Dr. Marc Breedlove

That is, so there are, sometimes you'll see in the news, someone will find a genandromorph.

In birds, yep.

Ginandromorphs.

So half female, gin, and half male, andro.

And when it happens in cardinals, for example, it's like the animal's been split down the middle.

No.

Yes, where the one side is the bright red of a male with a crest, et cetera, and the other side isn't.

Right?

So these occur occasionally.

And our best understanding of what happened there, first of all, the sex chromosome is a little different in birds than mammals.

I'm going to gloss over that.

But our best understanding of what happened there is this is a case where two embryos, one that was carrying male sex chromosomes and the other female sex chromosomes,

came together at an early stage.

And so what we have is a mosaic animal where one side is genetically male and the other side is genetically female.

Now, in a mammal, if that happened, the testis on the male side would masculinize everything by using hormones.

The clue that something else is going on

in birds is that in this case, there's not been this blending.

And when Art Arnold and others looked at the brains of genandromorphs, sure enough, the sex differences where this region, HVC, for example, tends to be larger in males than in females.

In these animals, it was larger on one side of the body than on the other.

So they were indeed