I’m right-handed, but I have a left-handed brother. About 90 percent of the population is right-handed, but we’re not exactly sure why.

How much is genetic? Does evolution play a role?

Dr. Thomas Merritt, a professor of chemistry and biochemistry at Laurentian University in Canada, has long been fascinated by handedness. He wrote about handedness for the online journal The Conversation, and he talked to The Show about it via Skype.