I wouldn't do justice to an explanation. Something to do with muscle-building genes, and a substantial difference between the genetic makeup of our brains.

randomness:... this is why I do not hold out faith that humans will change and become peace-loving creatures who live in harmony. Many people claim they would be that way, but the moment they perceived a threat to themselves or a loved one, they would fight to protect them. It's in our blood. Everything is linked to survival, whether or not we want to admit it.