Neal Shepperson asks, "What determines left or right handedness and why are us lefties in the minority?"

When we started investigating this question it became clear that there were just too many scientific mysteries to squeeze into one episode. So there are two whole episodes devoted to this very Curious Case.

One in ten people are left-handed, but where does this ratio come from and when did it appear in our evolutionary past?

Hannah talks to primatologist Prof Linda Marchant from Miami University about Neanderthal teeth and termite fishing.

Adam consults handedness expert Prof Chris McManus from University College London. He's been trying to track down the genes responsible for whether we're right or left handed.

If you have any Curious Cases for the team to investigate please email curiouscases@bbc.co.uk

Presenter: Adam Rutherford & Hannah Fry
Producer: Michelle Martin.