You know, your point of "better infrastructure, can only lead to less hectic lives for city-dwellers. That will lead to more sex and more kiddos." rings really true. I wonder if all these reasons/explanations given in this article and that I see floating around boils down to free time. Like how when NYC had that summer blackout a few years ago there was a mini baby boom ~9 months later. The lack of power meant everyone was board and hot and in the dark so they decided to bone. The frenetic pace of life without support systems (e.g., close extended family) has just pushed sex down as a priority. So the way to get people to make more babies is to give them more free time. I bet this is an evolutionary thing too. If you're constantly on the run from predators and stuff, you shouldn't be making children. Only when things calm down would it make sense to procreate. So sex drive is probably directly related to free time...