I don't know, but since there obviously is a way that our brains distinguish between men and women and assign sexual attraction based on that distinction, I don't know that the mechanism is relevant to this discussion unless you're really into writing image classification algorithms.

What I'm saying here is that I tend to treat a lot of complex brain functions, like image recognition or motor control, as primitives that we get for free from nature. This seems to be the only way to make a cache-lookup-based brain work in practice.