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Domestication and Disease
William McNeill wrote a fascinating history of disease. It’s sprinkled with some sparkles of outside-the-box ideas. First, some basics. In the family of life, parasites are the eaters, and hosts are the eaten. You are host to billions of tiny microparasites (bacteria, viruses, and multi-celled critters) that live within your body, from infancy to the finish line. Usually, they are good guys. They promote your survival, while enjoying a free lunch on the nutrients they find within you. There are also large bodied macroparasites, like lions, tigers, sharks, and humans.
Not all microparasites are our buddies. Some can cause disease. They can trigger infections that result in mild illness, or intense infections that can kill you. Sometimes their attempts at invasion are blocked by a robust counterattack from your immune system. Hosts can sometimes serve as carriers of disease-causing parasites, helping them hitch free rides to uninfected new hosts. Carriers sometimes don’t display symptoms, or feel noticeably sick.
Hominins evolved in Mother Africa. Tropical rainforests are the ecosystems having the highest biodiversity of plants, animals, and parasites. Over the course of many thousands of years, Big Mama Nature nurtured the coevolution of parasites and hosts so that the balance between eaters and eaten was generally stable over the eons. This discouraged single species of renegade plants or animals from overturning the ecological boat. Everyone in the family of life, from microbes to crocodiles, simply played their assigned role. In the never-ending sacred dance, we all feed each other, and it is right and good.
Because of this general equilibrium, lions and herds of large herbivores could share the same grasslands for century after century. The predator’s objective was not to eliminate as many prey as possible. Their job was to have a nice time participating in the sacred dance. Unfortunately, the equilibrium got more and more wobbly as humans shifted from the slow lane of genetic evolution, and swerved into the dangerous express lane of cultural evolution (weapons, fire, language, etc.).
Epidemics of highly contagious cleverness fever enabled some cultures to live way too fast and hard, causing serious damage to their ecosystems. This process was similar to how disease-causing microparasites sicken or kill their hosts. McNeill concluded that civilization could be seen as a macroparasite that is ravaging the family of life — like “an acute epidemic disease.” He wrote in 1976. Today, we would call it a devastating global pandemic.
Before the plague of cleverness fever, Big Mama Nature lovingly kept our ancestors humble. In the good old days, the notion that we were the glorious Crown of Creation was unknown, because it was idiotic. Tsetse flies laugh out loud at the myth of human supremacy. When an anthropologist asked some wild folks how humans were different from other animals, they were baffled. There is no difference. What a stupid question! A Kuyukon elder once told Richard Nelson: “Every animal knows way more than you do.”
Before cleverness fever and agriculture, we didn’t suffer from devastating population explosions, because our bloodthirsty carnivorous macroparasite brothers and sisters regularly invited us to lunch. Over time, disease-causing microparasites came to assume a larger role in preserving the equilibrium. Both teams weeded out the weak, elderly, and unlucky. This was their sacred mission — a lovely sustainable circle dance, not a horror show blitzkrieg.
The high biodiversity of tropical rainforests enabled a huge variety of parasites to feast on a huge variety of hosts. McNeill noted that monkeys and tree-dwelling apes are hosts to 15 to 20 species of malaria (humans just 4). Wild primates are also hosts for legions of mites, fleas, ticks, flies, worms, protozoa, fungi, bacteria, and more than 150 insect-borne viruses.
He suspected that this daunting parasite heaven was probably a significant reason why civilization emerged more slowly in Africa. Civilization is about growth and control, not equilibrium. The incredible biodiversity of rainforests creates a powerful communal life force that regularly frustrates the efforts of clever tropical primates to become the domineering King of the Jungle.
According to McNeill, some super-important events in the human saga included our transition from tree dwellers to ground dwellers, the domestication of fire, and the colonization of snow country. The climate in snow country was temperate, not tropical. While warm moist tropical rainforests were ideal habitat for a staggering number of species, snow country was less complex. Organisms that could not tolerate freezing temperatures, or low humidity, were absent from the playground.
