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diseases—overview 543

Kiple, K., & Ornelas, K. C. (Eds.). (2000).The Cambridge world history the organism that causes malaria, were seriously debili-
of food. Cambridge, UK: Cambridge University Press. tating. Sleeping sickness, spread by tsetse flies, was so
Lappe, F. M. (1998). World hunger: 12 myths. New York: Grove Press.
Mann, J., & Truswell,A.A. (2002). Essentials of human nutrition. Oxford, lethal for human hunters that parts of East Africa
UK: Oxford University Press. remained uninhabited until recently, thus preserving vast
McNeill,W. (1976). Plagues and peoples. Garden City, NJ: Anchor Press.
Schwartz-Nobel, L. (2002). Growing up empty. New York: HarperCollins. herds of game animals that tourists now come to see.All
Shayerson, M., & Plotkin, M. J. (2002). The killers within. Boston: Little, the same, it is probable that our early ancestors were tol-
Brown and Co. erably healthy and vigorous most of the time.That, at any
Watts, S. (1997). Epidemics and history. New Haven, CT: Yale University
Press. rate, is the case among surviving African foragers as
observed by modern anthropologists. Probably infec-
tious organisms and their human hosts were fairly well
adjusted to one another, having evolved together in trop-
Diseases— ical Africa; and diseases of aging scarcely mattered since
their lives were far shorter than ours.
Overview Since many of Africa’s tropical parasites could not sur-

vive freezing temperatures, infections probably dimin-
isease refers to many kinds of bodily malfunction; ished sharply when human bands expanded their range,
Dsome lethal, some chronic, and some merely tem- penetrating cooler climates and spreading rapidly around
porary. Some diseases, like cancer and Alzheimers, the entire globe. Leaving African infections behind pre-
increase with age and result from disordered processes sumably increased human numbers and helped to sustain
within our bodies; others arise from infection by invad- their extraordinary geographic expansion.
ing germs and afflict children more frequently than adults But infections began to increase again when, in differ-
because we develop immunities after early exposure to ent parts of the earth, a few human groups began to cul-
them. Symptoms of infectious diseases vary with time tivate the soil and settled down in the same place all year
and place, owing to changes in human resistance and to round.That was partly because food production allowed
evolutionary changes in the germs themselves. Conse- more people to crowd together and exchange infections,
quently, written descriptions of ancient infections, even and more especially because supplies of water were liable
when quite detailed, often fail to match up with what to become contaminated by bacteria from human wastes.
modern doctors see. Hence, even when records exist, This increased exposure to infections of the digestive
exactly when a particular infection first afflicted people in tract. Moreover, wherever farmers resorted to irrigation,
a given place is often unknowable. And no one can wading in shallow water exposed them to a debilitating
doubt that major disease encounters also took place infection called schistosomiasis (or bilharzia), shared
among peoples who left no records for historians to with snails.And whenever cultivators came to depend on
examine. Nonetheless, and despite all such difficulties, a single crop for nearly all their food, dietary deficiencies
some landmarks in the history of the human experience were liable to set in. A diet of maize, for example, lacks
of disease are discernible from the deeper past, while in some of the amino acids humans need and provokes a
recent times the changing impact of diseases and medical chronic disease called pellagra. Finally, the domestication
efforts to control them are fairly well known. of animals, though their meat and milk improved farm-
ers’ diets, intensified disease transfers back and forth
Diseases among Foragers between humans and their flocks and herds.A large array
and Early Farmers of bacteria and viruses traveled this path.
It is safe to assume that our remote foraging ancestors Yet intensified exposure to such diseases did not halt
encountered many sorts of parasites, some of which, like the increase in farming populations. Instead more people