s efficacious,
than was required by the initial impetus of life, essentially directed
toward free actions: the same organism could not with equal force
sustain the two functions at once, of gradual storage and sudden use. Of
themselves, therefore, and without any external intervention, simply by
the effect of the duality of the tendency involved in the original
impetus and of the resistance opposed by matter to this impetus, the
organisms leaned some in the first direction, others in the second. To
this scission there succeeded many others. Hence the diverging lines of
evolution, at least what is essential in them. But we must take into
account retrogressions, arrests, accidents of every kind. And we must
remember, above all, that each species behaves as if the general
movement of life stopped at it instead of passing through it. It thinks
only of itself, it lives only for itself. Hence the numberless
struggles that we behold in nature. Hence a discord, striking and
terrible, but for which the original principle of life must not be held
responsible.

The part played by contingency in evolution is therefore great.
Contingent, generally, are the forms adopted, or rather invented.
Contingent, relative to the obstacles encountered in a given place and
at a given moment, is the dissociation of the primordial tendency into
such and such complementary tendencies which create divergent lines of
evolution. Contingent the arrests and set-backs; contingent, in large
measure, the adaptations. Two things only are necessary: (1) a gradual
accumulation of energy; (2) an elastic canalization of this energy in
variable and indeterminable directions, at the end of which are free
acts.

This twofold result has been obtained in a particular way on our planet.
But it might have been obtained by entirely different means. It was not
necessary that life should fix its choice mainly upon the carbon of
carbonic acid. What was essential for it was to store solar energy; but,
instead of asking the sun to separate, for instance, atoms of oxygen and
carbon, it might (theoretically at least, and, apart from practical
difficulties possibly insurmountable) have put forth other chemical
elements, which would then have had to be associated or dissociated by
entirely different physical means. And if the element characteristic of
the substances that supply energy to the organism had been other than
carbon, the element characteristic of the plastic substa