Why Are There Righties & Lefties?

In “Why Are There Righties & Lefties?,” host Hank Green of the web series SciShow shares some interesting thoughts on why there are more people who prefer to use their right hand over their left hand. Today we learned that five of the last seven U.S. presidents have been south paws!

About 10% of the world population is left-handed. But why does handedness exist and what determines which hand is dominant? Scientists have suggested several theories, but the answer may well lie with evolution.