And so, the brave pioneers wandered out of their tropical homeland, and into a gentler cooler world. Snow country was home to far fewer disease-causing parasites, none of which specialized in infecting primate hosts. Snow country was also home to vast numbers of large game animals that had never seen humans before, and had no instinctive fear of them.
Large game was the pioneer’s primary energy source, and it was eventually depleted by overhunting, over the course of thousands of years. A band could dine on a mammoth for a week, or they could invest far more time and effort killing a ton of bunnies. As the pioneers expanded into new regions, megafauna extinctions followed in their wake. Eventually, folks had to make a painful choice — labor-intense food production (agriculture) or mindful conservation via voluntary self-restraint (family planning). Because they were basically ordinary animals, they lacked the mental bandwidth to automatically deal with this complicated predicament.
Today, our primary energy source is fossil energy (ancient sequestered carbon), which we are depleting at an insane rate, over the course of mere decades, with complete disregard for how this will impact our beloved kiddies. (Sorry!) We’re burning it up like crazy, to support the survival of way too many people, who live like there’s no tomorrow, for no good reason. One estimate is that, of all the carbon emitted during the entire human saga, more than half of it has been emitted just since 1990 — a single generation (my generation). (Blush!)
Anyway, to human supremacists, the escape from a tropical parasite heaven would seem like a wonderful triumph. Pioneers were now “liberated” from the constant threat of many killer diseases. We’re so smart! Their impulsive joyride of adolescent cleverness inspired them to hippity-hop blindfolded into an ecological minefield. Oh-oh! The tropical diseases they had escaped from had actually been their allies. Their parasite partners, both macro- and micro-, had worked hard to prevent population outbursts, which therefore discouraged overhunting, which therefore discouraged starvation. Imagine that! In the good old days, we didn’t need wisdom, foresight, or troublemaking smarty pants. All we had to do was dance.
Deep ecology thinkers, on the other hand, would be likely to perceive the invasion of snow country as an extremely dangerous experiment (i.e., stoopid). See, Big Mama Nature was blessed with deep wisdom, not juvenile cleverness. Under her guidance, genetic evolution had slowly and carefully fine-tuned us for survival in tropical regions. Our ancestors got sun protection from their beautiful brown skin and curly hair, and increased heat tolerance from their sleek furless exterior, combined with a high performance collection of juicy sweat glands.
Earlier in this word dance, I talked about the snow monkeys of Japan, who faithfully obeyed every commandment of genetic evolution, and allowed Big Mama to very slowly and carefully provide them with luxurious warm coats. They were so lucky to avoid the curse of cleverness. As a result, they had no need to domesticate fire, make hunting weapons and clothing, destroy the topsoil, destabilize the climate, trigger pandemics, and so on.
The human pioneers who invaded snow country, on the other hand, violated every commandment. Rather than patiently evolving for many thousands of years, the smarty pants impulsively took a blind leap into the unknown — sink or swim, let’s go! Whee! They bet everything on cleverness, and managed to survive, but their winnings were tiny, compared to the enormous cost of the countless unintended consequences they conjured into existence — the wobbly, wheezing, delirious, jam-packed world outside your window, for example.
As mentioned earlier, the temperate grasslands of Eurasia were home to lots of wild sheep, goats, cattle, and horses — herd animals that were suitable for domestication. They eventually became vital assets for metastasizing empires and civilizations. Over time, herds of enslaved livestock accumulated wherever green grass was abundant.
As mentioned earlier, monocultures of crop plants are irresistibly attractive to legions of ambitious parasites seeking free lunches, like potatoes attract blight fungus. Similarly, concentrated mobs of herd animals are also powerful magnets for swarms of hungry uninvited parasites. Uninvited? Methinks monocultures of domesticated plants and animals are essentially impossible-to-ignore invitations to parasites. Today, a sprawling herd of seven-point-something billion tropical primates has a “Kick Me” sign taped to its back, and billions of giggling disease-causing parasites are eager to obey. Monocultures are embarrassing abnormalities that ecosystems must resolve.
