Smelling babies' heads alters aggression

When we think of a newborn baby, often their smell springs to mind: it’s a distinguishing feature. And perhaps that odour has a specific purpose. Noam Sobel and Eva Mishor from the Weizmann Institute of Science in Israel, have reason to believe that smell is something not to be sniffed at, as Harry Lewis has been hearing...

Noam: You know, there's a term from German zoology; umwelt. Umwelt refers to the primary perceptual world an animal lives in. So granted, human's umwelt is visual and then auditory. Now that is not true for many other mammals. If you would ask your dog or your cat, they would certainly give up vision and audition before they would give up olfactions. So animals differ in that way and yet for humans, even though it's not the primary sensory aspect we use to perceive the world, it's still super, super important. Our nose guides very, very important decisions in our lives.

Harry - Does it affect then, the way in which we socialise as well?

Noam - For sure. We were contacted by colleagues from Germany who studied chemosignalling, not in humans but in mice. And that is the communication using chemicals, using body odours. We studied this quite extensively. They identified a specific molecule hexadecanal, and we'll call it 'hex' from here on just for convenience. So they identified hex as a molecule that's emitted primarily in the faeces of mice and has social influence in mouse behaviour. Or put in simple terms, it makes mice chill. Now researchers went on to identify the very specific olfactory receptor that responds to hex and moreover, they then observed that this particular receptor is highly conserved evolutionarily. That is that you see it or it's homologues in lots and lots of mammals, including humans. So they actually sent us a bottle of the stuff by mail and it said 'we think it's going to do something in humans because it does this and this in mice. And we think this is highly conserved across mammals.'

Harry - And thank goodness they did. How does one even go about testing using this hex that's arrived in the post to see how aggression changes?

Eva - So aggression is a social behaviour. We brought participants to the lab. We had to make them frustrated.

Noam - I think we made people angry more than we made them frustrated.

Harry - I imagine you're very good at this now, but how do you two make people angry?

Eva - We asked them to reach cooperation with someone else, which was in fact a computer algorithm and not a very nice computer algorithm. So here we told them. 'Now it's a completely different task. This task is a time reaction task, just press as fast as you can. But then if you press faster than this other participant, you get to noise blast them.' Then we just provided an outlet.

Harry - I've got a little clip of the sound actually. So let me play it for you at home.

[sound plays]

Harry - It's a pretty grating sound isn't it? What do you find?

Eva - So when men were exposed to hex, it was a small effect but incredibly consistent. They used 'noise blasts' that are lower in their volume, like less severe noise blasts. But to women, when we're exposed to hex they use more severe noise blasts.

Harry - Why is it that hex has this effect? Do we have any idea?

Noam - Typically in the animal kingdom, definitely in the mammalian kingdom and sadly also in humans, paternal aggression and male aggression is often sadly directed at offspring. By contrast, maternal aggression is typically protective. So if you are an offspring, you have a vested interest in making your mother more aggressive and then making your father less aggressive.

Harry - An interesting hypothesis, 'the smellier your baby, the more aggressive the mum and the more chilled out the dad.'

Noam - The final icing on the cake here that I should add. We went to a paper that was published just a few years ago by a group out of Japan. So this was really cool because it was hypothesis driven. We came to them and said, 'Look, we're expecting to find hex here. And lo and behold hex was the most abundant, semi volatile they found in heads of babies. So this came full circle, because not only do we hypothesise that it should be there, but it, in fact, is there at very high levels?