Читать книгу The Greatest Benefit to Mankind: A Medical History of Humanity - Roy Porter - Страница 9

PEOPLES AND PLAGUES

IN THE BEGINNING WAS THE GOLDEN AGE. The climate was clement, nature freely bestowed her bounty upon mankind, no lethal predators lurked, the lion lay down with the lamb and peace reigned. In that blissful long-lost Arcadia, according to the Greek poet Hesiod writing around 700 BC, life was ‘without evils, hard toil, and grievous disease’. All changed. Thereafter, wrote the poet, ‘thousands of miseries roam among men, the land is full of evils and full is the sea. Of themselves, diseases come upon men, some by day and some by night, and they bring evils to the mortals.’

The Greeks explained the coming of pestilences and other troubles by the fable of Pandora’s box. Something similar is offered by Judaeo-Christianity. Disguised in serpent’s clothing, the Devil seduces Eve into tempting Adam to taste the forbidden fruit. By way of punishment for that primal disobedience, the pair are banished from Eden; Adam’s sons are condemned to labour by the sweat of their brow, while the daughters of Eve must bring forth in pain; and disease and death, unknown in the paradise garden, become the iron law of the post-lapsarian world, thenceforth a vale of tears. As in the Pandora fable and scores of parallel legends the world over, the Fall as revealed in Genesis explains how suffering, disease and death become the human condition, as a consequence of original sin. The Bible closes with foreboding: ‘And I looked, and behold a pale horse’ prophesied the Book of Revelation: ‘and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.’

Much later, the eighteenth-century physician George Cheyne drew attention to a further irony in the history of health. Medicine owed its foundation as a science to Hippocrates and his successors, and such founding fathers were surely to be praised. Yet why had medicine originated among the Greeks? It was because, the witty Scotsman explained, being the first civilized, intellectual people, with leisure to cultivate the life of the mind, they had frittered away the rude vitality of their warrior ancestors – the heroes of the Iliad – and so had been the first to need medical ministrations. This ‘diseases of civilization’ paradox had a fine future ahead of it, resonating throughout Nietzsche and Freud’s Civilization and its Discontents (1930). Thus to many, from classical poets up to the prophets of modernity, disease has seemed the dark side of development, its Jekyll-and-Hyde double: progress brings pestilence, society sickness.

Stories such as these reveal the enigmatic play of peoples, plagues and physicians which is the thread of this book, scotching any innocent notion that the story of health and medicine is a pageant of progress. Pandora’s box and similar just-so stories tell a further tale moreover, that plagues and pestilence are not acts of God or natural hazards; they are of mankind’s own making. Disease is a social development no less than the medicine that combats it.

In the beginning … Anthropologists now maintain that some five million years ago in Africa there occurred the branching of the primate line which led to the first ape men, the low-browed, big-jawed hominid Australopithecines. Within a mere three million years Homo erectus had emerged, our first entirely upright, large-brained ancestor, who learned how to make fire, use stone tools, and eventually developed speech. Almost certainly a carnivorous hunter, this palaeolithic pioneer fanned out a million years or so ago from Africa into Asia and Europe. Thereafter a direct line leads to Homo sapiens who emerged around 150,000 BC.

The life of early mankind was not exactly arcadian. Archaeology and palaeopathology give us glimpses of forebears who were often malformed, racked with arthritis and lamed by injuries – limbs broken in accidents and mending awry. Living in a dangerous, often harsh and always unpredictable environment, their lifespan was short. Nevertheless, prehistoric people escaped many of the miseries popularly associated with the ‘fall’; it was later developments which exposed their descendants to the pathogens that brought infectious disease and have since done so much to shape human history.

The more humans swarmed over the globe, the more they were themselves colonized by creatures capable of doing harm, including parasites and pathogens. There have been parasitic helminths (worms), fleas, ticks and a host of arthropods, which are the bearers of ‘arbo’ (arthropod-borne) infections. There have also been the micro-organisms like bacteria, viruses and protozoans. Their very rapid reproduction rates within a host provoke severe illness but, as if by compensation, produce in survivors immunity against reinfection. All such disease threats have been and remain locked with humans in evolutionary struggles for the survival of the fittest, which have no master plot and grant mankind no privileges.

