more the power of change: this diminishes in time, if we rightly apprehend
the idea, partly through the waning of vital force, partly through the
fixity acquired by heredity--like producing like, the more certainly in
proportion to the length and continuity of the ancestral chain And so the
small variations of species which we behold are the feeble remnants of the
pristine plasticity and an exhausted force.[XII-2] This force of variation
or origination of forms has acted rhythmically or intermittently, because
each movement was the result of the rupture of an equilibrium, the
liberation of a force which till then was retained in a potential state by
some opposing force or obstacle, overcoming which it passes to a new
equilibrium and so on Hence alternations of dynamic activity and static
repose, of origination of species and types, alternated with periods of
stability or fixity. The timepiece does not run down regularly, but "la
force procede par saccades; et . . . par pulsations d'autant plus
energiques que la nature etait plus pres de son commencement."

Such is the hypothesis. For a theory of evolution, this is singularly
unlike Darwin's in most respects, and particularly in the kind of causes
invoked and speculations indulged in. But we are not here to comment upon
it beyond the particular point under consideration, namely, its doctrine of
the inherently limited duration of species. This comes, it will be noticed,
as a deduction from the modern physical doctrine of the equivalence of
force. The reasoning is ingenious, but, if we mistake not, fallacious.

To call that "evolutive force" which produces the change of one kind of
plant or animal into another, is simple and easy, but of little help by way
of explanation. To homologize it with physical force, as M. Naudin's
argument requires, is indeed a step, and a hardy one; but it quite
invalidates the argument. For, if the "evolutive force" is a part of the
physical force of the universe, of which, as he reminds us, the sum is