on of the past, and, in so far as we have children, they
become disseminated throughout the population of the future. Upon such
traits society is built; good or bad they determine the fate of our
society. Apart from migration, there is only one way to get socially
desirable traits into our social life, and that is reproduction; there
is only one way to get them out, by preventing the reproduction. All
social welfare work is merely education of the germs of traits; it does
not provide such germs. In the absence of the germs the traits can not
develop. On the other hand, it is possible with difficulty, if possible
at all, by means of the strongest repressive measures merely, to prevent
the development of undesirable hereditary traits. Society can treat the
delinquent individual more reasonably, more effectively, and more
humanely, if it knows the 'past performance' of his germ-plasm."

In addition to their importance to society, a knowledge of the traits of
a pedigree has a great direct importance to the individual; one of the
most valuable things to be learned from that knowledge is the answer to
the question, "What shall a boy or girl do? What career shall one lay
out for one's children?" A knowledge of the child's inborn nature, such
as can be had only through study of his ancestry, will guide those who
have his education in hand, and will further guide those who decide, or
help the child decide, what work to take up in life. This helps to put
the problem of vocational guidance on a sound basis,--the basis of the
individual's inherent aptitudes.

Not too much must be expected from vocational guidance at the present
time, but in the case of traits that are inherited, it is a fair
inference that a child is more likely to be highly endowed with a trait
which both parents possess, than with one that only one parent
possesses. "Among the traits which have been said to occur in some such
direct hereditary way," H. L. Hollingworth[164] observes, "or as the
result of unexplained mutation or deviation from type, are: mathematical
aptitude, ability in drawing,[165] musical composition,[166] singing,
poetic reaction, military strategy, chess playing. Pitch discrimination
seems to depend on structural factors which are not susceptible of
improvement by practice.[167] The same may be said of various forms of
professional athletic achievement. Color blindness seems to be an
instance of the conspicuous absence of such a unit characte