Initial European reports about the New World spoke of a veritable Eden, populated by healthy, long-lived people, who could cure illness with exotic medicinal plants and did not know the diseases common in other parts of the world. Columbus said he found ''Paradise-on-Earth'' in the newly discovered Indian Islands. Glowing reports of the idyllic conditions and wealth to be found in the New World could be attributed to ignorance, or to the hyperbole of an advertising campaign designed to attract European settlers and investors. In any case, within decades, the discovery and conquest of the Americas led to an unprecedented interchange of peoples, plants, animals, and pathogens on a global scale. With the demographic catastrophe that overcame Native Americans and the demands of Spanish colonizers for labor, the establishment of the slave trade brought vast numbers of Africans to the New World. Thus, within a few decades, the Americas became the site of the mixing of the peoples and germs of previously separate continents.
By the end of the twentieth century, historians had generally agreed that a new comparative and common history of the Americas was essential. Also necessary was recognition of the fact the so-called New World was only new to Europeans; the Americas had long ago been discovered and settled by ancestors of those now called Native Americans, Indians, or Amerindians. Because the history of the native peoples of America is known primarily through documents produced by European explorers, conquerors, missionaries, and settlers, a Eurocentric bias is probably inevitable. Moreover, except for the earliest accounts of the Spanish conquerors, European reports were composed in the wake of the catastrophic demographic collapse that virtually destroyed the foundations of Native American civilizations and cultures. Scholars are now attempting to transcend the assumptions implicit in such terms as Discovery, New World, and European Expansion in order to understand the history of the Americas before 1492, but given the fragmentary nature of the evidence, the desired grand synthesis of the history of the Americas remains a formidable and unfinished task.
Historians and scientists continue to debate the nature and timing of the earliest migration of humans into the Americas. Some scholars believe that human beings first crossed a land bridge from Siberia to the New World at the end of the last Ice Age, that is, about 10,000 years ago. These migrants might have been skilled nomadic hunters who eventually contributed to the extinction of mastodons, mammoths, horses, camels, and other species of large mammals. Other evidence suggests that human beings might have arrived in the New World about 20,000 years ago, and pursued a way of life in which gathering plants was as important as hunting. Sites in both North and South America have provided evidence of human artifacts that appear to be 15,000 to 20,000 years old, but most early sites are very poorly preserved. The evidence is so fragmentary and ambiguous that each discovery of prehistoric tools and artifacts renews the arguments about migration patterns, the identity of the first people to arrive in the Americas, and their relationship to contemporary American Indians.
Some scientists believe that Ice Age skeletons and DNA tests might settle the debate about the identity of the people who originally arrived in the Americas. By the end of the twentieth century scientists had found genetic evidence that suggested independent waves of migrations of people from Asia, Polynesia, and even Western Europe. Nevertheless, the evidence from artifacts, human remains, and even human DNA remains ambiguous. Whenever humans first came to the Americas, significant waves of immigration from Eurasia presumably ceased when the land bridge linking Alaska and Siberia disappeared, leaving the populations of the Americas isolated from the rest of the world. The relative genetic homogeneity of native Americas might have affected their response to Old World infectious agents. The distribution of blood types in the Americas, for example, is less variable than that found in Eurasia.
Uncertainties about the pattern of early migrations lead to uncertainty about the disease patterns that would have prevailed in the prehistoric New World. Scholars have suggested that the migration through the Bering Strait into America served as a ''cold filter'' that screened out many pathogens and insects, but that does not mean that pre-Columbian America ever was a disease-free Garden of Eden. Throughout most of the Americas, however, population density was presumably too low to support the endless cycles of epidemic and childhood diseases common in the urban centers of the Old World. There were, of course, dangerous animals, poisonous reptiles and plants, as well as insects and arthropods that could serve as vectors of disease.
Diseases that were almost certainly present in the Americas before 1492 include arthritis, cancer, diseases of the endocrine system, nutritional deficiency diseases, osteoporosis, intestinal parasites, dysentery, bronchitis, pneumonia, tuberculosis, rickettsial and viral fevers, pinta, Carrion's disease (Oroya fever or Verruga Peruana), uta (American leishmaniasis), and Chagas' disease. (Trypanosoma cruzi, the parasite that causes Chagas' disease, is transmitted by the bloodsucking barbeiro, or kissing bug. The clinical course of this incurable disease is quite variable, but the infestation may damage the liver, spleen, and heart. The causative agent and means of transmission were identified by the Brazilian scientist Carlos Chagas (1879-1934). Epidemiologists estimate that about 18 million people in Latin America are infected with Chagas' disease; about 50,000 die of the disease every year.) There is considerable uncertainty about the pre-Columbian prevalence of tuberculosis in the Americas, but studies of Peruvian mummies have revealed evidence of pulmonary tuberculosis, as well as tapeworm, pinworm, and roundworm.
