Re: exogamy, kinship, and heterozygosity

Robert Snower (
Wed, 02 Oct 1996 21:54:05 GMT (Gerold Firl) wrote:

>This is an amnplification of a brief note to daniel maltz about how
>culture-specific rules of exogamy and kinship exert an influence on
>levels of heterozygosity. Many in the soft sciences who loudly profess
>their fear and loathing for sociobiology seem to believe that they are
>struggling to oppose the encroachment of biological determinism into
>the study of culture and the arts; that is a misapprehension. I will
>try to explain how incest rules influence human genetics, specifically
>the level of heterozygosity.

Most sociobiologists believe that the prohibitions against inbreeding
which are found so frequently in human societies find their
explanation as you are suggesting here--they are adaptations
reflecting the benefits of heterozygosity, the injurious effects of
homozygosity. The former promotes variability, the latter reduces

Anthropologists, again as you suggest, sometimes prefer a less
biological explanation, a more cultural explanation.

Wilson, in his later works, held for this conventional view, the one
about homozygosity and reduction of variability. But in his original
_Sociobiology_ he was very much on the fence, pointing out that
inbreeding promotes kin selection and altruism, which would work in
the opposite direction.

Shapiro, whose side I always seem to come down on, states flatly, in
_The Sociobiology of Homo Sapiens (1978)_, that heterozygosity and
homozygosity have nothing whatever to do with the incest prohibitions,
the endogamy/exogamy rules, the kinship constructions, of human

His argument is as follows. Long before human societies came along,
the behavioral inclination pro heterozygosity, con homozgyosity was
selected for, spreading through the mammalian populations which
supplied the precursors for Homo sapiens. That is why there is
evidence that incest is rare among mammals, that they have built-in
behavior which inclines against it. So, for humans, the problem has
already been solved. There is every reason to believe the genetic
advantage of heterozygosity had already been selected for, by the time
they came along.

Yet the pre-historic human societies found it necessary to solve it
again, with fantastically complicated, extensive systems. Why?

These systems were eminently successful in, among other things,
prohibiting incest. If there is one thing typical of ancient
societies, it is that they don't commit incest, except in the most
special and regulated of situations. Then why, if the problem was
being so successfully dealt with, should incest, and incest
prohibition, become a prevailing theme of the myths and literature of
the historic culture for which these ancient societies were
precursors? Why is it necessary to deal with this problem again, and
then again, and in such elaborate fashion?

Shapiro's answer is that the temptation of incest, along with its
prohibition, was a primordial social construct, originally highly
adaptive, accounting for the beginnings of human culture and society.
This primordial construct evolved into what we now see displayed in
myth, literature. Freudian, but entirely different from Freud's own
anthropological theories, which people do not take seriously.

Best wishes. R. Snower