McNeill noted that humans did acquire some diseases via wild animals — bubonic plague (rodents), rabies (bats), yellow fever (monkeys), and so on. But most of the classic infectious diseases of civilization were acquired from close contact with herd animals, primarily domesticated critters. Once acquired, and over time, some of these parasites became capable of direct person-to-person transmission. These included tuberculosis, measles, smallpox, chicken pox, whooping cough, mumps, and influenza. By and by, human health in the Old World took a sharp turn for the worse following the domestication of herd animals. In the Bible, “plague” appears 128 times, and “pestilence” 50 times.
James Scott noted that humans share a large number of illnesses with farm yard animals, including poultry (26), rats and mice (32), horses (35), pigs (42), sheep and goats (46), cattle (50), and dogs (65). When different species live crowded together in close proximity to a herd of humans, trouble is sure to follow.
This was not the case in Australia, where zero plants or animals were domesticated. Bill Gammage wrote about the Aborigines. Over the course of many thousands of years, they developed time-proven strategies for living well in a challenging land. They built no cities, but some groups inhabited simple villages during the months when local food resources were seasonally abundant. Consequently, no serious diseases were native to Australia.
The story was similar in the New World, where only two species of herd animals were domesticated, alpacas and llamas. They did not live in enormous herds in any of the vast American grasslands. Their range was limited to remote regions of the Andes Mountains in western South America. Neither has been associated with the emergence of any epidemic disease.
Why were just two large herbivores domesticated in the New World? McNeill pointed out that around 12,000 years ago, the megafauna species in the Americas were sharply thinned by extinction spasms. Some of the large herbivore species that vanished may have been suitable for domestication, but they blinked out. Modern science has not yet figured out how to domesticate extinct animals.
On the plus side, no powerful epidemic diseases were native to the Americas. On the downside, Native Americans had zero immunity to the nasty microparasites that crossed the Atlantic in the 1500s, and eventually killed maybe 90 percent of them. The spectacularly deadly Old World disease pool crashed head-on into maybe 100 million helpless sitting ducks.
Disease pool? Long ago in the Old World, different diseases emerged in different regions, as local parasites learned how to infect local hosts (sort of like how scattered tribes developed unique languages). In the beginning, these local diseases resided in limited territories. Over time, expanding trade networks and civilizations linked more and more communities and regions together. So, homegrown diseases had more opportunities to hit the road, and infect defenseless populations elsewhere. At the same time, it became easier for exotic diseases from elsewhere to visit your neighborhood, and spur a surge in coffin sales.
Communities along the entire coastline of the Mediterranean Sea were extensively interconnected by regular commerce. Because of these trade webs, the population of the Mediterranean Basin shared the same mob of diseases. McNeill called the residents of this region a disease pool. India’s disease pool hosted a different assortment of microparasites. China’s pool had yet another collection. He jabbered at great length about how the different Old World disease pools expanded and blended together over the centuries. By 1500, Eurasia was essentially home to one unified disease pool, a powerful hurricane of pathogens. It then leaped across the Atlantic and absorbed the New World into its pool.
Alfred Crosby described the diseases present in the Americas prior to colonization. They included “pinta, yaws, venereal syphilis, hepatitis, encephalitis, polio, some varieties of tuberculosis, and intestinal parasites” (syphilis and tuberculosis are controversial). McNeill noted that the native traditions about precolonial times did not mention epidemics. Aztec history described just three disasters (in maybe 780, 1320, and 1454) that caused many deaths, but they seem to have been the result of crop failure or famine. In the early days of colonization, elderly natives told Spaniards that they had no memory of disease prior to conquest.
Obviously, the European diseases overwhelmed the Native Americans. Today, folks with white faces are now the majority in many regions of North and South America. This is far less true in Africa. When whites colonized the Americas, the natives had no immunity to their diseases, and they were massively swept away. When whites tried to colonize Africa, many Africans were swept away, but they were not alone. Mother Africa was not amused by the disruptive infestation of spooky looking albino-like primates from outer space, and she punched back very hard, using her deadly arsenal of tropical diseases, which white folks had little immunity to.
