PEOPLE can recognise the smell of their close family members â but surprisingly, they donât like it. This aversion may help prevent incest, the discoverers speculate.
Most studies of smell recognition in humans have looked at mothers and their newborn babies, who learn to recognise each otherâs smell soon after birth. But Tiffany Czilliâs team at Wayne State University in Detroit wanted to know how well all the other members of the family would fare in a sniff test.
She recruited 25 families with at least two children aged between 6 and 15, and gave the participants odourless T-shirts, odourless soap and resealable bags with their names on them. The volunteers were instructed to sleep in the T-shirts for three nights, wash only with the soap provided and seal the shirts into the plastic bags each morning.
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Czilli then asked everyone to sniff two T-shirts, one worn by a family member and one by an unknown and unrelated person. She asked fathers and mothers if they could detect the scent of their children, and children if they could identify their parents or siblings. She also asked each of the participants which odour they preferred.
Both mothers and fathers recognised their pre-adolescent offspring, Czilli found, though mothers tended to be more accurate. Neither parent could distinguish between their children, however. For their part, pre-adolescent children aged 5 to 8 did not recognise their motherâs smell, while older children, aged 9 to 15, did. Breastfed sons were the exception: they could recognise their mothers. And all the children recognised dadâs smell.
When asked which smells they liked, the answers were even more intriguing. The volunteers far preferred the smells of other people to those of their own family members. Mothers especially disliked their childrenâs smells, while children had a strong aversion to their dadâs scent. âRecognition and preferences can operate independently,â Czilli says.
She thinks that disliking the smell of close family might be part of the mechanism that helps prevent incest. Particularly notable is the fact that opposite-sex siblings disliked each otherâs smells, while same-sex siblings did not. She also speculates that the aversion to dadâs odour could reflect social distancing and independence in the child.
The avoidance of inbreeding could definitely be at work, says Dustin Penn at the University of Utah in Salt Lake City. But he warns that asking people about their preferences can be unreliable. âJust because people say they âpreferâ something doesnât mean theyâll act in a preferential way,â he says. Smell preference is context dependent, he adds. Liking someoneâs smell doesnât always mean youâd like to sleep with them.
