Historians took a long time to appreciate the importance of biological factors in human history. As the French naturalist Jean Henri Fabre (1823-1915) said: "History celebrates the battlefields whereon we meet our death, but scorns to speak of the plowed fields whereby we thrive. It knows the names of the King's bastards, but cannot tell us the origin of wheat." No doubt Fabre's criticism helped in turning the tide against the old-fashioned sort of history. History books now being written are more inclusive, more interesting. Some of them even mention population. A century before Fabre was born, even the fact of population growth was denied by some otherwise well-informed scholars. In 1721 the Baron de Montesquieu asked, in all sincerity, "How does it happen that the world is so thinly peopled in comparison with what it once was?"1 Until the nineteenth century the taking of censuses was a sporadic activity; most of the world, most of the time, lived uncensused. Primitive travel and slow communication made the counting of population over large areas difficult—and perhaps pointless. Without censuses or sampling, general impressions had to serve. When speaking of "the world" as "it once was," the baron, an educated European, no doubt had in mind the last days of the Roman Empire. There is much uncertainty about the size of world population in the olden days, but the following estimates are probably not far off.2 Over a period of about thirteen hundred years, ending in Montesquieu's time, the population of the world increased from some 190 million to about 610 million. This was more than a threefold increase, but an intelligent European could easily be unaware of both the direction and the extent of the change—for several reasons. To begin with, most of the increase in population took place outside Europe. Despite reports like Marco Polo's, to European eyes Europe was the world. Viewing the sparsely inhabited ruins of Rome, eighteenth-century Europeans deduced a decrease in world population. Awareness of long-term growth was made more difficult by erratic (but normal) fluctuations in populations. It was quite common for a region to lose a percent or two of its population during a single year because of disease.