The microorganisms that cause wound infections, boils, sore throats, and food poisoning were probably fairly common. ''Fevers'' were certainly endemic in the Americas, but the pre-Columbian status of malaria and yellow fever are uncertain. Many regional febrile diseases caused by microbes and parasitic worms were probably transmitted by American mosquitoes, ticks, flies, fleas, and bugs. Rocky Mountain spotted fever, for example, is caused by a peculiar pathogen (Rickettsia rickettsii) found only in the Americas. Other American diseases with high mortality rates—including Colorado tick fever, St. Louis encephalitis, Western equine encephalitis, and Eastern equine encephalitis—are caused by arboviruses (viruses transmitted by arthropods, such as mosquitoes and ticks) that find a reservoir in reptiles, birds, and mammals.
Cholera, plague, smallpox, measles, scarlet fever, malaria, typhus fever, typhoid fever, influenza, and probably gonorrhea and leprosy were unknown in the pre-Contact period. There is even uncertainty about the kinds of vermin native to the New World. For many epidemic and endemic diseases, vectors, such as insects, arthropods, and rodents, are critical factors in their distribution and transmission. Ticks, biting ants, mosquitoes, flies, lice, gnats, chiggers, scorpions, spiders, flies, and poisonous snakes were indigenous to the Americas, but Europeans probably brought new species of fleas, roaches, lice, bedbugs, and rats.
Malaria has been a powerful agent in world history, but its pre-Columbian global distribution is uncertain. Even if malaria was originally present in the Americas, more virulent African strains could have been imported in association with the slave trade. Whether or not human malaria was a significant problem in pre-Columbian America, quinine, the drug that made it possible to cure malaria, was found in the New World. Quinine, which is extracted from a plant indigenous to South America, was originally known as cinchona or Peruvian bark.
Native Americans suffering from an epidemic fever allegedly discovered the therapeutic value of cinchona when they drank water from a pond bordered by cinchona trees. Eventually the story of cinchona became linked to that of the Countess of Chinchon, wife of the Viceroy of Peru. Sadly, the story of the feverish Countess and the Native American remedy seems to be a myth used to explain the export of Peruvian bark to Europe in the 1630s. Francesco Torti's (1658-1741) book Therapeutice specialis (1712), on pernicious intermittent fevers, was instrumental in establishing the value of cinchona bark therapy.
Although many sixteenth-century physicians considered syphilis a new disease that had been imported from the New World, the pre-Columbian distribution of syphilis is still controversial. There is, however, evidence that other members of the treponematosis family were widely distributed throughout the world; the form known as pinta was present in the Americas. The global epidemics of syphilis that followed 1492 could have been the result of exchanges of previously localized strains of treponemes. Other sexually transmitted diseases presumably existed in the Americas, but gonorrhea was probably absent.
The origin of yellow fever is almost as mysterious and controversial as that of syphilis and concerns the same problem of Old versus New World distribution of disease in pre-Columbian times. Claims that Mayan civilization was destroyed by yellow fever or that epidemics of this disease occurred in Vera Cruz and San Domingo between 1493 and 1496 remain doubtful. Some epidemiologists contend that yellow fever, a viral disease transmitted to humans by mosquitoes, caused epidemics in the Americas long before European contact, but others believe that the disease was imported from Africa.
Unlike the controversy surrounding syphilis and yellow fever, there seems to be general agreement that tuberculosis existed in pre-Contact America. Tuberculosis infections, in communities where the disease is endemic, are usually contracted in early childhood, via the respiratory route. Primary lesions may develop in the lungs and viable bacteria may remain encapsulated, until some kind of stress or stimulus reactivates the infection. Thus, the skeletal lesions characteristic of tuberculosis may occur in only a small percentage of infected individuals.
Human skeletal remains and mummies provide evidence for the presence of certain diseases in pre-Contact America, but there is much uncertainty and difficulty in the interpretation of such materials. As the techniques of molecular biology improve, researchers might gain critical information through studies of DNA recovered from human remains. Some scholars argue that all attempts to attach modern diagnostic names to ancient remains are futile, although the urge to do so seems to be irresistible. Others argue that, social constructionism notwithstanding, diseases should be thought of as true biological entities that persist through time.
