Why is everything contralateral?

Question

The left brain controls the right parts of the body while the right brain controls left part of the body. Why is this so?

Answer 1

Very good question.

This phenomenon of nerves crossing over is called decussation. Although it's existence is well established there has been very limited research into the evolution of the phenomenon.

Only one major theory has been proposed to explain the phenomenon. I won't go into it in detail, as the article below explains it very well.

http://www.washingtonpost.com/wp-dyn/content/article/2005/06/12/AR2005061201009_2.html

The original paper it refers to is here (if you have access to scientific journals online via a university):
http://www.thelancet.com/journals/laneur/article/PIIS1474442205009907/abstract

Answer 2

Great question!

Here's an article. I hope it helps. I'm not sure how accepted this theory is but it sounds logical.