He does rely on anecdotal evidence but also expresses doubt how a gay gene would carry since gays cannot naturally have children unless they override their natural sexual preferences for procreation.

There's a plausible genetic explanation, and for "simply gay" it's pretty straightforward: the same gene that would cause men to be strongly attracted to men would also cause women to be strongly attracted to men - and this causes enough of a boost to the number of children a woman has for that gene to persist.