by Sean Martin
Out of all the microbes currently known – there are around a million – only 1,415 are known to cause disease in humans.10 Many are helpful, such as the bacteria that help us digest food, and those that decompose matter and return it to the soil (including human corpses). Some viruses even produce things that we deem beneficial, or pleasing: the bands of colour in variegated tulips, for instance, are caused by a virus. Some bacteria are not naturally harmful to humans, but are only made so by a type of virus called a bacteriophage, or phage for short. The bacteria that cause cholera and diphtheria, for instance (Vibrio cholerae and Corynebacterium diphtheriae), would be harmless were it not for their resident phages ‘switching on’ the disease.
And then, around five hundred and fifty million years ago, the socalled Cambrian explosion happened: the first vertebrate life crawled out of the sea and onto dry land.
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Mediaeval philosophers were fond of referring to the Book of Nature. If you could but read the Book of Nature, they argued, you would attain wisdom. In some senses, they were right: scientists researching the very early history of life on earth have the fossil record to consult. The fossil chapters from the Book of Nature tell us much about the earliest things to have lived on Earth, such as the Strelley Pool bacteria, or the weird and wonderful extinct life forms preserved in the Burgess Shale in the Canadian Rockies.
Human fossils are relative newcomers. Fossils of our ancestor homo erectus, from around 1.5 million years ago, show evidence of yaws.11 This is a tropical disease of the bones and skin that produces unsightly swellings and lesions, and leaves skeletal traces. (Yaws is also related to syphilis, although not transmitted by sexual contact. But more of that later.) Paleopathology can tell us what diseases leave traces in the bone: various forms of dental decay, osteoarthritis, rheumatoid arthritis, osteomyelitis, tuberculosis, leprosy, venereal syphilis, poliomyelitis, fungal bone infections, osteoporosis, rickets, scurvy, thyroid disease, diabetes and anaemia.12 Tumours can also leave traces, and bones of course will leave clear evidence of trauma (breakages) and disorders of growth and development. Some of these diseases are also found in animal remains. Arthritis, for instance, is found in the remains of cave bears.
Paleopathology has its limitations, however, as Charlotte Roberts and Keith Manchester note. Although a disease may appear to have been present in a body, it is not necessarily the cause of death. Bones can be fragile, and may not survive the process of excavation and examination, so the cause of death is often guesswork. A skeleton may not be representative of the community from which it came – the person could have been a relative newcomer, for instance – and total access to a complete cemetery is the exception, rather than the rule. Furthermore, if a person or community had not developed immunity to a disease due to surviving a previous occurrence, acute infective disease is ‘likely to have killed people very quickly in antiquity, especially if the individual had had no previous exposure or experience of the invading organism. Therefore, no evidence of abnormal bone change developed.’13
In other words, you die before your bones know what’s hit you. Roberts and Manchester point out that ‘Many diseases also only affect the soft tissues and therefore would not be visible on the skeleton. It is therefore quite possible that skeletons from the younger (nonadult) members of a cemetery population were victims of an acute, or soft-tissue, disease because frequently they do not have any signs of abnormal bone change. Additionally, their immune systems may not have been fully developed to defend against disease.’14 Despite these and other limitations, paleopathology can provide vital clues for trying to reconstruct what diseases our ancestors suffered from. ‘What can be indicated are the disease processes an individual may have been suffering from in life and whether the disease was active or not at the time of death.’15
Human bones aren’t the only thing to bear traces of disease. Coprolites, or fossilised faeces, also tell us something about prehistoric disease. From fossilised poo, a general state of health can be deduced. They can tell us whether the person had been infested with parasites such as worms, for instance. As Arno Karlen notes, paleoparasitologists, who study coprolites, prove that ‘one man’s mess is another’s treasure’.16
When groups of homo erectus moved from Africa to Italy, around half a million years ago, yaws made the trip with them.17 As to why early humans left Africa, there was probably no one reason. Huntergatherer communities could have been following game; they could just have easily been escaping other tropical diseases. Dorothy Crawford notes that sleeping sickness could have been a major problem for early peoples in Africa, as it’s endemic to the continent’s tsetse fly belt, and is always fatal if not treated.18 We know that the tsetse fly was active around a million years ago, as fossilised specimens attest. (The fly could also have been responsible for a sizeable extinction of prehistoric horses in North America.19) Starting with a headache, sleeping sickness progresses to attack the lymph nodes, produces a rash on the skin and makes the joints ache. When the trypanosome (the protozoan that causes the disease) enters the brain, lethargy, coma and death aren’t long in following.
