One of the most startling results of the expanded neocortex, the primate brain that appeared about sixty million years ago, is the development of the social group. Primatologists have determined that, due to their highly social nature, all primates need to maintain personal contact with other members of their social group; in non-human primates, this is usually through grooming, activity in which individuals in a group clean or maintain each other's body or appearance. It is a major social activity, and a means by which animals who live in proximity can bond and reinforce social structures, family links, and relationships. Such social groups function as protective cliques within the larger physical groups in which the primates live. Social grooming plays an important role in establishing and maintaining alliances and dominance hierarchies for building coalitions and for reconciliation after conflicts. It is a resource that is exchanged for other resources, like food and sex.

The number of social group members a primate can track appears to be limited by the volume of the neocortex region of their brain. This suggests that there is a species-specific limit for the size of these social groups that is dependant on the average size of the neocortex. Evolutionary psychologist Robin Dunbar has determined that this number is about 150 for both archaic and modern humans. Among hunter-gatherers, this probably defined the upper limit of clans and tribes with several smaller divisions into hunting bands and foragers dependent on what their habitat could comfortably support. Once that level was reached, some of these smaller divisions might break off to form new populations, to follow prey through separate migratory routes or to seek new territory where there was less competition for resources.

According to a recent article in BusinessWeek , despite any accumulation of friends and likes on social networks, 150 is still the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar

What Dunbars research represents is that no matter how the march of technology goes on, fundamentally were all human, and being human has limits, says Dave Morin, one of Paths co-founders. To developers such as Morin, Dunbars insistence that the human capacity for connection has boundaries is a challenge to the ethos of Facebook, where one can stockpile friends by the thousands. Dunbars work has helped to crystallize a debate among social media architects over whether even the most cleverly designed technologies can expand the dimensions of a persons social world. As he puts it, The question is, Does digital technology in general allow you to retain the old friends as well as the new ones and therefore increase the size of your social circle? The answer seems to be a resounding no, at least for the moment.