Evolution - at a species level or a societal level - has no “guiding hand”. It throws shit at a wall to see what sticks, and the best-adapted variants tend to propagate.

Selfish behavior is very powerful in a large and strong society where most people are producing more value than they’re consuming. There’s so much wealth to be found that if you don’t care about the enemies you make, you can just jump from victim to victim as you amass power faster tab the people you leave behind. The problem is, this drives the society towards no longer being one of such surplus.

In a smaller society where people are largely just surviving, selfish behavior will cripple your own ability to survive. If everybody has only a modest surplus, they only want to share it with people they can trust to return the favor when they’re the one in need. If you make enemies with everyone in a small community, you’re going to have a hard time finding community support.