You make a good point.
However, we've always been gregarious and the challenges of society are no different today than those of 15,000 years ago.
Sure, we have nuclear weapons today than can anihilate the entire mankind and the vast majority of species in a snap. However the challenges posed to us as individuals from society, have always been there.
Contrary to what many people think, there are such things as alpha males in humans. Just look at the guy who's banging half the chicks at your gym, while you revel in the fact tha one of them smiled at you and *might* be interested in you (Okay, maybe it's not that bad, but you see my point). That's always been there, and will always be there. That's certainly a challenge.
As long as we've been gregarious, we've always had someone tell us what to do. It's not the simple 'go clean after yourself' from your parents, it's the man in charge of the hunting (which always went on in groups of males) telling what you need to do, the girl you're banging telling you what you need to do (honey, there's a big bad wolf outside and it'll eat us both if you dont go outside and kill it with your bring stron bodybuilder arms), there'll be other in your group telling you how to behave (Now dont go 'roun killin the man jus cuz he called you 'Ugha bugga').
It's real simple: Where there's a group of people, or even animals, there are rules to be followed, people to obey to, people to watch out for; there are the ones who have it all and are the envy of all, and there are the ones who are happy just because they have some.
Tens of thousands of years ago, I'd bet you anything if you killed someone unfairly, you'd be dealt with accordingly (read: killed or secluded) by your peers. We've always had an inherent sense of justice which is WHY we have our judicial system, not the other way around (sure our judicial system may differ from the muslim one, but it's still there).
We've always had events like parties - Our ancestors, who often went for weeks with little to no food would often celebrate and eat their asses off when there was a big harvest (when a whole bunch of animals were killed, and so forth). That would carry them for a while longer.
We've always had leaders - how else do you get hundreds/thousands of people, each wanting to do things their way, to do what needs to be done when it needs to be done?
All the infrastructure we have now, is the infrastructure our ancestors had (the ones who didnt have things like an equivalent of a judicial system, a place to learn a trade such as making arrows, using animal skin to cover your privates...would be anihilated by tribes with a keener sense of order and organization, as this order allows them to evolve further and develop stronger defense and attack mechanisms). Weapons or no weapons, military or no military, college or no college, work or no work, these needs have always been there, and their equivalent was there in any group of people or tribe that was to survive for any reasonable period of time.
Good post though. Im sure if our ancestors knew of beer, they'd have had invented nightclubs and spent their friday nights getting hammered till daylight, and then forget all about it till the coming friday, lol.