ch they have developed?" and answers the question with the
astounding statement, "It seems reasonable to suppose that they have
this power, it being simply a phase of heredity, the tendency of like to
beget like."

The right understanding of this famous problem is therefore fraught with
the most important consequences to eugenics. The huge mass of
experimental evidence that has been accumulated during the last quarter
of a century has, necessarily, been almost wholly based on work with
plants and lower animals. Even though we can not attempt to present a
general review of this evidence, for which the reader must consult one
of the standard works on biology or genetics, we shall point out some of
the considerations underlying the problem and its solution.

In the first place, it must be definitely understood that we are dealing
only with specific, as distinguished from general, transmission. As the
germ-cells derive their nourishment from the body, it is obvious that
any cause profoundly affecting the latter might in that way exercise an
influence on the germ-cells; that if the parent was starved, the
germ-cells might be ill-nourished and the resulting offspring might be
weak and puny. There is experimental evidence that this is the case; but
that is not the inheritance of an acquired character. If, however, a
white man tanned by long exposure to the tropical sun should have
children who were brunettes, when the family stock was all blond; or if
men whose legs were deformed through falls in childhood should have
children whose legs, at birth, appeared deformed in the same manner;
then there would be a distinct case of the transmission of an acquired
characteristic. "The precise question," as Professor Thomson words it,
"is this: Can a structural change in the body, induced by some change in
use or disuse, or by a change in surrounding influence, affect the
germ-cells in such a _specific_ or representative way that the offspring
will through its inheritance exhibit, even in a slight degree, the
modification which the parent acquired?" He then lists a number of
current misunderstandings, which are so widespread that they deserve to
be considered here.

(1) It is frequently argued (as Herbert Spencer himself suggested) that
unless modifications are inherited, there could be no such thing as
evolution. Such pessimism is unwarranted. There _is_ abundant
explanation of evolution, in the abundant supply of germinal variations