A groundbreaking study published in Science Advances reveals that an odorless chemical excreted by newborns, known as hexadecanal (HEX), heightens aggression in women while calming men.
Previous research, including a 2015 study, showed HEX reduces stress in mice via "social buffering." More recent work indicated it modulates human startle responses. This latest investigation from the Weizmann Institute of Science in Israel extends those findings to human aggression.
Researchers recruited 200 participants for behavioral experiments measuring aggressive responses. Exposure to HEX significantly influenced aggression levels. "HEX has no noticeable odor, but sniffing it alters how you behave toward others, particularly your aggressive responses," explains lead author Eva Mishor, PhD.
Notably, effects varied by gender: women showed increased aggression, while men exhibited reduced aggression.
fMRI scans revealed heightened activity in the left angular gyrus across participants. However, connectivity patterns differed by sex, promoting greater "social regulation" in men and heightened vigilance in women.
Why the sex differences? The researchers hypothesize HEX helps newborns boost survival odds. They found higher HEX levels on newborns' scalps, suggesting it's a key chemical signal to parents.
"Babies can't speak, so chemical communication is crucial," notes senior author Noam Sobel, PhD. "For a baby, ramping up maternal aggression while dialing down paternal aggression makes evolutionary sense."
This ties to infanticide risks in mammals, where aggressive fathers pose threats, but protective mothers enhance offspring survival. "A mechanism increasing female aggression and regulating male aggression would improve infant survival chances," the study concludes.
These insights stem from a study of 200 adults; larger trials are needed to confirm HEX's role in brain activity and behavior.