Hunter-gatherer peoples would have been generally healthy, albeit with a fairly short life span of around 30 years. Many of the diseases that affected them would have been ‘wear and tear’ diseases like arthritis and rheumatism. (Although some of these conditions could have been hereditary, too.) Comprised of several large family groups – perhaps no more than fifty people – hunter-gatherers would have led a life dictated by the seasons and the movements of animals. They hunted, trapped, fished and stalked their prey. This search for food was constant. But there was a balancing act between hunter-gatherer and the environment. As Dorothy Crawford has pointed out, ‘On average, hunter-gatherers required around one square mile of foraging area per person, so the number of people in a band was critical: past a certain tipping point further increase would be self-defeating’.20 It’s thought that, if a group got too large, it would practise infanticide, or split into two.
But human populations grew, communities behaving unwittingly like bacteria in ceaselessly splitting into more and more groups, and following more and more big game for food. It did not end well, either for the hunter-gatherers, or the big game. Early humans are thought to have ‘exterminate[d] up to 90 per cent of the larger species’ between 50,000 years ago in Africa, 20,000 years ago in Europe and Asia and around 11,000 years ago in the Americas.21 This theory, known as the overkill theory, holds that mastodons, giant sloths and sabre-toothed tigers were all hunted to extinction in order to feed a growing human population. Following them into the cooking pot were gomphotheres, four species of mammoth, ground sloths, glyptodonts, giant armadillos, giant beavers, giant peccaries, the stag moose and the dwarf antelope, brush and woodland musk oxen, the American camel and the American lion, short-faced bears, the dire wolf and the dirk-toothed cat. Australia lost the diprotodon, the ‘one-ton wombat’, while New Zealand said goodbye to the moa, a flightless bird whose biggest specimen was larger than an ostrich.22
The diminishing number of animals to eat, and the threat of diseases like sleeping sickness, would have driven hunter-gatherers further afield. At this point, hunter-gatherers would have increased what is known as the human disease burden. There have been several shifts in this, and they have all caused irrevocable shifts in the pattern of disease.
The earliest human ancestors were apes, who lived largely in the trees. Some diseases would have been either endemic to life in that environment, or at least more common than they would have been on the ground. Certain birds, mammals and insects spend their entire lives in the canopy, and never come down to ground level. Other species, in contrast, require the shade and moisture of life on the ground. All creatures, regardless of what level of the forest they lived in, would have had their own viruses, parasites and diseases. As Arno Karlen notes, ‘Changing its niche by only a few meters can radically alter a species’ prey, predators and microbes.’23 Karlen also speculates that it
could have been diseases acquired in the trees that may have first forced our ancestors to come down to ground level. Ancestral forms of viral diseases like polio and meningitis could have ‘left our arboreal ancestors too crippled to swing through the branches, and enough survivors squeaked out a marginal adaptation to the forest floor to launch a new species.’24
When our ancestors shifted their habitat down to the ground, they naturally also made themselves vulnerable to the new diseases that existed there, such as parasitic worms from animal droppings. And the flies that plagued those animals would have given the new ground-based human ancestors sleeping sickness. This was the first shift in disease burden, but over time, our ancestors – and their diseases – adapted to each other. Changes in diet could have led to a second shift: it is probable that our very early ancestors were herbivores, but life on the ground presented them with new opportunities in the shape of animals.
Eating meat, or an increase in the amount of meat in the diet, caused the second shift in the disease burden. Humans were now in more regular contact with animals in order to kill, butcher and eat them. This would have made them susceptible to animal diseases, which were able to make the species jump from animals to humans, known as zoonoses, or zoonotic diseases. This would be particularly true if the animal caught was itself sick; sick animals being slower and easier to catch than healthy ones. However, zoonoses don’t enter the human story in quantity at this time, as we’ll see.
