Immunology and the single life

Fascinating.

If you could take a genetic test to determine long-term compatibility with your partner, would you take it?

I already see you boys and girls sneaking looks at the quizzes in Cosmo while waiting in the check-out line. But the thought of a cheek scraping gives you cold feet?

Here's what I'm talking about: NewScientist.com recently highlighted a study linking a set of genes to "how faithful and sexually responsive" partners are in long-term relationships. (You can find the whole story here.)

What is this magical set of genes? None other than what yours truly works on: the major histocompatibility complex, a.k.a. the MHC. The MHC is a set of genes for receptors that bind molecules from pathogens (like the cold virus, * cough cough *) allowing the buggers to be identified as foreign and then targeted for elimination. Different MHC in the human population mean people respond to different pathogens which -- historically -- allowed some of us to carry on even in the face of devastating superbugs. Happy thought, right?

Anyway, the logic goes that mixing MHC -- which sounds only a little dirtier than it should -- gives the offspring a better chance to survive. In other words, finding a mate in the next tribe over rather than your own tribe endows your children with a better chance to survive avian flu. Or whatever the pandemic was 10 000 years ago.

And what if you could somehow sense other people's MHC? Wild idea, right? Hold on to your asses: You do. How does this happen? You sniff them (other people's MHC, that is, not their asses -- we're not talking dogs here).

Take this other study, for example: In what can only be attributed to genius, researchers had women sniff sweaty shirts that were worn by different men and then rate the shirts by odor. In the next room (or wherever -- but I like to imagine it was the next room), researchers then sequenced the men's DNA at the MHC. See where this is going? Women liked the shirts worn by men whose MHC were most dissimilar from their own. (In an earlier study, researchers found this to be the case with mice sniffing each other's pee. God, I love this field!)

Cutting to the chase: Last fall researchers in New Mexico decided to do a follow-up study and check whether "female sexual responsivity" correlated with MHC dissimilarity. Here's the result (used without permission):

I'm not exactly sure why the x-axis goes below 0, and the data seem pretty noisy, but according to statistical magic, you get a significant correlation. (Let's not even get into the methodological difficulties of measuring "female sexual responsivity" or why that scale goes below 0. Clearly the couple at (0.36, -7) just needs to call it quits. Seriously, guys.)

In other words, you get in more satisfying relationships with people immunologically dissimilar from yourself. Go forth and find your opposite.

The authors sum up their findings in slightly drier language (but include a bonus dig at cheaters):

"As the proportion of MHC alleles couples shared increased, women’s sexual responsivity to their partners decreased, their number of extrapair sexual partners increased, and their attraction to men other than their primary partners increased."

I'm awaiting the day we find DNA sequencers in bars:

Guy [to girl]: "Hey, how are you? Wait, can we step over here and do a swab?"

[Guy inserts dollar in machine. Guy and girl swab cheeks, insert toothpicks into slot, exchange uncomfortable looks over the next 30 seconds. Finally, a ticker tape emerges. Guy grabs it.]

Guy [reading the tape]: "Hmm, looks like this isn't going to work out. Can I call you sometime, though?" [Girl is already swabbing cheeks with someone else.]