From among the passages in which Professor Weismann himself shows a
desire to hedge I may take the following from page 170 of his book:-
"I am also far from asserting that the germ-plasm which, as I hold,
is transmitted as the basis of heredity from one generation to
another, is absolutely unchangeable or totally uninfluenced by
forces residing in the organism within which it is transformed into
germ-cells. I am also compelled to admit it as conceivable that
organisms may exert a modifying influence upon their germ-cells, and
even that such a process is to a certain extent inevitable. The
nutrition and growth of the individual must exercise some influence
upon its germ-cells . . . "
Professor Weismann does indeed go on to say that this influence must
be extremely slight, but we do not care how slight the changes
produced may be provided they exist and can be transmitted. On an
earlier page (p. 101) he said in regard to variations generally that
we should not expect to find them conspicuous; their frequency would
be enough, if they could be accumulated. The same applies here, if
stirring events that occur to the somatic cells can produce any
effect at all on offspring. A very small effect, provided it can be
repeated and accumulated in successive generations, is all that even
the most exacting Lamarckian will ask for.
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