How did human butts evolve to look that way?

C C Offline

EXCERPTS: What makes humans different from other animals? Ask any ten people and you're likely to get ten different answers, ranging from our relatively large brains, to our incredible use of language and symbols, to our ability to dramatically modify the world around us. But if you asked me, I'd say that it's our butts.

Take a look around the animal kingdom. Even our closest living relatives among the great apes (chimpanzees, bonobos, and gorillas), don't have proportionally as big butts as humans do. The main reason for this probably comes down to our unique style of locomotion. We're the only mammals alive today whose primary way of getting around is walking on two legs. And becoming upright bipeds has had some important consequences for our derrières.

[...] The pelvis is made up of three parts: two innominates (or "hip bones") and the sacrum. Each innominate is also made up of three bones (the ilium, ischium, and pubis) that fuse together during growth and development. And it's the ilium that's the real difference-maker between us and our ape relatives. ... The ilium has generally gotten shorter, broader, and more curved over time, which means our butt has been on a multi-million year journey to becoming the lyric inspiring piece of anatomy that it is today.

The last thing that helps make human butts unique is the fat - which might also have something to do with us becoming bipeds. [...] Our bodies store energy as fat, and we have a relatively high percentage of it for a non-aquatic mammal. This has led anthropologists to suggest that our body fat helps buffer our metabolically-expensive brains against lean times...

[...] While all of these changes sound pretty great, our peculiarly human arrangement of muscle and fat on our backsides comes with at least one major butt-related downside: a messier pooping situation than many other primates have. Picture a quadruped, like a chimp - its trunk and legs meet up and form an angle, with the butt at the corner and its anus pointing more outward. And that opening isn't trapped between large buttcheeks. For us, there's no angle - it's just a straight line. By standing up, we've rotated the anus to point more downward, then added additional padding around it. Hence, messier pooping. Thanks, evolution... (MORE - details)
confused2 Offline
If you watch girls jogging (in the interests of science of course) you see there is a considerable difference between them what wears a sports bra and them what doesn't. I could be wrong but I suspect the difference isn't just in the entertainment value - the presence of mobile fat in the chest region may actually be a small (or large) handicap when it comes to running. If you planned to hunt or escape hostile things by running then I suspect fat stored in the butt region would be much less of a handicap for the runner than fat stored anywhere else.

In the days before food preservation a .. no no, I'm not going there.
Zinjanthropos Offline
Whether 90 lbs or 900 lbs, a woman’s posterior is easily recognizable by men. Of course mistakes can be made but for the most part guys get it right. Perhaps an approach from the rear left little room for an ancestral error if the intention was to pass on some genetic material. 

Does sex change surgery involve reshaping the butt too?

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