Arno Karlen speculates that more meat in the diet would have had another lasting effect on human beings: by getting more protein more quickly, early humans would have had more time available for the development of culture. Neanderthals were known to bury their dead, for instance. One grave, from Shanidar cave in northern Iraq, dating from around 60,000 years ago, contains flowers buried alongside the dead man. There is no way the flowers could have got into the grave by accident, as they didn’t grow in that locality. Scientists were further astounded to find that the flowers in the grave – hollyhock and yarrow – have medicinal properties.25
So, with humans growing in number, they spread out geographically, as we’ve noted above, causing the third major shift in disease burden. Whether that was due to escaping illness in one area, or chasing animals they wanted to eat, is immaterial for a moment. This new shift in disease burden meant that, as with coming down from the trees, in moving to new lands, humans exposed themselves to new microbes, and new diseases.
This particular shift in disease burden is something most of us are familiar with. When I was growing up, it was a mysterious affliction known as ‘holiday tummy’. It happened on holiday, along with traffic jams and bad weather. When at one’s chosen destination, one scoured the menu for something sufficiently familiar to eat. Not finding it, one was then forced to sample the local cuisine, usually accompanied by varying degrees of protest or caution. Shortly afterwards, with the strange foreign concoctions safely off the plate and in the tummy, the toilet would need to be visited, usually to more protests, and this time with speed rather than caution. You have eaten new food in a new area, and have exposed yourself to new microbes, and are spending more time than usual in the bathroom. But this, in miniature, is a shift in your disease burden.
Eventually, around 12,000 years ago, humans began to settle, the socalled Neolithic or Agrarian revolution. The hunter-gatherer became a farmer. This caused another shift in disease burden, perhaps the most significant one in history. As soon as people gave up nomadism, they began to attract the attention of microbes in the soil, and also those of animals, which were increasingly being domesticated. It’s ironic that doing nothing more than staying put should mark one of the biggest changes in human experience, but that’s precisely what it did. As soon as sedentary communities began to appear, people exposed themselves to the billions of bacteria in the soil, and what their gardens and fields didn’t give them in the way of disease, their animals did.26
This is where zoonoses really began to make their mark. The list of diseases we’ve caught from our animals is a long one. Tuberculosis from cattle and birds; anthrax from grazing herbivorous mammals; leprosy from mice; rabies from dogs and bats; chicken pox is, unsurprisingly, from chickens; measles probably originated in canine distemper or rinderpest; while the common cold probably comes from horses. There are dozens more examples. The fossilised bones of a mother and child, dating from around 8,000 BC, found in the now-submerged town of Atlit-Yam, off the coast of modern Israel, show that both had suffered from tuberculosis.27 TB is also thought to have been active in Chile as early as 2,000 BC, which suggests it was brought over the Bering Land Bridge when the Americas were settled some 15,000–20,000 years ago.28
Certain roles within communities would have exposed their practitioners to disease: butchers and tanners, for example, would have been coming into contact with animal meat and hides on a regular basis, and would have therefore had a greater exposure to zoonoses. Tilling and ploughing the ground would have exposed the Neolithic farmer to millions of microbes in the soil that could easily enter the human body through cuts or cracks in the skin, or through eating with dirty hands. These were the first ‘occupational’-related diseases. Houses that lacked adequate ventilation would have led to respiratory and eye problems.29
But it was still a life of hard manual labour: bodies from one of the earliest known settled communities, Aşıklı Höyük in modern-day Anatolian Turkey, occupied between 8,200–7,400 BC, show evidence of joint disease and trauma, and spinal deformities. These suggest rigorous lives of tilling, cutting timber, hauling, and the carrying of heavy loads. (Interestingly, people in Aşıklı Höyük were buried beneath the floors of houses, rather than in a cemeteries.)
