I came here to say essentially this. But what is the name of this process where groups of people select for variety instead of optimal individuals?
In a nutshell - "The problem with group selection is that for a whole group to get a single trait, it must spread through the whole group first by regular evolution... a group where altruism was universal would indeed outcompete a group where every creature acted in its own interest, so group selection might seem feasible; but a mixed group of altruists and non-altruists would be vulnerable to cheating by non-altruists within the group, so group selection would collapse."