When Europeans got to the interior of New Guinea, they found the people split up into groups that each spoke a different language — almost a thousand different languages, most of them mutually unintelligible. That's not just the accumulation of random variations: something was driving these languages apart and keeping them apart. It was the fact that the people didn't want to speak the same language as their enemies! A village would split up into two smaller villages, they would go to war against each other, and then the inhabitants of Village A would find ways of distinguishing themselves from the inhabitants of Village B. Different hairstyles, different designs on the pots, different words.

You can see the same thing happening between contrasting groups within a single society. Developed societies have a special age group for people who are no longer children but are not yet adults, and this group becomes a source of social change. In societies that have only two age groups, children and adults, a culture can go along virtually unchanged for generation after generation, but as soon as there's a special age group for teenagers, things start to happen. The teenagers look for ways of demonstrating their fealty to their own age group — ways of showing that they're different from adults. They use weird forms of adornment that adults find unacceptable, and they invent new words or use old words in new ways. If people didn't keep graduating out of the teenage group and taking their vocabulary with them, eventually they would create a whole new language and the adults wouldn't be able to understand them. Which, of course, is just what they're after!

JB: What makes you think that what's true of language is true of culture in general? Doesn't language have its own module in the brain?

HARRIS: Lots of things have their own module. Language is just one of the many things that babies need to learn in order to become acceptable members of their society. It's complicated, yes, but so are the other things they have to learn. I don't see any essential difference between learning a custom that is called "language" and learning the other behaviors and skills of the culture.

Let me end this discussion by coming back to the question you asked me at the beginning: am I an extremist? The children of immigrants who speak English with a heavy accent, if they grow up in a neighborhood of native-born Americans, end up speaking English with no foreign accent at all. They don't end up with something in between what they learned from their parents and what they learned from their peers: they end up, pure and simple, with the language of their peers. That's why I am an extremist: because children don't do things half way. Children don't compromise.