The beginning of Zuckerberg’s letter is less an argument about Facebook than it is an argument about the organizing principles of human progress. “History is the story of how we've learned to come together in ever greater numbers,” he writes. The theory reads as heavily informed by the book Sapiens, which Zuckerberg has recommended on, well, Facebook.

Sapiens, which is written by the Israeli historian Yuval Harari, is a mind-bending look at why and how homo sapiens took over the earth. It begins by establishing our species’ lowly beginnings. “The most important thing to know about prehistoric humans is that they were insignificant animals with no more impact on their environment than gorillas, fireflies or jellyfish,” Harari writes.

So what changed? Humans learned how to cooperate, and nothing else did. But cooperation, Harari emphasizes, is no easy task. The basic way humans form and sustain groups is by using language to tell common stories about their community — gossip, in other words. But he cites research suggesting that “the maximum ‘natural’ size of a group bonded by gossip is about 150 individuals.” Harari continues:

How did Homo sapiens manage to cross this critical threshold, eventually founding cities comprising tens of thousands of inhabitants and empires ruling hundreds of millions? The secret was probably the appearance of fiction. Large numbers of strangers can cooperate successfully by believing in common myths.

The key word there is “common.” For the purpose of human cooperation, the issue isn’t whether people believe true things, or good things, but whether enough of them believe the same things. Human beings — through stories, through religion, and eventually through governments, laws, and political ideologies — create common understandings of reality that provide the basis for massive, evolutionarily unprecedented levels of cooperation. And that’s why humans dominate the earth.