Mothers who want to bond with their babies should carry them on their left hand side, because it creates a natural social connection, a new study suggests.

Previous research has shown that upto 85 per cent of women will naturally cradle an infant to the left, the Daily Telegraph reports.

But Russian scientists were keen to find out whether the same pattern was present in other mammals, which would suggest it was a behaviour which evolved millions of years ago to aid bonding.

To find out they studied populations of walruses and flying foxes, whose body structures differ dramatically from humans. They found they were more than twice as likely to carry their offspring on the left hand side.

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The researchers also found that when an infant was separated from its mother, it subconsciously positioned itself to remain in her left visual field.

Experts believe that left cradling is the best way for a mother to notice and respond to a baby's behaviour, such as crying or laughter. In that position, important cues are directed to the right side of the mother's brain, the hemisphere that is used for emotional processing.

So cradling on the left gives the mother a faster way to pick up her baby's requirements.

"A significant population level preference for the position which facilitates the use of the left visual field in both mother and infant was revealed in walruses and flying foxes," said Dr Andrey Giljov, of St Petersburg State University, Russia.

"Our results show that the left-sided positional bias in face-to-face mother–infant interactions is not a unique feature of primate evolution, and occurs in different groups of mammals.

"This consistent pattern may have emerged owing to mutual perceptual benefits resulted from enhanced social processing by the right hemisphere."

Some parenting experts also believe that keeping a baby's head close to the mother's heart helps naturally soothe the child, which remembers the sound from being in the womb. Others claim the bias is based on handedness.

Left-handed women say they prefer to hold their infant in their stronger left arm. Right-handers argue it keeps their dominant hand free to attend to the child.

The research was published in Royal Society: Biology Letters.