Personal preferences determine what features are most beautiful to each individual. Whether it be plump lips, lengthy legs, or a voluptuous rear, attraction varies from person to person.

In the early 1990s, Sir Mix-A-Lot released "Baby Got Back," an ode to curvaceous women all over. Men's enthusiasm for voluptuous derrieres has been persistent since then—and Kim Kardashian's Instagram posts show it. It could even be argued that behinds have replaced breasts as the body part that gets the most attention.

The University of Texas at Austin conducted research that suggested men are not particularly attracted to a large derriere, but rather the curvature of the spine that gives the appearance of a voluptuous bottom.

Investigating a group of approximately 100 men between 17 and 34 years old, scientists had them rate the attractiveness of images of a female form from the side. The images had been changed to have different angles of the lower back—causing the woman's rear to protrude in various amounts. In the end, the results were unsurprising: Most men preferred the most extreme angle where the lower spine was curved at a 45-degree angle, from back to buttocks.

Intriguingly, the researchers sought to determine whether or not the size of the posterior makes a difference. Two hundred men were presented with pictures of women with varying booty sizes and curvatures of the spine, and it was found that men were attracted to women with a spinal curve of 45 degrees, irrespective of their gluteal mass.

The reason why guys are adoring those pushed-out tushes could be attributed to ancient influences, as opposed to modern beauty standards. According to David Lewis, lead author of the study, the center of gravity shifts forward during pregnancy, allowing pregnant women to better balance their weight over their hips, thus enabling them to forage more efficiently and guarding against spinal injuries. Subsequently, men who selected women with those traits would have had mates who could better take care of fetus and offspring and endure multiple pregnancies without being hurt.

This furthers a burgeoning array of data that beauty is not completely subjective, or 'left to the viewer', as many in general social science presumed, but has a logical evolutionary justification. This is basically a polite way of expressing that preconceived notions that go all the way back to Neanderthal times.

This contributes to a mounting accumulation of proof that beauty is not completely random, or 'depending on the observer', as many in popular social science accepted, but instead has a consistent functional sense. This is essentially a polite way of expressing that genders roles that reach all the way back to Neanderthal days.