Humans today interact socially with multiple individuals within multiple communities. Consider the number of groups you interact with on a daily basis; family, school, work, friends from sports clubs, church groups, cultural groups, Facebook, Twitter, Instagram etc. Technology means we now have multiple interactions with people who we do not see face to face.
Anthropologist Robin Dunbar from the University of Oxford has suggested that living in larger groups had an evolutionary advantage for our ancestors. The larger group size offered security of food supply and increased protection, Dunbar has also shown that living in large groups requires intelligence. Figure 6 shows that group size in primates is correlated positively to brain size. In particular the noecortex, a part of the brain associated with higher order functions such as sensory perception, motor control, spatial reasoning, conscious thought and in humans, language is larger in comparison to the rest of the brain in species that live in larger groups. Based on correlations with other primates such as chimpanzees who live in groups of 50, Dunbar predicted that humans have evolved to live in groups of about 150 individuals.
A similar relationship with social network size has been found with the brain’s amygdala, a structure involved in functions such as interpreting other’s facial expressions and trusting strangers. Among humans, amygdala size correlates with social network size (Bickart et al 2010), suggesting it too helps with the skills required for a successful complex social life (Figure 7).