Actually, let me get a redo - I think I can do better than that last one. You don't even have to read this if you don't want to but I'm enjoying trying to explain my thoughts on this in a way that makes sense to a fellow autistic person:

Engaging in selfishness alone is a high risk behavior. When you exploit the fellow members of your tribe, you risk ostracization for minimal reward. Selfishness occurs in all species to varying degrees, but this explains why ruthless selfishness is not a common trait in the most evolutionarily successful species.

Let's say you're in an early modern human tribe. While engaging in selfish behavior alone is risky, engaging in selfishness as a group reduces that risk - every person you add to your group decreases the risk of ostracization or retaliation and reduces the numbers that could oppose you. There is less reward, though, unless:

A.) You come to dominate the group, and the rest of the tribe returns to its initial state with a little less resources to go around,

or

B.) You work together with the group to take more reward than you were previously taking. The risk increases the more you take, but it is still lower by nature of the power in your group's growing numbers.

Option A leads to the cycle repeating on a smaller scale within the selfish group while simultaneously encouraging the emergence of new selfish groups to compete with. That leads us to our present point in human history. Power struggles within power struggles within power struggles.

Option B leads to two possibilities:

B1.) A return to the original state as the roles of the groups come to be reversed, exploiter becoming exploited, leading us again to the cycle repeating.

Some people will switch groups, slightly altering the way this dynamic plays out. Ultimately the most ruthless still come to dominate unless we reach...

B2.) A return to our initial state of total equality with the newfound tools born from generations of struggle resulting from the conflict of the self and the other.

And so history ping-pongs back and forth, briefly fractalizing as empires rise and fall, until we arive at option B2, communism.