Mr. Galton contends that the reproductive elements become sterile when
used in forming and maintaining the individual, and that only a small
proportion of them are so used.[68] He holds that the next generation
will be formed entirely, or almost entirely, from the residue of
undeveloped germs, which, not having been employed in the structure and
work of the individual, have been free to multiply and form the
reproductive elements whence future individuals are derived. Hence the
singular inferiority not infrequently displayed by the children of men
of extraordinary genius, especially where the ancestry has been only of
a mediocre ability. The valuable germs have been used up in the
individual, and rendered sterile in the structure of his person. Hence,
too, the "strong tendency to deterioration in the transmission of every
exceptionally gifted race." Mr. Galton's hypothesis "explains the fact
of certain diseases skipping one or more generations," and it "agrees
singularly well with many classes of fact;" and it is strongly opposed
to the theory of use-inheritance. The elements which are used die almost
universally without germ progeny: the germs which are _not_ used are the
great source of posterity. Hence, when the germs or gemmules which
achieve development are either better or worse than the residue, the
qualities transmitted to offspring will be of an inverse character. If
brain-work attracts, develops _and sterilizes_ the best gemmules, the
ultimate effect of education on the intellect of posterity may differ
from its immediate effect.