Language not only defines humans as a species, placing us head and shoulders above even the most proficient animal communicators, but it also beguiles us with its endless mysteries. How did different languages come to be? Why isn't there just a single language? How does a language change, and when it does, is that change indicative of decay or growth? How does a language become extinct?  

In today's rebroadcast, I speak with John McWhorter, a linguist from Columbia University. He addresses these and other issues, such as how a single tongue spoken 150,000 years ago has evolved into the estimated 6,000 languages used around the world today, everything from proto-Indo European to Ebonics English in the United States.