To make the distinction, one ought to be familiar with an individual
from birth, and to have some knowledge of the conditions to which he was
exposed, in the period between conception and birth,--for of course a
modification which takes place during that time is as truly an acquired
character as one that takes place after parturition. Blindness, for
example, may be an inborn defect. The child from conception may have
lacked the requisites for the development of sight. On the other hand,
it may be an acquired character, due to an ill-advised display of
patriotism on July 4, at some time during childhood; or even to
infection at the moment of birth. Similarly small size may be an inborn
character, due to a small-sized ancestry; but if the child comes of a
normal ancestry and is stunted merely because of lack of proper care and
food, the smallness is an acquired character. Deafness may be congenital
and inborn, or it may be acquired as the result, say, of scarlet fever
during childhood.
Now the inborn characters (excepting modifications _in utero_) are
admittedly heritable, for inborn characters must exist potentially in
the germ-plasm. The belief that acquired characters are also inherited,
therefore, involves belief that in some way the trait acquired by the
parent is incorporated in the germ-plasm of the parent, to be handed on
to the child and reappear in the course of the child's development.
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