Why are you left-handed?

Are you left-handed? I.e. do you do the following things with your left hand.

1. Hold a pen
2. Throw a ball, play tennis or tennis table

Most likely, you are a right-handed person. Left-handed persons are believed to be about 10% of the population only.

But why is it that way? Why this ratio? Why not 50% ?

That is a question science doesn't currently know the answer.

Our brain is used to control our body. As we grow up, the left part and right part of our brain specialize into different functions. A left-handed person's brain can be seen as the symmetric (mirror image) of a right-handed person. Have we answered our question? Not really.

We know the organization of the brain explains a person's preference for one hand over another. We don't know why the brain develops 90% of the time to make a right-handed person and 10% to give a left-handed person. Some of us believe it ought to be a very simple mechanism, in the early stages of the embryo development. Maybe one day a scientist will publish an image showing the cellular development of the brain responsible for this ratio. Maybe some stem cells get pushed into a blood vessel that divides into two extremities - one large, and a second one that is a tenth of the first one. Something at some microscopic level ought to be responsible for this particular ratio.

Maybe you want to be a scientist yourself to research this area. Please post a comment when your article has been accepted by Nature. I am a left-handed person myself and I am very very interested in the answer...