Survey of multiple species suggests mother's preference for cradling baby on left tied to bonding

January 10, 2017 by Bob Yirka, report
Credit: CC0 Public Domain

(—A team of researchers with members from Russia, the U.S. and Australia has found evidence that supports the theory that left-side support of babies by their mothers is tied to brain hemispherical functions. In their paper published in the journal Nature Ecology & Evolution, the researchers describe their study of multiple mammal species and how their discovery bolsters a common theory of mother/offspring bonding behavior.

Many people may not have noticed, but have a very strong tendency to support their babies on their left sides, especially when cradling them. Scientists have debated the reason for this with some suggesting that it allows the babies to hear the mother's heart beat better. Others have suggested that it is due to differences in function in the two . The left side is believed to be primarily concerned with processing language and making calculations, while the right side is more involved with processing emotions, recognizing faces, and music. The two hemispheres are also responsible for muscle control, of course, but it gets reversed in the processing—the right side of the brain controls the left side of the body while the left side of the brain controls movement of the right side of the body. A mother cradling her baby on the left, the theory goes, allows for both parties to engage more with their right hemispheres, which results in stronger bond building.

To test this theory, the researchers conducted a survey of mothers and their offspring regarding left/right tendencies in multiple mammal species including oxen, reindeer, antelope, horses, walruses, sheep, three species of whales and two species of kangaroo. In so doing, they discovered that all of those surveyed had a similar preference for cradling on the left. They also found that during normal activities, offspring tended to hang around on the left side of their mothers—during times of crisis, however, offspring were moved to the other side, presumably to allow the mother to better offer physical protection.

These findings, the researchers suggest, bolster the proposition that left/right preferences between mothers and is based on hemispherical function.

Explore further: Study finds pregnant women show increased activity in right side of brain

More information: Karina Karenina et al. Lateralization of mother–infant interactions in a diverse range of mammal species, Nature Ecology & Evolution (2017). DOI: 10.1038/s41559-016-0030

Left-cradling bias is a distinctive feature of maternal behaviour in humans and great apes, but its evolutionary origin remains unknown. In 11 species of marine and terrestrial mammal, we demonstrate consistent patterns of lateralization in mother–infant interactions, indicating right hemisphere dominance for social processing. In providing clear evidence that lateralized positioning is beneficial in mother–infant interactions, our results illustrate a significant impact of lateralization on individual fitness.

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2.3 / 5 (3) Jan 10, 2017
Right. And sugar in coffee or tea must be mixed clockwise in Northern hemisphere and anticlockwise in Southern, so the water molecules align correctly.

Delusional irrational wishful thinking. Very good at making connections where there are none. Good job, Anna Karenina. Now asylum is calling, reminding you missed to take your meds.
5 / 5 (1) Jan 10, 2017
I would have guess that is is because most people are right handed, so you cradle the child in the left to access it easier.
3 / 5 (1) Jan 10, 2017
In the womb, the offspring hears and senses the beat of its mother's heart. The heart is on the left side of our chest cavity. I'm rather sure the offspring are more at peace and settled when they can feel the beat of its mother's heart. Simple as that. Save the money and time.
not rated yet Jan 10, 2017
ShaneB ---- I agree Right Handedness seems the logical assumption as that position leaves the right hand free to multitask. The test should have specifically included left handed people to rule that out. Also, they could have tested the Baby's activity in both positions to see if the heart sounds changed the sleeping or activity of the babies.
not rated yet Jan 10, 2017
some suggesting that it allows the babies to hear the mother's heart beat better

The heart is pretty much in the centre of the chest and judging from the position of that baby's head in the picture, I would venture that left or right would make very little difference.
not rated yet Jan 18, 2017
Good job, Anna Karenina. Now asylum is calling, reminding you missed to take your meds.

Hey NoStrings, I'll bet money YOU haven't gotten anything published in Nature; but at least you figured out you can comment on other peoples work. Better luck next time, holmes.

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