Dr. Marc Breedlove

And so at that point, the mother's immune system is going to see these male-specific antigens that it's never seen before.

Of course, it's going to regard it as an invader and it's going to start making antibodies to it.

So their hypothesis is that each time a woman delivers another son,

her immune system is going to generate more of these antibodies.

And if she has a subsequent son,

antibodies cross the placenta just fine.

And so, in fact, the placenta very actively sends antibodies across to protect the young.

And so that would mean that her antibodies are going into this third son and somehow altering the development of their brain.

And the strong evidence they found in favor of this is that in women who have sons where there's this pattern that looks like that might have happened,

It turns out they have higher levels than control mothers of antibodies to a male-specific antigen, quite specifically, an antigen to a protein called neuroligin 4Y.

So, neuroligin... Cell adhesion molecule.

Exactly.

You know that neuroligins are important for synapse formation.

And it turns out there are several copies, not unusual in humans.

And this one, neuroligin 4, there's one on the X chromosome and one on the Y chromosome, and they're slightly different.

And so the fact that these mothers are making antibodies to this male-specific antigen and that

In their particular family, it looks like subsequent sons were more likely to be gay.

You can imagine that's what's going on, that her immune system has perturbed the development of that subsequent son enough that when they grow up, they're more likely to be gay.

Whatever the mechanism is, it has to be that it's the mother's body that is remembering how many sons she's carried before them.

and it's got to be the mother's body that somehow is doing something to perturb the development of her subsequent sons to make them more likely to be gay.