what the group reported was that some of the bring-food-to-mouth neurons would also activate if the monkey observed someone else (monkey or human) making that movement. ... Consistently, about 10 percent of the PMC neurons devoted to doing movement X also activated when observing someone else doing movement X—very odd for neurons a few steps away from commanding muscles to move. The neurons were concerned with the mirroring of movements. And thus were “mirror neurons” announced to the world.

Going easy on ourselves also reflects a key cognitive fact: we judge ourselves by our internal motives and everyone else by their external actions. And thus, in considering our own misdeeds, we have more access to mitigating, situational information. This is straight out of Us/Them—when Thems do something wrong, it’s because they’re simply rotten; when Us-es do it, it’s because of an extenuating circumstance, and “Me” is the most focal Us there is, coming with the most insight into internal state.

A group forms a stable, linear hierarchy where the alpha individual dominates everyone, the beta individual dominates everyone except the alpha, gamma everyone except alpha and beta, and so on. Hierarchies establish a status quo by ritualizing inequalities. Two baboons encounter something good—say, a spot shaded from the sun. Without stable dominance relations, there’s a potentially injurious fight. Likewise over the figs in a fruiting tree an hour later, and for the chance to be groomed by someone after that, etc. Instead, fights rarely occur, and if a subordinate forgets his status, a “threat yawn”—a ritualistic display of canines—from the dominant male usually suffices.

What was most interesting was that across all the cultures, lying was of a particular type. ... The lying showed a pattern that, based on prior work, could be explained by only one thing—people rarely made up a high-paying number. Instead they simply reported the higher roll of the two. You can practically hear the rationalizing.

Or consider male peacocks paying a price, in terms of natural selection, for their garish plumage—it costs a fortune metabolically to grow, restricts mobility, and is conspicuous to predators. But it sure boosts fitness via sexual selection.

Open-book play mediates a uniquely sophisticated type of human cooperation, namely “indirect reciprocity.” Person A helps person B, who helps C, who helps D. . . . The reciprocity between two individuals in a closed interaction is like barter. But indirect, pay-it-forward reciprocity is like money, where the common currency is reputation.

This is the essence of learning. The lecturer says something, and it goes in one ear and out the other. The factoid is repeated; same thing. It’s repeated enough times and—aha!—the lightbulb goes on and suddenly you get it.

The first is the persuasive power of the incremental. ... We rarely have a rational explanation for an intuitive sense that a line has been crossed on a continuum. What incrementalism does is put the potential resister on the defensive, making the savagery seem like an issue of rationality rather than of morality. This represents an ironic inversion of our tendency to think in categories, to irrationally inflate the importance of an arbitrary boundary. The descent into savagery can be so incremental as to come with nothing but arbitrary boundaries, and our descent becomes like the proverbial frog cooked alive without noticing.