Many writers have discussed the impact of disease on history, but never before has there been such an overall synthesis, such a weaving together of biology with political and social history. The result is a panorama wherein many separate details fall together into an interesting pattern. To be sure, the evidence is fragmentary, yielding a hypothesis rather than a demonstration. And although only the future can tell how much of Professor McNeill's insight is true, we meanwhile have a stimulating account.
McNeill makes history a part of biology, subject to the forces operative in all living creatures. Particularly relevant here are food chains with their complex ecologic interactions and resulting predation and parasitism. To the concept of micro-parasites—the sphere of microbiology wherein microorganisms prey on man (and other animals)—McNeill adds what he terms macroparasites, man preying on man. This occurs when we reach a certain density of population, with societal