The Power of Plagues. Irwin W. Sherman

The Power of Plagues - Irwin W. Sherman


Скачать книгу
with a large amount of indigestible material such as bark or that were poisonous, low in nutritional value, or tedious to prepare and gather. The desirable attributes of plants that make them suitable for domestication include having a larger proportion of edible parts (large seeds) and a lower proportion of woody, inedible parts; being easy to harvest en masse (with a sickle); a seasonal nature; being easy to grind, easy to sow, and easily stored; and being high in yield and high in calories. Plants with these characteristics were selected for domestication. They fall into four categories: grasses (wheat, barley, oats, millet, and rice), legumes (peas and beans), fruit and nut trees (olives, figs, dates, pomegranates, grapes, apples, pears, and cherries), and fiber crops (flax, hemp, and cotton).

      There was a downside to animal domestication. Domesticated animals could be the source of human disease. As human populations settled down, they created heaps of waste—middens of animal bones, garbage, and feces. These served as the breeding grounds for and a source of microparasites; they also attracted insects that could act as vectors of disease, as well as wild birds and rodents carrying their own parasites and potential new sources of human disease. With each domesticated species of animal came the possible human exposure to new disease agents—parasites. For example, the numbers of diseases acquired from domestic animals (zoonotically) has been estimated to be: dogs, 65; cattle, 45; sheep and goats, 46; pigs, 42; horses, 35; rats, 32; and poultry, 26. Specifically, the human measles virus has its counterpart in the distemper virus of dogs and rinderpest in cattle. Smallpox has its closest relatives in the virus of cows and poxviruses in pigs and fowl, and human tuberculosis is a cousin of bovine tuberculosis. More recent examples of the “jump” from one animal species to another include HIV, in which a chimpanzee virus became humanized; monkey pox transmitted to humans by the bite of pet prairie dogs; SARS from civet cats; and Ebola from bats.

      With the clearing of forests, the planting of crops, and destruction of wild game animals, new ecological niches were created for insects and scavenging rodents. Mosquitoes and flies that once fed on game animals now found a new source of blood: humans. These “bloodsuckers” could act as vectors for malaria, yellow fever, and African sleeping sickness. Ditches, irrigated fields, and pottery vessels could also serve as breeding grounds for insects and snails, facilitating the transmission of blood fluke disease, yellow fever, malaria, elephantiasis, and river blindness.

      The crowd diseases of humans such as smallpox, measles, pertussis (whooping cough), tuberculosis, and influenza were initially derived from very similar ancestral infections of domesticated animals. At first those who hunted, farmed, and domesticated animals fell prey to the parasites they acquired, and some died, but in time resistance to these new diseases developed. When such a partially immune people came in contact with others who had had no such experience, a devastating epidemic could occur. It was these contagious diseases (caused by a wide variety of worms and “germs”) that would ultimately play a decisive role in the European conquests of native Americans, Africans, and Pacific Islanders; determine the outcomes of wars; loom large in the economic growth and prosperity of nations; and contribute to slavery and colonialism.

      3

      Six Plagues of Antiquity

image

      By 8000 B.C. the human population was settled in villages—first in the valleys of the Tigris and Euphrates Rivers in Mesopotamia and then along the Nile in Egypt, the Indus in India, and the Yellow River in China. Agriculture provided increased amounts of food for the people, but it also contributed to the conditions that would result in a decline in human health. It was the agricultural revolution, with the cultivation of crops and animal husbandry, that provided the driving force for the growth of cities (urbanization). Urban life also enhanced the transmission of certain diseases through the air and water; by direct contact; and by vectors such as snails, mosquitoes, and flies. The diseases of antiquity (5000 B.C. to A.D. 700) were characterized by parasites with long-lived transmission stages (e.g., eggs) as well as those involving person-to-person contact. Thus, most became established only when a persistent low level of infectious individuals could be maintained, i.e., were endemic; this required populations greater than a few hundred thousand.


Скачать книгу