There are 6,000 languages in the world, in so much variety that many languages would leave English speakers wondering just how a human being could possibly learn and use them. How did these languages come to be? Why isn’t there just a single language?

This course answers these questions. Like animals and plants, the world’s languages are the result of a long “natural history,” which began with a single first language spoken in Africa. As human populations migrated to new places on the planet, each group’s version of the language changed in different ways, until there were several languages where there was once one. Eventually, there were thousands.

Languages change in ways that make old sounds into new sounds and words into grammar, and they shift in different directions, so that eventually there are languages as different as German and Japanese. At all times, any language is gradually on its way to changing into a new one; the language that is not gradually turning upside-down is one on the verge of extinction.

This kind of change is so relentless that it even creates “languages within languages.” In separate populations who speak the same language, changes differ. The result is variations upon the language—that is, dialects. Often one dialect is chosen as the standard one, and when it is used in writing, it changes more slowly than the ones that are mostly just spoken because the permanency of writing has an official look that makes change seem suspicious. But the dialects that are mostly just spoken keep on changing at a more normal pace.

Then, the languages of the world tend to mix together on various levels. All languages borrow words from one another; there is no “pure” vocabulary. But some borrow so much vocabulary that there is little original material left, such as in English. And meanwhile, languages spoken alongside one another also trade grammar, coming to look alike the way married couples sometimes do. Some languages are even direct crosses between one language and another, two languages having “reproduced” along the lines of mitosis.

Ordinarily, language change is an exuberant process that makes languages develop far more machinery than they need—the gender markers in such languages as French and German are hardly necessary to communication, for example. But this overgrowth is checked when history gets in the way. For example, when people learn a language quickly without being explicitly taught, they develop a pidgin version of it; then, if they need to use this pidgin on an everyday basis, it becomes a real language, called a creole. Creoles are language starting again in a fashion—immediately they divide into dialects, mix with other languages, and start building up the decorations that older languages have.

Just as there is an extinction crisis among many of the world’s animals and plants, it is estimated that 5,500 of the world’s languages will no longer be spoken in 2100. Globalization and urbanization tend to bring people toward one of a few dozen politically dominant languages, and once a generation is not raised in a language, it no longer survives except in writing—if linguists have gotten to it yet. As a language dies, it passes through a “pidgin” stage on its way to expiration. This course, then, is both a celebration and a memorial of a fascinating variety of languages that is unlikely to exist for much longer.