In Natural Experiments of History, a collection of essays published a decade ago, editors Jared Diamond and James Robinson wrote, “The controlled and replicated laboratory experiment, in which the experimenter directly manipulates variables, is often considered the hallmark of the scientific method” – virtually the only approach employed in physics, chemistry, molecular biology. Yet in fields considered scientific that are concerned with the past – evolutionary biology, paleontology, historical geology, epidemiology, astrophysics – manipulative experiments are not possible. Other paths to knowledge are therefore required, they explained, methods of “observing, describing, and explaining the real world, and of setting the…