Even strongly-marked differences
occasionally appear in the young of the same litter, and in seedlings from
the same seed-capsule. At long intervals of time, out of millions of
individuals reared in the same country and fed on nearly the same food,
deviations of structure so strongly pronounced as to deserve to be called
monstrosities arise; but monstrosities cannot be separated by any distinct
line from slighter variations. All such changes of structure, whether
extremely slight or strongly marked, which appear among many individuals
living together, may be considered as the in definite effects of the
conditions of life on each individual organism, in nearly the same manner
as the chill effects different men in an in definite manner, according to
their state of body or constitution, causing coughs or colds, rheumatism,
or inflammation of various organs.
With respect to what I have called the in direct action of changed
conditions, namely, through the reproductive system of being affected, we
may infer that variability is thus induced, partly from the fact of this
system being extremely sensitive to any change in the conditions, and
partly from the similarity, as Kolreuter and others have remarked, between
the variability which follows from the crossing of distinct species, and
that which may be observed with plants and animals when reared under new or
unnatural conditions.
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