on the one hand we’ve got the westermarck effect, presumably coded for by some gene/s that have been selected for ’cause too much close inbreeding is maybe not a good idea. at the very least, it kinda defeats the purpose of sex (whatever that might be — apart from fun, that is).
on the other hand, we’ve got genetic sexual attraction, presumably coded for by some other gene/s that have been selected for ’cause, well, genes just “wanna” reproduce themselves, and if you mate with someone like yourself you wind up with little ‘uns who have LOTS of those genes.
sounds like an example of intragenomic conflict to me.
(note: comments do not require an email. cute bundle o’ genes!)