If the question is why do pictures with nudity on them generate more primary appeal than those with any other subject, the answer surely is: it's our egoistical genes having us respond to a stimulus that promises procreation and thereby the immortality of those selfsame genes.
Aesthetic and sociological ruminations come later.
wow...not sure what to say to that..
so it's our genes trying to reproduce themselves? hmm have to blame the procreation/egoistical genes thingy the next time I surf and the wife looks over my shoulder.