But it seems that for our sins, or for some inscrutable judgement of God, in all the entrances of this great Ethiopia that we navigate along, He has placed a striking angel with a flaming sword of deadly fevers, who prevents us from penetrating into the interior to the springs of this garden.
A disease is by its very nature a distortion of the normal, healthy functioning of the human body. It acts to prevent some of our internal systems working properly, causing disorder, debilitation, even death. Many diseases are caused by mutations in the DNA coding inherited from our parents or acquired during our lifetime, such as the copying errors that trigger cells to begin proliferating out of control and cause cancer.
A huge number of diseases are caused by microscopically small organisms, microbes, invading our body. Such pathogenic microorganisms can be transmitted to humans in a variety of ways. Some are contagious through direct contact, such as leprosy or HIV/AIDS; others are airborne and enter the throat and lungs, such as influenza or COVID-19; others still, like cholera, spread through drinking water contaminated with human waste. Then there are those transmitted via an intermediary or ‘vector’ – typically parasitic, bloodsucking insects such as the mosquito (malaria, yellow fever, dengue), tsetse fly (sleeping sickness), flea (bubonic plague) louse (typhus) or biting arachnids such as ticks (Lyme disease).1
But regardless of the mode of transmission, what pathogens share is their ability to survive in the internal environment of a body and exploit particular features of the host’s biology to complete their own life cycle. Some are even able to completely evade the body’s surveillance and defence mechanism, the immune system, like a con artist disguised as a contractor, complete with high-vis jacket and clipboard, walking unchallenged past the security desk. Thus there is often an intimately close relationship between the biology of a pathogen and that of its host, honed over evolutionary time so that the pathogen can reproduce and proliferate.fn1
The necessity of such well-tuned adaptations means that only a tiny sliver of all microbial life on Earth is able to infect and then reproduce in the human body. Of the countless millions of different species of microorganisms on the Earth,3 only 1,128 are known to do so – around half are bacteria, a fifth are viruses, and the remaining third or so are fungi and parasitic protozoa.4 A further 287 organisms that cause diseases in humans are not microbes but parasitic worms.5
And the majority of these pathogenic microbes – about 60 per cent – are zoonotic; they are transmitted to humans from animals. Thus at the source of the great pestilences and plagues that have stalked humanity since the dawn of civilisation are the wild beasts we domesticated as livestock and began living in close proximity with. Dispersed bands of hunter-gatherers are generally healthy, save for parasites, and as long as they survive childhood many can expect to live to over 60 years old.6 Most of the diseases that affect them are not infections caught from one another, but ‘wear and tear’ afflictions such as arthritis and rheumatism.7 There are some ancient infectious diseases that predate the development of agriculture, such as malaria and leprosy,8 which are able to sustain themselves in small, dispersed populations of humans or survive in animal hosts if susceptible humans are scarce. But once humans started settling down in ever-denser concentrations in agricultural villages and then cities, we created the perfect breeding conditions for infectious diseases to jump not only the species barrier but from person to person. History saw a surge of ‘crowd diseases’.
When a pathogen first breaks into a new population, in which individuals’ immune systems are unprepared for the attack, it can spread very quickly as an epidemic with a staggering initial death rate. But many diseases wane in severity over time, as the population acquires resistance or the pathogen mutates. They may circulate among the population as a constant presence, perhaps flaring up occasionally in outbreaks – a simmering, background burden rather than a raging firestorm. Some diseases can disappear completely. English sweating sickness, for example, appeared in London in 1485, probably brought by Flemish mercenary troops who had helped Henry VII seize the throne from Richard III at the end of the Wars of the Roses. It raged across Britain, seeming to preferentially strike rural middle-aged men of the more affluent social classes during summer,9 with an extremely sudden onset and high mortality – death occurred typically within just hours. The mysterious contagion recurred in a series of outbreaks over seventy years, before vanishing entirely in the mid-sixteenth century, never to return.10
In the past, a widespread disease outbreak would be termed a plague or pestilence. Nowadays, the more technical term is ‘epidemic’ – derived from the Greek epi, ‘among’, and demos, ‘the people’ – or, in its most extreme case, ‘pandemic’, a disease that has spread to many people across a very large area. ‘Endemic’, denoting a disease found in a particular area, derives from the Greek for ‘within the people’. Both endemic and epidemic diseases have had far-reaching impacts on whole societies and civilisations, so I decided to dedicate two chapters to exploring their effects on human history. The difference between the two is not a matter of taxonomy, however: the same pathogen can swirl around a partially resistant population with only minimal impact and then break into a new population to trigger a devastatingly lethal plague. One region’s endemic disease is another population’s epidemic. But I believe the different effects that the two patterns of disease have had on human history still make for a sensible distinction.
