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31 May 2023updated 12 Oct 2023 10:36am

How germs shape history

Jonathan Kennedy’s Pathogenesis reveals how diseases have built and broken empires and economies.

By Kathleen Jamie

In order to study the quality of threads in cloth, the 17th-century Dutch draper Antonie van Leeuwenhoek designed his own lenses, but soon turned his attention to the strange new world those lenses revealed. He identified “animalcules”, and is today recognised as a pioneer of microbiology.

Two hundred years were to pass before Louis Pasteur proved that microbes could enter bodies and cause disease. More recently, they’ve been understood as beneficial. Certain gut bacteria, or lack of them, have been discovered to be associated with depression. Treatment for psychiatric disorders may soon come via the intestine. Microbes inhabit us, and are also our ancestors – the first life on Earth emerged as single cell organisms 3.5 billion years ago. As Jonathan Kennedy says: “It is a bacterial world, and we are just squatting here”.

Kennedy is an academic specialising in politics and global health and Pathogenesis is a grimly fascinating book. He attests that microbes have had a profound effect on our human evolution and history, mostly in the shape of infectious diseases. He brings together research on how bacteria, viruses and the like have affected and even caused global events. Recent knowledge has been obtained through DNA analysis of ancient skeletons, sometimes very ancient.

He begins with the question of how we came to occupy our lonely position as the only human species in existence. What happened to the Neanderthals, and other species? Are homo sapiens really so much smarter, more violent, more capable of symbolic thought and language? The more archaeologists learn about Neanderthal culture, the less exceptional we seem. Yet each species had its own coterie of pathogens, and it appears it was immunity that cast the die in favour of homo sapiens. When the two species did contact each other – even interbreeding – sapiens developed immunities to Neanderthal diseases more quickly than they did to ours. That and their cold climate, and an already sparse population, proved their undoing.

So the tone is set. Human history has been shaped not by Great Men, but by tiny microbes. Every migration or invasion, every contact or disruption through the ages, has been accompanied by, or weaponised by, pestilence and disease. Disease has placed populations where they are, and shaped the Old World and the New. Disease has set borders and attitudes, we are all the result of plague after plague.

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An early example would be the “Neolithic Plague” which appears to have assisted a wholesale population replacement across much of northern Europe. Early Europeans, the Stonehenge builders, were dark-skinned and dark-haired: Cheddar Man is an example. But in circa 4700 BP (before present), his kind suffered a sharp fall in population. The possible cause has been detected through DNA analysis of Neolithic skeletons and especially their dental pulp, where, protected by tooth enamel, even the people’s attendant microbes can be identified. Mass graves are rare in Neolithic times but one discovered in Sweden, containing the remains of about 80 people, showed traces of Yersinia pestis– the Black Death. It was not flea-borne in those times, but spread by coughs and sneezes. It likely arrived in northern Europe via trade routes from what is now Ukraine, where there were already sizeable towns.

The population collapse in northern Europe enabled new arrivals to settle from the east. These people had some immunity to endemic diseases, and were fair and light-skinned. They spoke a proto-Indo-European language. Your “typical” Europeans: not so indigenous after all.

The plagues of the prehistoric world gave way to those that shaped the classical world (the Iliad opens with a plague) and on into the Middle Ages where Yersinia pestis re-emerged in Europe. Kennedy’s point is that, amid much else, it was repeated waves of bubonic plague that shoved the European economy from a stagnant feudalism into an urbanised capitalist system, albeit over several centuries. (It also took several centuries for populations to recover.)

Then, as Europeans explored and exploited, there erupted the “colonial plagues” which eradicated indigenous South American civilisations. (The figures are still appalling: a century after Hernán Cortéz’s arrival in South America, an estimated population of 20 million native people had fallen to 1.5 million, killed not by God’s will or European “superiority”, but wave after wave of imported pathogens.)

Why didn’t it cut both ways, in a mutual destruction? Why were the conquistadors not likewise annihilated by South American germs? They brought home syphilis, which was ghastly but hardly a fair exchange. Again, they had better immunity. That said, there is one known case of Europeans being felled. The Scottish colonial misadventure to Panama, the Darien scheme, resulted in the deaths by disease of almost all the 2,500 would-be colonisers, the near bankruptcy of Scotland and hence the union with England, giving us the fractious UK we know today.

[See also: Did the US start germ warfare?]

It is these political and social legacies that Kennedy foregrounds. What has shaped the world? Not gods, not heroes, not even conquistadors, but germs. Far from being an unfortunate extra, they are here accounted as major, if amoral, players in almost every human development and attitude.

Take racism. Slavery is as old as agriculture itself, but it was only racialised when the Caribbean was colonised. The original inhabitants of the Caribbean, eradicated through diseases, were supplanted by indentured labourers firstly from Europe. Black African labourers were in a minority. But when yellow fever arrived, plantation owners soon noticed that black African people were not as susceptible as Europeans. Thus, Kennedy says, their immunities made black people a more “rational” economic choice.

Likewise in the southern states of North America. Malaria arrived there in 1680, and thereafter the number of enslaved Africans increased dramatically, for the same economic reason. Plantation owners knew black people were a better investment, especially those stolen from malaria-ridden places. “Once black Africans had become inextricably linked with slavery in the European imagination, modern ideas about race were developed to justify this iniquitous situation.” Native peoples came to be regarded as “weak” because they so often succumbed after contact with white people. That black people were considered suited to a life of hard labour was influenced by their immunities.

It is all bleakly fascinating, and worrying. Pathogenesis describes a human condition that is utterly Hobbesian. Surely, in the 21st century, we are out of the (infested) woods? Hardly. We can deal better with the pathogens we know, and respond better to emergent ones. If we don’t do so, Kennedy says, it’s down to political will – and colonial legacy. A Covid vaccine was developed with astonishing speed, but Western nations cut deals and stockpiled so African nations went without, as they are obliged to go without the basic sanitation and healthcare that would encourage well-being and economic growth.

Even within nations there are gross inequalities, not least in the UK and US. Our government may have hoarded Covid vaccines, but it chooses to ignore other major public health issues, especially those that afflict the poor. As Kennedy says, the old pathogens are curtailed (smallpox, cholera, tuberculosis ) largely through improvements in sanitation and housing, but we have instead entrenched non-communicable conditions such as heart disease, obesity, cancers and diabetes. These conditions are so rife and affect the poor so readily that they are having a similar impact to infectious diseases. People are dying young in this country from what he calls “plagues of poverty”, and what doctors are calling “shit life syndrome”, but there is no political will to intervene.

[See also: What cells tell us about life]

Jonathan Kennedy concludes that humans are in a very precarious position. We live among microbes that are mutating all the time, so we still face grave threats posed by infectious diseases. The more we encroach on the natural world, the more new pathogens, presently circulating among animals or birds, will find us. What can we do? “There is one universally incorrect choice: to do nothing.” We must collaborate, he says, and reduce inequalities. It doesn’t seem likely to happen, but in the past, as this book demonstrates, pandemics have driven momentous political and economic transformations. It’s up to us.

Pathogenesis: How Germs Made History
Jonathan Kennedy
Torva, 384pp, £25

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This article appears in the 31 May 2023 issue of the New Statesman, The Rise of Greedflation