International Left-Handers' Day: Why are some people left-handed?

If you prefer to use your left hand, then you're in luck because it's International Left-Handers' Day!

It's believed that around one in 10 people are left-handed.

But no-one really knows why left-handed people like to use their left hands.

Left-handed Martin's been looking at some of the theories, and how life's not always been easy for lefties...