THE CO-OPERATION OF THE FACTORS.
§ 169. Thus the phenomena of Organic Evolution may be interpreted in the
same way as the phenomena of all other Evolution. Fully to see this, it
will be needful for us to contemplate in their _ensemble_, the several
processes separately described in the four preceding chapters.
If the forces acting on any aggregate remain the same, the changes produced
by them will presently reach a limit, at which the outer forces are
balanced by the inner forces; and thereafter no further metamorphosis will
take place. Hence, that there may be continuous changes of structure in
organisms, there must be continuous changes in the incident forces. This
condition to the evolution of animal and vegetal forms, we find to be fully
satisfied. The astronomic, geologic, and meteorologic changes that have
been slowly but incessantly going on, and have been increasing in the
complexity of their combinations, have been perpetually altering the
circumstances of organisms; and organisms, becoming more numerous in their
kinds and higher in their kinds, have been perpetually altering one
another's circumstances. Thus, for those progressive modifications upon
modifications which organic evolution implies, we find a sufficient cause.
The increasing inner changes for which we thus find a cause in the
perpetual outer changes, conform, so far as we can trace them, to the
universal law of the instability of the homogeneous. In organisms, as in
all other things, the exposure of different parts to different kinds and
amounts of incident forces, has necessitated their differentiation; and,
for the like reason, aggregates of individuals have been lapsing into
varieties, and species, and genera, and orders. Further, in each type of
organism, as in the aggregate of types, the multiplication of effects has
continually aided this transition from a more homogeneous to a more
heterogeneous state. And yet again, that increasing segregation and
concomitant increasing definiteness, associated with the growing
heterogeneity of organisms, has been aided by the continual destruction of
those which expose themselves to aggregates of external actions markedly
incongruous with the aggregates of their internal actions, and the survival
of those subject only to comparatively small incongruities. Finally, we
have found that each change of structure, superposed on preceding changes,
has been a re-equilibration necessitated by the disturbance of a preceding
equilibrium. The maintenance of life being the maintenance of a balanced
combination of functions, it follows that individuals and species that have
continued to live, are individuals and species in which the balance of
functions has not been overthrown. Hence survival through successive
changes of conditions, implies successive adjustments of the balance to the
new conditions.
The actions that are here specified in succession, are in reality
simultaneous; and they must be so conceived before organic evolution can be
rightly understood. Some aid towards so conceiving them will be given by
the annexed table, representing the co-operation of the factors.
§ 170. Respecting this co-operation, it remains only to point out the
respective shares of the factors in producing the total result; and the way
in which the proportions of their respective shares vary as evolution
progresses.
Astronomic }
changes }
} alter the }
Geologic } incidence }
changes } of inorganic }
} forces. }
Meteorologic } }
changes } }
}
}
} on each species: affecting
} |
} |
} |
} |
} |
Enemies } } |
Competitors } } |
} varying in } } |
Co-operators } number } } |
Prey } } alter the } |
} incidence } |
Enemies } } of organic } |
Competitors } } forces. } |
} varying in } |
Co-operators } kind } |
Prey } |
|
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|
| { which, partially in the first
| { generation, and completely in
| { the course of generations, are
| { directly equilibrated with the
| { changed agencies.
| { immediately {
| { through their { which have their direct
| { functions; { equilibration with the changed
| { { agencies, aided by indirect
| { { equilibration, through the more
| { { frequent survival of those in
| { { which the direct equilibration
| { { is most rapid.
| {
| { its individuals, { { positively--by aiding the
| { { { multiplication of those whose
| { { { moving equilibria happen to be
| { { { most congruous with the
| { { mediately { changed agencies: thus, in the
| { { through the { course of generations, indirectly
| { { aggregate of { equilibrating certain individuals
| { { individuals; { with them.
--{ {
{ { negatively--by killing those
{ { whose moving equilibria are
{ { most incongruous with the
{ { changed agencies: thus, in
{ { the course of generations,
{ { indirectly equilibrating each
{ { of its surviving individuals
{ { with them.
{
{ { by acting on it in some parts of the habitat
{ { more than in others; and thus differentiating
{ its aggregate { the species into local varieties.
{ of individuals, {
{ { and thus causing
{ { differentiations of
{ { the species into
{ by acting differently { varieties, irrespective
{ on slightly-unlike { of locality.
{ individuals in the {
{ same locality; { and thus causing
{ modification of the
{ species as a whole,
{ by abstracting a
{ certain class of
{ its units.
At first, changes in the amounts and combinations of inorganic forces,
astronomic, geologic, and meteorologic, were the only causes of the
successive modifications; and these changes have continued to be causes.
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. And as fast as
types have multiplied and become more complex, so fast have the mutual
actions of organisms come to be more influential factors in their
respective evolutions: eventually becoming the chief factors.
Passing from the external causes of change to the internal processes of
change entailed by them, we see that these, too, have varied in their
proportions: that which was originally the most important and almost the
sole process, becoming gradually less important, if not at last the least
important. 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 yet
organisms had small abilities to coordinate their actions, and adjust them
to environing actions, natural selection worked almost alone in moulding
and remoulding organisms into fitness for their changing environments; and
natural selection has remained almost the sole agency by which plants and
inferior orders of animals have been modified and developed. The
equilibration of organisms that are almost passive, is necessarily effected
indirectly, by the action of incident forces on the species as a whole. But
along with the evolution of organisms having some activity, there grows up
a kind of equilibration which is in part direct. In proportion as the
activity increases direct equilibration plays a more important part. Until,
when the nervo-muscular apparatus becomes greatly developed, and the power
of varying the actions to fit the varying requirements becomes
considerable, the share taken by direct equilibration rises into
co-ordinate importance or greater importance. 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 civilized human races, the equilibration becomes
mainly direct: the action of natural selection being limited to the
destruction of those who are constitutionally too feeble to live, even with
external aid. As the preservation of incapables is secured by our social
arrangements; and as very few save incarcerated criminals are prevented by
their inferiorities from leaving the average number of offspring; it
results that survival of the fittest can scarcely at all act in such way as
to produce specialities of nature, either bodily or mental. Here the
specialities of nature, chiefly mental, which we see produced, and which
are so rapidly produced that a few centuries show a considerable change,
must be ascribed almost wholly to direct equilibration.[54]