natural selection being limited to the destruction of those who are
too feeble to live, even with external aid."
Returning to our scheme of Originative and Directive Factors, let us
inquire into Spencer's views regarding Variation and Selection.
Spencer recognised three causes of variation. _First_ there is
heterogeneity among progenitors which "generates new deviations by
composition of forces"; in other words new patterns arise from the
mingling of diverse hereditary contributions in fertilisation.
_Secondly_, functional variation in the parents produces unlikeness in
the offspring; those begotten under different constitutional states are
different. In other words, fluctuations of nutrition in the parental
body may cause variations in the germ-plasm. [In mammals there are also
_modifications_ produced during the pre-natal life of the offspring
which are congenital in the sense that they are present at birth in
latent or patent form, which do not, however, really affect the
germ-plasm since they disappear in the third generation.] _Thirdly_, an
organism exposed to a marked change of external conditions, may have its
equilibrium altered, and the offspring may be influenced. "The larger
functional variations produced by greater external changes, are the
initiators of those structural variations which, when once commenced in
a species, lead by their combinations and antagonisms to multiform
results. Whether they are or are not the direct initiators, they must
still be the indirect initiators."
But Spencer admitted that there were numerous minor so-called
"spontaneous" variations, which could not be referred to the causes
noticed above. He attributed these to the fact that no two ova, no two
spermatozoa, can be identical, since the process of nutrition cannot be
absolutely alike. Minute initial differences in the proportions of the
physiological units will lead, during development, to a continual
multiplication of differences. "The insensible divergence at the outset
will generate sensible divergences at the conclusion." This is not
different from the general idea that nutritive fluctuations in the body
provoke variations in the complex germ-plasm, "still it may be fairly
objected that however the attributes of the two parents are variously
mingled in their offspring, they must in all of them fall between the
extremes displayed in the parents. In no characteristic could one of the
young exceed both parents, were there no cause of "spontaneous
variation" but the one alleged. Evidently, then, there is a cause yet
unfound."
Spencer's further answer was that the sperm-cells or egg-cells which any
organism produces will differ from each other not quantitatively only
but qualitatively, because inheritance is multiple. In some the paternal
units, in another the maternal units, in another the grand-paternal or
the grand-maternal units will give the impress. "Here, then, we have a
clue to the multiplied variations, and sometimes extreme variations,
that arise in races which have once begun to vary. Amid countless
different combinations of units derived from parents, and through them
from ancestors, immediate and remote--and the various conflicts in their
slightly different organic polarities, opposing and conspiring with one
another in all ways and degrees, there will from time to time arise
special proportions causing special deviations. From the general law of
probabilities it may be concluded that while these involved influences,
derived from many progenitors, must, on the average of cases, obscure
and partially neutralise one another; there must occasionally result
such combinations of them as will produce considerable divergences from
average structures; and at rare intervals, such combinations as will
produce very marked divergences. There is thus a correspondence between
the inferable results and the results as habitually witnessed."
In conclusion, after his wonted manner, Spencer pointed out that
Variation, like everything else, is necessitated by the Persistence of
Force. "The members of a species inhabiting any area cannot be subject
to like sets of forces over the whole of that area. And if, in different
parts of the area, different kinds or amounts or combinations of forces
act on them, they cannot but become different in themselves and in their
progeny. To say otherwise, is to say that differences in the forces will
not produce differences in the effects; which is to deny the persistence
of force."
_Selection._--As we have seen, Spencer incorporated into his scheme the
Darwinian concept of Selection, and sought to show that it could be
included under the general concept of Evolution as "a continuous
redistribution of matter and motion." "That natural selection is, and
always has been, operative is incontestable.... The survival of the
fittest is a necessity, its negation is incontestable."
That he did not take a narrow view of the process of Selection, which
has so many forms and operates at so many levels, will be admitted; and
we may illustrate this by showing that he had a prevision of what Roux
called "intra-individual selection" or "intra-selection."
In his essay on "The Social Organism" (1860), he wrote:--
"The different parts of a social organism, like the different parts
of an individual organism, compete for nutriment; and severally
obtain more or less of it according as they are discharging more or
less duty." (See also _Essays_, i. 290.) And, again, in 1876, in
his _Principles of Sociology_, he amplified his statement thus:
"All other organs, therefore, jointly and individually, compete for
blood with each organ,... local tissue formation (which under
normal conditions measures the waste of tissue in discharging
function) is itself a cause of increased supply of materials... the
resulting competition, not between units simply, but between
organs, causes in a society, as in a living body, high nutrition
and growth of parts called into the greatest activity by the
requirements of the rest." And once more: "For clearly, if the
survival of the fittest among organisms is a process of
equilibration between actions in the environment and actions in the
organism; so must the local modifications of their parts, external
and internal, be regarded as survivals of structures, the reactions
of which are in equilibrium with the actions they are subject to."
Clearly Spencer had a prevision of what Roux calls "_Der Kampf der
Theile im Organismus_" (The struggle of parts within the organism),
and we have here another example of his biological insight. That
Spencer was not far from the idea of a struggle between hereditary
units, we see from the following passage: "In the fertilised germ
we have two groups of physiological units, slightly different in
their structures. These slightly different units severally multiply
at the expense of the nutriment supplied to the unfolding
germ--each kind moulding this nutriment into units of its own type.
