Dr. Marc Breedlove

Statistically.

But, you know, you show me a picture of the gay men's chorus, and I can't point out which man is gay because of that because there are other men.

factors that can influence whether someone grows up to be gay.

So again, it's one of these things where the statistical comparison is of great theoretical importance even though it offers no predictive value for a given individual.

It's a beautiful hypothesis.

And you first hear about this and that's the first thing you think.

Well, maybe the younger brother got bullied or – Or beat up his older brothers.

Right.

Maybe the older brother somehow inhibited the younger brother from developing in a full masculine fashion.

But it turns out Tony Bogart started looking at these data and he started asking, well, what about stepbrothers?

Do older stepbrothers make any difference in the odds of sexual orientation?

And the answer was a clear no.

On the other hand, older brothers who came from the same mother but were raised apart had just as much of an effect as those that were raised with.

So it does not seem to be socially mediated.

In fact, Ray Blanchard and Tony Bogart have come up with a very plausible hypothesis called the maternal immunization hypothesis.

And it runs something like this, that the first time a mother carries a son,

That son is carrying some genes that her immune system has never seen before.

All the genes on the Y chromosome, there's no way her immune system could have seen it.

And as long as that first son is in utero, her immune system never sees it.

But inevitably at birth, whether it's cesarean section or vaginal delivery, there's always blood and there's always mixing of blood.