are in reality not variations at all, but
modifications; although these may be of the greatest value to the
individual modified, they are artificial things without permanent
value to the race. So many of the distinguishing personal traits are
the results of nurture rather than of nature. They represent the
result of the incidence of special factors in the environment. It is
extremely difficult and at times impossible to distinguish between
variations and modifications in adult characters, but in general the
distinction is usually clear upon careful analysis.

The changing of the innate characters of the human race is a slow
process, depending chiefly upon the advantage taken of the appearance
of real mutational variations. On the other hand, it is comparatively
easy to improve the condition of the individual by improving his
environing conditions--cleaning him, educating him, leading him to
higher ideals in his physical and mental and moral life. But as this
is easy, so it is impermanent. All this is modificational and has no
influence upon the stock. This is not opposed by the Eugenist; it
simply is no part of his province, for its effect is not racial. By
releasing a deforming pressure it may permit the individual to come
back to his real structurally determined condition, but the
structural condition itself is not thus affected. It is temporary and
must be done over with each generation, or on account of the
unfortunate habit of "backsliding," even at intervals shorter than
that of a generation.

* * * * *

Let us now turn to another phase of our subject and consider the
biological methods of the description and measurement of heredity, as
a preliminary to our next chapter in which we shall discuss the
bearings of the facts of human heredity upon the possibility of the
formation of a permanently improved human breed.

The fact of heredity is one of the most familiar and patent things
about organisms. "Do men gather grapes of thorns or figs of thistles?"
For we may define heredity as the fact of general resemblance between
parent and offspring. This simple definition is disappointing to many
persons. "Heredity" is so often supposed popularly to refer only to
some occasional, striking, and unusual similarity within a family
respecting certain traits or peculiarities. Very often the idea of
heredity seems shrouded in mystery: it is some uncanny relation which
explains peculiarities an