produced by Europe's exploitation of America can be said to be the only cause of the Industrial Revolution, but it is hard to see how the colossal effect could have come about without the Columbian exchange. THE DEMOGRAPHIC EFFECTS The impact of the Columbian exchange did not always enhance population growth. Columbus triggered population explosion among some peoples and implosion in others. His effect on the Amerindian population, for example, was annihilating. Fifty years ago Alfred Kroeber, then perhaps the premier anthropologist in the United States, estimated the total Amerindian population of 1492 at 8.5 million. He believed that his figure might possibly be a bit low, but it is unlikely that he thought that scholars would ever conservatively estimate the number of fifteenth-century Amerindians at 30 to 50 million, or that others, at least as well informed, would not hesitate to say 100 million. Extraordinary numbers! At that time Europe from the Atlantic to the Urals had only 80 million people, with Spain's population perhaps 7 million. The mammoth increase in the estimates of fifteenth-century Amerindian populations during the past few decades quite properly arouses skepticism because the data these figures are based on are, by twentieth-century standards, disconcertingly imprecise. These estimates are the end results of careful examination and meticulous analysis of all the sources available (which are admittedly doubtful, if taken one at a time, but in total impressive). These include the off-the-cuff guesses of the first Europeans to arrive in a given area, the sober judgments and censuses of colonial administrators and churchmen, travelers' accounts, and whatever other scraps of pertinent information that can be found. All are measured against approximations of the carrying capacity of the environment and the size of the Amerindian population suggested by the density of pre-Columbian artifacts and ruins. These figures are matched against each other and then tested by sophisticated demographic techniques, such as careful extrapolation backward from later and more credible data. At the end the demographic historians make their estimates. We can and should argue about these estimates, but we should also note that they do not stand in suspicious uniqueness: The sources about Australia, New Zealand, and the Pacific islands also indicate that their aboriginal populations were much larger when Europeans first arrived than two or three generations later.