just a loose thought, probably obvious

some tree species self-selected themselves for height (ie. there's no point in being a tall tree unless taller trees are blocking your sunlight)

humans were not the first species to self-select (for humans, the trait being intelligence) (although humans can now do it intentionally, which is a qualitatively different level of "self-selection")

on human self-selection: https://www.researchgate.net/publication/309096532_Survival_of_the_Friendliest_Homo_sapiens_Evolved_via_Selection_for_Prosociality