“Schumpeter emphasizes a “demand-side” explanation for such clustering of innovation. One might also consider a complemen tary “supply-side” explanation: since innovators are, in many cases, working with the same components, it is not surprising to see simultaneous innovation, with several innovators coming up with essentially the same invention at almost the same time. There are many well-known examples, including the electric light, the airplane, the automobile, and the telephone.”