I'd expect that your brain has to figure out who it's attracted to. The fact that on the order of 90% of the population reports themselves as straight (surely s

I'd expect that your brain has to figure out who it's attracted to. The fact that on the order of 90% of the population reports themselves as straight (surely some closeted and bisexual folks in straight relationships included in that number, but it's probably not too far off) suggests that evolution has largely organized us well for reproduction, but obviously isn't perfect. I mean, when I find men attractive it's often for the same reasons straight women do, modulo individual differences in type. That being said, I suspect you're right that evolution is much more constrained than evo-psych explanations give it credit for (though I wonder what a non-gene-centered theory of evolution would look like!). There are only 20,000 genes or so, and most of them are just simple recipes for necessary proteins. Obviously evolution does a lot with a little, but it still strains credibility to suggest that every aspect of human behavior is so well controlled by so few genes.