The unusually large brains in primates has long been a puzzle. Some studies suggest that it may have been the particular demands of more intense forms of pair bonding that was the critical factor that triggered this evolutionary development. Primate sociality, indeed, differs from that found in most other birds and even other mammals. The brain is second only to the heart in terms of running costs per unit mass. It has long been a puzzle as to why the brain has continued to grow larger than the minimum size required to stay alive. There are many different theories that aim to understand both social cognition generally, and, in particular explaining differences between humans, apes and monkeys.

Friendship has often been called the single most important factor influencing our health, well-being and happiness. A person’s network is, of course, of very high importance. There are processes that give rise to these patterns and their evolutionary origins need to combine multidisciplinary insights. Much evidence has emerged on the important role of friends both in the sphere of moral and emotional supports but as well as protection from external threats and the stresses of living in groups.

Dunbar’s Number

Dunbar’s number is that there is a limit to the number of friends we can manage at any one time. This particular limit is imposed by a combination of time and the cognitive demands of maintaining various relationships. Typically, the average size of personal social networks seems to be around 150 people. This is also a common size for human organizations, including community size in hunter-gatherer societies and village size in many small-scale traditional and historical societies. This number seems to hold true cross culturally. However, variance is high and thus the average size may range from 100-250 people and this is largely attributed to personality type (i.e. extraversion).

Social Promiscuity

The average 20-year-old has more friends than the average 60-year-old. This is often because many young adults are more socially promiscuous meaning that they search widely to find lifelong friends and romantic partners. Gradually, as one ages many relationships are shed to concentrate on relationships where time and effort is both 1) available 2) most important.

How Time Limits Friendship Networks

Time is a limited resource and relationships require a time investment. Each individual makes conscious choices on how to distribute his or her available social effort or capital across their network. The idea of a social investment has real implications. Mentalizing has been shown, using both reaction time tasks (RT) and fMRI to be more cognitively demanding than working with more conventional physical facts. There is also known to be a consistent upper limit of about four on the number of people that can be involved in a given conversation.

There are a lot of cognitive demands of maintaining friendships that underscore the “social brain hypothesis.” This hypothesis correlates brain size and social group size in primates. Many neuroimaging studies of humans have now shown that individual differences in social network size correlate with neocortex volume. This hypothesis is especially interesting given that it applies not just between species but also within species.

The Pillars of Friendship

-Place of Origin
-Educational History
-Sense of Humor
-Worldview (moral, religious, political etc.)

  1. Lang