Trees don’t need brains, and solitary creatures can get by with relatively simple ones. Social animals, however, require brains with additional, flexible capabilities.
The evolutionary anthropologist Robin Dunbar (1993, 1996) compared the brain sizes of many different species to see what behavioral differences went with bigger brains. (Brain size is always adjusted for body weight, because bigger animals generally have bigger brains. For example, human men have bigger brains than women, but that’s mainly because men are bigger all over.) Did big-brained species eat better foods, or more complicated foods such as fruit (which ripens and turns rotten rapidly)? Did they roam over larger territories, so that they needed a bigger brain to maintain a more complex mental map? No. What Dunbar found was that bigger brains were mainly linked to having larger and more complex social groups. Small-brained animals tend to live alone or in small, simple groups, whereas bigger-brained, presumably smarter animals have more relationships with each other and more complicated groups (such as those with dominance hierarchies and competing allies).
Th is conclusion is highly important. The human brain did not evolve because it helped us outsmart lions and tigers and bears, or build better shelters, or invent calculus. It evolved mainly in order to enable human beings to have rich, complex social lives. Th e brain is not for understanding the physical world around us, so much as it is for understanding each other. It is not so much a calculating brain or a problem-solving brain as it is a social brain.
Again, what is inside is there to enable the creature to satisfy its needs and, ultimately, to survive and reproduce. Social animals (including humans) accomplish those things by means of social interaction. Much of what goes on inside the human mind is designed to help the person relate to others. Social psychologists spend much time studying people’s inner processes, including their thoughts and feelings and, recently, how human brains work. Th ey study those things because inner processes serve interpersonal functions. Remember that phrase; it will be one of the themes of this book, and it is a good basis for understanding social psychology.