After farms, the next stage of the Neolithic revolution was the development of large villages or towns. Bones found at the Neolithic town of Çatalhöyük, close to Aşıklı Höyük, thriving around 7,000 BC, indicate that its inhabitants probably suffered periodic outbreaks of malaria and some form of lung disease, in addition to arthritis, which was common in both young and old alike. Notes made from the 1997 season of excavations at Çatalhöyük suggest that ‘Epidemics of infectious disease are a possibility, wiping out whole families or returning year after year. Plague, malaria, enteric dysentery are possibilities. The habitual cleanliness of the house would have controlled infection.’30
Given the size of Çatalhöyük – at its largest, it had a population of 10,000 – contagious diseases would have certainly been known. Crowds are good for some pathogens in that they need a certain number of susceptibles in order to remain active. Measles, for instance, as David Quammen notes, ‘seems to have a critical community size of roughly 250,000 humans; in an isolated human population smaller than that (on an island, for instance), the virus disappears after everyone has been exposed.’31 The bigger somewhere like Çatalhöyük and communities close to it got, the more chances diseases had in gaining a foothold. Other diseases couldn’t possibly have existed at this time. As Alfred W Crosby notes, ‘Because it only persisted by passing from one human to another, smallpox could not have existed with its historical characteristics among the sparse populations of the Paleolithic Age.’32 When smallpox did finally appear in humans – possibly in late antiquity or the early Middle Ages – it probably came from dogs or cattle (and is related to cowpox, as Edward Jenner would find out many centuries later).
Sheer numbers of people would be aided and abetted by dirt, refuse and sewage. As soon as any of those things contaminated the drinking water and food, diseases would rip through a settlement. This had never been a problem for hunter-gatherers, who would be getting their water from streams or rivers, and probably doing what bears do in the woods, or digging cesspits. Either way, the possibility of contaminating their water and food was minimal.
One burial at Çatalhöyük begs more questions than answers. Like those at Aşıklı Höyük, graves in Çatalhöyük were beneath the floors of the houses. One grave discovered in 1998, known as Space 115 (or Skeleto
n 3368, Burial 285, cut 3369, Space 115 Midden deposit, to give it a fuller description), however, was not under a house – it would have been out in the open when the body was interred, a space interpreted as a ‘courtyard midden’, making it ‘unique in the records so far’.33 The body is of a young adult male with seriously diseased bones, which suggests that the man had been an outcast because of his condition.
This midden burial at Çatalhöyük also indicates that disease is not just something that can affect the body and leave traces in the bones, but is also social. The disfigured, disabled or otherwise different were to be regarded as unclean, possessed by bad spirits or perhaps just unlucky, and ostracised (to judge from the uniqueness of the midden grave at Çatalhöyük). People struck low with a disease could have also been subject to early forms of surgery. Again, in the absence of written records, the bone record is our best guide here. Skulls from around the time of Çatalhöyük, perhaps a bit later (maybe 5000 BC), found in locations as diverse as France, Poland, South America and the Pacific, bear the distinctive signs of trepanation. This is the ancient art of drilling a hole in the skull, presumably to let bad spirits out.
As medical historian Roy Porter notes, ‘Illness is thus not just biological but social, and concepts of the body and its sicknesses draw upon powerful dichotomies: nature and culture, the sacred and the profane, the raw and the cooked. Body concepts incorporate beliefs about the body politic at large.’34 If someone within a community is designated sick, Porter argues, it is a reflection of that community’s principles of organisation. But the limits of where normal health ends and disease begins are fluid. This is perhaps reflected in modern semantic problems with the word ‘disease’, that we noted in the introduction. In addition, disease can carry a moral weight. The man seemingly outcast in death at Çatalhöyük could well have been an outcast in life, too. Some diseases have always been seen as punishment for wrongdoing and sin – leprosy being the prime example, associated in the Middle Ages with lust and improper desire. But as Porter points out, disease could also have a beneficial side: ‘“Sick roles” may range from utter stigmatisation (common with leprosy, because it is so disfiguring) to the notion that the sick person is special or semi-sacred (the holy fool or the divine epileptic). An ailment can be a rite de passage, a childhood illness can be an essential preliminary to entry into adulthood.’35
