Now all this fuss about a single one of our traits tells us there's something worth explaining. And that is how and why did this remarkable trait evolve, and why did it evolve only in our species? Now it's a little bit of a surprise that to get an answer to that question, we have to go to tool use in the chimpanzees. Now these chimpanzees are using tools, and we take that as a sign of their intelligence. But if they really were intelligent, why would they use a stick to extract termites from the ground rather than a shovel? And if they really were intelligent, why would they crack open nuts with a rock? Why wouldn't they just go to a shop and buy a bag of nuts that somebody else had already cracked open for them? Why not? I mean, that's what we do. Now the reason the chimpanzees don't do that is that they lack what psychologists and anthropologists call social learning. They seem to lack the ability to learn from others by copying or imitating or simply watching. As a result, they can't improve on others' ideas or learn from others' mistakes -- benefit from others' wisdom. And so they just do the same thing over and over and over again. In fact, we could go away for a million years and come back and these chimpanzees would be doing the same thing with the same sticks for the termites and the same rocks to crack open the nuts.