Do we still have insticts related to 'natural selection' (or whatever it is)?

I probably used all the wrong words, but i was thinking of how when kids are at school when they’re really young (like four or whatever), they will all gang up on the ‘weaker’ people or ones that dont ‘fit in’ with them…
so is this kind of instictive from when we would have had to fight to surivive, and therefore do they instictively reject the people who might have been ‘weaker’ members of the species?

(i dont know if weak is the right word but its all i can think of, but you probably get the idea anyway…)
=)