Whether left-handed or right-handed, human mothers have a tendency to pick up and cradle their babies with the left side, a fact that allows them to use the right hemisphere, a part of their brains with a fundamental role in social processing, to improve exchange of information between them and their baby.
A research team from the University of Saint Petersburg has shown in an article published in the journal Biology Letters that this preference is not exclusive to humans. Marine and terrestrial non-primate mammals, such as walruses and Indian flying foxes, share the left-sided bias when it comes to holding their young during their face-to-face space interactions and resting with them on top. A fact that the researchers think could have arisen due to the benefits conferred by the improved social processing of the right hemisphere. Something that gives mother and baby an optimal perception of each other.
“Several decades ago, it was a popular belief that this brain asymmetry was just a human thing,” says Andrey Giljov, a zoologist and lead author of the study, in The Scientist magazine. However, through previous studies by the same author and with the recent publication, the opposite is being demonstrated. Through this type of hugging “the baby can see the mother with the left eye and the mother can see the baby with her left eye,” continues Giljov.
But why focus on such rare study subjects? It turns out that the researchers were interested in mammals that had unique offspring and had a tendency to cradle their young for long periods of time. For this, the habits of the Indian flying foxes ( Pteropus giganteus ) and the Pacific walruses ( Odobenus rosmarus divergens ) were more than adequate animals.
However, these are not the only beings in which this preference has been studied. Heather Hill, an associate professor of psychology at St. Mary’s University in San Antonio, Texas, studied beluga whales, cetaceans that also seem to have a preference for their left side. “Basically, the hypothesis that social information is processed more efficiently in the right hemisphere from a behavioral perspective is solidifying, and increasingly, the great diversity of species that have developed this capacity is beginning to be discovered.” Hill tells The Scientist.
While traditionally it has been believed that the left hemisphere is in charge of language, numerous neuroscience studies have shown that the right hemisphere is key in recognizing new external stimuli, in showing emotions, social behaviors and in identifying other individuals. In fact, it is believed that we are more expressive on the left side of our face for this reason. This difference could have evolved in our brains to allow us to perform two actions at once, communicating with words and emotions at the same time. Despite the advanced knowledge that we have today, there is still a long way to go for science, and it remains a challenge for the future to know the reason for brain asymmetry, that is, the reason why different regions of the brain adopt specific functions .
References:
Giljov, A., Karenina, K., & Malashichev, Y. (2018). Facing each other: mammal mothers and infants prefer the position favouring right hemisphere processing. Biology Letters, 14(1), 20170707. https://doi.org/10.1098/rsbl.2017.0707
Zimmer, K. (2018, April 17). Like Humans, Walruses and Bats Cuddle Infants on Their Left Sides. The Scientist Magazine®. https://www.the-scientist.com/news-opinion/like-humans-walruses-and-bats-cuddle-infants-on-their-left-sides-30434
