Humans are, scientifically speaking, the ape species most obsessed with sex (narrowly edging out our close relatives the bonobos, who’ve also been known to get pretty freaky). We’ve also evolved to have more visual erotic triggers on our bodies than any other primate. This includes having fuller lips, bigger penises (in males), more prominent breasts (in females) and scattered tufts of pubic hair to signal all the bits we should be looking at.
But why is it that some male humans zoom in further on that sexual obsession, becoming fixated on specific, isolated female body parts? What makes one Homo sapiens define himself as a “boob man” while another will testify to being way more fascinated by a woman’s butt, while a third specimen isn’t seeing anything but her legs? To find out, let’s take a look at each type of guy in turn.

The Boob man

Although the media has focused increasingly on butts in recent years, boob men are still the largest group of body-part worshippers. But even after decades of debate, scientists haven’t reached a consensus as to why it is guys really dig breasts. “The most likely explanation is that women’s breasts develop as they reach adulthood, and so larger breasts signify that a woman is likely to be fertile,” says Robert Burriss, an evolutionary psychologist at Basel University, Switzerland, who hosts the monthly Psychology of Attractivenesspodcast. Mammary glands in human females have evolved to be far more prominent than in other primate species. This development, Burriss suggests, was caused by thousands of generations of men preferring more noticeable breasts.

In spite of the cliche, however, this doesn’t necessarily mean that bigger is better. As Burriss points out, “Research on breast-size preferences is mixed.” Some investigations have suggested that men are more attracted to smaller cup sizes than the management at Hooters would have you believe: One such study, conducted in 2006 at University College London, asked 114 students to rate women’s profiles in silhouette and found “an overall preference for small breasts,” concluding that breast size was among the “minor cues of female physical attractiveness.”

So what are men looking for?

According to some earlier research, it may be symmetry, rather than bulk, that’s the real aesthetic driving male boob preferences. _“Choosy males that prefer females with symmetrical breasts may experience a direct fitness benefit in terms of increased fecundity [that is, fertility], and an indirect benefit in terms of attractive or fecund daughters,” _researchers from Denmark, Spain and New Mexico wrote in a 1995 paper.
Let’s put that in less creepy terms: Having either sexier or more fertile daughters results in their hottest mate-attracting features being passed down to more and more women through subsequent generations. What you end up with is the evolution of the perfectly balanced boob, all driven by the same unconscious desire that informs most men’s actions:

The need to make sure their DNA is carried as far into the future as possible.

By choosing a mate with near-objectively attractive features — in this case, symmetrical breasts — they’re improving the chances of their offspring also being attractive, and passing on the genes once again.
It’s the perfectly symmetrical circle of life.

The Butt Man

The science is even less conclusive on what’s going on in the mind of a derrière dude, although there are a number of theories. One speculative notion, popularized in Desmond Morris’s 1967 book The Naked Ape, is that the appeal of a curvy backside goes back to a time in our evolutionary history before face-to-face sex became standard — back when our female ancestors’ sexual signaling was optimized for rear mounting (i.e., doggy style). Butt men find butts hot, essentially, because that’s what our ancestors were looking at as they approached their mates for sexy-times.

Burriss, on the other hand, points to the way fat is distributed in the female body as the likely source of rear-end appeal: “Women who are most fertile tend to have a waist-to-hip ratio of around 0.7 [a waist that’s 70 percent of the circumference of their hips]. This explains why the ‘hourglass figure’ is so attractive to men.”

But is it just the implications of fertility that makes some men so attracted to those hips? There is evidence that ass appreciation isn’t always innate — it can be influenced by the society you grow up in. Eye-tracking research from the University of Buenos Aires from 2012 seemed to confirm the legendary reputation Argentinian men have for being obsessed by women’s posteriors: In the experiments, 59 percent of the men who took part preferred booty to boobies — a far higher number than in similar tests in other countries, where breasts are almost always preferred. This suggests that in Argentinian heterosexual society, the preference for butts is, at least in part, determined by cultural norms: Basically, they look longer and more longingly at butts because that’s what every other man around them does.

The Leg Man

As to why some men are into legs, the psychologists are pretty much stumped. So instead, we turned to a true lower-limb connoisseur for insight, Jason Timson, a London-based photo editor who has worked for men’s magazines such as Maxim and various celebrity image libraries, to unpack his personal love of legs:_ “Long legs are best, but proportion is key — Kylie Minogue, for example. Well-toned calves emphasized by a high heel are a winner in my eyes.”_

It may, indeed, be the high heel that’s the most important part. While Burriss doesn’t see — from a psychological perspective — women’s legs as a particularly important cue to their overall attractiveness, he says there’s research that shows slipping on high heels will make the same woman around 20 percent more attractive in men’s eyes. He adds, “A field study in Franceshowed that when a 19-year-old woman dropped a glove on the street, 62 percent of male pedestrians stopped to pick it up when the woman wore flats, but 93 percent did when she wore heels.”

It seems the leg man is entranced not so much by the length of the calf and thigh on display, but by the sway of their owner’s gait:_ “Men and women walk differently, with women more likely to rotate their hips and take shorter strides,”_ explains Burriss. Since heels exaggerate this style, “women who wear high heels may be perceived as more feminine.”

BONUS ( yes I'm a Butt Man)