Prehistoric Incidence of Disease
According to L. E. St. Hoyme (1969): “[I]t is easy enough to explain why few diseases entered the New World with man; it is far harder to explain the origin of those diseases that man acquired in the New World before the coming of Columbus.” The entry of humans into the Nearctic realm through the land bridge of the Bering Straits area up to 35,000 years ago (Yi and Clark 1985) has been assumed to have been sporadic, small scale, and across a harsh environment.
More recently, the founding groups have been seen as limited to between 300 and 500 and possibly associated with but three waves of migration - the so-called Amerind, Na-Dene, and the Aleut-Eskimo - none older than 15,000 B.C.; the order of chronology, however, remains uncertain (Greenberg, Turner, and Zegura 1986). Given this general scenario, it is claimed that the numbers would be far too small to sustain a human-to-human mode of infection (Cockbum 1963; St. Hoyme 1969). However:As man wandered around the world, he would take many of his parasites with him. Those such as the louse, the pinworm, herpes virus, typhoid bacillus, and others that were closely attached to him would not have great trouble in travelling in this fashion. Others that required transmission by a specific intermediate host would die out once the territory of the necessary intermediate hosts was left behind. (Cockbum 1963)
Moreover, it now seems possible that human tuberculosis made the voyage as well, in that one or more of the Bering Strait migrants may have had a childhood primary infection that, like 5 percent of cases today, developed into chronic destructive tuberculosis (Myers 1965; Steinbock 1987). The predisposing factors for this transformation (any condition that impairs acquired cell-mediated immunity) include poor nutrition, diabetes, or an acute infection possibly from a traumatic incident.
All of these could have occurred in a band of hunter-gatherer adventurers in spite of the “cold screen.” At least one scholar (Klepinger 1987), however, denies that there is any evidence of the disease being carried over by the Beringia transmigrants, and claims that it would be more likely to arise de novo in the Western Hemisphere.But what of the “cold screen” or, perhaps more correctly, the cold filter? T D. Stewart (1960), arguing that New World populations were relatively free of Old World pathogens, stated that “the cold of the Far North has been characterized as a screen serving in past times to prevent the flow of many pathological germs along with the movements of their human hosts,” a position that has become widely accepted in the literature (Jarcho 1964; Hare 1967; Dunn 1968; St. Hoyme 1969; Crosby 1972, 1986; Newman 1976; Martin 1978; Dobyns 1983). Thus it has been claimed that
[n]ot only did very few people of any origin cross the great oceans, but those who did must have been healthy or they would have died on the way, taking their pathogens with them. The indigenes were not without their own infections, of course. The Amerindians had at least pinta, yaws, venereal syphilis, hepatitis, encephalitis, polio, some varieties of tuberculosis (not those usually associated with pulmonary disease), and intestinal parasites, but they seem to have been without any experience with such Old World maladies as smallpox, measles, diphtheria, trachoma, whooping cough, chicken pox, bubonic plague, malaria, typhoid fever, cholera, yellow fever, dengue fever, scarlet fever, amebic dysentery, influenza, and a number of helminthic infestations. (Crosby 1986)
The aborigines, then, seem to have been relatively disease-free, as a result of their isolated and limited populations initially, and the harsh climate. Moreover, given the nature of the immigrant economy, and the paucity of animal domesticates, only the guinea pig, turkey, and South American cameloids served along with the dog in the New World as reservoirs for horizontal transfer of disease (Newman 1976).
Thus we have an image of human beings in a nearly ideal state of physical health, removed from the main channels of human disease (Dubos 1968). However, B. Trigger (1985) has rightly warned:Scholars should not succumb to the temptation of believing that in prehistoric times illnesses had not been prevalent or of concern to native people [for] [t]he extraordinary levels of mortality and other misfortunes that followed European contact must have caused them to idealize earlier times as a halcyon age of physical health, economic prosperity, and social harmony.
Alfred Crosby (1986) maintains that the spirochetal diseases of pinta, yaws, and venereal syphilis were present in pre-Columbian America. A great deal has been written regarding Treponema pallidum (the organism causing venereal syphilis) and its virulent expression in Europe following the discovery of Nearctica (Cockburn 1971; Crosby 1972). However, it appears now that like many other organisms this one spirochete has adapted over time to present different clinical patterns under different climatic and sociological regimes (Hudson 1963, 1965, 1968). Moreover, C. J. Hackett (1963, 1967) has argued that pinta was brought into the Americas by the founding groups and has “a long duration of infectiousness which would maintain it in small population groups, even in families, which suggests that it is the early human treponematosis.”
Additionally, there is some suggestion that the treponematosis that causes yaws produced depressions in some prehistoric Indian crania, which may indicate a northern extension of yaws in earlier times up the Mississippi into the Midwest (St. Hoyme 1969). On the other hand, as recently as 1967, it was argued that there was no Osteological proof of pre-Columbian yaws and that the traditional view that it had been introduced by African slaves was still acceptable (Stewart and Spoehr 1967). In addition, recent reports (Rothschild and Turnbull 1987) of syphilis in a Pleistocene bear skeleton in Nebraska have been discounted, as no authenticated treponemal infections have been found in a nonprimate (Neiburger 1988).
In summary, sparse populations of indigenes would be fairly free of diseases transmitted from other humans, although their contact with game, and especially their ingestion of raw meat and of water, would bring them into contact with some invasive pathogens (Fenner 1970). Their necessarily mobile hunting-and-gathering life-style would protect them from a degree of self-contamination, but failure of the hunt would periodically stress them and accidents would traumatize some.
As the sedentary maize-based cultures spread north from Mexico, villages appearing after 7000
B. C. and, later, larger settlements (possibly as large as 40,000 as at Cohokia, Illinois) created other health problems, among them those of sanitation (Heidenreich 1971; Crosby 1986). Furthermore, the invasion of settlements by rodents and fleas would have led to human contact with the illnesses of native animals (Dobyns 1983). One can only speculate as to the impact of these concomitant aspects of agriculture; but while the carrying capacity of local areas, and hence their population densities, grew, there is no firm evidence that morbidity declined. Rather, there may well have been a shift in the causes of death, reflecting the new relationship between human and land (Martin 1978; Dobyns 1983).