Generally, about 15 percent of the skeletons found in typical North American archeological samples show evidence of identifiable conditions like trauma, infection, and arthritis. Of course, the conditions that are recognizable in skeletons were not necessarily the immediate cause of death, because few acute diseases leave a characteristic mark in the bones. Moreover, very different conditions may produce similar lesions. The kinds of acute, viral diseases that probably had the greatest impact on Native Americans after contact with Europeans are unlikely to affect the skeleton, but evidence of injury and death from European weapons can be found in Indian cemeteries.
Where conditions are favorable, biological anthropologists have analyzed the remains of pre- and post-Conquest populations and compared this evidence with European observations about early encounters with Native Americans. Studies of early human remains from the Georgia coastal region, for example, indicate that even prior to contact, the quality of life had deteriorated. By the twelfth century, these coastal people had begun cultivating maize, which resulted in less dietary variety and increases in the frequency of nonspecific bone inflammation and dental caries. Increases in population size were supported by a basically sedentary subsistence economy that included farming, hunting, gathering, and fishing.
Researchers have used the techniques of molecular biology to study DNA recovered from ancient human remains. For example, some of the skeletons recovered from a peat bog in Florida contained intact crania and preserved, but very fragile brain matter. Although the Windover site skeletons had been in the peat bog for about seven thousand years, scientists were able to perform some studies on their mitochon-drial DNA.
Estimates of the population of the Americas in 1492, as well as the magnitude and specific causes of the demographic collapse that followed the arrival of Europeans, are controversial and very far from precise. Demographers have attempted to compare archeological evidence concerning settlement patterns, burials, and accumulations of refuse with population estimates recorded by early European explorers. Despite the increasing sophistication of analytic techniques, population estimates for the early encounter period have been characterized as underestimates, overestimates, or even ridiculed as ''numbers from nowhere.''
Despite universal agreement that Old World diseases had a catastrophic effect on Native Americans, assessing the impact of European contact is not a simple matter. Population change is the result of complex forces and estimates of populations in the past lack precision. Demographers can generally be divided into two schools of thought. ''High Counters'' argue that there was a very large pre-Contact Native American population and that it was drastically reduced by the epidemic diseases, chaos, and exploitation that followed the Conquest.
''Low Counters" argue that European invaders exaggerated the numbers of people they encountered in order to magnify their victories.
Some scholars argue that the pre-Contact population for the entire New World was probably between 8 and 13 million, but estimates for the population of Mexico in 1492 have ranged from as low as one million to as high as thirty million. Whatever the absolute figures might have been, contact between the Old and New Worlds apparently led to the worst demographic disaster in human history. When Spanish bureaucrats attempted to conduct a census of Mexico in the late 1540s, observers guessed that the population was less than a third of the pre-Conquest level. A census conducted in the 1570s reflected further decreases in the native population due to war, disease, and other hardships. Winning over the demoralized survivors, the conquerors and their priests displaced native shamans, priests, and chiefs and substituted European agriculture and animal husbandry for native systems of production. Environmental damage and social disruption were exacerbated by the introduction of European domesticated animals.
Unfortunately, little direct evidence remains concerning the pre-Columbian medical beliefs and practices of the diverse peoples of the Americas. What is known is often obscured by the difficulties of decoding the meanings of ancient symbols, artifacts, and artwork. Observations made by Europeans compound the problem, because of inevitable misunderstanding and deliberate distortions. By the time Native Americans began using European alphabets to record their own histories and concepts, New World people, plants, and animals had undergone profound dislocations.
The Americas confronted Europeans with an array of new plants, animals, and human beings. In many ways, such discoveries must have been a profound shock to Europeans, but much of the new information was incorporated into biblical and traditional systems of thought. European herbals were soon full of pictures of exotic plants from the New World, accompanied by fabulous accounts of their medical virtues. Indeed some physicians predicted that the medical wealth of the New World would prove more valuable than gold and silver. The Americas offered exotic new foods and medicinal substances, such as cocaine, curare, guaiac, ipecac, jalap, lobelia, Peruvian balsam, sarsaparilla, tobacco, and quinine. Today, about one-third of the world's most important plants can be traced back to the New World. Europeans did, however, bring many plants and animals to the Americas, including wheat, barley, rice, legumes, various fruits, sugarcane, pigs, horses, cows, sheep, donkeys, mules, chickens, and goats. Thus, contact between Europe and the Americas resulted in many changes, both deliberate and accidental, in the distribution of plants and animals throughout the world.
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