One can hardly imagine, I think, how poor we would be today were it not for the rapid population growth of the past to which we owe the enormous number of technological advances enjoyed today. Another instance of external economies is parallel. Our artistic heritage is much like our technology; it is a part of our public capital. If I could re-do the history of the world, halving population size each year from the beginning of time on some random basis, I would not do it for fear of losing Mozart in the process. (Phelps, 1968.) What does this have to do with our study of endogenous growth? Can you relate Phelps's statement to your answer in 1?