I really can't say, but considering how primal it feels to look at a woman's butt, I'd guess it's something primal within us men. Who knows, maybe subconsciously we think the woman will be more fertile or doggystyle was the position for cavepeople and a nice round booty looked like it could take the pounding. Who knows. All I know is that I love to look and I hate to say, stare, b/c it's not a good thing when you get caught. *l* For me the bigger and more round the better. I'm with Sir Mix-a-lot, I like big butts. *l* Although, most butts turn me on, b/c they sooooo sexy. I especially love it when it shakes. Very hot and sexy.