At the end of Social Climbers, David Attenborough presents us with the skulls of several different primates and arranges them on a boulder by size. The primates with the smallest brains, he explains, live in very small groups. The ones with the largest brains live in very large groups.
Now picture New York City, Mumbai or Tokyo.
Human brains are larger than our skulls. We have expanded them with writing, math, computers and the Internet. As Bruce Schneier recently pointed out while relating Dunbar’s number: “as group sizes grow across these boundaries, they have more externally imposed infrastructure.”