come from violation of any tribal custom,
this throws no light on the origin of the feeling of horror in question.
Absence of sexual attraction between persons brought up together,[786]
though the absence of such feeling is said to have been observed in some
of the lower animals, is not assured for savages; its existence in
civilized communities is due to the acceptance of the established
usage, which makes certain unions impossible, so that they are not
considered, and the germ of such a public opinion may perhaps be assumed
for early tribes. Probably the horror of incest is a derivation from
economic and other situations and laws that arose naturally in early
society--it is a habit hardened into an instinct.

+436+. Though exogamy differs from totemism in origin and function, the
two are often found associated--their conjunction may be said to be the
general rule. There are, however, exceptions.[787] Totemic clans are not
exogamous in Central Australia, the Melanesian Banks Islands, among the
Nandi of East Africa, and the Bakuana of South Africa. On the other
hand, exogamy is found without totemism in the tribes just mentioned,
among the Todas of Southern India, in Sumatra, among the African Masai
and Ashanti, and in Southern Nigeria, and local exogamy among tribes
(for example, the Kurnai of Southeast Australia, and the Californian
Maidu and Shasta) in which totemic divisions are not perceptible.

+437+. In all such cases, however, the absence of records makes the
history of the organizations uncertain--we do not know whether or not
one of the elements, totemism or exogamy, formerly existed and has
yielded to disintegrating influences. Thus local exogamy may have
superseded clan exogamy in many places, the former representing the more
settled habit of life, and the absence of the totemic constitution may
indicate a process of decay of totemism. No general rule for the
decision of the question can be laid down--every case must be judged for
itself.[788]

+438+. Since a custom of exogamy presupposes at least two social groups
(clans), and totemism appears to be connected originally with single
clans, the natural inference is that the latter has everywhere preceded
the former in time. Both have undergone great changes produced by
similar sets of circumstances, and in both cases the simplest form is
probably the oldest, though here again definite data are lacking.
However, comparison of the known exogamous systems poin