ced far, the group must remain small in order
to pick up enough food to sustain life on a given area.

Starting out with a single pair, when the family increases in size a
separation is necessary; and clans are an outcome of the process of
division and redivision, the bond between the clans and their union
in a tribe resulting from their consciousness of kinship. Now, it is
a well-known condition of exogamy that, while a man must marry without
his clan, he must not marry without his tribe, and for the most part,
in fact, the clan into which he shall marry is designated. In other
words, allied clans gave their women in exchange mutually. This was
a natural arrangement, both because the two groups were neighbors and
because they were friendly, and at the same time the psychological
demand for newness was satisfied. When a family was divided into
two branches, Branch A had a property interest in its own women, but
preferred the women of Branch B because of their unfamiliarity. The
exchange took place at first occasionally and not systematically, and
the women parted with in each case were not, perhaps, in all cases the
youngest, and we may assume that they had in all cases been married
before they were given up. But gradually, and when the habit of
exchange had been established, men came to look forward to the
exchange and to desire to secure the girl at the earliest possible
moment, until finally young women were exchanged at puberty, and
virgins. When for any reason there is established in a group a
tendency toward a practice, then the tendency is likely to become
established as a habit, and regarded as right, binding, and
inevitable: it is moral and its contrary is immoral. When we consider
the binding nature of the food taboos, of the _couvade_, and of the
regulation that a man shall not speak to or look at his mother-in-law
or sister, we can understand how the habit of marrying out, introduced
through the charm of unfamiliarity, becomes a binding habit.

I think, therefore, we have every reason to conclude that exogamy is
one expression of the more restless and energetic habit of the
male. It is psychologically true that only the unfamiliar and
not-completely-controlled is interesting. This is the secret of the
interest of modern scientific pursuit and of games. States of high
emotional tension are due to the presentation of the unfamiliar--that
is, the unanalyzed, the uncontrolled--to the attention. And although
th