To admit this view is, as it seems to
me, to reject a real for an unreal, or at least for an unknown, cause.
It makes the works of God a mere mockery and deception; I would almost
as soon believe with the old and ignorant cosmogonists, that fossil
shells had never lived, but had been created in stone so as to mock
the shells now living on the sea-shore.
SUMMARY.
Our ignorance of the laws of variation is profound. Not in one case
out of a hundred can we pretend to assign any reason why this or that
part differs, more or less, from the same part in the parents. But
whenever we have the means of instituting a comparison, the same laws
appear to have acted in producing the lesser differences between
varieties of the same species, and the greater differences between
species of the same genus. The external conditions of life, as climate
and food, etc., seem to have induced some slight modifications. Habit
in producing constitutional differences, and use in strengthening, and
disuse in weakening and diminishing organs, seem to have been more
potent in their effects. Homologous parts tend to vary in the same
way, and homologous parts tend to cohere. Modifications in hard parts
and in external parts sometimes affect softer and internal parts. When
one part is largely developed, perhaps it tends to draw nourishment
from the adjoining parts; and every part of the structure which can be
saved without detriment to the individual, will be saved.
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