I was pointed to this research (via David) that is just out about the correlation between variation on DRD4 and "sexual arousal." From the press release:

Interestingly, some forms of variants in this gene were shown to have a depressing effect on sexual desire, arousal and function, while other common variant had the opposite effect - an increase in the sexual desire score. The latter is believed to be a relatively new mutation, and it is estimated that it appears in Homo sapiens "only" 50,000 years ago at the time of humankind's great exodus from Africa. Approximately 30% of many populations carry the heightened arousal mutations, while around 60% carry the depressant mutation.

In short, it seems like a very sexual orientation is a derived trait, while the ancestral character tends to be more "repressed." My first thought was that someone should forward this to Geoffrey Miller, his theories relating to sexual selection and cognitive evolution are predicated on weak pair-bonding and operational polyandry as males and females form temporary relationships which dissolve within 5 years after sexual novelty has expired (you need lots of reproductive skew to really ramp up sexual selection, and polygyny is the normal way to go about that). In contrast, other theorists, like pervert-cum-anthropologist Desmond Morris, have posited the importance of pair bonding and monogamy in the natural history of our species. The relatively trivial sexual dimorphism among humans (around 10%) between the sexes in terms of overall size and canine ratio suggests a more monogamous past, while the sperm competition research implies a more "mixed" picture (one problem is that the words do not really map onto to the full distribution well). The short of it is that monogamous species tend to be less "sexy" in many ways because they don't need to be, whether that be in behavior, display or semen volume (much of this costs resources and so can detract from fitness). The spread of a sexy variant within the last 50,000 years is very interesting, because it is within the last 50,000 years that the cultural explosion has erupted that made us more than just "anatomically modern" humans, that is, behavorially modern. Honestly, I would have guessed that the sexy variant was ancestral, but this data will surely result in new stories being told over the next few years if future research confirms and elaborates on it, because sex + evolution = mucho $$$ in terms of book sales.

The paper to published in Molecular Psychiatry is Polymorphisms in the dopamine D4 receptor gene (DRD4) contribute to individual differences in human sexual behavior: desire, arousal and sexual function. Click through and you will see why Jews are relevant, the study was done in Israel on university students, and found that particular DRD4 variants correlated with questionnaire responses. Is this generalizable to other populations?

Well, DRD4 has shown up elsewhere. For example, DRD4 promoter SNPs and gender effects on Extraversion in African Americans. And of course, there is the Harpending and Cochran review in PNAS, In our genes, which argues that the variation in the allele frequencies between populations is suggestive of their respective evolutionary histories.

I had some issues with figuring out their notation for the mutation, and the fact that I don't have full access to the journal article in question doesn't help, but here is a map from Alfred which shows regional variation at the promoter C/T mutation. On visual inspection I really don't have anything much to say in regards to the map and the allele frequencies (I assume that the C variant is associated with sexiness since it is in the minority). If any readers have access to the article I would suggest you might clear up of the extra-Israeli distributions of these variants as I wouldn't be surprised if it is mentioned in the discussion.

Addendum: Perhaps sexiness evolved to "spice" up the monogamous pair bond?