Jessica Wynn

Women, 10 percent.

Why that is, is still a complete unknown.

I mean, it's not a huge difference, but statistically significant.

Yes.

Anyway.

Yeah.

I mean, there's some other interesting patterns, too.

Studies show children born to mothers over 40 are more likely to be left handed.

Yeah, that could have been a factor for sure.

In the case of mom's age, there's a scientific theory that points to prenatal hormones and how the brain develops in the womb.

That influences which side of the brain becomes dominant, and that determines a bunch of stuff, including our handedness.

So for whatever reason, people born to older moms, they just swing left.

Right.

Yeah.

So the brain's asymmetry, meaning how the left and right hemispheres develop, is set really early on.

Most people's language centers end up on the left hemisphere, which controls the right hand.

But for lefties, it's often reversed or it can be shared between both sides.

Yeah, yes, yeah.

It's all decided before we ever pick up a crayon.

And in the 1990s, researchers identified a rare gene variant that they think plays the biggest role in the asymmetric left-right brain split.