We’ll look first at how human susceptibility to endemic diseases has played a significant role in world history.
In the late 1600s, Scotland was struggling. Its economy, based almost entirely on agriculture, had been suffering years of poor harvests and famine. Despite the fact that England and Scotland had been ruled by the same monarch since 1603 – when Queen Elizabeth I died without an heir and her distant cousin James VI of Scotland succeeded to the English crown – Scotland remained fiercely independent of its powerful southern neighbour. The English, in turn, imposed oppressive economic restrictions on the Scots, including protectionist trade bans with France and the North American colonies. In order to place itself on a more secure economic footing, and avoid being forced into an unfavourable union with England, the Scottish people began to look further afield. England had grown rich on foreign trade, and the Scots yearned for a piece of this mercantile pie that could deliver such handsome returns. Previous Scottish settlement attempts – in Nova Scotia, East New Jersey and South Carolina – had not been successful, but the solution to turning around the country’s economic and political fortunes was still considered to lie in the establishment of its own overseas colony to capitalise on maritime trading routes.
An ambitious plan was hatched, masterminded by the Scottish-born financier (and one of the founders of the Bank of England) William Paterson. The Scots would establish a colonial settlement on the Isthmus of Panama, the narrow thread of land linking the North and South American continents. With a port and trading post positioned here, they reasoned, they would be able to participate in the vigorous commercial network strung between the islands of the Caribbean, and across the Atlantic to Africa. But Paterson also had further, even more ambitious, plans for the colonial endeavour.
At the time, ships from Europe or the Atlantic coast of North America heading west to China and the Spice Islands had to sail all the way down the coast of South America, around Cape Horn and back up again to cross the Pacific – a huge continental diversion. So why not build a road across the thin, 80-kilometre-wide sinew of the Panama isthmus that could link shipping on both sides – a shortcut to convey goods between the two greatest oceans of the planet? It would slash the time needed to reach the Orient, and therefore the expenses involved, by over half.11 Ultimately, Paterson envisaged digging an artificial water route for shipping to pass directly between the oceans – a Panama canal. And with the Scots controlling this gateway between the Atlantic and Pacific they could secure a sizeable income from the tariffs charged on the passage of cargo. The location that Paterson had carefully chosen for this trading colony was on a small peninsula, with a well-protected bay for shipping, in the Darien region of the Panama isthmus. So this daring plan to transform Scotland’s destiny became known as the Darien Scheme.
The colonial endeavour was orchestrated through the newly established Company of Scotland Trading to Africa and the Indies, which, it was hoped, would grow to rival England’s East India Company. The company quickly secured around 1,400 Scottish investors, drawn from right across the social spectrum, ranging from MPs to farmers. It has been estimated that between a quarter and a half of all liquid capital in Scotland at the time was poured into this bold, enterprising venture.
In July 1698, five ships set sail from Edinburgh loaded with 1,200 colonists and the hopes of a nation. The cargo holds were full of the materials, tools and equipment needed to establish a new colony from scratch, along with provisions for the voyage and first months of arrival. The settlers had been carefully chosen for the different skills needed at their destination. They arrived there at the end of October and founded the colony of New Caledonia, with New Edinburgh as its capital and defensive fortifications built on the sheltered peninsula.
Word was sent back to Scotland that the colony had been successfully established and was flourishing, enjoying peaceful relations with the indigenous population. Yet these first letters were whitewashing the truth in order to encourage further ships and supplies to be dispatched. The reality was that New Caledonia was already in dire straits.