Throughout the process of development the two kinds of units,
mainly agreeing in their proclivities and in the form which they
tend to build themselves into, but having minor differences, work
in unison to produce an organism of the species from which they
were derived, but work in antagonism to produce copies of their
respective parent-organisms. And hence ultimately results an
organism in which traits of the one are mixed with traits of the
other; and in which, according to the predominance of one or other
group of units, one or other sex with all its concomitants is
produced" (_Principles of Biology_, vol. i., revised ed., p. 315).
While Spencer had this wide appreciation of the scope of selection, he
firmly held that biologists burdened it unjustifiably by disbelieving in
the transmission of acquired characters, and, as we have seen, he gave a
number of examples of phenomena which he believed the Darwinian theory
minus the Lamarckian factor was quite inadequate to interpret. He went
the length of saying: "Either there has been inheritance of acquired
characters or there has been no evolution." Spencer indicated three
general difficulties or limitations besetting the theory of Natural
Selection.
(1) "The general argument proceeds upon the analogy between natural
selection and artificial selection. Yet all know that the first cannot
do what the last does. Natural Selection can do nothing more than
preserve those of which the _aggregate_ characters are most favourable
to life. It cannot pick out those possessed of one particular
favourable character, unless this is of extreme importance."
[It is admitted that we cannot prove that Natural Selection effected
this or that result in the distant past, but we know that a process of
discriminate elimination is a fact of life, and we argue from the
present to the past. Given variations enough and time enough, it is
difficult to put limits to the efficacy of selection. If in a race of
birds fairly well adapted to the conditions of their life, variations
occur in the length of wing, there is no theoretical difficulty in
supposing that if a longer wing is advantageous, this particular
favourable character may in the course of time become through selection
the property of the whole race.]
(2) "In many cases a structure is of no service until it has reached a
certain development; and it remains to account for that increase of it
by natural selection which must be supposed to take place before it
reaches the stage of usefulness."
[One variation is often correlated with another, and the stronger
variation may afford _point d'appui_ for the action of natural
selection, and thus act as a cover for the incipient variation until
that reaches the stage of usefulness and becomes itself of
selection-value. What Spencer himself says in regard to the selection of
aggregates rather than items, seems half the answer to his difficulty.
It has also been suggested that adaptive modifications may act as
fostering nurses of germinal variations in the same direction. Let us
suppose a country in which a change of climate made it year by year of
the utmost importance that the inhabitants should become swarthy. Some
individuals with a strong innate tendency in this direction would
doubtless exist, and on them and their similarly endowed progeny, the
success of the race would primarily, and might wholly depend. At the
same time, there might be many individuals in whom the constitutional
tendency in the direction of swarthiness was too weak and incipient to
be of use. If these, or some of them, made up for their lack of natural
swarthiness by a great susceptibility to acquired swarthiness, to
becoming tanned by the sun, it is conceivable that this modification,
though never taking organic root, might serve as a life-saving screen
until coincident congenital variations in the direction of swarthiness
had time to grow strong and become of selection value. We can also
imagine that a stock without great mental ability might succeed, in
conditions where a premium was put on brains, by their application and
docility, till eventually innate variations in the direction of real
cleverness became established in the stock. Similarly, many animals by
increased 'will-power' or intelligence may survive until bodily
variations of an adaptive kind arise to economise the higher energies.
Here and everywhere we venture to say that the more anthropomorphic we
can _reasonably_ make our conception of organic evolution the truer it
is likely to be.
A third answer to Spencer's second difficulty is afforded by Weismann's
subtle theory of Germinal Selection.]
(3) "Advantageous variations, not preserved in nature as they are by the
breeder, are liable to be swamped by crossing or to disappear by
atavism."
[We have already referred to various answers to this difficulty--in
terms of Isolation, Prepotency, and other conceptions. But the answer
which will occur to everyone at the present time is in terms of
"Mendelism," into a discussion of which we cannot enter. Suffice it to
say, that for the cases with which he dealt, Mendel has given evidence
that variations which arise suddenly and are discontinuous--mutations,
as De Vries calls them--are not likely to be swamped by in-breeding with
the normal form, and that he has given a reason why this swamping does
not occur.]
In regard to the second directive factor--Isolation, Spencer had no
criticism to offer. It seemed to him that "in whatever way effected, the
isolation of a group subject to new conditions and in course of being
changed, is requisite as a means to permanent differentiation."
But after allowing full play to variation and modification, selection
and isolation, Spencer felt that "though all phenomena of organic
evolution must fall within the lines indicated, there remain many
unsolved problems." "We can only suppose that as there are devised by
human beings many puzzles apparently unanswerable till the answer is
given, and many necromantic tricks which seem impossible till the mode
of performance is shown; so there are apparently incomprehensible
results which are really achieved by natural processes. Or, otherwise,
we must conclude that since Life itself proves to be in its ultimate
nature inconceivable, there is probably an inconceivable element in its
ultimate workings."