environment of the two sexes, but are even more due to a radical and
fundamental difference in their whole nature. The belief that the two
sexes would become like each other in character if given the same
environment is, therefore, erroneous. That these differences are
original, or inborn, and not acquired, may be readily seen by observing
children of different sex. Even from their earliest years boys are more
active, restless, energetic, destructive, untidy, and disobedient, while
little girls are quieter, less restless, less destructive, neater, more
orderly, and more obedient. These different innate qualities fit the
sexes naturally for different functions in human society, and there is,
therefore, a natural division of labor between them from the first.
Indeed, the division of labor between the two sexes may be said to be
the fundamental division of labor in human society.

The causes which produce sex in the individual are not known to any
extent and are probably beyond the control of man. In each species the
relative number of the two sexes is fixed by nature, probably through
some obscure working of natural selection, and in practically all of the
higher species of animals, man included, the number of the two sexes is
relatively equal. In human society much depends upon this relative
numerical equality of the two sexes. Hence it can be readily seen that
it is fortunate that man does not know how to control the sex of
offspring, for if he did the numerical equality of the two sexes might
be disturbed and serious social results would follow.

(2) _The Influence of Parental Care._ Sex alone could never have
produced the family in the sense of a relatively permanent group of
parents and offspring. We do not begin to find the family until we get
to those higher types where we find some parental care. In the lowest
types the relation between the sexes is momentary and the survival of