MICHAEL TOMASELLO: What you'll see with the human mother and baby is that the mother is constantly trying to show the baby what to do, and the baby is trying to tune into what the mother wants. And so you have a full triangle of mother and baby and the thing in the environment that they are trying to work on.
REBECCA SAXE: It's a special cognitive achievement. For some reason kids do this naturally, almost immediately. And curiously, apes can't get into that.
MICHAEL TOMASELLO: At the moment we have no evidence that apes have shared goals based on shared commitments. They do things together, they coordinate their actions together, but they don't have a shared commitment to a shared goal.
NARRATOR: The triangle is the core skill that makes teaching possible. Humans have it; apes seem to lack it. But apes are also missing one more thing. It's a key emotional driver: the passion to cheer each other on.
TETSURO MATSUZAWA: "Good," "good job," "well done." This kind of facilitation, giving a hand, encouragement, is the base of teaching.
REBECCA SAXE: It seems like it's not just a cognitive capacity that's necessary for teaching. There's this other thing, which is wanting to teach, that seems to be really pervasive in humans and maybe mysteriously missing in apes.
NARRATOR: The pieces are now coming together. Apes have culture, a rare achievement in the animal world. They can learn from each other by imitation. But this process is passive, often slow and can easily backslide.
BRIAN HARE: Probably there's a lot of slippage. There's a lot of loss of cultural innovations between generations when you're talking about a chimpanzee.
MICHAEL TOMASELLO: If an ape invents something new and important and interesting, maybe some others will learn it, maybe they won't.
NARRATOR: Unique among animals, humans have both the passion and mental skill to teach each other. When you're a student rather than a spectator, learning jumps to warp speed. That's because teaching locks in progress.