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Why we favour our left side to carry the baby?

On which side of your body do you carry or cradle your baby?

If you answered “left”, you’re not alone. As it turns out, 75-80 per cent of women and girls display what scientists call a “left cradling bias” – the tendency to hold infants (or dolls) on the left side of their body. It’s not a result of being left or right-handed, and interestingly, the same phenomenon isn’t observed in males.

So why do we favour the left side?

As it turns out, cradling a baby on the left side has more to do with the structure of the brain than which hand you write with. And it all has something to do with creating and strengthening the bond between you and your bub.

If it’s been a little while since high school biology, remember that the right side of the brain, or the right hemisphere, controls the left hand side of the body. The left side of the brain (the left hemisphere) controls the right.

In a new study, published last week in Nature, Ecology and Evolution, a team of researchers set out to explore the evolutionary origins of this left cradling bias. After examining 11 species of marine and terrestrial mammals (including horses, reindeer, antelopes, oxen, sheep, walruses, three species of whale and two species of kangaroo), the researchers found that humans are in fact just one of many species who demonstrate the same pattern of “mother-infant spatial relations”.

“This is likely to be a pervasive mammalian feature of ancient evolutionary origin,” the study authors note.

So what is it, exactly, about the right side of the brain? Well, the right hemisphere is implicated in processing social cues as well as forming close relationships – key components, of course, when it comes to caring for our young.

“A left cradling bias arises from the right hemisphere’s advantage for social processing,” the authors explain. “For example, visual recognition of infant facial expressions.The position of an infant on the mother’s left side may optimise maternal monitoring, by directing sensory information predominantly to the mother’s right hemisphere.”

Previous research has also uncovered that the right side of the brain is “superior” to the left when it comes to “directed and sustained” attention. As such, cradling a baby on the left side may also help a mother focus her attention towards her baby.

In a nutshell, based on their findings, the authors conclude that “sensory lateralization” facilitates mother-infant bonding.

So there you have it: cradling baby on your left hand-side is actually helping to strengthen the precious bond between you and your bub.