There is a short piece in the New York Times Sunday Magazine by Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology.
In it, Tomasello suggest that individual human infants are not much smarter than adult chimpanzees or orangutans. What makes humans more successful, he suggests, is our ability to form social groups and our use of communication (including not just language but also paralinguistic communication). Writes Tomasello:
Human infants, in addition, gesture and talk in order to share information with others — they want to be helpful. They also share their emotions and attitudes freely — as when an infant points to a passing bird for its mother and squeals with glee. This unprompted sharing of information and attitudes can be seen as a forerunner of adult gossip, which ensures that members of a group can pool their knowledge and know who is or is not behaving cooperatively. The free sharing of information also creates the possibility of pedagogy — in which adults impart information by telling and showing, and children trust and use this information with confidence. Our nearest primate relatives do not teach and learn in this manner.
Aristotle defined human beings as zoon politikon, the animal that lives in cities. Linguist Paul Chilton (among others) suggests that it is our capacity for abstract language that makes humans successful as political animals - that is, among other things, it allows us to work together in groups. Similarly, Tomasello concludes
Human beings have evolved to coordinate complex activities, to gossip and to playact together. It is because they are adapted for such cultural activities — and not because of their cleverness as individuals — that human beings are able to do so many exceptionally complex and impressive things.