It's a glorious time to be an ass man: Nicki Minaj exists, yoga pants are a thing, and women everywhere are squatting their way to more shapely backsides.
But of course, your obsession with the female butt is nothing new. In fact, it's primal, says David Buss, Ph.D., a psychology professor at the University of Texas at Austin.
You're drawn to a woman's heinie for the same reason you're attracted to her breasts, hips, and a little waist: because those traits would have been indicators of fertility to your ancient ancestors, Buss says.
Man evolved to seek out women who could procreate, Buss says. If a woman has a full tush, that's a signal to your primitive brain that she's probably carrying enough fat to become pregnant, he says. And if her bum is perky and round, that means she's probably young—which, in caveman days, would make her a good candidate to carry your cavechild.
And then there's the dirty factor.
"It's a taboo," says Eric M. Garrison, a sex expert and author of Mastering Multiple Position Sex. "We're not allowed to go there. And when it comes to sex, there's something animalistic and dirty about mounting from the rear."
Geography and culture can sway just how into fannies you are. For example: 59 percent of Argentinian men dig butts even more than boobs, a University of Buenos Aires study found. But British men don't pay all that much attention to the booty, according to University College London research.