Re: exogamy, kinship, and heterozygosity

Bryant (
4 Oct 1996 10:05:59 -0600

In article <5326b0$>,
Robert Snower <> wrote:
> (Bryant) wrote:
>>In the IQ literature it's observed that first-cousin matings result in
>>offspring with significantly impaired cognitive performance.
>I have trouble with this one.

Here's one ref on the topic: "Inbreeding depression and intelligence among
north indian children," Badaruddoza and Afzal, Behavior Genetics,
23(4): 343-347.

Also see "Reproductive behavior and health in consanguineous marriages,"
Bittles et al. 1991, Science, 252: 7899-794. Here's their abstract.
Even if their last line down there is correct, small fitness impacts can,
over time, constitute a steady selection pressure on allele frequencies.
Presumably, they can also affect cultural strategies for meeting evolved
drives, desires, and needs.


In many regions of Asia and Africa, consanguineous marriages
currently account for approximately 20 to 50% of all unions, and preliminary
observations indicate that migrants from these areas continue to contract
marriages with close relatives when resident in North America and Western
Europe. Consanguinity is associated with increased gross fertility, due
at least in part to younger maternal age at first livebirth.
Morbidity and mortality also may be elevated, resulting in
comparable numbers of surviving offspring in consanguineous and non-
consanguineous families. With advances in medicine and public health, genetic
disorders will account for an increased proportion of disease worldwide.
Predictably, this burden will fall more heavily on countries and
communities in which consanguinity is strongly favored, as the
result of the expression of deleterious recessive genes. However, studies
conducted in such populations indicate that the adverse effects
associated with inbreeding are experienced by a minority of families.

>Best wishes. R. Snower