The settlers soon discovered that the terrain inland was far too difficult to permit an overland coast-to-coast passage – and there certainly was no prospect of being able to dig a canal to link the oceans. Nonetheless, establishing a profitable entrepôt embedded in the bustling trade routes in the region was still seen as a viable possibility. But far more serious a problem was that almost immediately the colonists began succumbing to the diseases rife in the region. During his fourth and final exploratory voyage to the Americas in 1502, Columbus and his crew had been so tormented by insect bites along a stretch of the isthmus that they dubbed the region the Mosquito Coast.12 The Scots had arrived in peak mosquito season and were soon ravaged by mosquito-borne diseases – malaria and yellow fever.
Malaria is the disease that has probably been with humans the longest and killed the most. The infection is characterised by a fever that begins with intense chills and uncontrollable shivering, leading to a spike in temperature and then profuse sweating and fatigue, with the pattern repeating every few days. It is caused by a single-celled parasite – a kind of plasmodium – that is transferred from the blood of one individual to the next by the bite of a mosquito. The fact that malaria is spread by a flying vector means that, unlike crowd diseases, it doesn’t require dense populations of people to sustain itself, and so it is thought to predate the emergence of agriculture. In fact, malaria may be a truly ancient disease – the parasite that infects us probably evolved from those afflicting our closest evolutionary cousins, the great apes, in the tropical rainforests of Africa.13 Malaria had long been endemic over much of sub-Saharan Africa but was brought to the Americas only with European contact, probably aboard early slave ships from Africa.14
Yellow fever is a viral disease and also originated in Africa, jumping into humans from primates some 1,500 years ago.15 The first definitively classified epidemic in the Americas occurred in Guadeloupe in 1647,16 although the virus first arrived in the previous century aboard slave ships from Africa, before spreading widely across the Caribbean and two continents, as far north as Quebec.17 The early symptoms of the disease include fever, muscle pains and headaches, and in more severe cases this progresses to liver and kidney damage with a high mortality rate. Its name refers to the jaundice resulting from liver failure, and those who don’t die of haemorrhagic fever – in Spanish it is known as vomito negro on account of the tar-coloured vomit caused by internal bleeding18 – recover completely with life-long immunity.19
The New Caledonian colonists were thus hit with a double whammy of lethal diseases. Within six months they had lost almost half of their initial number, with as many as a dozen dying every day in the small settlement.20 The expedition had met with ruin, and the surviving settlers returned to their ships and abandoned the colony in July 1699, leaving behind those who were too weak to move. But the fleeing colonists continued to die in droves at sea: only 300 out of the original 1,200 settlers survived the ordeal.
However, word of New Caledonia’s abandonment had not reached home before a second wave of resupply ships was dispatched bearing extra provisions and 300 more settlers. When they reached Darien, they found a ghost town of empty huts and overgrown farm fields. They promptly turned around and sailed home. But still, news of the failure did not arrive in Scotland soon enough to prevent another large fleet of colony ships, carrying more than 1,200 further settlers,21 setting sail for Darien. This group of colonists stayed, but the second attempt at making New Caledonia a success fared no better than the first, and within months around a hundred were dying every week of malaria and yellow fever, with the colony now also being harassed by Spanish raids. In April 1700, the survivors surrendered to Spain. Of this second wave of colonists, fewer than a hundred made it back home. New Caledonia was abandoned for good, and the Scottish dream of an American colony and overseas trading riches collapsed with it.
The Darien Scheme had abjectly failed. Perhaps as many as 80 per cent of the 2,500 Scottish settlers who had sailed to New Caledonia were killed by malaria and yellow fever, their dire situation compounded by isolation from the English colonies and outright hostility from the Spanish.fn2 Had the Scottish colony been able to successfully link the Atlantic and Pacific Oceans, or at least maintain their strategically placed entrepôt to challenge the regional trade dominance of England and Spain, it may have changed the course of history. In the event, the dream of digging an artificial waterway to link the Atlantic and Pacific Oceans was not realised for another two centuries after the failure of New Caledonia.fn3
With the loss of the colony, the huge amount of investment that had been raised in Scotland to support the venture had evaporated. Indeed, the failure of the Darien Scheme brought Scotland to the brink of financial ruin and was a decisive factor in forcing Scotland into a political union with England. For a century after the Union of the Crowns in 1603, Scotland had remained an independent kingdom with its own parliament. This autonomy was now threatened by the dire financial straits Scotland found itself in. England promised assistance by reimbursing the Company of Scotland shareholders and ending the economic restrictions on trade.25 This was an irresistibly tempting offer for the Scottish elites – the aristocracy and mercantile class that had lost heavily in the economic fallout of the failed Darien venture – who felt their best option was to tie their future to the growing English trade empire and its international might. Six years after the loss of New Caledonia, the Scottish parliament was left with no choice but to consent to the union with England.
