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A special note if you are stranded between 200,000 BCE and 50,000 BCE and you are thinking, "The humans here are crazy and I am definitely doomed forever"

Great news! You can actually be the most influential person in history!

As your careful study of the flowchart on the previous pages likely revealed, humans first evolved around the year 200,000 BCE. We call them "anatomically modern humans," and they mark the moment when humans with skeletons exactly the same as ours first appeared. As an experiment, we could put your skeleton beside that of an anatomically modern human from 200,000 years ago and it would be impossible to tell them apart.

We will not be performing this experiment, but we could.

But what's fascinating is despite the fact that modern human bodies were now available, nothing really changed. For more than 150,000 years, these humans behaved pretty much the same as any other protohuman species. And then, around the year 50,000 BCE, something happened: these anatomically modern humans suddenly started acting like us. They began to fish, create art, bury their dead, and decorate their bodies. They began to think abstractly.

Most important, they began to talk.

The technology of language—and it is a technology, it's something we've had to invent, and it took us over 100,000 years to do it—is the greatest gift we humans have ever given ourselves. You can still think without language—close your eyes and imagine a really cool hat and you've just done it—but it limits the kinds of thoughts you can have. Cool hats are easy to imagine, but the meaning of the sentence "Three weeks from tomorrow, have your oldest stepsister meet me on the southeast corner two blocks east from the first house we egged last Halloween" is extremely difficult to nail down without having concrete words for the concepts of time, place, numbers, relationships, and spooky holidays. And if you're struggling to express complex thoughts even in your own head, it's pretty evident that you won't be having those complex thoughts as often, or at all.

It was language that gave us the ability to imagine better, grander, more world-changing ideas than we otherwise could, and most important, it gave us the ability to store an idea not just in our own heads but inside the minds of others. With language, information can spread at the speed of sound, or, if you're using sign language instead of speaking, at the speed of light. Shared ideas lead to communities, which are the basis of culture and civilization, and which brings us to our first Civilization Pro Tip: 

CIVILIZATION PRO TIP: Language is the technology from which all others spread, and you've already got it for free.

This huge expanse of time—the 150,000 years between 200,000 BCE, when humans first appeared, to 50,000 BCE, when they finally started talking—is where you can have the single greatest effect on history. If you can help humans of this era become behaviorally modern as soon as they became anatomically modern—if you can teach them to talk—then you can give every civilization on the planet a 150,000-year head start.

It's probably worth the effort.

We once thought the change from anatomical to behavioral modernity was due to some physical change in our brains. Perhaps a random genetic mutation in one human—who suddenly found themselves able to communicate in ways no animal had done before—provided us with the huge advantage of a new capacity for abstract thought? However, the historical record doesn't support the idea of this great leap forward. The things we most associate with...