The primary factor in evolution is the "struggle for existence."
This involves a "natural selection" among the many variations of
the organism. If we seek the underlying causes of the struggle,
we find that the necessity of food and (in a lesser degree) the
desire for a mate are the principal causes of contention. The
former is much the more important factor, and, accordingly, we
find the greater degree of specialisation based upon it.
The present view assumes a dynamic necessity for its demands
involved in the nature of the organism as such. This assumption
is based on observation of the outcome of its unconstrained
growth, reproduction, and life-acts. We have the same right to
assert this of the organism as we have to assert that retardation
and degradation attend the actions of inanimate machines, which
assertion, also, is based on observation of results. Thus we pass
from the superficial statements that organisms require food in
order to live, or that organisms desire food, to the more
fundamental one that:
_The organism is a configuration of matter which absorbs energy
acceleratively, without limit, when unconstrained._
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This is the dynamic basis for a "struggle for existence." The
organism being a material system responding to accession of
energy with fresh demands, and energy being limited in amount,
the struggle follows as a necessity. Thus, evolution guiding' the
steps of the energy-seeking organism, must presuppose and find
its origin in that inherent property of the organism which
determines its attitude in presence of available energy.
Turning to the factor, "adaptation," we find that this also must
presuppose, in order to be explicable, some quality of
aggressiveness on the part of the organism. For adaptation in
this or that direction is the result of repulse or victory, and,
therefore, we must presuppose an attack. The attack is made by
the organism in obedience to its law of demand; we see in the
adaptation of the organism but the accumulated wisdom derived
from past defeats and victories.
Where the environment is active, that is living, adaptation
occurs on both sides. Improved means of defence or improved means
of attack, both presuppose activity. Thus the reactions to the
environment, animate and inanimate, are at once the outcome of
the eternal aggressiveness of the organism, and the source of
fresh aggressiveness upon the resources of the medium.
As concerns the "survival of the fittest" (or "natural
selection"), we can, I think, at once conclude that the organism
which best fulfils the organic law under the circumstances of
supply is the "fittest," _ipso facto._ In many
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cases this is contained in the commonsense consideration, that to
be strong, consistent with concealment from enemies which are
stronger, is best, as giving the organism mastery over foes which
are weaker, and generally renders it better able to secure
supplies. Weismann points out that natural selection favours
early and abundant reproduction. But whether the qualifications
of the "fittest" be strength, fertility, cunning, fleetness,
imitation, or concealment, we are safe in concluding that growth
and reproduction must be the primary qualities which at once
determine selection and are fostered by it. Inherent in the
nature of the organism is accelerated absorption of energy, but
the qualifications of the "fittest" are various, for the supply
of energy is limited, and there are many competitors for it. To
secure that none be wasted is ultimately the object of natural
selection, deciding among the eager competitors what is best for
each.
In short, the facts and generalisations concerning evolution must
presuppose an organism endowed with the quality of progressive
absorption of energy, and retentive of it. The continuity of
organic activity in a world where supplies are intermittent is
evidently only possible upon the latter condition. Thus it
appears that the dynamic attitude of the organism, considered in
these pages, occupies a fundamental position regarding its
evolution.
We turn to the consideration of old age and death, endeavouring
to discover in what relation they stand to the innate
progressiveness of the organism.
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THE PERIODICITY OF THE ORGANISM AND THE LAW OF PROGRESSIVE
ACTIVITY
The organic system is essentially unstable. Its aggressive
attitude is involved in the phenomenon of growth, and in
reproduction which is a form of growth. But the energy absorbed
is not only spent in growth. It partly goes, also, to make good
the decay which arises from the instability of the organic unit.
The cell is molecularly perishable. It possesses its entity much
as a top keeps erect, by the continual inflow of energy.
Metabolism is always taking place within it. Any other condition
would, probably, involve the difficulties of perpetual motion.
The phenomenon of old age is not evident in the case of the
unicellular organism reproducing by fission. At any stage of its
history all the individuals are of the same age: all contain a
like portion of the original cell, so far as this can be regarded
as persisting where there is continual flux of matter and energy.
In the higher organisms death is universally evident. Why is
this?
The question is one of great complexity. Considered from the more
fundamental molecular point of view we should perhaps look to
failure of the power of cell division as the condition of
mortality. For it is to this phenomenon--that of cell
division--that the continued life of the protozoon is to be
ascribed, as we have already seen. Reproduction is, in fact, the
saving factor here.