You Smell Good (to Me): MHC and Genetic Compatibility

On the relationship science team, we optimize for long-term relationships and put very little emphasis on short-term compatibility. We’re very future-oriented, which means that we match people with extremely compatible personalities, core values, romantic tendencies, and life goals. Sometimes though, those same matches that would be compatible otherwise might also end up being “turned off” by each other in ways that psychology can’t explain (but biology can!).

One of my favorite biological explanations for short-term sexual attraction involves the major histocompatibility complex (or MHC, for short), a group of genes that helps detect foreign substances in your immune system. It exists in all vertebrates , but in humans specifically it’s called the human leukocyte antigen (HLA). 

So what does detecting foreign substances in your immune system have to do with compatibility? The answer has to do with ✨genetic diversity✨.

Without delving too deeply into the biochemistry of it all, the basic idea is that you can literally smell other people’s immune systems through their body odor, with the help of their MHC. 

According to evolutionary biologists, we’re wired to be sexually attracted to the person who will give us the best, most genetically diverse offspring. One way we figure out who that person is is through body odor and MHC. The more dissimilar (read: foreign) their immune system is to yours, the more likely you’ll enjoy how they smell. 

This process is completely unconscious and involuntary, having been thoroughly tuned through millions of years of evolution. So if you’ve ever been captivated by someone’s natural smell, know that it’s probably because you two have very dissimilar, but compatible immune systems, and your kids would basically be superhumans (just kidding. They’ll just be very immunocompetent).

To recap, the more foreign their MHC is to yours, the more likely it is that your kids will have an optimal immune system, because of some complex genetics reasons. It’s also interesting to note that this effect was the opposite for women on hormonal birth control, for whom someone with a more similar MHC was more attractive to them. 

For obvious reasons, we don’t collect information about your body odor or genetic profiles. Maybe that means we can’t fully optimize for short-term, sexual attraction– at least not through your MHCs. But that’s okay! Sexual attraction declines over time for most people anyway, as the deeper emotional intimacy that characterizes successful long-term relationships develops. 

For now, we’ll continue to match you based on that goal of long-term emotional intimacy, and leave it to you to figure out whether you like how the other smells. At the end of the day though, I hope you’ll bust out this new, cool, super niche human bonding concept at your next social gathering. I know I will.