Beginning in the early 1970s, cognitive scientists began studying two opposing hypotheses to explain of the anatomical differences between the brains of humans and the brains of other primates: the social brain hypothesis, which posited social factors are the primary force driving the development of the human brain and the ecological brain hypothesis, which posited ecological factors. After decades of study, the social brain hypothesis was best supported by the evidence (Dunbar 2007). Having discovered the origins of humans’ unusual brain development; they have since turned attention to understanding social perceptions, cognition, and behaviors.
Humans’ social interactions depend on several complex brain functions including the perception of subtle signals, the recognition of patterns, the construction of and recollection of complex ideas, and the control of actions in response to all of these. Brains are compartmentalized organs; different sections are associated with different cognitive functions, and when a section of the brain is more active, several measurable changes occur in that section. Most social interaction is associated with increased activity in neocortex of primate brains. (The neocortex is the outermost layer of the cerebrum. You can locate the cerebrum under your skull by pulling a baseball cap down tight over your head—it will just about cover the part of your skull protecting your cerebrum.)
In primates, the size of the neocortex is positively correlated with social interactions; the bigger the neocortex, the greater social interaction observed in the species. Of the primates, humans have the largest neocortices. The social interactions that are associated with the size of the neocortex include the size of the group with which an individual can maintain grooming relationships, the ability of an individual to interact without using force, and the frequency of play. It turns out that “playing well with others” is important for human survival and human brains are designed to play well with others.
The highly social groups that characterize human populations also depend on human beings’ theory of mind. According to this theory, a human has the capacity to be aware of what he or she is thinking and at the same time understand that other humans are also thinking, and the other may be thinking either the same idea or a different idea. Steven Pinker (1997), a professor of psychology at Harvard University, explains this ability to guess what others are thinking with these words:
We mortals can’t read others people’s minds directly. But we make good guesses from what they say, what we read between the lines, what they show on their faces, and what best explains their behavior. It is our species’ most remarkable talent (30).
As Pinker suggests, theory of mind is a component of the social brain appears to be uniquely human.
Dunbar, Robin. 2007. “Brain and Cognition in Evolutionary Perspective.” In Evolutionary Cognitive Neuroscience, edited by Steven Platek, Julian Keenan and Todd Shackelford, 21-46. Cambridge, MA: The MIT Press.
Pinker, Steven. 1997. How the Mind Works. W. W. Norton & Company.