Unto Others has a section in it that has always stuck with me about division of labor in large groups vs small ones. Members of small groups tend towards being jacks of all trades, and their roles and duties look very similar to one another, and few functional distinctions can be made between them because anyone might have to do anything at any time. Large groups have a lot more specialization of labor within their structure.

It's not specifically a book about humans, more of a dry text about the evolutionary theories surrounding altruism. Humans demonstrate it well, but it's a dynamic that other social animals like ants demonstrate too.