Bitch modern humans have been on this earth for six hundred thousand years creating an enormous number of distinct and unique cultures which shape the people living under them. The absolute arrogance to think you can generalize a hundred billion people's worth of experience based on what you've experienced in your one tiny lifetime. Humans are so fucking diverse there is VERY little you can say is "human nature." But no please tell me more about how people are just selfish by default despite all the fucking evidence to the contrary.
See I'm not even 100% sure on this, cause there a plenty of people who (in our current society) are selfish and uncooperative. I'm sure under a better system those same people could be better but the fact that they aren't now indicates to me that even cooperation for mutual benefit has to be encouraged by the environment to manifest.