ierra Leone and Egypt, 10 years. From
these data we should naturally he led to infer that there would be great
variations in the age at which other manifestations of the sexual life
first make their appearance, and experience justifies this inference.

Some writers attribute to climate a great influence in this respect;
whilst others regard this view as erroneous, and believe that the
differences observed depend rather on racial peculiarities. By advocates
of the former view it is assumed that a hot climate leads to the early
appearance of menstruation, whilst a cold climate retards the
development of this function. Those who dispute the influence of climate
bring forward instances of a contrary kind. Thus, among the Samoyede
Eskimos, menstruation begins at the age of twelve or thirteen,
notwithstanding the fact that they dwell within the Arctic circle;
whereas, among the Danes and the Swedes, menstruation begins at about
the age of sixteen or seventeen years. Again, we are told that among the
Creoles of the Antilles, as in France, menstruation rarely begins before
the fourteenth year, whilst in the same islands, girls of African race
begin to menstruate, as in Africa, at ten or eleven years of age.[68]
These objections to the climatic theory are certainly serious ones. But
when we are considering the possible influence of climate upon
menstruation, we have to remember that it is possible that climate may
exert its influence cumulatively in successive generations, and may not
produce its full effect upon the age at which menstruation begins, until
after the lapse of several generations. We certainly lack evidence to
show that in isolated individuals a change of climate affects the first
appearance of menstruation. But it is not impossible that climate may
exert such an influence in the course of several generations. Such a
view would appear to receive support from our observations on animals,
for the sexual life of the latter is notably influenced by the seasons,
and change of season resembles in many respects change of climate. In
most animals, and more especially in those living in a state of nature,
the sexual impulse becomes active at stated intervals only, and these
intervals are related to the duration of pregnancy in such a way that
the birth of the young occurs always at a season in which the nutritive
conditions are favourable. It is widely assumed that even in the human
species there remain vestiges of such a p