hands no more nimble...

The following is from Thomas K. Landauer:

The story of the human race is one of ever-increasing intellectual capability. Since our early cave-dwelling ancestors, our brains have gotten no bigger, our hands no more nimble, but there has been a steady accretion of tools for intellectual work--how to grow crops, domesticate animals, build shelters, paint paintings. It includes governing and inspiring and, unfortunately, waging wars. It includes how to build and operate airlines, television sets, and football teams. This shared capacity was first manifest in language, later in writing, math and science, and in the huge collections of experience and discovery stored in books and libraries. By comparison with our forebears, each of us has become a genius. From The Trouble With Computers, 1995, MIT Press. Page 365.

While there is no way to prove it, I suspect Landauer misstates the beginning of it all which was no more likely the result of language, than of the first humans making and using tools. Due to the fossil record, we have evidence of tools and their role in the expansion of intellect in early man, but no evidence of language having that same effect.