Dr. Marc Breedlove

I would have said, well, let's try it and see.

If anything, you're right.

Yeah, right.

Well, I did too.

So Wendy Brown and I did that first.

And, you know, I'd worked with mice and rats all my life.

But, you know, I'd never noticed that the first digit is the shortest and that the –

third digit is the longest and that sometimes the second digit is longer.

You know, it's like, I mean, you know, evolution's real, right?

It happened.

And so, yeah, there's a sex difference there.

And a group looked at mice and did lots of genetic manipulations.

And it turns out that if you...

make the androgen receptor dysfunctional, the sex difference goes away.

And they showed that in mice at least, there's more androgen receptor in the growing bones of the fourth digit than the second digit.

And then they showed that that's why the fourth digit grows a little bit more than the second digit.

Well, in terms of prenatally, we don't know, but the very famous study from Simon LeVay, who was already a highly respected neuroscientist, lots of wonderful papers in development of the visual system, Simon LeVay got everyone's attention well before we did, when he looked at a brain region in the hypothalamus, a specific region called the preoptic area, or POA, and

He looked there and compared the size of the POA in the brains of gay men versus straight men.

And he looked in the preoptic area because in rats, there's a very prominent sexual difference or sex dimorphism in a nucleus in the rat brain in the preoptic area.

And the nucleus got named the sexually dimorphic nucleus of the preoptic area, the SDNPOA.