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Hereditary Genius
xv
appealing to experimental evidence, it is now certain that the tendency of
acquired habits to be hereditarily transmitted is at the most extremely small.
There may be some few cases, like those of Brown-Sequard's guinea-pigs,
in which injury to the nervous substance of the parents affects their
offspring; but as a general rule, with scarcely any exception that cannot be
ascribed to other influences, such as bad nutrition or transmitted microbes,
the injuries or habits of the parents are found to have no effect on the
natural form or faculties of the child. Whether very small hereditary
influences of the supposed kind, accumulating in the same direction for
many generations, may not ultimately affect the qualities of the species,
seems to be the only point now seriously in question.
Many illustrations have been offered, by those few persons of high
authority who still maintain that acquired habits, such as the use or disuse of
particular organs in the parents, admit of being hereditarily transmitted in a
sufficient degree to notably affect the whole breed after many generations.
Among these illustrations much stress has “been laid on the diminishing size
of the human jaw, in highly civilized peoples. It is urged that their food is
better cooked and more toothsome than that of their ancestors,
consequently the masticating apparatus of the race has dwindled through
disuse. The truth of the evidence on which this argument rests is
questionable, because it is not at all certain that non-European races who
have more powerful jaws than ourselves use them more than we do. A
Chinaman lives, and has lived for centuries, on rice and spoon-meat, or such
over-boiled diet as his chopsticks can deal with. Equatorial Africans live to
a great extent on bananas, or else on cassava, which, being usually of the
poisonous kind, must be well boiled
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