Why is it that some people feel compelled to send each other photos of their naked bodies? According to this analysis found on Wired, turns out that the sexting is a primal urge that's more connected to "the design of our sexual brains" rather than celebrity culture or digital connectivity. And that men and women feel compelled to sext based on different "primal" reasons.

Research shows more than half of women's sexual fantasies "reflect the desire to be sexually irresistible."  As for men, they just pretty much just want to show off their wang, similar to how male monkeys and apes display their penises to females to display their sexual interest. This may be why the internet is never short in supply of penis photos. The writer concludes:
"Though hordes of men pay to peruse amateur photography depicting the anatomy of ladies, not a single website collects cash from ladies interested in surveying amateur photography of phalluses. It is this marked gender difference in interest that reveals the dichotomous evolutionary pressures shaping male and female exhibitionism: Women feel the conscious desire to catch the universally attentive male eye, but since women's erotic attention is rarely ensnared by a penis, the male exhibitionist urge is comparatively vestigial."
Of course, there are exceptions to this analysis. Just like how not all women feel the need to distribute shots of their tits just for a little attention, we're guessing that not all guys would be eager to have pictures of their penis floating around the web.