When I was pregnant with my first child, I bought half a dozen books to guide me through the life-altering event. They were full of "dos and don'ts" — but there was one thing in the litany of advice that all the books had in common. They all measured the pregnancy, and then, the development of the child, in terms of milestones. First you reach one marker, then you move on to the next, in nice, clear, seemingly choreographed steps. The perfect pregnancy, the perfect child.