Re: exogamy, kinship, and heterozygosity

Bryant (
3 Oct 1996 13:31:49 -0600

In article <52uo9m$>,
Robert Snower <> wrote:

[re: Shapiro's incest taboo hypothesis:]

>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.

When viewing folks as long-term mates, Westermarck seems to have been
right; we have modules for avoiding mateships with those we grew up with
(such as sibs). However, there is a surprisingly high level of sexual
contact between sibs, it turns out. A fellow I know who is studying
sexual development in homosexual men cited to me heterosexual incest
(older brother rates for sisters) of nearly 10%. I still think that
*must* be an exaggeration. At any rate, it's happening out there.

In the IQ literature it's observed that first-cousin matings result in
offspring with significantly impaired cognitive performance. This may have
been observed by non-scientific cultures as well, often enough to generate a
sense that it's not too great to mate with close relatives.

What baffles me is why the incest avoidance behavior isn't better
canalized in our species. Is there a benefit to practicing sexual
behavior with whomever is handy?