"The truth is that everyone on this planet is already engaged in a type of cohort study. We watch our children take shape alongside their cohort of siblings, cousins and friends, and we diligently document the process through diaries, height charts, photos and school reports. A generation before that, we started to participate in our own cohort study as we grew up surrounded by our peers; we are watching them still, and wondering quite how their lives diverged from ours. There is a deep and endless fascination with watching human life unfold."