The
impress on the parental _body_ must in some way be transferred to the
parental _germ-plasm_; and not as a general influence, but as a specific
one which can be reproduced by the germ-plasm.
This idea was held almost without question by the biologists of the
past, from Aristotle on. Questionings indeed arose from time to time,
but they were vague and carried no weight, until a generation ago
several able men elaborated them. For many years, it was the question of
chief dispute in the study of heredity. The last word has not yet been
said on it. It has theoretical bearings of immense importance; for our
conception of the process of evolution will be shaped according to the
belief that acquired characters are or are not inherited. Herbert
Spencer went so far as to say, "Close contemplation of the facts
impresses me more strongly than ever with two alternatives--either that
there has been inheritance of acquired characters, or there has been no
evolution." But its practical bearings are no less momentous. Again to
quote Spencer: "Considering the width and depth of the effects which the
acceptance or non-acceptance of one or the other of these hypotheses
must have on our views of life, the question, Which of them is true?
demands beyond all other questions whatever the attention of scientific
men.
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