I'm a software engineer. I have a blog at niknoble.com.
My best guess is, the genome can guess where concepts are going to form, because it knows in advance:
Loosely speaking, it feels like knowing the relative distances between concepts should determine the locations of all of the concepts "up to rotation," and then knowing the locations of the low-level concepts should determine the "angle of rotation," at which point everything is determined.
I think this is how the brain does sexuality, as an earlier commenter mentioned. For males, it guesses where you will place the concept "I am having sex with a woman" and hardwires that location to reward.
I think fetishes and homosexuality (which are probably the same phenomenon) arise when these assumptions break down and you place your concepts in unexpected places. For example, the concept of "man" and "woman" are symmetrical enough that it may be possible to switch their locations, depending upon your experiences as a young child. This propagates up to higher level concepts so that the address which would have held "I am having sex with a woman" instead holds "I am having sex with a man."
I really like this as an explanation for homosexuality in particular, because it explains why evolution would allow something so apparently counterproductive. The answer is very LessWrong in flavor: it's just an alignment failure. If you make a truly flexible intelligence that learns its concepts from scratch, you're going to have a hard time making it do what you want. Evolution was ok with the tradeoff.