Pheromones are chemicals many primates produce to "communicate" with each other via smells. They can "talk" about how fertile they are, their age, if they want to fight, and much more.
Humans, on the other hand, have a rather shoddy sense of smell. As such it was always thought pheromones weren't a big deal for us. Plus the organ in our nose which senses pheromones is vestigial; rendered useless by a mutation 23 million years ago.
Nevertheless, there is some evidence that these vestigial smells can still influence our behaviour. Strippers, for example, earn more tips when they're releasing pheromones associated with fertility. And t-shirts worn by fertile women are ranked as "sexier smelling" by men.
However, a strip club isn't the best place to conduct research. An attempt to replicate how female pheromones influence male behaviour has found that the changes aren't as statistically significant as first reported. In fact, in many cases the results weren't significant at all.
Fun with pheromones
For the new world monkeys, pheromones are kind of a big deal. Their noses has a specialised set of senses - called the vomeronasal organ (VNO) - to process that information. Because of this they can use these smells to trigger fights, signal fertility, and much more.
However, the old world primates don't have place as high a value on these smells. Their VNO was ruined by a mutation 23 million years ago. Researchers speculate that even before that, pheromones weren't a big deal. Hence why a mutation could break the system and the primates not care. Colour vision may have provided an alternative way for communicating.
Humans are old world monkeys. But the situation is even worse for us. We arguably have one of the worst noses in the animal kingdom, with mutations ruining millions of our smell receptors. Again, likely because we don't use our nose too much either; much like the VNO. Our hair has almost all disappeared too. This traps pheromones in other primates, allowing them to really build up and make a stench.
Despite all this there's a growing body of evidence that pheromones still have a big impact on our behaviour. Particularly in interactions between males and females.
(As an interesting aside, some old world monkeys also seem to have this low level pheromone response like humans. A female chimp who produced more of these chemicals than normal was also the only one impregnated during a study).
Stripping for science
The most childish, yet most interesting, of examples of pheromones influencing behaviour is one I've already cited. But it's so amusing it's worth repeating: female strippers will earn almost twice as much money in tips during their most fertile period, compared to their least fertile period. It's argued that this could be because their clients are picking up on their fertility pheromones; making them seem more attractive.
There are countless other examples where female pheromones seem to influence male behaviour. Exposing men to them makes them less likely to co-operate, more attracted to women, less able to identify "unattractive" women, and view themselves are more attractive to women. In fact, men seem so good at being influenced by these chemicals they're able to distinguish between the body odour of an ovulating lady and a regular one; when given 4 day old t-shirts worn by women.
The key pheromones involved in all this are a series of fatty acids produced by the vagina. These are called "copulins" and are produced in higher quantities when women are at their most fertile (although this is reduced if someone is on the pill). They were initially identified in monkeys, but have been confirmed in humans. The question is, can they still impact our behaviour; given how we've lost many of the pheromone sensing adaptations.
The results discussed above would seem to indicate that they do play a role in it. However, much of this research is. . . questionable to say the least. It's hard to conduct a rigorous study in a strip club, after all. You can't even guarantee it's the same men returning every night; so it might just be on certain days more "generous" fellas turned up. Or maybe the stripper took a dancing class in between. Many of the other studies also have relatively low sample sizes, which is also problematic. The classic "sniff a t-shirt to see if the smell is sexy" study only examined four women.
There's also the fact that all this research was carried out on Westerners. But that's a whole other story.
Inhaling copulins
To try and finally figure out how much copulins influence male behaviour a pair of American researchers conducted one of the biggest studies on the subject. They recreated the mix of copulins found in fertile vaginas and made 100 men smell it.
Or rather, they made 50 men smell their fake vagina pheromones. The other 50 were given a control condition. Both were given surgical masks to wear, but only one group had a mask scented with copulins. All participants then had to answer a series of questions about how attractive they thought they were and how interested they were in defending their mate from competing males. They also had to rate a series of pictures of women.
If the copulins did really mind-control the men then those who had smelled it should:
- Be more driven to guard their mate, so they can mate with her since she's (fake) fertile
- Think they were more attractive to women, to motivate them to go and seek out (fake) fertile mates
- Rank more women as more attractive, showing less discrimination. This would encourage them to mate with the pictures.
And to an extent, these results were found. Men who smelt the copulin-scented mask thought they were more attractive and thought the women in the pictures were more attractive. Except these changes were negligible. To the point where they weren't statistically significant at all. The authors note that they were "trending towards significance" but that's just a fancy way of saying "only just not completely wrong".
In other words, the impact of pheromones is only really present in small samples and unusual situations (like getting your face all up in a 4 day old t-shirt). In a more general setting (as if getting a surgical mask of copulins can be considered general) the effect of these pheromones becomes so small it's insignificant.
The chemicals are still in women. And they can still influence men. But the process of getting the copulins from one person to the other is very difficult; what with our rubbish noses, no VNO, and naked bodies. As such it's unlikely men will ever experience this influence significantly in day to day life.
Although the researchers behind this latest study want to continue investigating it; given their results were "trending towards significant". Perhaps they will find some secret chemical warfare between the genders, but at this point it seems unlikely it will be a significant factor. Not when the largest, most rigorous study says it doesn't happen (much).
Men, you may remove your nose pegs.
tl;dr
Female pheromones might have an impact on male behaviour, but rigorous research shows it's small to non-existent.
References
Michael, R.P., Bonsall, R.W. and Kutner, M., 1975. Volatile fatty acids,"copulins", in human vaginal secretions. Psychoneuroendocrinology, 1(2), pp.153-163.
Williams, M.N. and Jacobson, A., 2016. Effect of Copulins on Rating of Female Attractiveness, Mate-Guarding, and Self-Perceived Sexual Desirability. Evolutionary Psychology, 14(2), p.1474704916643328.
Zhang, J. and Webb, D.M., 2003. Evolutionary deterioration of the vomeronasal pheromone transduction pathway in catarrhine primates. Proceedings of the National Academy of Sciences, 100(14), pp.8337-8341.
