As wave after wave of Europeans landed on the shores of the New World in the years following Columbus's first sighting of San Salvador Island in the Bahamas, they brought with them not only a mélange of different languages and cultures, but a catalog of new diseases as well. Smallpox, measles, typhus, plague, and influenza were among the maladies previously unknown in the Americas, and therefore, the native populations had little immunological resistance to them. The large-scale epidemics that followed roundly devastated indigenous communities, producing great mortality and cultural disruption. This greatly weakened their capacity for military response and inadvertently paved the way for rapid European expansion and cultural dominance.

While these general points are widely known and accepted, now scholars gradually are documenting the next level of detail in these events: namely, the variability of impact of the European-introduced diseases, the size of the native population (and the size of the losses), and the disease picture in the Americas prior to European contact.

The European Introduced Diseases

Although historians agree that European contact with the native peoples of the Americas profoundly altered the morbidity and mortality profile of New World civilizations, the impact of disease and subsequent reduction in size of native communities actually was shaped by a variety of social and geographical factors. The hardest-hit areas were the major population centers, where large numbers and high densities facilitated the spread of infectious disease. In some cases, it is likely that disease even preceded actual European contact by spreading through native trade networks and other day-to-day human contacts. Small isolated populations were not affected until later and suffered less impact than did the larger, more centrally located ones. At the same time, nomadic groups fared better than those whose settlement remained relatively stationary.

Although direct mortality from disease was a major factor in the aboriginal depopulation of the Americas, the resulting social, economic, nutritional, and cultural disruption also began to take a toll on native groups. Many of those who survived the initial epidemics suffered decreased fertility that delayed demographic rebound, while their altered cultural and economic status created nutrition-related problems that further impaired overall health status.

Population Size

Estimates of the size of the aboriginal population of the Americas prior to European contact vary widely, ranging from 8.4 million to 100 million. These highly contrasting figures reflect the limited data available and the variable manner in which they can be interpreted. The lower estimates rely heavily on early European census data and the belief that indigenous group size may have been limited by pre-Columbian disease, geographical isolation, and various cultural factors.

On the other hand, some of the upper-end estimates reflect modern scholarly beliefs that prior to the Europeans' arrival, disease impact was minimal or even negligible. Such high numbers also convey interpretations that by the time early European explorers were in sufficient contact with native groups to record their numbers, the damage already had been done. In this perspective, the earlier (i.e., lower-end) census data reflect not the aboriginal numbers, but the survivors of already-transpired major epidemics.

Most of what scientists know today about the presence and impact of disease in the Americas prior to European contact flows from evidence gathered from the study of human skeletal biology and paleo-pathology. Careful study of human remains recovered from archeological contexts throughout the Americas has revealed abundant evidence of significant morbidity and mortality prior to European contact. Research has documented the pre-Columbian presence of such pathological conditions as tuberculosis, as well as a syphilis-like form of treponemal disease (caused by spirochetal bacteria). Demographic studies of recovered skeletal samples have revealed high proportions of infants and other young individuals who died before reaching adulthood, suggesting that dying an early death, for whatever reason, was a fairly common phenomenon throughout the region.

Temporal studies of pre-Columbian remains from different parts of the Americas further suggest that sickness and premature death were increasing over time. Although reasons for this were likely complex, an important factor was the gradual increase in population size and density, coupled with changes in nutritional and settlement patterns that stemmed from the rise of agriculture and a growing reliance upon crop production.

As populations shifted subsistence patterns from hunting, gathering, and fishing toward agricultural pursuits, they not only changed what they ate, but how and where they lived. New and larger villages with more sedentary populations began to spring up. The resulting higher densities of people living together for longer periods of time presented greater opportunity for disease transmission.

In areas of the Americas where corn was the primary agricultural staple, it is likely that nutritional deficiencies resulted as well. The diversity of the former hunting, gathering, and fishing diet may have had advantages over the newer, perhaps more restrictive, agriculture-based diet.

The Case of Ecuador

Since the early 1970s, the excavation and analysis of human remains from archeological sites in Ecuador gradually have yielded assembled data that provide scientists a unique opportunity to evaluate long-term patterns of morbidity and mortality. The earliest of these samples, 192 individuals from the Vegas Complex on the Santa Elena Peninsula, dates back more than 6,000 years to a time prior to the introduction of agriculture and ceramics. This civilization consisted largely of hunters, gatherers, and fishermen who chose to bury their dead in a central location.

