Why'd It Take So Long To Invent The Wheel?

This NPR story is a graphic story of the likely stages of development in the process to invent the wheel. 

Johnnie Hughes is cited in this article. For further reading about how ideas evolve, check out Jonnie Hughes' book about the evolution of ideas is called On the Origin of Tepees: The Evolution of Ideas (and Ourselves), (Free Press, Simon & Schuster, 2011).