Visiting the prehistoric sites of East Africa the authors of this book taught themselves how to make the same stone tools that the earliest humans had. They were astonished to discover how effective these tools were - they were able to skin and cut up an elephant using only stone flakes a couple of inches long. The authors experiments provide evidence for the idea of early technology and brain evolution being in a positive feedback loop: more technology gives more advantage to bigger brains, which come up with even more technology. They also found that right-handedness can be traced back a far as 1.9 million years ago; this suggests that the left-right brain specialization that gave rise to speech is at least as old.