The reason the chimpanzees don't do that is that they lack what psychologists and anthropologists call social learning.


That is, 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, learn from others' mistakes, or even 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 rocks to crack open the nuts.


Okay, so what this tells us is that, contrary to the old saying, "monkey see, monkey do," the surprise really is that all of the other animals really cannot do that -- at least not very much.


But by comparison, we humans can learn.


We can learn by watching other people and copying or imitating what they can do.


We can then choose, from among a range of options available, the best one.


We can benefit from others' ideas. We can build on their wisdom.


And as a result, our ideas do accumulate, and our technology progresses.


And this cumulative cultural adaptation, as anthropologists call this accumulation of ideas, is responsible for everything around you in your bustling and teeming everyday life.


I mean the world has changed out of all proportion to what we would recognize even 1,000 or 2,000 years ago.


And all of this is because of cumulative cultural adaptation.


For instance, the chairs you're sitting in today, the lights in this lecture hall, my microphone, the iPads and the smart phones that you carry around with you -- all are a result of cumulative cultural adaptation.


But, our acquisition of social learning would create an evolutionary dilemma, and the solution to the dilemma, it's fair to say, would determine not only the future course of our psychology, but the future course of the entire world.


And most importantly for this, it'll tell us why we have language.


And the reason that dilemma arose is, it turns out, that social learning is visual theft.


What I mean is, if I can learn by watching you, I can steal your best ideas, and I can benefit from your efforts, without having to put in the same time and energy that you did into developing them.


Social learning really is visual theft.