In the case of the horns, only two types were possible, absence or
presence of the character. Likewise there are only two types of primary
sex, i.e., of sex glands proper. But seven different types or grades of
body for each sex were found to exhibit themselves in the moths. In more
complicated bodies, we should of course expect many more, and where many
races (instead of two) are mixed, as in man, a classification merely on
the basis of physical characteristics would be much more complicated.
Indeed, we may well be sceptical as to the possibilities of cataloguing
differences of the sort between men and women by body type alone.

In society, however, we are much more interested in the mental than the
purely physical qualities of the two types of bodies, especially since
the use of machines has so largely replaced brute strength with skill.
Most employments do not even require a muscular skill beyond that
possessed by ordinary individuals of both sexes.

Even this ignores the primary consideration in the sex problem in
society, the first of the following two parts into which the whole
problem may be divided: (1) _How to guarantee the survival of the group
through reproduction_ of a sufficient number of capable individuals; and
(2) How to make the most economical use of the remaining energies, first
in winning nutrition and protection from the environment, second in
pursuing the distinctly human values over and above survival. The sex
problem as a whole is concerned with adjusting two different general
types of individuals, male and female, to the complicated business of
such group life or society. The differences between these two sex-types
being fundamentally functional, the best way to get at them is to trace
the respective and unlike life cycles.

We have already shown in rude outline how a difference (apparently