questions of much interest and importance may be
raised.

1. _Degree of difference between the sexes._--It is an established fact
that, physically considered, the contrast between males and females is
not equally great in all types of mankind. The bearded races, for
instance, show us a greater unlikeness between the two than do the
beardless races. Among South American tribes, men and women have a
greater general resemblance in form, &c., than is usual elsewhere. The
question, then, suggests itself--Do the mental natures of the sexes
differ in a constant or in a variable degree? The difference is unlikely
to be a constant one; and, looking for variation, we may ask what is its
amount, and under what conditions does it occur?

2. _Difference in mass and in complexity._--The comparisons between the
sexes, of course, admit of subdivisions parallel to those made in the
comparisons between races. Relative mental mass and relative mental
complexity have chiefly to be observed. Assuming that the great
inequality in the cost of reproduction to the two sexes, is the cause of
unlikeness in mental mass, as in physical mass, this difference may be
studied in connexion with reproductive differences presented by the
various races, in respect of the ages at which reproduction commences,
and the periods over which it lasts. An allied inquiry may be joined
with this; namely, how far the mental developments of the two sexes are
affected by their relative habits in respect to food and physical
exertion? In many of the lower races, the women, treated with great
brutality, are, physically, much inferior to the men: excess of labour
and defect of nutrition being apparently the combined causes. Is any
arrest of mental development simultaneously caused?

3. _Variation of the differences._--If the unlikeness, physical and
mental, of the sexes is not constant, then, supposing all races have
diverged from one original stock, it follows that there must have been
transmission of accumulated differences to those of the same sex in
posterity. If, for instance, the prehistoric type of man was beardless,
then the production of a bearded variety implies that within that
variety the males continued to transmit an increasing amount of beard to
descendants of the same sex. This limitation of heredity by sex, shown
us in multitudinous ways throughout the animal kingdom, probably applies
to the cerebral structures as much as to other structures. Hence the