In this TED Conference, the neuroscientist Giorgio Vallortigara talks about how the human race, in all countries and at all latitudes, has a majority that prefers to use their right hand, whereas only a small minority of people are left-handed.

The interesting thing is that this curious and seemingly unexplainable phenomenon is not only limited to human beings, but is also widespread in other animals, as demonstrated in many experiments: when you give a tube of honey to a chimpanzee, it usually holds it with its left hand and tries to get the honey out using its right one. Or there is also the case of common toads: to remove adhesive tape from their faces, they predominantly use their right paw.

We know that the preference over which hand we use has to do with our brains: the right side controls the left limb and vice versa. And the two halves of the nervous system do different things. In our species, the left hemisphere controls language, whereas the right side is assigned other tasks (recognizing faces, spatial orientation…).

This – observes Vallortigara – is a seemingly very strange way to build a brain. There must have been important reasons why brains are built in an asymmetrical manner.

We are aware of some of the reasons: for example, by channelling several functions all to one side, we save the use of nervous tissue. Then, in the case of important decisions to be made immediately, it is essential that half of the brain takes control. Finally, the asymmetry offers us the possibility to carry out two tasks simultaneously.

But why is there a majority of right-handed people and a minority of left-handed ones?

First of all, by studying the solutions that respond better from an evolutional point of view, it has been discovered that the most stable ones are neither half and half (50-50), nor represent the total (100%), but rather those that have a majority and a minority. However, to answer this question, Vallortigara takes a look at the branch of mathematics known as game theory, according to which, “what is best for an individual to do depends on what the majority of individuals in the group to which it belongs do”.

So how is this principle applicable to our discussion? Simple: left-handed people have a competitive advantage, because they are a minority and are part of a larger group of “conformists”. And this little “defect” is good for everyone, because it is functional to improving the resources at the disposal of the species.