Human evolution is marked by the emergence of a special kind of social–cognitive process, unique to hominids: distributed cognition, performed in mind-sharing cultures. Human social groups are more cognitively complex than others, but, at the time of our emergence as a species, human social groups were not necessarily larger in population than their predecessors. The increased complexity of their cognitive system was inherent, not so much in group size, but in the nature of the cooperative, interactive social cognitive processes that apparently characterized species Homo from the outset.