The smell of babies calms men but makes women aggressive

From birth, parents are encouraged to soak up the scent of their newborn. Indeed, the molecules volatiles that the human body produces are chemical messages intended for the brain that can modulate our behavior. Neurobiologists at the Weizmann Institute in Israel describe the effect of hexadecanal, a molecule produced by the skin, faeces and respiration of mammals, on aggressiveness. First identified in mice, it turns out that humans have a receptor similar to that present in mice and which recognizes hexadecanal. It would also be very conserved in mammals.

A group of volunteers, 67 men and 60 women, took part in an aggression test after being exposed to hexadecanal or a neutral odor. The behavior of both sexes is modified by hexadecanal, but not in the same way: men are less aggressive while it is the opposite in women. They publish the details in Science Advances.

Testing aggressiveness

To measure participants’ aggressiveness, the scientists used a well-known test: the Taylor aggression paradigm. the protocol consists of two phases. A first phase of “provocation” to frustrate the participants and a second “aggression” where they can take revenge. Scientists have therefore created a video game in which participants have to sharemoney facing a computer stingy. They can then punish him by sending him a sound signal with an intensity proportional to their aggressiveness. Before playing, half of the participants were exposed to hexadecanal and the other half to the neutral scent. Women exposed to hexadecanal demonstrated more aggressive behavior than those exposed to the neutral scent. In contrast, men exposed to hexadecanal are calmer than those in the control group. In their brains, the angular gyrus, a region involved in complex cognitive tasks, is activated indifferently in men than in women.

Improve the survival of the offspring?

Scientists then wondered if there was an explanation for this difference? According to them, the answer would be to be found on the side of evolution. Indeed, maternal aggression in the animal world can be triggered by odors. For example, a rabbit can kill its litter if one of the cubs door the smell of another female. Corn female aggressiveness often has a positive impact on litter survival. Typically, it is directed at a threatening intruder. While that of the males is often directed against the cubs themselves. By their smell, Babies animals may thus improve their chance of survival by influencing the behavior of adults.

This theory, if it seems plausible, remains to be proven experimentally in humans; just like a causal link between hexadecanal and angular gyrus activation – scientists have not established light, here, that a correlation.