Baboons cradle their babies in their left arms just like humans do

Monkeys, just like humans, prefer to cradle their babies in their left arm and not their right, scientists have discovered. 

It is believed this preference evolved because the child is closest to the mother’s left eye, which is controlled by the brain’s emotion-processing right hemisphere. 

This half of the brain, in both monkeys and humans, ‘specialises in the perception of emotional facial expression ‘ and helps mothers understand their baby’s feelings.  

Previous studies found human mothers suffering from post-natal depression and stress often use their right arm, not the preferred left, to hold their offspring. 

It is now believed baboons also switch from left to right when they’re under pressure, which can be brought on by feeling spurned by their societal groups. 

Now the left arm bias has also been seen in primates as well as humans, scientists think the behaviour first evolved in a common ancestor around 35 million years ago. 

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Monkeys, just like humans, prefer to cradle their babies in their left arm and not their right, scientists have discovered. Scientists from the French National Centre for Scientific Research (CNRS) studied 44 olive baboons to determine if monkeys hold their babies in their left arm

Up to 72 per cent of human mothers cradle their babies on the left-hand side but it was unknown if other primates also have a left arm bias.  

Scientists from the French National Centre for Scientific Research (CNRS) studied 44 olive baboons to determine if the monkeys also hold their babies in their left arm. 

‘We found a significant left-side maternal cradling bias in an Old-World monkey, the olive baboon, in an almost identical proportion (67.45 per cent) to the one usually found in human mothers (64 per cent in the most recent study),’ the scientists write in their study. 

Similar findings have also been seen in apes, including chimps and gorillas, in previous studies. 

Humans hold their children in their left arm almost exclusively for the first 12 weeks of the baby's life. This is the opposite of other acts, where the right arm is preferred (stock)

Humans hold their children in their left arm almost exclusively for the first 12 weeks of the baby’s life. This is the opposite of other acts, where the right arm is preferred (stock)

Monkeys are more distantly related to humans than apes are, last sharing a common ancestor around 35 million years ago. 

‘We suggest that the origin of a left-cradling bias may be much older than the origin of humans and even older than hominids and hominoids, dating back to common ancestor of humans and Old-World monkeys about 25–35 million years ago,’ the scientists say. 

Humans hold their children in their left arm almost exclusively for the first 12 weeks of the baby’s life. 

This is the opposite of other acts, where the right arm is dominant. 

Mothers cradle their young in their left arm because it enhances their relationship  

Studies have found humans naturally cradle their babies in their left arms. 

Around 70 per cent of women use their left arm. 

It lasts for around 12 weeks after the baby is born.

However, the right hand is dominant for carrying inanimate objects. 

Scientists have discounted several theories to explain the phenomenon, including that it allows the right hand free for  feeding and that it puts the baby closer to the mother’s heart.

The most common theory states that a left-cradled baby exposes its face to the left eye of the mother more than the right. 

This feeds directly into the right hemisphere of the brain, which  specialises in processing emotions and facial expressions.

On the other hand, right-side cradling is associated with higher pre-and postnatal maternal anxiety and depression.      

For example, holding inanimate objects and performing medial tasks — such as carrying shopping — is often performed using the right arm, not the left, by humans. 

Scientists pursued an explanation for this peculiarity and now believe it is due to how the brain processes visual stimuli. 

Objects in the left side of the field of vision are processed by the right hand side of the brain, which is adept at detecting subtle emotional variation.

Scientists say the cradling in the left arm therefore favours the mother’s monitoring of the infant’s emotional state.

A baby in the left arm also looks up at the left side of the mother’s face, which studies show is the most expressive side of the face. 

However, the researchers found this harmonious left-leaning relationship can be interrupted. 

In humans, right-side cradling is associated with higher pre-and postnatal maternal anxiety and depression, the researchers say in the paper, published recently in the journal Scientific Reports. 

This can inhibit communication between mother and child and affect emotional perception. 

In the baboons studied by the French researchers, ‘the maternal left-cradling bias would be, just like in humans, altered by stress’, the researchers say. 

Baboons become stressed when living in highly populated groups, the researchers write. 

They add: ‘Higher densities increase the occurrence and frequency of conflicts involving severe aggression. Such conditions involve higher levels of stress.’