Darwin is rubbish. He just rediscovered an ancient line of thought which the ancient Greeks had been onto thousands of years before him:
en.wikipedia.org
Proposals that one type of animal, even humans, could descend from other types of animals, are known to go back to the pre-Socratic Greek philosophers. Anaximander of Miletus proposed that the first animals lived in water, during a wet phase of the Earth's past, and that the first land-dwelling ancestors of mankind must have been born in water, and only spent part of their life on land. He also argued that the first human of the form known today must have been the child of a different type of animal (probably a fish), because man needs prolonged nursing to live.[8][9][7] In the late nineteenth century, Anaximander was hailed as the "first Darwinist", but this characterization is no longer commonly agreed.[10] Anaximander's hypothesis could be considered "evolution" in a sense, although not a Darwinian one.[10]
As far as what you're referring to, that would be "tribalism" anyway, not "selfishness". Such as how, in ant colonies, ants other than the queen are forced not to procreate, because their individual or "selfish" interest threatens the welfare of the tribe:
Explore worker ants' reproduction strategies as they face repercussions from their colonies for attempting to procreate.
www.discovermagazine.com
But, obviously, animals and more barbaric cultures do things in the interest of their "survival" that more enlightened cultures would find barbaric, and do not do. And the enlightened cultures are more successful in the long run.
Such as how, if we look at multicultural nations like America and Japan, we see huge technological and cultural advancements. While "tribalistic" cultures which don't integrate with the world around them, like North Korea or primitive African tribes remain regressive and unadvanced.