children are born.

(6) Finally, not all of the childless and small families in the native
American stock are due by any means to voluntary causes, or even
involuntary causes of the kind that we have mentioned. There are also
certain other obscure physiological causes at work producing sterility
in American women. The sterility of American women is greater than that
of any other civilized population, even apart from the causes which have
just been mentioned. Some say this is due to physical deterioration in
the native white American stock, and there are other things which seem
to point in that direction. It may be, however, that this deterioration
is in no sense racial, but only individual, affecting certain
individuals who lead a relatively unnatural life. Our American
civilization puts a great strain upon certain elements of our
population, and this strain in many cases falls even more upon the women
than upon the men. The social life of the American people, in other
words, is oftentimes such as to produce exhaustion and physical
degeneracy, and this shows itself in the women of a population first of
all in sterility. It is evident that the remedy for this cause is a more
natural and more simple life on the part of all, if it is possible to
bring this about.

Thus, the causes which influence birth rate are evidently very complex.
In the main they are doubtless economic causes among all peoples, but
there is no reason to believe that these economic causes act alone in
determining birth rate, nor is there any reason to believe that the
other psychological and biological causes may be in any way derived from
the economic. So far as we can see, then, industrial conditions are
mainly responsible for the lessened birth rate in the native white
American stock. But mingled with these industrial conditions, operating