The other sexy and controversial body part must be the butt. We know already so many men are so attracted to female butt but have you ever thought why?
Part of the reason could even be about evolution. Your butt has nerves, muscle and fat which stimulate nerve endings which create sexual pleasure when touched or rubbed. The butt is believed to be the area where more nerve endings occur which increase sexual arousal between two genders. The size and shape of women's butts had ways of indicating women's fertility as humans were progressing evolutionarily. Men are attracted instinctively to body parts of females where it can be used to indicate whether they are capable of being reproductive. Certain cultures also viewed rounder butts to be sexually attractive rather than non-rounder butts which would not be indicative of having sufficient fertility to be able to bear a male child.
Other than the butt being a sexual organ, men could be attracted to butts because of butt sex. Some people may even find butt sex to be more arousal than penetrative sex as anal nerves would be stimulated.
Nonetheless, everyone has different preferences and sexual orientations. It may be that some people would like butts more than others and other people may prefer other body parts. Due to having personal interests, each individual would surely find particular people to have different interests; when pondering why men are attracted to their butts during sex, it would surely be only one part of a huge puzzle.
