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What's that smell?

I'm back from vacation, which included a closeup look at this research submarine with Q&A by an expert technician, and seeing the family of our next president in a beach park. But lots of interesting work accumulated while I was gone, so my comments on this week's paper will be brief. You can read the whole thing on line.

"MHC-correlated odour preferences in humans and the use of oral contraceptives" was published in Proceedings of the Royal Society by Craig Roberts and colleagues. This is another women-sniffing-tee-shirts paper, but with some interesting new results.

One theory to explain why many species reproduce sexually (that is, by using genes from two individuals, rather than just one) is that the resulting genetic diversity decreases the chance that a disease epidemic will kill all of an individual's offspring. So we might expect females to prefer to mate with males who are more different genetically from themselves. This is apparently true for mice, with odors playing a key role in identifying genetic differences.

Similarly, women were previously reported to prefer the odors of men who differed from themselves in a particular set of genes known as the major histocompatability complex or MHC. This week's paper repeated this work, with some additional variations. Their results:

1) On average, women did not show the same preference for the odors of tee-shirts worn by men differing in MHC, relative to those with similar MHC. Apparently other studies have had mixed results. Do we need larger sample sizes, more consistency in methods, or new theoretical advances to guide future experiments?

2) When data were split by relationship status, women in relationships tended to prefer different-MHC smells, whereas unattached women preferred similar-MHC smells (see their Figure 3a). The authors suggested that this could reflect an (unconscious?) interest in having more genetic diversity in one's offspring. But could causality go in the opposite direction, with women seeking variety being more likely to form attachments?

3) Starting birth control pills shifted female preferences in favor of similar-MHC male odors.

I expect we will be hearing more about this.

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