Scotland had surrendered its sovereignty, and Great Britain was born, as a result of the mosquito-borne diseases in a remote part of Panama.26
Europeans had initially benefitted from an enormous epidemiological advantage in their conquests of the New World from the early sixteenth century: as we’ll see in the next chapter, they brought with them pathogens that wiped out indigenous populations. But over the following centuries, the tide turned.
Endemic diseases are often thought of as a curse. An inescapable and ever-present sickness stalks the land like an evil spirit, exacting its toll on the health of the population and in particular on young children. But with many endemic diseases, those who survive to adulthood are bestowed with lifelong immunity, or at least greater levels of resistance. Endemic disease can therefore protect a seasoned native population against foreign invaders. In their native disease environment, defenders benefit from a home ground advantage compared to the susceptible intruders. European armies arriving to quell uprisings within their colonial lands in the Americas found they were at a distinct disadvantage, succumbing to the endemic diseases at far higher rates than their opponents, especially in tropical climes where many of the cash crop plantation systems had been established. And the ramifications of this disease biology has had profound consequences for how history has played out.
The American Revolution grew out of years of mounting tension and discontent among British colonies along the Atlantic coast over imperial Britain’s squeezing of their autonomy and imposition of taxes without representation in parliament. In late 1774, the Thirteen Colonies formed the Continental Congress to coordinate their resistance to British rule, which erupted into open conflict the following spring. The colonies had united in opposition and soon declared their independence; now they just needed to win the war.
At the start of the American War of Independence, the British Army was one of the most highly trained, best-equipped fighting forces in the world. Many of the red coat soldiers were battle-hardened from action around the world against the French and Spanish during the Seven Years War the previous decade. Though Britain was still cash-strapped after this global struggle for imperial supremacy, it was on a far stronger economic footing than the Thirteen Colonies. And British command of the Atlantic Ocean by the Royal Navy allowed it to strike right along the North American seaboard and blockade the small American fleet in port, choking off imports of food and war matériel. In contrast, the revolutionaries started with only militias of self-trained civilians, before the Continental Army was formed a couple of months into the war.
The British were able to push home their military advantage in the early stages of the conflict. They quickly captured the principal colonial ports of Boston and New York but were unable to land a decisive victory against the Continental Army to end the rebellion. The revolutionaries manoeuvred around the countryside, deftly avoiding being drawn into pitched battle and annihilated before they could secure more American support or the involvement of other foreign powers. The colonists didn’t win their first big victory until two and a half years into the war, at the Battle of Saratoga in New York state in October 1777. This demonstrated to the world that the Americans had a fighting chance, and the French and then Spanish now entered the conflict on their side. French warships were able to crack open the Royal Navy blockades; the Spanish supplied arms and provisions through the port of New Orleans; and the arrival of professional French soldiers in the second half of the war helped tip the balance in the colonists’ favour.
When stalemate had been reached in the north, the British decided to try a new tack, launching a fresh strategy at the end of 1778 in the south. The hope was to recruit large numbers of loyalists in the most recently founded colonies of Georgia and the Carolinas, secure the profitable plantations, and crush the rebellion once and for all.
