Monday, December 5, 2011

Health & the Rise of Civilization

The emergence of agriculture and civilization represented an astonishing advance for humankind.  Or did it?  A growing number of people are raising questions about this cherished belief.  Mark Nathan Cohen, an anthropology professor, wrote Health & the Rise of Civilization to shine a light on the history of human health.  His book is fascinating.
Hunter-gatherers did not enjoy perfect health, but they were vulnerable to far fewer maladies than people in agricultural societies.  In hunter society, dying from accidents was common.  Intestinal parasites were common, and hunters were vulnerable to zoonotic diseases, which could use humans and other animals as hosts, but couldn’t be transmitted from human to human.  Diseases that could be transmitted from human to human were rare.  Cancer, heart disease, and other degenerative diseases were very rare, as was starvation. 
There are scientists who study the health of dead folks via their bones or mummified remains.  Their research reveals that big game hunters were the best nourished group in human history.  Animal foods are the best source of complete proteins, and they are rich in other nutrients.  When big game declined, we shifted to intensified foraging, and hunted for small game.  The people of this new phase were shorter and experienced more infections. 
With the shift to farming, the quality of our health plunged.  Infection rates doubled at some Illinois sites.  Tuberculosis became common.  Intestinal parasites increased.  Reduced nutrition led to shorter people.  Life expectancy did not increase. 
Wild hunter-gatherers were nomadic.  They frequently packed up and moved, leaving their excrement behind.  Wild grazing animals were also nomadic.  When they needed more vegetation, they moved on, leaving their excrement behind.  The nomadic life had two advantages — animals were free to move in pursuit of better nutrition, and by moving they left behind the risks of acquiring the diseases of filth and confinement. 
Farmers, on the other hand, spent their lives in one place, in denser populations, and their excrement remained on location.  This delighted fecal-oral diseases.  Farmers often confined numerous domesticated animals, which converted plant material into excrement that also accumulated on the farm.  Thus, the farm was transformed into a treasure chest of pathogens, worms, and intestinal parasites.  Domesticated animals suffered from diseases that were rare or unknown in wild animals.
The farm was home to a mixture of species: cattle, goats, sheep, pigs, horses, dogs, waterfowl, and poultry.  By keeping multiple species in close proximity, we encouraged the transfer of diseases from one species to another.  Humans acquired livestock diseases like measles, smallpox, influenza, diphtheria, and the common cold.
Living in permanent homes with stored food led to frequent visits from hungry rodents and insects, who sometimes carried pathogens.  Living indoors made it easier for contagious illness to spread from person to person.
Malaria and yellow fever were originally treetop diseases of non-human primates, but they spread to humans as farmers cleared forests.  Malaria is rare among nomadic people, but common in farming societies.  It is especially serious where farmers grow rice in flooded paddies (mosquito incubators).  Some believe that malaria has killed more people than any other disease.
Growing civilizations typically created extensive trading networks.  Trade and travel spread many diseases to new regions where the inhabitants had no immunity.  These include bubonic plague, smallpox, and tuberculosis.  Speedy new steam ships and locomotives enabled cholera to spread explosively in the last 200 years, killing millions.
Hunters enjoyed a diverse and nutritious diet, and farmers didn’t.  The farm diet majored in cereals and tubers that were rich in calories but contained fewer nutrients.  This diet often lead to illnesses from mineral and vitamin deficiencies — pellagra, anemia, thyroid problems.  Tooth decay was almost unknown among hunters, but cavities are a common problem for people who consume gummy cereal foods and sugar.
The spread of disease closely followed the spread of civilization, and the growth of population centers.  Measles originated in cattle.  It couldn’t survive in human communities of less than 500,000 people, because there were not enough babies to provide an adequate supply of new hosts.  Thus, measles is a new disease for humans.  I was surprised to learn that there was little contagious disease prior to the shift to agriculture.
Modern people tend to be physically inactive, and consume generous portions of calorie-intense processed foods that are very low in fiber — an excellent recipe for obesity.  The twentieth century witnessed the emergence of degenerative diseases that had previously been rare — cancer, heart disease, diabetes, etc.  It seems that most of the amazing technology of modern medicine is used to counteract the unintended consequences of the rise of civilization.  With seven billion people, vast numbers of confined livestock and poultry, a high-speed global transportation system, and a growing number of drug-resistant pathogens, the conditions are perfect for the creation and spread of catastrophic pandemics.
The idea of “progress” first appeared around 1800, and it proudly celebrated recent improvements over the horrid life of the 14th to 18th centuries.  Cohen said that the people of this dark era “may have been among the nutritionally most impoverished, the most disease-ridden, and the shortest-lived populations in human history.”  Members of the progress faith incorrectly projected this horror farther back, to include healthy, well-nourished prehistoric hunters.   
Cohen concluded that our beliefs in the benefits of civilization are in need of revision, because civilization did not make life better for most people.

Mark Nathan Cohen, Health & the Rise of Civilization, Yale University Press, New Haven, 1989. 
For additional information on health in civilized societies, Man and Epidemics by Charles Edward Amory Winslow (1952) is excellent.  Laurie Garrett contemplated future health risks in The Coming Plague (1994).

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