gamy of many tribes there is among other savages a
system of _endogamy_, described by MacLennan; this is the prohibition
of marriage between different clans. Spencer and MacLennan have
different explanations of this custom which seem hardly natural.
Westermark appears to be nearer the truth in remarking as follows: The
sexual appetite, especially in man, is excited by new impressions and
cooled by habit. It is not the fact of a man and woman being related,
but intimate companionship since youth, which produces in them a
repugnance to sexual union. We find the same repugnance between
adopted brothers and sisters and between friends who have been
intimate since childhood. When, on the contrary, brothers and sisters
or near relatives have been separated from each other since an early
age, they often fall in love with each other when they meet later on.
There is, therefore, no innate or instinctive repugnance to incest in
itself, but only against sexual union between individuals who have
lived together since childhood. As it is parents and their children
who are usually in this situation, everything is explained simply and
clearly.

The causes of exogamy are explained in the same way, by the fact that
members of the same clan often live together in close intimacy. It is
the small clans, formed of thirty or fifty individuals of a few
families living together, which have the most severe laws against
incest or endogamy. Where the families live in separate homes, such
prohibitions do not exist. The Maoris, who are endogamous, inhabit
villages which are widely separated, and marriage between relations is
allowed. Endogamy generally exists where the clan life is little
developed, and where relatives know and see little of each other. The
aversion to marriage between persons living together has thus created
prohibition of marriage between relations as well as that of marriage
between members of the same clan. It is the same reason which has led
to the prohibition of marriage between brothers-and sisters-in-law,
between brothers and adopted sisters, etc. In people living in small
communities, endogamy does not appear to have ever existed.

Incest between relatives living together appears to have everywhere
the same natural cause--the scarcity of women in isolated families
living in remote districts. There is also a psycho-pathological form
of incest associated with morbid appetites in the families of
degenerates. In animals livin