After initial successes, the British commander-in-chief General Henry Clinton left General Charles Cornwallis in command of the southern regiments of 9,000 soldiers and returned to defend New York against an anticipated counter-attack. Despite these victories, the tide of the war was already turning against the British. The southern strategy had committed a large proportion of their forces to the mosquito-ridden subtropical regions, exposing them to the onslaught of malaria and yellow fever – enemies that the British were ill-equipped for.27
Lifetime exposure to diseases like malaria and yellow fever bestows a degree of immunity, but medicine can also treat or prevent infections. The bark of the cinchona tree was known to be effective against malaria, but it was in short supply.fn4 At the outbreak of the war, George Washington, commander of the Continental Army, had urged the Continental Congress to buy up as much as possible.31 The British, on the other hand, were acutely short of this vital preventative medicine. At this time, the only source of cinchona was high in the Spanish-controlled Peruvian Andes, and the Spanish had completely cut the British off from this supply in 1778, shortly before they joined the war alongside the French in support of the American Revolution. In addition, the British had committed much of their quinine reserves to their troops maintaining order in India or fighting imperial scuffles in the Caribbean. Throughout the southern campaign, therefore, Cornwallis’s officers and men were plagued by malaria.32 The soldiers of the Continental Army were not immune to malaria, but having previously lived with local strains of the disease they were less severely affected – they had the home ground advantage of an endemic disease.
Cornwallis kept his army on the move across the Carolinas, trying to find areas that might offer a reprieve from the ‘miasmic diseases’, especially during the peak mosquito season from late June to mid-October.33 By the time Cornwallis had won the Battle of Camden in mid-August 1780, many of his soldiers were crippled by ‘fevers and agues’ and too weak for service.34 Throughout the early months of 1781, Cornwallis chased the American revolutionary forces around the Carolinas. All the while, the Americans constantly harried the British southern army with short skirmishes before withdrawing, denying the soldiers any rest and driving them to exhaustion. And while they conducted their hit-and-run, guerrilla-style tactics, the local mosquitoes kept up their onslaught against the unseasoned British troops. By April, the number of Cornwallis’s men fit for service had almost halved.35
When the main force of the combined French-American army marched into Virginia in late summer 1781, Clinton ordered Cornwallis to withdraw his southern army into Yorktown, on the coast of Chesapeake Bay, to construct a defensive position and await evacuation by the Royal Navy. Clinton still believed that Washington intended to attack New York and wanted to keep the southern army within reach of the navy if a rapid redeployment north became necessary. Cornwallis repeatedly questioned the wisdom of these orders to ‘hold a sickly defensive post in this bay’, surrounded by marshy estuaries and with growing numbers of his men falling prey to the fevers.36
The Franco-American army laid siege to Yorktown, and when the Royal Navy fleet sent from New York arrived in early September 1781, it was repelled by the French fleet guarding the mouth of Chesapeake Bay. Cornwallis was stuck with the worst of both worlds: his army pinned down on the coast during peak mosquito season and the Royal Navy still not able to reach him.37 With over a third of his remaining army too sick to fight,38 Cornwallis laid down arms on 19 October 1781. His surrender ended the war: the United States had won its independence.
The American revolutionaries would not have prevailed without the intervention of the French and Spanish in their favour. Their supply of weapons, provisions and reinforcements, as well as their fleets challenging the Royal Navy and breaking the blockades, were all key to the success of the revolutionary struggle. But also hugely influential was the weakening of British forces by endemic diseases during the southern campaign – their susceptibility to malaria only compounded by the shortage of quinine. The American soldiers, on the other hand, benefitted from a home ground advantage bestowed by their lifelong seasoning to local endemic diseases.39
It wasn’t just the Thirteen Colonies that owed their success in the fight for independence in part to endemic diseases. Shortly afterwards, a similar scenario played out when the slaves in the French colony of Saint-Domingue, on the Caribbean island of Hispaniola, rose up against their masters.40
Hispaniola is the second largest island of the Caribbean after Cuba and was the site of the first European settlement in the Americas, established on Columbus’s world-changing voyage. But the Spanish largely lost interest after they realised that the island had no gold or silver to offer. The French established themselves before formally gaining the western third of the island in the peace treaty that concluded the Nine Years War in 1697. The French named their colony Saint-Domingue (which is now Haiti), and by 1775 it had become the most lucrative in the world.41 Saint-Domingue’s 8,000 plantations grew half of the global supply of coffee; it was also the world’s top producer of sugar and a leading exporter of cotton, tobacco, cocoa and indigo dye. This single colony accounted for over a third of France’s entire trade and produced a greater economic output than the thirteen British mainland colonies combined.42
For all that, Saint-Domingue depended on the transatlantic slave trade. The work of cultivating cash crops in the tropical heat was gruelling, and the staggeringly high death rate among the slaves demanded constant replenishment. By the late eighteenth century, around 30,000 new slaves arrived every year, a constant influx needed to sustain the total numbers at around half a million. Slaves made up some 90 per cent of the colony’s inhabitants.
