Also there's the possibility that the strongest ones will prevail upon the stupidest ones. no?
Not really. Smarter people have things to create, but dumb people have nothing to do but lie in wait and try to steal.
Think about it: the best peoples originated in areas where they were hard to reach.
They ran away from the masses so they could exist without morons stealing, lying, raping, cheating, and being otherwise parasitic.
It's easy as hell to live near the equator. Great civilizations arising there are few and quickly degenerated.