But you would presumably find it easier to cooperate with her than a stranger picked at random because you have a shared link. It's not so much that one thing

But you would presumably find it easier to cooperate with her than a stranger picked at random because you have a shared link. It's not so much that one thing is better as it is that you are more able to help those closest to you, in roughly the order yourself - family - community - country. Without some degree of nationalism it is hard to justify things like universal healthcare, the welfare state or even politics on a smaller than global level. We invest in our communities because they invest in us.