In August 1791, a group of them rose up against the brutal oppression of the plantation owners and violent revolt rapidly spread across the colony. Within weeks, their number had swollen to 100,000, and the following year the rebels controlled a third of the colony.
The British were unsettled by the slave revolt: if it were allowed to succeed, working slaves on other colonies would be encouraged to rise up too, leading to a domino effect of rebellions across the Caribbean. Being at war with France, the British also recognised an opportunity to secure the exceedingly lucrative French colony for themselves. But the conflict proved disastrous. British troops arriving on the island with no previous exposure to or resistance against tropical disease also succumbed in droves: around 65 per cent of the 23,000 British soldiers sent to Saint-Domingue died of yellow fever or malaria.43
After military intervention by the British, as well as the Spanish, a former slave, Toussaint L’Ouverture, had emerged as the most prominent leader of the Haitian Revolution and consolidated control of the colony, issuing a constitution and calling for Saint-Domingue to be an independent black state. He had earned his second name – meaning ‘The Opening’ – with his ability to find the ways through enemy ranks; both friends and enemies also referred to him as Black Spartacus or Black Napoleon.
In 1801, Napoleon himself dispatched General Leclerc, his son-in-law, with over 25,000 soldiers to quash the slave rebellion and regain control of the lucrative colony.44 At first, the highly trained and well-equipped French troops were successful in their engagements against the slaves and L’Ouverture was captured. But like the Americans two decades earlier, the rebel army harried the French from the inland hills with hit-and-run tactics of guerrilla warfare, confining them to the low-lying coastal regions.45 And these freedom fighters too were aided by the squadrons of mosquitoes on the island and the endemic diseases they transmitted – malaria and yellow fever. What’s more, another key biological difference between the African rebels and the European soldiers came into play.
As we have seen, the human body develops resistance to the malarial parasite after repeated infection – provided the individual survives the experience – and in malarial areas, surviving children develop a significant acquired immunity, known as seasoning, by age five.46 To misappropriate Friedrich Nietzsche: ‘That which does not kill me, makes me stronger.’47 But malaria has imposed such a burden upon exposed populations that different groups of humans have evolved with genetic mutations that confer innate resistance against the disease. These defences mostly affect the red blood cells, where the malarial parasite grows.48 Unsurprisingly perhaps, they’re mostly found in Africa, where malaria is endemic and humanity has spent the great majority of its evolutionary history. The most important of these mutations that provide shielding against malaria is that which causes sickle cell anaemia.fn5 The sickle cell trait is caused by a mutation in the gene that produces haemoglobin, the vital molecule inside red blood cells that makes them red and carries oxygen around the body. Everyone has two copies of this gene, one received from each parent. Individuals who inherit one normal version of the gene and one allele with the sickle cell mutation – who are said to be ‘heterozygous’ – are carriers of the disease.
Normal red blood cells are shaped like a thick disc compressed at the middle. But if they encounter conditions of low oxygen, the haemoglobin molecules produced by the mutated gene clump together and deform some red blood cells into a sickle-shape. Sickle cells can then get jammed in narrow vessels and block blood flow. Carriers of the sickle cell trait usually don’t experience many adverse effects – except in severe cases of oxygen starvation, such as strenuous exercise or, in modern times, unpressurised aeroplane flights.fn6
However, having one copy of the sickle cell allele is exceedingly effective at protecting the carrier against severe cases of malaria – it either hinders the parasite’s growth within the red blood cells, or makes it more likely that the affected cells are destroyed by the immune system.54
The problem is that individuals who receive two copies of the mutated gene from their parents – and are therefore homozygous – suffer dire consequences. The distortion of their red blood cells is much more common and they are stricken with sickle cell disease, which causes anaemia and blocks blood flow to the organs. Without modern medicine, those who are homozygous do not survive to adulthood. The sickle cell mutation is therefore a double-edged sword: it protects heterozygous carriers from malaria, but homozygous individuals suffer an affliction just as bad, if not worse, and die young.
