In most animals that can favor one hand (or paw) over the other, the population ends up split 50/50. But only about 10 percent of humans are left-handed — so that’s pretty weird.

Why do we favor one hand over the other in the first place? That’s not clear, but most people think it’s because of how our brains are structured. Human brains have two hemispheres, and generally speaking there are different brain regions devoted to different tasks.

Fine motor skills (aka hand use) take up a ton of brain power — and so does language. So some believe that the brain might put language centers and hand control close together in the brain as a way of conserving energy. That would explain why most of us are right-handed: Most humans process language in their left hemisphere, and the left hemisphere tends to control the right side of the body. If the fine motor control centers were located there, it might mean more dexterity in the right hand.

But as Joe Hanson explains in a PBS video, the theory isn’t totally straightforward — because most people who are left-handed have their speech centers on the left side, too. So the theory would explain why most of us are right-handed, but not why some of us go south paw.

We may not know the final answer on handedness yet, but our digits are definitely becoming less mysterious thanks to science. It was only a few months ago that scientists pinpointed the molecules that allow us to develop precisely five fingers in the womb.