Michael Williams said that she fetched her mojo bundle and mercilessly paddled white asses with dysentery, yellow fever, typhoid, and especially malaria. The mortality rate (deaths per thousand) for white folks in Africa was ten times higher than the rate for those who wisely remained back home in Europe. Africa was “the white man’s grave.” But the whites brought firearms, and before long began carrying away everything of value they could get their hands on (gold, diamonds, ivory, slaves, etc.). They were really into wealth and status.
Epidemic vs. Endemic Diseases
Alfred Crosby noted that when Siberian hunters first discovered America, they entered a continent that was home to no humans, or any of our close relatives (chimps, gorillas, etc.), so there was no existing pool of ape-loving pathogens ready to welcome them, infect them, and compost them. Nathan Wolfe added another point. Humans and Old World monkeys are more closely related genetically, because their ancestors have been hanging out together for 5 million years. New World monkeys are far less closely related to us, because our relationship is just 15,000 years old.
Also, when America was discovered 15,000 years ago, there were no domesticated animals in the entire world, except for dogs. Because of this, James Scott believes that epidemic diseases probably didn’t exist anywhere at that time. Most diseases probably emerged in the last five to ten thousand years, as an unintended consequence of domestication, civilization, and other variants of self-defeating cleverness.
Epidemic refers to diseases like smallpox, which hopped off a ship in North America, rapidly infected a population that had no immunity to it, and killed millions. It was an unfamiliar pathogen that infected a defenseless population for the first time. Likewise, when measles arrived in America, it also exploded with deadly epidemic force.
Back in Europe, measles had over time softened into a less lethal endemic disease, because it remained in the population as a chronic infection for many years. What we call “childhood diseases” are endemic — measles, mumps, whooping cough, etc. Endemic diseases can reside in cities and in locations near them, but not in small nomadic groups of wild people. The host population must be large enough to preserve the pathogen, by allowing it to pass from one generation to the next.
Prior to modern high mobility, endemic measles required a population of 250,000 to 500,000 to survive in a community. Today, as many millions travel everywhere all the time, it’s easy to get infected in locations far from Measles City. The shift to agriculture enabled the existence of dense populations. Before agriculture, endemic measles could not exist anywhere. Epidemic measles likely originated in cattle.
Crowd vs. Tropical Diseases
Nathan Wolfe and team analyzed the origin of 25 major infectious diseases that sicken humans. They sorted them into two categories: 10 tropical diseases, and 15 they called temperate. “Temperate” is not a precise description, because temperate diseases are also free to infect folks in the tropics. Infectious diseases are complicated rascals that don’t neatly fit into tidy categories. Wolfe summed it up like this: “The sources of tropical diseases tend to be wild primates. The sources of temperate diseases tend to be domestic animals.”
Measles originated in cattle, but cattle no longer function as a reservoir for the measles virus. So, cowgirls don’t catch measles from cows. The virus is preserved entirely in the human herd, so healthy cowgirls catch measles from infected people. This direct person-to-person transmission is a common characteristic of the diseases of civilization — crowd diseases. Crowd diseases include diphtheria, influenza, measles, mumps, pertussis, plague, smallpox, typhoid, and typhus. Two crowd diseases also have animal reservoirs, plague (rodents) and influenza (wild birds).
Tropical diseases include Chagas’ disease, dengue fever, yellow fever, sleeping sickness, and malaria. These are transmitted by insects. None of them require a significant population of hosts. Even small bands of nomadic hunter-gatherers are vulnerable to them. All of them originated in the Old World, except for Chagas’ disease, a New World parasite.
Tropical diseases originated in tropical regions, but some were free to visit temperate places. Geoffrey Marks noted that yellow fever arrived in New York by 1686, and it had a good time. It returned in 1702, 1743, 1745, and 1748. During Philadelphia’s yellow fever epidemic of 1793, terrified citizens either fled town, or stayed off the streets and shut themselves indoors. They obsessively cleaned their dwellings. When they went outdoors, they held handkerchiefs or sponges soaked with vinegar or camphor near their noses. Burials had no ceremonies; no friends or relatives appeared. People quit shaking hands, and were affronted when a hand was offered. Four thousand died between August and October.
Like animal domestication, plant domestication also had a devastating impact on human health. Evolution optimized tropical primates for a life of foraging and scavenging in a warm climate, while living in small, widely scattered, nomadic bands. Much later, when some folks got addicted to agriculture, they multiplied in number, established permanent villages and towns, and adapted a sedentary lifestyle. They lived in greater concentrations, and became something like herd animals — highly attractive to parasites, similar to how wheat fields are highly attractive to locusts.
Steven Johnson wrote about the London cholera epidemic of 1854. At the time, London was the biggest city in the world, and it was suffering from a population explosion. One question tormented the minds of urban bureaucrats: “What the <bleep> are we going to do with all this shit?” Londoners got their water from shallow wells in their neighborhoods. Sewage and other wastes were stored in cesspools. When your cesspool was full, the night soil men hauled the dreck out to farms, where it was applied to fields.
As the city expanded, the distance to farms increased, as did the cost of removal. So, more and more stinky muck remained in town. Dung heaps grew to the size of large houses. The entire city had a powerfully intoxicating aroma. Parliament had to shut down during a heat wave 1858, when the flowing sewer known as the Thames River emitted the Great Stink.
The center stage of Johnson’s book was a well pump at 40 Broad Street, in the Soho district. Near the end of August 1854, the six month old daughter of the Lewis family got sick and died. Her soiled diapers went into the cesspool, and caused the biggest cholera outbreak in London history. The cesspool was only accessible to the Lewis family. Other tenants in the building “tossed their waste out the windows into the squalid courtyard at the back of the house.” The cesspool was in the cellar, and the brick-lined well was just 32 inches (81 cm) away. Oh-oh!
All the experts, except one, agreed that the cause of cholera was miasma — stinky air. Since miasma was certainly the cause of the problem, the solution was to move the stink elsewhere. So, in the name of public health, they built sewer systems, and directed the smelly crud into river. Before long, “the Thames had been transformed from a fishing ground teeming with salmon to one of the most polluted waterways in the world.” Meanwhile, the epidemics raged.
In this era, private water companies were also growing, in response to the trendy flush toilet fad (flushes filled cesspools even faster). There was no unified city plan. So, it was not uncommon for water company intake pipes to be just a bit downstream from sewer system discharge pipes. Guess what happened.
Hans Zinsser was the scientist who identified the parasite that caused typhus, and then he wrote about its history. Typhus has been a very popular disease for centuries — not among small groups of wild nomads, but among civilized people who live in dense concentrations. The bacteria is transferred to humans via lice, and it favors folks whose personal hygiene habits were minimal to none. In the good old days, taking a bath once in a while was not at all trendy. Few if any baths were taken after October.
He wrote that prior to 1890, “Cities and villages stank to heaven. The streets were the receptacles of refuse, human and otherwise. The triangular intervals which one sees between adjacent medieval houses in streets still inhabited are apertures through which waste, pots de chamber, and so forth, could be conveniently disposed of from upper stories….”
Typhus was really fond of soldiers, sailors, and prisoners. At the conclusion of the First World War the victor was clear, “Typhus won the war.” Epidemics in Russia killed 2.5 to 3 million people between 1917 and 1921. John Gunther wrote that in the Congo, all Urundi women shaved their heads to avoid typhus (lice).
To be continued…
Here are my reviews of some disease-related books:
Bird Flu by Michael Greger
Epidemics by Geoffrey Marks and William K. Beatty
Health & the Rise of Civilization by Mark Nathan Cohen
Nutrition and Physical Degeneration by Weston Price
Plagues and Peoples by William McNeill
The Antibiotic Paradox by Stuart Levy
The Ghost Map by Steven Johnson
The Plague of the Spanish Lady by Richard Collier