Human mothers and babies share a trait with animals and their offspring that is quite unique — the tendency to care for our young and look to our caregivers from the left hand side of our bodies. Researchers in the journal Nature Ecology & Evolution have dubbed this “positional bias,” and they say there is cerebral reasoning behind it.
Previously, when most human moms were observed holding their babies on their left side, it was assumed it was done because of hand preference — that right-handed moms needed to have this hand free. But there is also a neurological reason for why they make that choice.
When women position their infants or children on their left hand side, it activates the brain’s right hemisphere, which governs the social activity processing area of the mind and involves communication and bonding. Human mothers tend to do this most when their babies are young and vulnerable but have been known to switch favored sides as children get older and are more independent.
Similarly, a 2014 study found that when children approached adults, they continually did so in a way that kept adults on their left hand side.
When it comes to mother and baby interaction, the left side/right brain hemisphere has an intricate and inseparable link that expands to not only humans but animals as well.
Why Baby Mammals Look For Mothers On Their Left
Kangaroos, horses, walruses and orcas are among the baby mammals that look for their mothers on their left sides, according to Russian researchers. It’s believed that this position assists the youngling with survival and social bonding with its parent.
“If there is no eye contact, or it is wrong, there is no activation of the right hemisphere of the infant…the right hemisphere is responsible for social interactions,” Dr. Yegor Malashichev of Saint Petersburg State University told BBC News. “We suggest that this bias is even more widespread and may be a characteristic of all mammals, with few exceptions.”
Janeane Ingram from the University of Tasmania Australia studied 11 wild mammals from around the world, including those listed above, plus reindeer, antelopes, oxen and sheep. She and a team of researchers recorded nearly 11,000 choices of positions across 175 animal infant and mother pairs and found that, for three-quarters of the time, infants of all species were more likely to place themselves so that their mother was on their left side. Her research concluded that it was because it was easier for the baby mammal to bond with the mother and they were less likely to be left behind.
“Infants keep their mother on their left in normal situations such as moving forward or suckling,” says Ingram. “But when faced with stressful situations such as when fleeing, mothers prefer their infant on their left side so they can better monitor them.”
It’s believed that this favored positioning of the left hand side/right brain hemisphere in mother-infant interactions has roots in evolutionary behavior. This approach to mother/child connection is an ancient, natural and basic way of life.
“If you’ve got different functions to perform, you can do that more effectively if you allocate different kinds of processing to each brain hemisphere,” says Lesley Rogers at the University of New England in Armidale, Australia. “So it makes sense for the right hemisphere to be dedicated to social behaviour.”