Human cognition and thinking are much more complex than the cognition and thinking of other primates. Human social interaction and organization are much more complex than the social interaction and organization of other primates as well. It is highly unlikely, we would argue, that this is a coincidence. Complex human cognition is, of course, responsible for complex human societies in the sense that human societies would fall apart if human-like cognition were not available to support them. But this cognition- to-society causal link is not a plausible direction for an account of evolutionary origins. For that direction of effect, there would need to be some other behavioral domain in which powerful cognitive skills were selected, and then those skills were somehow extended to solving social problems. But it is not clear what other behavioral domain that might be, given that we are trying to explain the many particularities of cognitive skills supporting humans’ unique forms of collaboration and communication, including in the end such things as cultural conventions, norms, and institutions. It seems highly unlikely that cognitive skills adapted for, say, individual tool use or the tracking of prey could be exalted in this way for such complex cooperative enterprises. And so, in the current view, the most plausible evolutionary scenario is that new ecological pressures (e.g., the disappearance of individually obtainable foods and then increased population sizes and competition from other groups) acted directly on human social interaction and organization, leading to the evolution of more cooperative human lifeways (e.g., collaboration for foraging and then cultural organization for group coordination and defense). Coordinating these newly collaborative and cultural lifeways communicatively required new skills and motivations for co-operating with others, first via joint intentionality, and then via collective intentionality. Thinking for co-operating. This, in broadest possible outline, is the shared intentionality hypothesis.
Read also: A Natural History of Human Thinking