A lot has been made of that recently. A point I often make is that we still have the instincts of our Mesolithic ancestors: great apes who lived in packs of extended family units, and of necessity regarded other packs as trespassers on the finite capacity of their hunting and gathering territory. Everyone we were willing to trust and care for was someone we were intimately acquainted with, and usually a close blood relative.
The permanent settlements and agriculture of the Neolithic Era required us to live in trust, harmony and cooperation with people who were not part of our family. The cities that were built at the end of the Stone Age required us to extend that peace to a large number of nearly total strangers. Nations and empires forced us to make nice with people who look different, speak different languages, and worship different gods. Eventually we had to manage a civilization by working with people we never even met personally.
Today we have to live in brotherhood with people on the opposite side of the planet, people whose names we don't know, people who are really nothing more than abstractions to us. And we do it! Sure, the system breaks down, we've had many nasty wars, and there's still a lot of ethnic animosity.
But what's wondrous is that for the most part the system really works; we've transcended our instincts. Since our species' violent tendencies peaked in WWII, we've become more peaceful and cooperative with every passing decade. We're still Mesolithic hunter-gatherers born with an instinct to trust only a few dozen close kinfolk, yet towns of 20,000 people thrive with very little governmental oversight, and cities of millions manage to muddle along productively with remarkably little breakdown of the social order by Mesolithic standards. The entire race is inexorably assimilating into one giant community, one single tribe.
Our massive forebrains give us an ability unique in the Animal Kingdom: We can override our instincts with learned and reasoned behavior.
