Jean-Paul Goude/Paper

OK, so by now everyone has seen Kim Kardashian's booty-baring, Internet-breaking cover for Paper magazine. And sure, seeing Kim's bare bum is a shocker on some levels, but what's behind the deeper, visceral reaction to the pics? Science!

Nowadays -- if popular music is to be believed -- we're currently "all about that bass." Prominent posteriors are everywhere on the Billboard charts -- Nicki Minaj’s “Anaconda” ode to big butts, Meghan Trainor’s “All About That Bass” curvy-girl “bringing the booty back” anthem, and, of course, Jennifer Lopez and Iggy Azalea’s “Booty” celebration. (Not to mention Beyonce’s always-revered rear.)

Butts are clearly having, well, their biggest moment ever, a fact that evolutionary psychologists like Gordon G. Gallup Jr. of the University of Albany finds unsurprising. According to Gallup, men's attraction to women with bigger butts -- see Trainor's assertion that "boys like a little more booty to hold at night" -- is woven into their genes.

Evolution isn't about survival of the fittest, Gallup told MTV News. It's about pairing your genes with someone "who has genes that code for health and vitality and fertility." In some cases, that means all the right junk in all the right places.

"The reason narrow waists and broad hips are so prized -- the reason males rate these as being attractive, even though they don't have any insight into why they do -- is twofold," he said. "It means, if a woman has a narrow waist, she's not pregnant. And if she has broad hips it means that the underlying skeletal morphology is probably such that she'd be able to have a relatively unencumbered childbirth."

Translation: An hourglass shape indicates that a woman is single and ready to mingle -- or, you know, to birth healthy spawn.

And speaking of those babies, women with big butts apparently have smarter kids -- and tend to be more intelligent themselves. The fat stored in women's butts -- called gluteofemoral fat -- has unique long-chain polyunsaturated fatty acids (science!) that are important for babies' brain development, Gallup said.

"They've done research that shows that as gluteal femoral fat stores go up, so do the cognitive scores of babies born to women with large hips," Gallup said. "And not only are babies advantaged, but even the mothers are. Mothers with large hips and butts also have a significant advantage on cognitive tests."

Gallup said that men aren't aware of these rather logical reasons why they're attracted to larger butts ... but attracted they are. So keep watching those "Anaconda" and "Booty" videos. Science approves!