That means a really strong chimp could, in theory,

lift around sixteen people over its head.

But, can eating bananas and swinging around in trees

really account for this difference?

After all, aren't we supposed to share 99% of our genes?

Studies have shown differences in the way our muscles are built

but muscle control may be a much more important factor

Chimps seem to have less control over how much muscle they use at once.

While this may sound counter-intuitive, this can account for the difference in strength.

Let's take a look at why.

Compared to humans, chimps have less gray matter relative to body weight.

Gray matter is the part of the nervous system

that contains the nerves responsible for controlling motion.

These branch out from the spine into the muscles

to control individual muscle fibers.

Some neurons can contact many muscle fibers at once.

Activating these neurons causes all of the muscle fibers that touches

to contract at once.

Creating a lot of force.

This combination of neurons and muscle fibers

is called the large motor unit.

And these are used for gross motor skills

like jumping and climbing.

Some neurons contact only a few fibers

making a small motor unit.

These don't have a lot of power

but they are a lot more precise.

Small motor units let us do delicate complex tasks

like playing a video game or plucking a ukulele.

Things that we can do and

chimps can't.

So chimps who have less gray matter

have fewer motor neurons.

Therefore, their motor neurons are more likely

to be dedicated to large motor units.

This means when they do engage their muscles

it's an all-or-nothing response which we see as strength.

Unlike chimps, our neurons control smaller bundles

so we have more specific muscle control.

So keep this in mind the next time you think of challenging a chimp in a pub;

You might want to try thumb wrestling instead.

For Scientific American, I am Yasmin Tayaq.