also equally difficult to see on what basis other than that of a
more closely associated sexual system the combined and harmonious
efforts needed for social progress could have developed. It is
probable that at least one of the motives for exogamy, or
marriage outside the group, is (as was probably first pointed out
by St. Augustine in his _De Civitate Dei_) the need of creating a
larger social circle, and so facilitating social activities and
progress. Exactly the same end is effected by a complex marriage
system binding a large number of people together by common
interests. The strictly small and confined monogamic family,
however excellently it subserved the interests of the offspring,
contained no promise of a wider social progress. We see this
among both ants and bees, who of all animals, have attained the
highest social organization; their progress was only possible
through a profound modification of the systems of sexual
relationship. As Espinas said many years ago (in his suggestive
work, _Des Societes Animales_): "The cohesion of the family and
the probabilities for the birth of societies are inverse." Or, as
Schurtz more recently pointed out, although individual marriage
has prevailed more or less from the first, early social
institutions, early ideas and early religion involved sexual
customs which modified a strict monogamy.

The most primitive form of complex human marriage which has yet
been demonstrated as still in existence is what is called
group-marriage, in which all the women of one class are regarded
as the actual, or at all events potential, wives of all the men
in another class. This has been observed among some central
Australian tribes, a people as primitive and as secluded from
external influence as could well be found, and there is evidence
to show that it was formerly more widespread among them. "In the
Urabunna tribe, for example," say Spencer and Gillen, "a group of
men actually do have, continually and as a normal condition,
marital relations with a group of women. This state of affairs
has nothing whatever to do with polygamy any more than it has
with polyandry. It is simply a question of a group of men and a
group of women who may lawfully have what we call marital
relations. There is nothing whatever abnormal about it, and, in
all probabi