The smell of babies causes different reactions in fathers and mothers

It is common to hear parents declare how particular and kind the smell of their own babies is to them. Now researchers at the Weizmann Institute of Sciences in Rehovot have discovered that the smell emanating from the scalp of newborn mammals, both humans and other animals, has one purpose: the survival of the species.

Specialist Noam Sobel from the Department of Brain Science and his colleague Eva Mishor, in cooperation with the Azrieli National Institute for Imaging and Research of the Human Brain, recently published an article in the peer-reviewed journal Science that reveals details of this discovery.

Scientists found that in land mammals, volatile chemicals emanating from the body can effectively trigger or block aggression in the same species. In their research process, they analyzed whether hexadecanal (HEX), a volatile compound in the human body that appears as a social chemical signal of mammals, affects human aggression. They found that sniffing HEX, whose smell cannot be identified by human smell, blocked aggression in men but triggered aggression in women.

Then, using functional brain imaging, they discovered a pattern of brain activity that reflects behavior. In both men and women, HEX increased activity in the left angular gyrus, an area of the brain involved in the perception of social signals. They created a computer game that was divided into two: a stage of provocation aimed at arousing aggression among the 130 men and women involved in the study; and a stage of reaction in which they were allowed to discharge the aggression they accumulated. Half of the participants were exposed to the HEX molecule, while the other half served as a control group.

“The reason for this evolution was that male aggression in mammals is often expressed violently towards offspring, but in females it is expressed as protecting the baby,” explained Mishor. Researchers estimate that a quarter of male mammals, including rodents and primates, kill some of their young, especially when they live in large groups. “Because babies can't communicate verbally with their mothers, they have the ability to communicate with chemicals,” Sobel said.

The team contacted a Japanese scientist who is investigating the smell molecules of babies. They decided to collaborate with their data and discovered that HEX is one of the most common chemicals released by the scalps of children. Animals are known to release chemical signals from their olfactory organs and affect social behaviors, but prior to Weizmann's study it was not known that they also influence humans. “Humans smell each other all the time,” Sobel concluded. Now we apparently understand what happens when it is done with babies, how our brain processes this information, and what the evolutionary role of this effect could be.”

Another recent study found that babies can recognize those they have close relationships with based on saliva. Learning to manage social relations is a fundamental skill for survival in human societies. For babies and toddlers, that means learning who they can count on to care for them. That new study by researchers at Harvard and the Massachusetts Institute of Technology (MIT), including psychologist Elizabeth Spelke, shows that children 8 to 10 months of age infer that two people are likely to have a close relationship if they see them having interactions that involve a transfer of saliva.

Such activities include kissing, biting each other's food, and sharing the same fork or straw. The study indicates that babies understand all these activities as social cues that indicate whether people are on casual terms or share stronger bonds.

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