Hi Helen, I think the best explanation for what you are describing comes from the social psychologist Muzafer Sherif's work on Realistic Conflict Theory. Essentially, the idea is that you work with a group to obtain resources, and when multiple groups are in competition for those resources, it builds conflict among the groups; as a result, you support your group (what you are calling nonkin nepotism). Read up about Sherif's "Robber's Cave" experiment. It's a really interesting experiment that was very important in the field of social psychology and our understanding of group dynamics. Here is a link to a brief synopsis of the experiment: http://www.simplypsychology.org/robbers-cave.html

Group selection then. Even worse. Still non-kin.

This has nothing to do with group selection. If you are after a strict "selfish gene" theory to explain this: Humans are social creatures and often work together to obtain resources because it benefits each individual; there is selection in favor of cooperative behaviors, but in the event that working as a group no longer allows individuals to benefit, they will stop.

But honestly, I'm not really sure it's at all helpful to try to explain human behavior through evolutionary theory, particularly when you seem so set on a simplistic understanding of the issue at hand. I'm not going to argue the point here, because many people have invested a lot of energy doing it elsewhere and you can find that on your own (look up the debates between the proponents and critics of the field of evolutionary psychology).

I do think it is highly relevant to think about human behavior from a evolutionary theory perspective. It is obvious that the group, what ever genes in it (!?), is very important for us at individual level and also make sense when resources are limited. I looked up the experiment Jeremy and it is interesting. It is just that animals usually work together in groups of relatives. Maybe we humans did that in the past too and part of our strong non-kin social need may comes from that.

Reciprocal altruism.. there you go.. that's one explanation.. tit for tat.

http://en.wikipedia.org/wiki/Reciprocal_altruism

@Jermeny Evolutionary story telling is a bit dangerous, but fine and helpful if you want to generate hypotheses. There are ample of theories that do explain these patterns, a whole field of theoretical biologists works on them. Saying it is the case when evidence is in line with one of these theories is not very helpful, generating hypotheses is. You can just suffice by saying men like women with red lips and thats the end of the study instead of making a big fuss about it that we evolved a love of red for whatever reasons etc.., without actually testing that fact..

it does goes both ways Filippo.

Mirre: thanks! Reciprocal altruism i ts. Partnership=Friendship. Research on cleaner fish may help us to understand our own social behavior. These fish interactions seem rather professional. They just have to watch out for cheaters.

Exactly, but that is how it looks. In the case of humans, what does the one in power gets? short-term, long-term. or nothing. I cannot see that the genes are secured this way. Or maybe, in an odd way.

Don't think of human groups under "group selection vs. individual selection" think of groups as where an individual obtains resources. A human group is a "resource". Except for rare places like the extreme North, our greatest competition and our greatest resources come from "other humans". They block resources (own) and they enable resources to be obtained (purchase). Your "job" is your resources, as well as any "real property", and you have to be "useful" to the group. Groups may compete, that is true, but within the group there is a hierarchy of pay scale. When economic times are "tight" who get laid off vs. who stays is rough selection, and often there is nepotism involved, especially in family bossiness. Selling ones valuable skills can highly increase resources, Why back in 1994 I had to address this in Sociology, because back then there was a "political" problems between Sociology and Evolutionary Biology.

Fain, H.D., Burns, T. J., Sartor, M. 1994. Group and individual selection in the human social environment: from behavioral ecology to social institutions. Human Ecology Review 1994 1(2):335-350.