[BruiseLee]

Well we did evolve big buttocks (bigger than other primates) that are apparently useful for sitting for extended periods of time.

[shock]

I'm not sure what you mean. In people who sit for long periods of time the gluteus mucles (buttocks) become atrophied. Do you mean the ass fat is useful for sitting?

Maybe you're just making a joke and I'm not getting it.

[yladiz]

It's likely more to support walking (and running) on two legs for extended periods of time.