I'll have to read the article when I get back from work, but I'm skeptical after reading the meta-analyses of similar studies that use bilateral symmetry to measure sex appeal to others -- these have shown that the link b/w asymmetry & attractiveness / health has been overhyped, and is of much lower magnitude than initially reported.

Inter-individual variation in bilateral symmetry is very slight, typically w/in the range of measurement error. Wouldn't this be so for variation in MHC dissimilarity between mated pairs? MHC genes are some of the most polymorphic, and the authors only examined 3 of the ~140 MHC genes... the symmetry studies have settled on making lots of re-measurements of symmetry, so it seems like a large number of repeat measures of MHC dissimilarity would be in order as well.

I wouldn't be surprised if there's something real here, but based on the similar case of symmetry, I'd guess that the effect is much smaller than reported. And there's probably lots of sub-structure -- those whose ancestral homelands have been mired in pathogens are predicted to be choosier for MHC dissimilarity than those whose homelands were left comparatively unscathed (e.g., Nigeria vs Finland).

Let's see. Does this finding help to explain aspects of certain cultures, like, say, the dominant culture in Arabia? A culture that promotes uncle-niece or cousin marriages would pair a lot of people with similar MHC. Some of them might prefer partners with different MHC. To discourage extra-pair mating, the society might resort to methods such as sex-segregation, veiling, and severe punishment for attempts to stray.

We've a lot of data to suggest that marriage customs like those I've mentioned promote various kinds of inbreeding depression. The variant-MHC-preference phenotype may be an adaptive mechanism to avoid the bad side effects of inbreeding.

these data are mixed though. some studies show that individuals prefer the MHC of the opposite sex parent.

re: mark, Does this finding help to explain aspects of certain cultures, like. probably not. uncle-niece marriage is most common south indian cultures. not really in islamic cultures. the primary component of variation of cultural practices seems to be historical/social factors. e.g., the rate of incest increased A LOT in northern europe after the reformation because the protestant churches did not look as negatively upon the practice as the catholic church. there wasn't any evolutionary change.

There may be, for every community, some "natural rate" of incest (inbreeding?), which would obtain if everyone chose mates freely. Some cultures may hold the incest rate above or below the natural rate. Perhaps the pre-Reformation incest rate in Europe was below the natural rate--Catholic societies certainly applied sanctions to discourage incest. Some modern Islamic societies (not exclusively; I'm just calling up a convenient example) may be forcing an incest rate above the natural rate with arranged incestuous marriages. Those societies seem to apply very stiff sanctions to discourage unarranged pairings. The evolutionary pressure against incest may be stronger than pressure for it (I do assume that some incidence of incest/inbreeding is adaptive). If so, that may help explain why in modern societies it seems to require somewhat less coercion to prevent incest than to enforce it. I'm not sure this been true throughout history--in the premodern world far fewer people travelled and much premodern incest may have reflected the difficulty of finding unrelated mates.

For consideration, I note that many modern Islamic leaders rail all the time about their people's promiscuity and lust for strangers. Perhaps people in their societies lust after strangers because their assigned mates are too closely related to inspire lusty feelings.

By contrast, pre-Reformation Catholic leaders sometimes railed against properly-married spouses lusting for one another! Of course, they railed against other lusts as well.