Steve has been talking about how Polynesian women tend to encourage the introgression of exoganous genetic material through liasons with men passing through (white, Melanesian, etc.). One reader suggests it is to counter-act inbreeding (Steve brings up the idea that genetic load of deleterious alleles could be purified by inbreeding, but GC has cited articles that throw a cloud over this idea). There is a lot of anecdotal evidence on the human level, but rare male preference is known in drosophila in controlled laboratory settings. Some of this might be due to heterozygote advantage in the MHC complex (an example of balancing selection). Obviously, an individual who is phenotypically extremely variant from you is almost certainly going to be unrelated to you, so there is a guarantee of having children with a novel HLA allele combination. Steve brings up the possibility that Eskimo women engage in this practice as well for a climatic antipode to contrast with the Polynesians. Interestingly, I read in Details magazine that Icelandic women also tend to engage in this practice, since most of their sexual partners are the equivalent of second cousins, an “exotic” look can give you a leg up if you are passing through town. Historically, disputes and conflict over sexual liasons between native women and European explorers are well documented, but if I recall correctly, African soldiers in the French army stationed in the Rhineland also caused similar problems (the mixed-blood offspring were sterilized or exterminated by the Nazis).
Personally, I would assert that there is some social rare male advantage in the United States (from personal experience), but this tends to diminish as one’s own phenotype exists beyond trivial levels in a locality. At this point, social anomie, stereotyping and inter-group dynamics can dampen the person-to-person interaction or attraction.
Update: “Rikurzhen” points out that drosophila don’t have adaptive immune systems, good point. I am not really sure if “rare male advantage” (which seems a form of “frequency dependent selection“) exists in humans, I just thought I’d throw it out there.
Also, I’d like to point out that there is research that indicates women are attracted to males with dissimilar MHCs. Another study indicates women are attracted to men with MHC profiles similar to their fathers. These sort of conflicts indicate the tradeoffs that every human makes when choosing a mate. For example, in matrifocal & matrilineal societies one might expect that women have more latitude in mate choice and so looking for diversity would be more common. In contrast in patrilineal & patrifocal societies this would be a moot point as males would dictate who women mate with much of the time. The cost of having a child whose father was a transient passerby would likely be far higher in a patrilineal and patrifocal society. In contrast, it might be less of an issue in matrilineal and matrifocal societies. Additionally, there might be more benefit in finding genetically dissimilar mates in a pathogenically stringent environment. Within the context of viability and survivorship, there is a cost to mating with someone whose immune system is variant, as children whose immune system differs greatly from the mother are more likely to be miscarried. But, once the child is born the one with the novel HLA profile might be at an advantage in the event of pathogenic sweeps through the local population. But a child who is genetically dissimilar from the local kin group might be at a inclusive fitness disadvantage in relation to a child born from a liason with a relatively close relative (cousin). The possibilities are endless….
On a mildly related note, the mestizo majority in much of Latin America is often perceived to have come about through genocide, rape, decimination & domination of natives. Much of this is true, but I also suspect that the genetic advantage that mestizo children had in comparison to pure indigenous children was significant. Native populations of the Americas have rather homogenous HLA profiles because of founder effect and the relatively benign pathogenic environment of the New World, going a long way toward explaining why they were such easy pickings for Eurasian bugs. The injection of European (and lesser extent African) HLA profiles into the gene pool would have served to innoculate the children of native women who had non-native fathers.
Update II: Additionally, I realized that I focused on the genetic advantages of having a dissimilar sperm donor, but what about the possible social-personal advantages of having an alien spouse? For example, if a woman lives among her kin in a tribe, call them A, and she is one of the few to marry someone from tribe C, she might have all the skills and accumulated “wisdom” of her own people, while her mate could bring information over from his own tribe. In contrast, someone who mates with a fellow tribe member does not add special skills to the couple, though they likely have a more natural rapport because of cultural and genetic similarities.
Posted by razib at 09:54 AM