Many additional samples from Ecuador have been studied dating from more recent times, including those from coastal populations during the period of transition to agriculture, as well as samples from still-later populations at a time when reliance upon agriculture was intensive and increased population size supported more complex political systems. Finally, other samples have been examined that were discovered at the foundation of the Convento de San Francisco in Quito. This monastery was part of the first elaborate religious structure built by the Spaniards in South America, and the samples offer a unique historical perspective on the life and disease patterns of highland populations during this period.

To obtain mortality information, investigators first estimate the age at death from each skeleton. For children, the most accurate estimates come from assessment of the stage of dental formation. For adults, a variety of age indicators are evaluated, including arthritic conditions, dental features, changes in the appearance of bones of the pelvis, ribs and skull, and, sometimes even microscopic examination of bone tissue. Sex estimates for adults come mostly from evaluation of pelvic bones. When linked together, these data can be used to construct mortality profiles and calculate life expectancy patterns for the represented populations.

Information is collected on all disease conditions noted on the remains. Of special interest are generalized indicators of morbidity and data that can be compared easily. These include dental features such as cavities, abscesses, and hypoplasias (defects in the tooth enamel produced by health problems during the early years of life while the teeth still were forming). Bone features that can be compared among skeletons include fractures, arthritic conditions, evidence of infection, and abnormally porous areas on the skull that could have been produced by the presence of a disease condition.

In the Ecuador study, the sample with the lowest frequency of these morbidity and mortality indicators is also the earliest: that of the Vegas Complex pre-agricultural society. As time moves on, the evidence for increased morbidity and mortality begins to mount.

One study also shows unusual regional variations that suggest climate may have played a role in disease impact as well. Pre-Columbian samples from the tropical northern coast showed high levels of morbidity and mortality, despite evidence that the populations in this area were relatively small with varied diets. On the other hand, highland samples showed the lowest evidence for health problems, in spite of the high-altitude environment. The coastal samples were from an intermediate time frame but suggest, with some variability, a gradual increase in health problems throughout the time prior to European contact.

The samples that postdate European contact reveal a greater variety of disease evidence than earlier ones, yet the overall frequency figures for morbidity and mortality in this group are not dramatically different. Collectively, the data suggest a gradual and generalized worsening of health conditions throughout the pre-Columbian era, despite regional variations. These problems persisted following Columbus's discovery, exacerbated by the arrival of new and mortal diseases from Europe.

Prior to European contact, Ecuador's indigenous populations not only were suffering from growing disease problems, but those in the sierra also struggled mightily with a large-scale Incan invasion from the south. Just decades prior to the Spanish arrival, an estimated 100,000 natives had died during protracted warfare with Inca rule.

The historical works of Suzanne Austin Alchon (1991), Linda A. Newson (1995), and others also indicate that Ecuador's native populations most likely suffered the impact of European-introduced diseases prior to actual physical contact with Europeans. As in the rest of the New World, the native population had little natural resistance to these new diseases, and the increase in mortality and morbidity was profound. There is some evidence of greater coastal impact, perhaps due to a climate more favorable to the spread of pathogens. Disease mortality, combined with decreased fertility and nutritional problems and aggravated by subjugation under harsh conditions of manual labor, conspired to dramatically reduce the size of the native population.

The population of Ecuador in the pre-Columbian era is estimated to have been as large as 1.6 million. Principally through disease mortality in the years following initial European contact, this number was reduced by a factor estimated at about 5 to 1 in the sierra, and about 21 to 1 on the coast. In the port city of Guayaquil, estimates of the reduction ratio run as high as 100 to 1.

New Discoveries for a New Millenium

Studies of the discovery and colonization of the New World, beginning with the decoding of ancient writings and chronicles left by early explorers, have shed new light on one of history's most exciting chapters. Yet these accounts do not--and cannot--tell us the whole story. Particularly within the realm of science, many questions remained unanswered, even as the various scientific disciplines gradually uncover the complex factors behind the decline of ancient civilizations and the dynamics that so profoundly altered the health situation and well-being of these populations.

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Douglas H. Ubelaker is a curator of physical anthropology in the Department of Anthropology at the Smithsonian Institution's National Museum of Natural History. Since 1973, he has worked extensively in Ecuador and other areas of the Americas on the excavation, analysis, and interpretation of human skeletal remains from archeological contexts, forming the basis for much of the research referenced in this article.