While it may be intuitive that social relationships require brain power, Dunbar explained a way to talk about social dynamics.

In the system called “orders of intentionality,” the first order is someone thinking about themself. The second order is thinking about someone else’s thoughts, and the third is, for example, thinking about what someone else thinks about what you think.

The limit for non-human animals is the second level, according to experiments designed so far.

In one vexing example, Dunbar said efforts to study dolphins failed after experimenters realized the mammals were picking up unintentional, nonverbal cues from researchers, not thinking about their state of mind.

Humans, if they can write the relationships out, can comprehend six or sometimes seven orders, but anything higher than that is exceedingly difficult, Dunbar said. (His limit is six).

Try this: Dunbar (1) hoped that his audience (2) could understand his thoughts (3) about how humans think (4) and about how they think other people think (5).

If you grasped that fifth-order thought without a headache, congratulations, you’re smarter than a chimp.