Thank you, tiny. Very interesting.
My original point was that we have evolved to pick up sensory cues from potential sexual partners as indicators of how fertile they are and how sexually compatible we are with them. These include smells, or maybe pheromones, but also many visual cues such as (I assume) colouring, facial features, body shape etc. We're generally turned off by the features which correspond to genes which run in our own families, I think, because incest does not produce offspring that have a good chance of survival and reproduction.
