pygophilous, pygophily 1. Loving sexy buttocks. 2. Men who have a special attraction for female buttocks.
I suppose the shape of the buttocks, like all other features, is determined by genes. Excepting of those few unfortunates who have no readily distinguishable bottom and those whose bottoms are super-sized by a diet of fried foods, I think most are note worthy. There is no need of gene splicing to improve the lot.
Girls spend hours of their teenage years modeling their bottoms in the mirror in their bedrooms. They know exactly what they are showing at all times.
Here are a few images that have been posted on OBB in the last few years. No intent to pick the best, just a variety.