Selfishness may have been selected for tens of millions of years ago in our evolution, but as pre-humans became social animals it's clear that selfless or other-centric thinking became strongly selected for as well. You otherwise couldn't have a species that's almost entirely other-dependent, throughout the whole life but especially for the first 10-15 years of it.

Humans can't sustainably exist outside of a society.

95% of the "wholesome human moments" are more or less tribalism/nepotism malfunctioning.

It's like when a mother cat adopts ducklings because she came across them shortly after birth. But if it was 8 hours before she'd hunt and eat them. The cat doesn't care about the ducks, it's just a brain chemistry acting in a weird case. Humans are not different, they just imagine their emotions/unconscious social calculations to be a part of themselves.