Well, I will say it is probably not good social science to assert causal relationship so categorically. The introductory quote from Edward Glaeser triggering this post is thus problematic. Urbanisation has a potentially positive impact on prosperity and that prosperity is most certainly guaranteed for certain segments of the urban population, but is it for all ? It appears large majority of new urban settlers end up in slums and shanty towns where it is really hard to see how their new life is better in material terms from the rural one they left. Yet a complex feel better factor also come to play generally, that is, despite their material poverty, new urban dwellers may still entertain a "modernity complex" which make them feel better than their erstwhile fellow rural dwellers. In short the potential of urbanisation to spur prosperity is there. But it is not an automatic relationship, it is just a potential that can or can't be realised depending on a complex sets of factors ranging from urban dwellers self-dynamism to good policy implementation by local and central governments. What is sure is that the 1960-70 perception of urbanisation a a calamity is not outdated. In fact could it be that The age of nations is over, the new urban age has begun (http://bit.ly/x2gnSg) ? And wither Africa in 50 years in the light of fast urbanisation: http://ledna.org/links/africa-50-years%E2%80%99-time-road-towards-inclusive-growth ?