@DrDanMarshall
Nepotism is not necessarily a human universal; it is a product of hierarchical societies rather than an inherent aspect of human nature.
Regarding "shared collective interests," it is the interests that benefit the community as a whole, rather than just individual members.
@Radical_EgoCom If I am an egotist, why should I care about the needs of the collective so long as my own needs are being served? If I am not egoist, what causes me to not be an egoist? (We have two, three, answers: kin selection, the bond between married co-parents, imagined communities. Do you have another?)
"Nepotism is not a human universal." Again, talk to the anthropologists, and show me an existence proof.