Six terms referring to horn shape, and "not fewer" than seventeen cattle colour terms were coined between AD 800 and 1450 in...[southern Africa]...So much linguistic innovation over such a large area...
Think about how much linquistic innovation has occurred in the past fifteen years. Then think about what constitutes "so much linguistic innovation" over a period of 650 years.
My guess is that if one just chose the English language and plotted linguistic innovation against time for the past 1300 years, one would see a hockey-stick graph comparable to the graph of economic growth. My guess is that the rate of linguistic innovation is a good proxy for the rate of change of both knowledge and productivity.
I'm a relative latecomer to this book. It is dense, and I am only about half way into it, but I have enjoyed plowing through it so far.