It is purely
destructive. Given an infinity of place and nourishment--do away,
that is, with all struggle and selection--and the living world would
have advanced, purely by the force of the progressive tendency, just
as far as it now has; only there would have survived an indefinite
number of intermediate forms. It would have differed from our
present living world as the milky way does from the starry
firmament.
He compares the plant kingdom to a great, luxurious tree, branching
from its very base, whose twigs would represent the present stage of
our different species. Left to itself it would put out a chaos of
innumerable branches. Natural selection, like a gardener, prunes the
tree into shape. Children might imagine that the gardener caused the
growth; but the tree would have been broader and have branched more
luxuriantly if left to itself.[A]
[Footnote A: See Naegeli, "Theorie der Abstammungslehre," p. 18;
also pp. 12, 118, 285.]
Every species must vary perpetually. Now this proposition is
apparently not in accord with fact; for some have remained unchanged
during immense periods. And natural selection, by removing the less
fit, certainly appears to contribute to progress by raising the
average of the species. The theory seems extreme and one-sided. And
yet it has done great service by calling in question the
all-sufficiency of natural selection and the modifying power of
environment, and by emphasizing, probably overmuch, the importance
of initial inherent tendency, whose value has been entirely
neglected by many evolutionists.
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