Despite carbon-dating and other sophisticated techniques used by palaeopathologists, we lack any semblance of a day-to-day health chart for early Homo sapiens. Theories and guesswork can be supported by reference to so-called ‘primitive’ peoples in the modern world, for instance Australian aborigines, the Hadza of Tanzania, or the !Kung San bush people of the Kalahari. Our early progenitors were hunters and gatherers. Pooling tools and food, they lived as nomadic opportunistic omnivores in scattered familial groups of perhaps thirty or forty. Infections like smallpox, measles and flu must have been virtually unknown, since the micro-organisms that cause contagious diseases require high population densities to provide reservoirs of susceptibles. And because of the need to search for food, these small bands did not stay put long enough to pollute water sources or accumulate the filth that attracts disease-spreading insects. Above all, isolated hunter-foragers did not tend cattle and the other tamed animals which have played such an ambiguous role in human history. While meat and milk, hides and horns made civilization possible, domesticated animals proved perennial and often catastrophic sources of illness, for infectious disease riddled beasts long before spreading to humans.

Our ‘primitive’ ancestors were thus practically free of the pestilences that ambushed their ‘civilized’ successors and have plagued us ever since. Yet they did not exactly enjoy a golden age, for, together with dangers, injuries and hardships, there were ailments to which they were susceptible. Soil-borne anaerobic bacteria penetrated through skin wounds to produce gangrene and tetanus; anthrax and rabies were picked up from animal predators like wolves; infections were acquired through eating raw animal flesh, while game would have transmitted the microbes of relapsing fever (like typhus, a louse-borne disease), brucellosis and haemorrhagic fevers. Other threats came from organisms co-evolving with humans, including tapeworms and such spirochaetes as Treponema, the agent of syphilis, and the similar skin infection, yaws.

Hunter-gatherers being omnivores, they were probably not malnourished, at least not until rising populations had hunted to extinction most of the big game roaming the savannahs and prairies. Resources and population were broadly in balance. Relative freedom from disease encouraged numbers to rise, but all were prey to climate, especially during the Ice Age which set in from around 50,000 BC. Famine took its toll; lives would have been lost in hunting and skirmishing; childbirth was hazardous, fertility probably low, and infanticide may have been practised. All such factors kept numbers in check.

For tens of thousands of years there was ample territory for dispersal, as pressure on resources drove migration ‘out of Africa’ into all corners of the Old World, initially to the warm regions of Asia and southern Europe, but then farther north into less hospitable climes. These nomadic ways continued until the end of the last Ice Age (the Pleistocene) around 12,000–10,000 years ago brought the invention of agriculture.

Contrary to the Victorian assumption that farming arose out of mankind’s inherent progressiveness, it is now believed that tilling the soil began because population pressure and the depletion of game supplies left no alternative: it was produce more or perish. By around 50,000 BC, mankind had spilled over from the Old World to New Guinea and Australasia, and by 10,000 BC (perhaps much earlier) to the Americas as well (during the last Ice Age the lowering of the oceans made it possible to cross by land bridge from Siberia to Alaska). But when the ice caps melted around ten thousand years ago and the seas rose once more, there were no longer huge tracts of land filled with game but empty of humans and so ripe for colonization. Mankind faced its first ecological crisis – its first survival test.

Necessity proved the mother of invention, and Stone Age stalkers, faced with famine – elk and gazelle had thinned out, leaving hogs, rabbits and rodents – were forced to grow their own food and settle in one place. Agriculture enhanced mankind’s capacity to harness natural resources, selectively breeding wild grasses into domesticated varieties of grains, and bringing dogs, cattle, sheep, goats, pigs, horses and poultry under control. This change had the rapidity of a revolution: until around 10,000 years ago, almost all human groups were hunter-gatherers, but within a few thousand years cultivators and pastoralists predominated. The ‘neolithic revolution’ was truly epochal.

