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Smell of babies appeases men and makes women more aggressive

22.12.2021

Translation: machine translated

A scent molecule on the scalp of newborns affects the two sexes differently. This may have provided an evolutionary survival advantage.

We know from animals that body signals in the form of volatile substances play an important role in communication. Many species, including insects, use pheromones to influence the behaviour of their fellow species. It is now known that our olfactory brain is also receptive to subliminal messages from fellow humans. But our knowledge of this is still limited. A team led by the olfactory researcher Noam Sobel of the Weizmann Institute of Science in Israel has now demonstrated that a volatile molecule secreted by human skin, the air we breathe and faeces has a direct influence on our brain as well as our level of aggression. It is found primarily on the scalp of newborns and evolutionarily may have offered a survival advantage.

First, the researchers invited 127 subjects (67 of whom were women) to take part in a behavioural experiment: they were supposed to play games on a computer with another subject. The first part was aimed at generating frustration in the participants (the "other player" takes the lion's share of the winnings); the second part was aimed at triggering aggression. Here, the volunteers were allowed to take revenge by maltreating the "teammate" with a corrosive sound by pressing a button. During the experiment, an odor sample was attached under their nose: One half of the group got to smell the pure carrier substance, the other additionally hexadecanal. However, neither produced any perceptible odor impression.

Surprisingly, there was a clear gender effect: the women reacted more aggressively under the influence of hexadecanal (turned up the volume), while the men seemed to be soothed by it. To investigate the underlying processes in the brain, the team conducted an fMRI experiment with another 49 participants (24 of whom were women). While these were in the scanner tube, they completed a similar aggression paradigm as the group before. They were given air enriched with either hexadecanal or only a carrier substance via a breathing mask.

Weibliche Aggression hingegen richtet sich für gewöhnlich auf die Verteidigung des Nachwuchses.

Eva Mishor, Neurowissenschaftlerin

The evaluation showed that hexadecanal activated a region central to social cognition, the angular gyrus, in both men and women. But connections to areas related to social evaluation and the regulation of aggression were enhanced in men under the influence of the signaling molecule, but diminished in women.

According to Eva Mishor, lead author of the study, the volatile substance may represent a cool-down signal for men, at the same time that it fuels aggressive behavior in women. "In the animal kingdom, male aggression often translates into aggression toward newborns. Female aggression, on the other hand, is usually directed at defending the offspring," the neuroscientist said. Evolutionarily speaking, then, sniffing the back of a baby's head makes sense.

Spectrum of Science

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