purpose of sexual reproduction is to bring about greater organic
variation. Now variation, as we have seen, is the raw material upon
which natural selection acts to create the higher types. The immense
superiority of sexual reproduction over asexual reproduction is due to
the fact that it multiplies so greatly the elements of heredity in each
new organism, for under sexual reproduction every new organism has two
parents, four grandparents, and so on, each of which perhaps contributes
something to its heredity. The biological meaning of sex, then, is that
it is a device of nature to bring about organic variation. From the
point of view of the social life we may note also that sex adds greatly
to its variety, enriching it with numerous fruitful variations which
undoubtedly further social evolution. The bareness and monotony of a
social life without sex can readily be imagined.

While the differences between the sexes have been mainly elaborated
through the differences of reproductive function, yet these differences
have come to be fundamental to the whole nature of the organism. In the
higher animals, therefore, the sexes differ profoundly in many ways from
each other. Biologists tell us that the chief difference between the
male and female organism is a difference in metabolism, that is, in the
rapidity of organic change which goes on within the body. In the male
metabolism is much more rapid than in the female; hence the male
organism is said to be more katabolic. In the female the rapidity of
organic change is less; hence the female is said to be more anabolic.
Put in more familiar terms, the male tends to expend energy, is more
active, hence also stronger; the female tends more to store up energy,
is more passive, conservative, and weaker. These fundamental differences
between the sexes express themselves in many ways in the social life.
The differences between man and woman, therefore, are not to be thought
of as due simply to social customs and usages, the different social