The preceding lectures have concerned interstate arms racing (mutualism) and war (competition). Let us now turn attention to intrastate processes. This lecture concerns revolutions. The next concerns the spread of drugs. Clinging to our Volterra-like “grand unified theory,” the processes of interest in these lectures is the threshold transmission of some “signal” through a population, epidemic-like processes, in short. Epidemics proper are fascinating—and obviously very important—things. You would certainly enjoy William McNeill’s wonderful book, Plagues and Peoples, which concerns the role of infectious diseases in human history.[ 66 ] Since these lectures proceed from the analogy to epidemics, perhaps an introductory word or two on dynamical analogies per se is in order.