Smell of babies calms men but brings out the fight in women

SMELLING a baby’s head makes men more placid but increases a woman’s willingness to fight, research has found.

Scientists believe that a chemical produced by humans called hexadecanal (HEX), which is emitted in high concentrations from the scalps of babies, affects men and women differently.

The phenomenon is thought to be a relic of a period when infanticide perpetrated by males was common, and females had to protect their babies.

While the murder of children by men is less common in the modern world, the pathway still exists, helping to tame men and make women more protective.

In men, HEX improves connectivity between the region in the brain that processes social cues and the region responsible for aggressive behaviour, but in women has the opposite effect.

Researchers recruited 127 people for a study, half of whom were exposed to the chemical, and assessed them as they played games against a computer.

Brain scans revealed the chemical changed how the male and female brains looked and worked. The academics, led by the Weizmann Institute of Science in Israel, said: “Whereas maternal aggression has a direct positive impact on offspring survival in the animal world, paternal aggression has a negative impact on offspring survival.

“This is because maternal aggression is typically directed at intruders, yet paternal aggression, and more so nonpaternal male aggression, is often directed at the offspring themselves.

“If babies had a mechanism at their disposal that increased aggression in women but decreased it in men, this would likely increase their survival.”

The study is published in the journal Science Advances.