Increasingly, historians are blaming diseases imported from the Old World for the big gap between the native population of America in 1492 new estimates of which jump as high as t00 million, or approximately one-sixth of the human race at that time -- and the few million full- blooded (纯血统的) Native Americans alive at the end of the nineteenth century. There. is no doubt that chronic disease was an important factor in the sharp decline, and it is highly probable that the greatest killer was epidemic disease, especially as manifested in virgin-soil epidemics.
Virgin-soil epidemics are those in which the population at risk have had no previous contact with the diseases that strike them and are therefore immunologically (免疫学地) almost defenseless. That virgin-soil epidemics were important in American history is strongly indicated by evidence that a number of dangerous rnaladies (疾病) -- smallpox, measles, malaria, yellow fever, and undoubtedly several more were unknown in the pre-Columbian New World. The effects of their sudden introduction are demonstrated in the early chronicles (编年史)of America, which contain reports of horrible epidemics and steep population declines, confirmed in many cases by quantitative analyses of Spanish tribute records and other sources. The evidence provided by the documents of British and French colonies is not as definitive because the conquerors of those areas didn’’t establish permanent settlements and began to keep continuous records until the seventeenth century, by which time the worst epidemics had probably already taken place. Furthermore, the British tended to drive the native populations away, rather than to enslave them as the Spaniards did, so that the epidemics of British America occurred beyond the range of colonists’’ direct observation.
Even so, the surviving records of North America do contain references to deadly epidemics among the native population. In 1616 — 1619 an epidemic, possibly of pneumonic plague, swept coastal New England, killing as many as nine out of ten.. During the 1630’’s smallpox, the disease most fatal to the native American people, eliminated half the population of the Huron and Iroquois confederations. In the 1820’’s fever ruined the people of the Columbia River area, killing eight out of ten of them.
Unfortunately, the documentation of these and other epidemics is slight and frequently un- reliable, and it is necessary to supplement what little we do know with evidence from recent epidemics among Native Americans. For example, in 1952, an outbreak of measles among the Native American inhabitants of Ungava Bay, Quebec, affected 99 percent of the population and killed 7 percent, even though some had the benefit of modern medicine. Cases such as this demonstrate that even diseases that are not normally fatal can have destroying consequences when they strike an immunologically defenseless community.
Which of the following can be inferred from the text concerning Spanish tribute records
A．They were being kept prior to the seventeenth century. B．They mention only epidemics of smallpox. C．They provide quantitative and qualitative evidence about Native American populations. D．They prove that certain diseases were unknown in the pre-Columbian New World.