“Historians,” he writes, “instinctively stop the backward search for the ultimate cause at the point where the state of affairs, whose alteration they seek to explain, flourished.”19 This is a rather clumsy way of stating, for history, a principle paleontologists have more elegantly called punctuated equilibrium. It has to do with the fact that evolution doesn’t proceed at a steady rate; rather, long periods of stability are “punctuated” by abrupt and destabilizing changes.
