Today is International Left Handers Day – so we thought we’d look into the question: why are people left handed? How is your dominant hand determined, and what are the evolutionary advantages or disadvantages of being left handed?

First, a couple of quick fun facts about left handedness:

  • About 10% of the world’s population is left handed
  • Identical twins with the exact same genes can have different dominant hands
  • Some theorize that being left handed evolved as a competitive advantage in fighting and sports, because the majority of the population is trained to compete against right handed people

For more details on left handedness – check out this terrific Ted-Ed video! And we hope all you lefties have a great day.

P.S. For more of our favorite brain science videos, try: