Is history inevitable? Could it have been different? Consider the following imaginary scenario: Native American Indians develop gunpowder, forge iron, organize militarily, and build sailing ships. They then set sail east across the Atlantic years before Columbus and conquer Europe. The great cathedral in Paris might be known today as Mother Earth instead of Our Lady (Notre Dame).

Let us ask some related questions: Why didn't Africa colonize Europe instead of the other way around? When explorers came to the New World, why was the arrow of disease essentially one way? Why did literate, industrialized, politically centralized states based on agricultural surplus appear in some areas and not others? And finally, the core topic in this unit: what is the effect of disease on human biological evolution?


In this article I will trace the origin of crowd diseases historically and argue that they have shaped society and us biologically. Geology and geography come before history. Resources and environment have shaped human opportunity and culture. I credit the overall theme of this article to Jared Diamond's Guns, Germs, and Steel.



In the broad sweep of time, hominids became bipedal, acquired the skilled use of tools, mastered fire, and developed symbolic thought. In Europe modern humans replaced the last of the Neandertals 35,000 years ago and burst upon the scene with exponentially accelerating rates of cultural and technological change.

The first big 'jump' is one we can only speculate about: the genetic changes in our bodies which made possible modern speech and brain function. The second great jump was the adoption of a sedentary lifestyle. That was linked to our adoption of food production, requiring people to remain close to their food supply. Sedentism and agricultural surplus have made today's lifestyle possible. The path has been turbulent and uneven as we will illustrate in the following sections.



Politics is about power in society, who has that power, and how it is used. If you grew up in Chicago, for example, you learn that your alderman is a very powerful person. He holds the key to how Chicago is run, dealing with city departments, and getting about anything done in this city.

When archaeologists examine an ancient city, irrigation project, temple, or pyramid requiring sustained human effort, planning, and materials-the political implications are clear: the society that did it was highly organized with concentrated political power.


In anthropology, four levels of political organization are recognized. We will describe these to illustrate important points later. Let us examine them in a concise fashion now.

(1) Bands are just dozens of people, a small group of related people, who are typically nomadic and do not have formal leadership. Band organization is historically ancient; all of the humanity lived this way before 12,000 years ago. They subsist on hunting and gathering. Nature is their storehouse.

(2) Tribes are largely loosely knit groups of a few hundred of people with informal leadership in an organization based on kinship by blood or marriage.

(3) Chiefdoms are thousands of people with power consolidated in a council or a single leader. Such a society now has classes with differences in wealth, prestige, and power. Wealth held by the elite is often accumulated by tribute, a technique just short of taxation.

(4) States have, since their origins 5300 years ago today govern every landmass on Earth (except Antarctica). They have social classes with extreme differentials in wealth, prestige, and power. They have armies, taxes, the power to coerce, bureaucracies, and a leadership based on religious or secular ideas.


Politics has shaped human destiny. For an illustration, let us imagine the following scenario. Long ago in a place far away in the South Pacific, two longboats leave a crowded country. They are off to find opportunity in new worlds. They bring pigs, chickens, and several domesticated plants they can plant in their 'new world' in the uncharted South Pacific Ocean.

One longboat goes north and finds them on an impoverished coral island with just enough resources to scrape by. They left a chiefdom, but by necessity revert back to be food foragers living in small groups of people on the limited resources. They've become a nomadic band society.

The other longboat goes south and comes upon a rich and diverse land. They indeed become fruitful and multiply, in time living in large settlements with a mastery of technology and effective political organization. But they have an oral tradition that tells of their 'other half' that went north.

They build ships and go off to find them. Finally, their search for their shared origins is successful. They find that lost coral island. But when they land, there is a fight. Who has the advantage?


This is a story of human conflict between peoples out of phase in history. It is what happened when Europeans reached out into Africa, the Americas, and the farthest corners of the globe. They went armed with their technology, military skill and political power. Unknowingly they were also armed with their epidemic diseases, but they thought it was the will of their Almighty God when disease decimated aboriginal peoples. We will develop this theme shortly.

(My note: does geography make history? It can be argued that geography is a necessary condition but is not a sufficient condition. Two examples of geography and history will be cited here.

One is the axis of a continent. This is illustrated in the figure at the end of this article. Eurasia had a running start because it had an abundance of grains in the Fertile Crescent to domesticate, and a broad expanse of suitable ecozone along the same latitude in which to grow them. In contrast, in the New World, the 'three sisters' of corn, beans, and squash were confined by the vertical axis of the Americas which crosses many ecozones. The remarkable potato never made it to North America until after Spanish conquest.

The second example is a contrast between China and Europe over the last 2,000 years. China long had a technological edge over Europe with its earlier invention of gunpowder, the magnetic compass, and paper. Europe took the lead, however, aided by its burgeoning universities and political fragmentation.

Geography may be the reason. China was politically unified (221 BC) long before Europe. It was aided by its two great rivers. Europe, in contrast, has a convoluted coastline and wrinkled landscape which fostered many 'statelets' in the Medieval period. That fragmentation, however, fostered intellectual freedom. Religious reformers and revolutionary thinkers could escape repression by just a short move to another territory.

Bands, tribes, and chiefdoms are virtually extinct. Few traces of them remain today. State type governments have claimed virtually every piece of land on Earth (except Antarctica). Historically, chiefdoms are often nudged into becoming states by violence, either actual or threatened. In 1500, states dominated only 20% of the Earth's area. When the explorers went to claim new lands for Church and crown they did so by right of discovery, treating aboriginals as if they didn't exist. States had a decisive advantage and expanded quickly.



When we mentioned bands in the previous section, we were touching upon a subsistence life style of food foraging. We 'forage' in the Jewel and at vending machines. Before domestication of plants and animals, all people foraged. Great Basin Indians still did it into the last century. Some Australian Aborigines returned to this lifestyle in the 1960s when drought decimated many of the cattle stations.

Farming developed first in the Middle East, but subsequently emerged independently in other parts of the world. People planted seeds, enhanced production and dramatically increased their food supply. They became settled farmers instead of nomadic foragers. Their numbers increased. While sedentism, domestication, and population growth are well documented, the cause and effect relationships is vigorously debated.

Domestication of animals provided labor, food, useful products, and first alert. Large herbivores such as cattle provided access to new food resources. The animals could eat things humans can't digest and convert them into usable human foodstuffs. Unfortunately, once into this new productive plenty, there is no turning back. When the land was irrevocably changed and there were more mouths to feed, there was no way out. It was hard work or starve. Indeed as the Bible said, 'we were indeed cursed to work in the sweat of our faces.'

People settled down. The natural birth space decreased. Population increased providing more labor for more production. In time, some specialists such as craftsmen, the religious, and political leaders emerged: agricultural surplus allowed them to escape from farm labor to do other things.

The resulting food surpluses and animal resources led to settled, politically organized, socially stratified, technologically innovative, complex societies committed to military conquest.

As we leave this section, consider this essential point: the availability of suitable plants and animals in some areas and none in others is why the Middle East and Asia flourished earliest. The people with the head start on food production had the advantage for decisive victory in military conquest.

In the next section we examine the role of disease colonization and conquest.



If people lived the foraging life before domestication, what was the state of their health? When camps were small and briefly occupied, sanitation was not a serious problem as it was in more permanent settlement. Epidemics dependent on direct person-to-person contact could not get established. If a disease such as measles found its way into a band of foragers, it would sweep through them and then disappear.

What diseases would foragers have had? Endemic parasites, such as head and body lice, pin worms and many intestinal protozoans. Diarrheal diseases would have been infrequent if they remained on the move. From time to time they would have been exposed to zoonotic infections. These are diseases which are endemic in the animal world and only accidently infect humans. Chronic low grade infections such as herpes simplex, yaws (caused by the same spirochete that is responsible for syphilis), and staphylococcal infections likely have an ancient connection with human life.


The shift from food gathering to food producing transformed human life and had a significant impact on health. The year-round ingestion of starches and carbohydrates largely as milled or cooked cereals or tubers led to widespread dental caries and more frequent malocclusion.

These events are well documented near here at the Dickson Indian Mounds south of Peoria. When cultivated maize replaced food foraging, the rate of dental caries and malocclusion increased. Similar events were documented world wide in the 1930s by Weston Price (cited at the end of this article).

With agriculture, human populations became subject to entirely new health problems, such as nutritional diseases, periodic famine and starvation. As societies grew and became more sedentary, there was more potential for intergroup strife, unsanitary conditions, and the spread of disease.


Humans in Australia had no suitable animals to domesticate. In the Americas, the turkey, guinea pig, and llama were just about it. This paucity of suitable animals to domesticate limited cultural development. It also made New World populations vulnerable to epidemic diseases when Europeans arrived in large numbers after Columbus. In their protected environment, they had no exposure to such diseases and were overwhelmed on contact.

The large herbivores that have shaped human destiny come from the Old World. Cattle, sheep, goats, pigs, water buffalo are all Old World domesticates that when brought under human control helped to transform society. But with them came a lethal gift: epidemic diseases that occur in large populations. We call them crowd diseases. Without large populations, they simply would not be sustained. Measles, for example requires a population density between a quarter to a half million people. Australia did not have endemic measles until ground and air travel developed sufficiently in the 1930s to unite the various urban population centers enough to sustain the disease.

Crowd diseases are something new, appearing just in the last few thousand years. They could only be sustained after intensive agriculture made possible large settled populations. Crowd diseases appear as epidemics rather than a steady rate of newly infected persons. They have several traits which we will briefly mention. They spread quickly so the whole population becomes infected in a short time. They are 'acute' diseases: you either die or acquire life long immunity. They tend to be human diseases with no animal reservoir. Once infected, all humans in a population die or recover and the disease disappears.

What is the evidence for their transmission to us from domesticated animals? Very closely related diseases are found in these animals. At some point those diseases mutated just enough to become exclusively human diseases. People became infected with animals diseases when there was prolonged close contact between the animals and people. Diseases represent evolution in progress. Here is a short list of deadly diseases acquired from our domesticated animal partners:

Measles......................cattle (rinderpest)


Smallpox....................cattle (cowpox) and other livestock with related pox viruses.

Flu.............................pigs and ducks

Pertussis.....................pigs and dogs

Some zoonotic diseases are animal diseases that only become epidemic human disease if conditions are right. The best historical example is plague, a disease transmitted by rat-born fleas, that wiped out millions of people in the fourteenth century. Incidentally, plague is now endemic in rodents in the western United States. Occasionally domesticated cats pick up infected fleas from the rodent population and an unsuspecting owner catches the disease. Properly diagnosed, plague is readily treated with antibiotics.


The major killers of humanity throughout our recent history--smallpox, flu, tuberculosis, malaria, plague, measles and cholera--are infectious diseases that evolved from diseases of animals. Some of them such as measles and smallpox became exclusively human diseases. HIV has joined the list possibly in just the last few decades. Ebola makes headlines from time to time. It is a viral disease so devastating, that it is called a 'slate wiper.'

Until World War II, more victims of war died of war-born microbes than of battle wounds. The victors of many wars were not always the armies with the best generals and weapons, but were often merely those bearing the nastiest germs to transmit to their enemies.

A classic in history is the dramatic conquest of the Aztecs in 1519. Cortez landed in Mexico with 600 Spaniards to conquer the Aztec Empire, an efficient militaristic society numbering several million people. Initially he lost 'only' two thirds of his troops and withdrew to the coast. The following year, smallpox brought in by a single infected slave spread with devastating consequences amongst the Aztecs. By 1618, Mexico's population decreased from 20 million to about 1.6 million. The Inca were similarly devastated by disease

Remember our question at the outset: why did disease flow to the New World and not the other way? There were no large animals to domesticate--and therefore no epidemic diseases of animal origin developed in the New World. Native Americans had lived in a protected, isolated environment without exposure to such microbes.

The Europeans came with a genetic resistance to the epidemics that had ravaged the Old World for thousands of years. All of us in this room are the descendants of those survivors. We carry the genes of those survivors. So, when explorers and conquistadores came in the name of Church and Crown they carried with organisms to which New World populations had no resistance or history of exposure.

'Where armies go, genes flow' is an old aphorism in anthropology. A corollary should be that 'they spread their diseases and bring home new ones.' Syphilis is suspected to have originated in the New World, but that is not a certainty. Some speculate that syphilis is a systemic version of yaws, a localized skin disease caused by the same spirochete.

The historical importance of animal derived diseases is that they have played a significant role in decimating native peoples. The Europeans who went out to colonize the world had in time been able to survive the epidemic diseases they acquired when animals were domesticated. The other point I wish to emphasize here is this: we tend to look upon evolution as mechanistic and that modern populations are the 'fittest' who survived. There is a chance factor--if one part of the Earth (the Old World) is blessed with the best natural resources from whence to domesticate, do so earliest, survive the epidemic diseases that result, create technology, and go out armed with these diseases. Then those folks will be the winners in conquest.



At the outset of this article, we asked the question: Why didn't Native Americans colonize Europe instead of the other way around? We have said that Asia and the Middle East had the benefit of the best selection of plants and large animals suitable for domestication. The availability of these resources in some areas and none in others were a causal factor in some peoples acquiring agricultural, political and technological sophistication in some areas and not in others.

We said that crowd diseases such as measles and smallpox came from animals, the most resistant people survived, and in conquest they were accompanied by those diseases with devastating results.

On an individual level, infectious disease is an arms race between host and parasite. When people came to live in permanent settlements, new animal-born diseases entered the human population and have shaped human history. Crowd diseases, a recent event in hominid evolution, were something new in Darwin's natural selection and survival of the fittest. They have led to the decimation of some populations and the reproductive success of others.

Humans have become the most widespread and dominant species on Earth to the advantage of some people and the disadvantage of others. Culture, disease, political system, organized monotheistic religions and conquest have been significant factors in those events.

..... CJ '99


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