The Pith: Human societies can solve the free rider problem, and generate social structure and complexity at a higher level than that of the band. That implies that much of human prehistory may have been characterized by supra-brand structures.
Why cooperation? Why social complexity? Why the ‘problem’ of altruism? These are issues which bubble up at the intersection of ethology and evolution. They also preoccupy thinkers in the social sciences who address fundamental questions. There are perhaps two major dimensions of the parameter space which are useful to consider here: the nature of the relationship between the cooperators, and the scale of the cooperation. An inclusive fitness framework tracks the relation between altruism and genetic relatedness. Reciprocal altruism and tit-for-tat don’t necessarily focus on the genetic relationship between the agents who exchange in mutually beneficial actions. But, in classical models they do tend to focus on dyadic relationships at a small scale.* That is, they’re methodologically individualistic at heart. So all complexity can be reduced to lower orders of organization. In economics a rational choice model of behavior is individualistic, as are the critiques out of behavioral economics.
There are other models which break out of this individualistic box, insofar as they make analogies between organisms at the individual scale to social entities which are aggregations of individuals (e.g., a colony or ethnic group). The society as an organism has an old intellectual pedigree, and was elaborated in great detail by Émile Durkheim. More recently David Sloan Wilson has attempted to resurrect this framework in an explicitly evolutionary sense. Wilson has also been the most vocal proponent of multi-level selection, which posits that the unit of selection can be above the level of the gene or individual. For example, selection operating upon distinctive ‘demes.’ Roughly, a breeding social unit.