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ways. They may either modify the body of the individual
or the sexual elements.
“ Some variations are induced by the direct action of the sur
rounding conditions on the whole organisation, or on certain parts
alone, and other variations are induced indirectly through the repro
ductive system being affected in the same manner as is so common
with organic beings when removed from their natural conditions.
The causes which induce variability act on the mature organism,
on the embryo, and, as we have good reason to believe, on both
sexual elements before impregnation has been effected.”—{The
Variation, vol. zz - ., p. 270.)
Mr. Darwin argues from the fact that changed con
ditions produce sterility ; that it is therefore probable
that changed conditions will modify offspriñg.
“ Slight changes in the conditions of life have a remarkable power
in causing a greater or less degree of sterility. Hence it seems not
improbable that beings generated through a system so easily affected
should themselves be affected. . . . On the whole, it is probable
that any cause affecting the organs of reproduction would likewise
affect their product—that is, the offspring thus generated.”—{The
Variation, vol. zV., p. 26S.)
Mr. Darwin also contends that, if such cause acted at all,
it would influence all subjected to its influence in the
same definite manner.
“ The following case, which has been carefully examined and
communicated to me by Dr. William Ogle, is highly instructive.
Two girls, born as twins, and in all respects extremely alike, had
their little fingers on both hands crooked ; and in both children the
second bicuspid tooth in the upper jaw, of the second dentition, was
misplaced ; for these teeth, instead of standing in a line with the
others, grew from the roof of the mouth behind the first bicuspids.
Neither the parents nor any other member of the family had ex
hibited any similar peculiarity. Now, as both these children were
affected in exactly the same manner by both deviations of structure,
the idea of accident is at once excluded ; and we are compelled
to admit that there must have existed some precise and sufficient
cause which, if it had occurred a hundred times, would have affected
a hundred children.”—(The Variation, vol. ii., p. 2jj.)