It is not just humans who are left- or right-handed. It turns out that some squirrels are also strongly lateralised, that is, they actively favour one side of their body over the other.


But unlike humans, where handedness is believed to make brains more efficient, scientists have found that squirrels who demonstrated a paw preference were less good at learning new tasks compared to their ambidextrous counterparts.

Dr Lisa Leaver, programme director of University of Exeter’s animal behaviour course and study author, said: “It has been suggested that being strongly lateralised makes brains more efficient, with each hemisphere focusing on different tasks.

“This could help animals survive, which would explain the evolution of laterality across the animal kingdom.

“In fish and birds, there is evidence that being strongly lateralised is linked to better cognitive performance (brain function).

“However, limited data from studies of mammals suggest a weak or even negative relationship.”

Read more about handedness:

To find out more, researchers from the University of Exeter observed 30 wild grey squirrels who were presented with a perspex tube containing peanuts.

Of them, 12 provided enough data to be included in the research paper, published in the journal Learning and Behaviour.

In order to access the nuts, the squirrels had to learn to use a paw, rather than their mouth as their faces were too big to fit through the holes of the tube.

We found that the squirrels who had stronger tendencies to use either their left or their right paws rather than being ambidextrous were the ones who didn't perform as well on the tasks
Dr Lisa Leaver

Dr Leaver said: “We were measuring how long it took them to stop using their faces and to start using their paws to reach into the tube.

“And once they started doing that, we measured which paws they were using – left or right.”

While some squirrels showed ambidexterity by using both their paws to access the nuts, others strongly favour one side.

The team then measured how quickly squirrels learned the task and how strongly they favoured a particular paw, assessing both learning and laterality.

Results showed that squirrels which strongly favoured a particular side did less well on a learning task.

Reader Q&A: Why are some people left-handed?

Asked by: Oliver Stewart, Cobham

Being left-handed is the result of genes and environment. About 50 per cent more males than females are left-handed and 17 per cent of twins are, compared with about 10 per cent in general. The ‘vanishing twin’ hypothesis suggests that left-handers were originally a twin, but the right-handed foetus failed to develop.

Brain dominance also appears to play a part. Most people are right-handed and have language controlled by the left hemisphere, and most left-handers are the opposite. However, some left-handers have language processing in the left hemisphere, or in both.

The genetic basis for left-handedness is complicated. Even if both parents are left-handed there is only a 26 per cent chance of their child being left-handed. Possessing the ‘LRRTM1’ gene increases the chances, but only if it is inherited from the father.

But whether you become left-handed or not is also dependent on development. It may be influenced by levels of testosterone or oestrogen during pregnancy, and early experience with holding and throwing things can also affect later hand use. Finally, damage to the right hand can make people left-handed.

Read more:

Dr Leaver said: “We found that the squirrels who had stronger tendencies to use either their left or their right paws rather than being ambidextrous were the ones who didn’t perform as well on the tasks.

“So they didn’t learn as quickly, they didn’t learn as thoroughly as the ones who were more ambidextrous.”


She said the findings were in line with these previous mammal studies which suggest “strong lateralisation is linked to poor cognitive performance” but added more research is need to “understand the complex relationship” between the two.


Alexander McNamaraOnline Editor, BBC Science Focus

Alexander is the former Online Editor at BBC Science Focus.