In the fertile crescent of the Middle East, wheat, barley, peas and lentils were cultivated, and sheep, pigs and goats herded; the neolithic peoples of south-east Asia exploited rice, sweet potatoes, ducks and chickens; in Mesoamerica, it was maize, beans, cassava, potatoes and guinea pigs. The land which a nomadic band would have stripped like locusts before moving on was transformed by new management techniques into a resource capable of supporting thousands, year in, year out. And once agriculture took root, with its systematic planting of grains and lentils and animal husbandry, numbers went on spiralling, since more could be fed. The labour-intensiveness of clearing woodland and scrub, weeding fields, harvesting crops and preparing food encouraged population growth and the formation of social hierarchies, towns, courts and kingdoms. But while agriculture rescued people from starvation, it unleashed a fresh danger: disease.

The agricultural revolution ensured human domination of planet earth: the wilderness was made fertile, the forests became fields, wild beasts were tamed or kept at bay; but pressure on resources presaged the disequilibrium between production and reproduction that provoked later Malthusian crises, as well as leading to ecological deterioration. As hunters and gatherers became shepherds and farmers, the seeds of disease were sown. Prolific pathogens once exclusive to animals were transferred to swineherds and goatherds, ploughmen and horsemen, initiating the ceaseless evolutionary adaptations which have led to a current situation in which humans share no fewer than sixty-five micro-organic diseases with dogs (supposedly man’s best friend), and only slightly fewer with cattle, sheep, goats, pigs, horses and poultry.

Many of the worst human diseases were created by proximity to animals. Cattle provided the pathogen pool with tuberculosis and viral poxes like smallpox. Pigs and ducks gave humans their influenzas, while horses brought rhinoviruses and hence the common cold. Measles, which still kills a million children a year, is the result of rinderpest (canine distemper) jumping between dogs or cattle and humans. Moreover, cats, dogs, ducks, hens, mice, rats and reptiles carry bacteria like Salmonella, leading to often fatal human infections; water polluted with animal faeces also spreads polio, cholera, typhoid and viral hepatitis.

Settlement helped disease to settle in, attracting disease-spreading insects, while worms took up residence within the human body. Parasitologists and palaeopathologists have shown how the parasitic roundworm Ascaris, a nematode growing to over a foot long, evolved in humans, probably from pig ascarids, producing diarrhoea and malnutrition. Other helminths or wormlike fellow-travellers became common in the human gut, including the Enterobius (pinworm or threadworm), the yards-long tapeworm, and the filarial worms which cause elephantiasis and African river blindness. Diseases also established themselves where agriculture depended upon irrigation – in Mesopotamia, Egypt, India and around the Yellow (Huang) River in China. Paddyfields harbour parasites able to penetrate the skin and enter the bloodstream of barefoot workers, including the forked-tailed blood fluke Schistosoma which utilizes aquatic snails as a host and causes bilharzia or schistosomiasis (graphically known as ‘big belly’), provoking mental and physical deterioration through the chronic irritation caused by the worm. Investigation of Egyptian mummies has revealed calcified eggs in liver and kidney tissues, proving the presence of schistosomiasis in ancient Egypt. (Mummies tell us much more about the diseases from which Egyptians suffered; these included gallstones, bladder and kidney stones, mastoiditis and numerous eye diseases, and many skeletons show evidence of rheumatoid arthritis.) In short, permanent settlement afforded golden opportunities for insects, vermin and parasites, while food stored in granaries became infested with insects, bacteria, fungoid toxins and rodent excrement. The scales of health tipped unfavourably, with infections worsening and human vitality declining.^*

Moreover, though agriculture enabled more mouths to be fed, it meant undue reliance on starchy cereal monocultures like maize, high in calories but low in proteins, vitamins and minerals; reduced nutritional levels allowed deficiency diseases like pellagra, marasmus, kwashiorkor and scurvy to make their entry onto the human stage. Stunted people are more vulnerable to infections, and it is a striking comment on ‘progress’ that neolithic skeletons are typically some inches shorter than their palaeolithic precursors.