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Whatsapp Humans mostly make decisions based on visual information, but our sense of smell is much better than we think and can even sniff out complementary genes.

Sniffing sweaty T-shirts seems like an extreme way of finding your perfect match, but there's more to body odour than first thought. New evidence suggests you're actually searching for an immunogenetically complementary mate, and that the perfumes we like to put on enhance our own genetic funk.

It may seem like a stunt. But the science is solid, stimulating even.

Later this month, the ABC’s Catalyst program will hold a Pheromone Party where young people are lined up to sniff each other's T-shirts and to choose someone to date. The shirts have been worn for three days and the wearers have used unperfumed soaps and eschewed powerfully flavoured foods like garlic and chili while doing so.

This fragrant soiree aims to investigate the research of Professor Manfred Milinski, an expert in sexual selection at the Max Planck Institute for Evolutionary Biology in Germany.

Milinski’s research has offered a novel explanation as to why we’re attracted to dirty laundry. The attraction you feel through the sniffing is not, as you’d imagine, to body odour—it’s subliminal. It’s chemical and beyond what you’d consciously expect.

Milinski’s theories grow out of his research into mice and fish, which he discovered seek out partners on the basis of odours that reveal a clear link to their immune system.

‘In mice it had been found out before, just by accident, that mice can smell out which immunogene versions potential partners carry,’ Professor Milinski says. ‘And because this part of the immune system is exactly the same in all vertebrates, we thought we could repeat the mouse experiment with humans.’

We think we do most decisions on visual information, which might be true, but our sense of smell is much, much better than we think. Human beings can distinguish more than 10,000 different kinds of smell.

‘And then we had males and females immune-typed so that we exactly knew which versions they carried, and then arranged a test so that each woman was presented with six T-shirts worn by six different men, and three were as similar as possible to the choosing woman, and three were as different as possible.’

‘And she had to decide—alone in a room, not influenced by anybody—which smelled good or which smelled nasty.’

‘And she found—and all these women found—that the ones worn by men which are different immunogene versions from the ones she carried smelled wonderful and the similar ones smelled bad. And so this means that we prefer as partners people who offer other immunogene versions than we carry ourselves. This is a very good solution because this provides our offspring with a broad range of immunogenes.’

Interestingly, Professor Milinski’s research may reveal not only why we’re attracted to certain people, but also why we have sex at all.

Sex, as Professor Milinski insists, is a crazy, inefficient way to reproduce. Why not simply split, like an amoeba? It’s quicker, more reliable (you get true, identical reproduction) and you can do it on your own. No dressing up or messy courting. Furthermore, as Woody Allen assured us: it’s with someone you really love—yourself.

‘The problem is that we still cannot explain why most plants and animals, including humans, reproduce sexually,’ Professor Milinski says.

‘The point is that for each reproduction you throw away half of your genes and then invest a lot of time and energy, which you call mate choice and display behaviour, to find somebody else to fill up what you have thrown away. This is ridiculous, but it must make sense, and it makes sense only if the environment changes all the time. So what you collected last time or your parents collected for you is no longer the best solution.’

‘You have to choose your partner in a way that [they] offer the optimum complement genetically to what you have retained yourself.’

In other words, we do sex for survival. If the environment changes and a new deadly disease turns up, the entire species can be wiped out—if it’s a monoculture. With a variety of genes for resistance you have options. And sex allows you to shuffle your pack, to gain half of another’s set to augment your own. The sniff tells you, however unconsciously, whether your date is well-equipped with an immunological difference, or has genes too much like your own.

Your nose will fancy your complementary stranger, without you really knowing.

And the test is in the offspring. With mice and fish it’s easy to show that well-shuffled parents have children more likely to survive, and more of them. And when you remember that some diseases like to the Black Death wiped out half of Europe’s population in the middle ages, the stakes are high.

The sweaty t-shirt test for selecting a mate Listen to more about the science behind the odours of potential mates at The Science Show.

Milinski's thesis also gives huge weight to our olfactory perception, often dismissed as a weaker sense.

‘We think we do most decisions on visual information, which might be true, but our sense of smell is much, much better than we think. Human beings can distinguish more than 10,000 different kinds of smell. This is quite a lot. So it's not surprising that we are able to do the same thing as mice can do and fish can do and birds can do.’

Weirder still, the research has some peculiar consequences for the perfume industry. After the T-shirt experiment, Milinski asked the same volunteers to choose a perfume that they’d like to wear, again under controlled conditions.

He found that subjects chose perfumes with similar immune gene versions to those they carried themselves.

‘We pay a lot of attention to how we smell, and we have used perfumes since at least 5,000 years in all cultures... And this suggested to me at least that your immune genes not only tell you—or force you—to select a partner that smells the way that offers the best immune genes for your immune genes, to produce resistant children. It also tells me that these immune genes force you to select a perfume on yourself that does not destroy this message and that it even amplifies your own message.’

Professor Manfred Milinski is head of the Max Planck Institute for Evolutionary Biology in Germany. And the pheromone party hosted by Dr Jonica Newby is on Catalyst on Thursday evening at eight, ABC1, July 25. Listen to Dr Newby’s interview with Professor Milinski at The Science Show.