In malarial sub-Saharan Africa, then, natural selection has been pulled in opposite directions. The outcome of this evolutionary tug-of-war between sickle cell disease and malaria is an equilibrium in the population: some 20–30 per cent of the population of malaria-infested Africa are carriers of the sickle cell variant of haemoglobin.55 The fact that the mutations to the genetic code causing sickle cell – a horrifying disease in its own right – would be so powerfully selected reveals a desperate Darwinian battle with malaria.56 The existence of sickle cell disease in the world today, affecting some 300,000 children born every year57 – mostly to parents of African descent – is the cost of evolution struggling to protect populations against the most destructive disease in human history.fn7
But let’s return to the Haitian Revolution and the slaves’ biological advantage over their European oppressors. As a result of their long evolutionary history in Africa, many of the slaves on Saint-Domingue would have carried an innate, genetic shield against malaria. What’s more, as a result of the particularly high influx of new slaves imported to the colony each year, most had also been born in Africa and so would have been exposed to malaria and yellow fever from a very young age. In short, they were already well-seasoned to malaria, and likely possessed lifelong, acquired immunity to yellow fever after having survived infection as a child.
The French troops, on the other hand, were protected by no such biological shields and suffered far more severely from both diseases. Before long, over a third of the French soldiers were sick. It seems that many of those that survived the yellow fever were then killed by malaria. General Leclerc himself died of yellow fever. Reinforcements were sent but they too succumbed to the mosquito-borne diseases in huge numbers.61 In total, around 50,000 French troops of the expeditionary force died on Saint-Domingue, most of them of malaria and yellow fever. Only a few thousand soldiers survived to be evacuated in 1803 when Napoleon abandoned the effort to reclaim the colony.62
The freed slaves, with aerial support from the common mosquito, had defeated not one but two of the most highly trained and best-equipped armies in the world.63
Saint-Domingue declared independence in 1804, the free nation renaming itself Haiti.64 But though now free of the shackles of slavery and imperial control, Haiti had become an outcast. The European imperial powers did all they could to diplomatically isolate and economically choke the development of the newly independent state. They imposed trade embargos on the island’s exports, and the French deployed gunboat diplomacy to exact compensation for their loss of revenue – the iniquity of freed slaves being forced to pay reparations to their former masters. The ‘debt’ was not repaid until the 1950s. Once the most prosperous colony in the world, Haiti is among the poorest nations on Earth today.
Yet the successful slave revolt bolstered the global abolitionist movement, and by the time of Haitian independence, all the northern US states had prohibited slavery; Britain banned the transatlantic slave trade three years later.65 But the effects of the Haitian slave revolt, aided by the endemic diseases of yellow fever and malaria, had other, far-reaching repercussions.
The hugely profitable Caribbean colony of Saint-Domingue had not only provided a crucial income to France’s coffers, it had also been regarded by Napoleon as a critical staging post for projecting military force into North America. The entire Mississippi river valley had been claimed in the late seventeenth century by French explorers who named it after their king, Louis XIV, with New Orleans as the capital of the Louisiana colony. Now the loss of Saint-Domingue both as a source of trade revenue and as a strategic naval base forced Napoleon to abandon any imperial designs on North America and instead focus on the European theatre of war. He looked to offload not only the port of New Orleans but also the whole colonial territory of Louisiana to raise cash for his European wars.66
The United States was reliant on trade along the Mississippi and through New Orleans, and over a third of their exports were flowing through the Gulf of Mexico.67 When US president Thomas Jefferson therefore approached France to buy New Orleans for $10 million, he was surprised to be offered the entire colonial territory for just $15 million (equivalent to $366 million today).68 The Louisiana purchase was completed in May 1803,69 with the US acquiring a huge tract of land stretching from the Mississippi to the Rockies and from the Gulf of Mexico as far as Canada. The United States doubled in size with the stroke of a pen, and for only $170 per square kilometre in today’s money. So effects of endemic disease in Saint-Domingue, and the biological resistance of the black revolutionaries, played no small part in the course of world history.
