Lots of animals pick their mate at least partly by how they smell. And a bunch of studies show that it may not be that different in people.

My favorite ones are those where women sniff the shirts of various men and pick out the ones that smell the best to them. The ones they like best are usually from men whose immune systems are most different from theirs.

This makes some sense if you think about it. The strongest immune system is a varied one. It can fight off lots of different kinds of bacteria, parasites, and viruses.

And since our immune system is programmed by our genes and our genes come from mom and dad, the more different mom and dad’s genes are, the more varied your immune system will be. So ideally you would choose a mate that would give your children the stronger immune system. That mate would have an immune system very different from yours.

One way you might be able to find that particular mate is if different immune systems have different odors. The stinky guys share your immune system; the pleasant smelling ones have a different one.

This seems to be what is happening in these armpit smelling experiments. So at least some amount of attraction between people is happening with the nose.

But what I found even more interesting was that oral contraceptives mess with this system. Women on the pill tend to prefer the smell of men with similar immune systems. Some scientists think this is because pregnant women prefer family around them and family tends to have a similar immune system.

When I first read this I thought, “Wow, this is going to really mess up future generations’ immune systems. Maybe it even helps to explain the recent rise in allergies and autoimmune diseases.”

But then I caught myself and thought a little harder. It is probably not that likely that the recent increases in allergies and autoimmune diseases would have happened so quickly if the pill were the main culprit. And besides, there is undoubtedly more to human mate selection than smell!

We are complicated. There are all sorts of cues that cause someone to fall in love. Pheromones may play a role but they are certainly not the whole story.

For example, some studies use photos and ask women which men are the most attractive. The women in these studies tend to pick men with more similar immune systems (apparently there is some correlation between facial symmetry and the immune system).

And when scientists look at couples who actually have children together, they get mixed results. An early study pointed to Europeans having children with partners with different immune system genes. But a deeper look at that data and looking at a larger group of couples showed that this didn’t seem to be the case. Differing immune systems had little impact on who women chose to have children with.

The most that could be said was that women tended to avoid men with really similar immune systems. A bit similar was OK.

Of course we could already be seeing the effects of the pill in these studies. Maybe if the women in these studies hadn’t been on the pill when they met their partners, they might have chosen someone with a more dissimilar immune system.

Scientists need to look at people who did not meet while women were on the pill. Then we will have a better idea of how big a role your nose plays in choosing your soul mate. And how worried we should be about the pill’s effect on that selection.

Nice PBS video about the t-shirt smelling experiments.

Sniffing Out Mr. Right 3 November,2011Dr. Barry Starr


Dr. Barry Starr

Dr. Barry Starr (@geneticsboy) is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA and runs their Stanford at The Tech program. The program is part of an ongoing collaboration between the Stanford Department of Genetics and The Tech Museum of Innovation. Together these two partners created the Genetics: Technology with a Twist exhibition.

You can also see additional posts by Barry at KQED Science, and read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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