The presence of endemic diseases in the tropical and subtropical regions that Europeans colonised from the sixteenth century hindered any large-scale settlements. The very high mortality rates among any Europeans living there led the colonial powers to operate extractive strategies that were designed with the primary objective of producing and then exporting profitable commodities like sugar, coffee and tobacco as quickly as possible. They were not interested in long-term development or creating an infrastructure beyond the bare minimum needed to plunder this natural wealth. The workforce was formed of slaves, and coercive control was imposed with an iron fist to maintain the outflow of profits. The few Europeans present in these colonies mainly served as administrators or soldiers to supervise the extractive operation and suppress resistance. Long after independence from colonial rule, therefore, such areas continued to be hampered by poor infrastructure and the lack of well-established legal and governmental systems that protect against expropriation of property and prevent abuses of state power. Many of the modern states in Africa, Asia and Latin America that have endured a history as extractive colonies are today among those with the lowest levels of development or economic stability.
On the other hand, colonies established in more temperate climates without high levels of lethal endemic diseases allowed the survival of European settlers. Such colonies were able to attract significant numbers of émigrés trying to build new lives for themselves and their families. They also brought with them their expectations of just government and protection through enforcement of the rule of law. Property laws protected the rights of individuals to be able to earn a livelihood by farming their own land, through claims over mineral rights and mining or through trade. They resisted the overreach of governmental power and built representative democracies for a more equitable society, which replicated key administrative, legislative, judicial and educational institutions of the colonial homeland. In short, settlers strove to recreate little European bubbles in remote colonies. The colonies where European settlers could survive and thrive established long-lasting institutions – though only for the benefit of the colonists and their descendants. These in turn created more stable social conditions that fostered ongoing investment, development of infrastructure and economic growth even after the settler colonies achieved independence from their imperial founders. The colonies that would become the United States, Canada, New Zealand and Australia all benefitted from these drivers for long-term development, born of the fact that European settlers were not severely ravaged by endemic diseases in these regions.
So the forms of colonies that developed in different regions of the world – extractive and settler colonies – were largely dictated by biological factors: the susceptibility of Europeans to the endemic disease environment. These initial conditions established contrasting patterns of development that either helped or hindered long-term economic trajectories, and still persist now, long after the colonies achieved independence as their own nation states. The economic disparity between many nations today has its roots in where the European colonists had a self-interest in establishing strong institutions. The GDP of these nations today is strongly correlated with the historical mortality rate of European settlers.70
The first civilisations to bear the brunt of the age of European conquest and colonisation were those of Central and South America at the dawn of the sixteenth century. From the seventeenth to the nineteenth century, Europeans settled the North American continent, exterminating its indigenous peoples in the process, fulfilling what they considered to be their manifest destiny. Western imperial interests turned to India in the eighteenth and nineteenth centuries, and targeted China in the mid-nineteenth, but did not attempt to penetrate into the deep interior of the vast continent of Africa until the late nineteenth century.
As we have seen, prevalent diseases shaped the colonisation – and history – of the Americas. Yet when European explorers first made contact with the New World, they encountered an effectively benign disease environment. We need to remember that malaria and yellow fever, which had such devastating effects on colonists, were not originally present in the Americas, but arrived with European contact and the slave ships from Africa. For historical reasons we’ll turn to in the next chapter, native American societies had few crowd diseases of their own, and the first settlers faced little hindrance from endemic disease. On the other hand, the infectious diseases that the Europeans unwittingly brought with them wrought apocalyptic devastation upon the native populations. Whole civilisations collapsed beneath the lethal onslaught of Old World diseases, bringing far more death and destruction than the weapons of the invading troops. The settlers following behind encountered largely emptied territory.
But the European powers benefitted from no such epidemiological advantage in their engagements with India, China and other societies across Asia. Trade networks operating across the breadth of Eurasia over the millennia had ensured a thorough distribution and mixing of infectious diseases, creating a single, common disease pool. European and Asian populations had acquired resistance against the same diseases. The imperial clash with India and China relied on the superior weaponry and the formidable armies and navies of European powers.
In Africa, the power balance was reversed. Having endured lethal tropical diseases for millennia, African populations exhibited much greater genetic resistance, such as the sickle cell trait, and lifetime seasoning. So the most lethal African diseases to outsiders, malaria and yellow fever, had relatively low mortality rates among African adults. And unlike many of the crowd diseases endemic across Eurasia – such as smallpox, influenza and measles – that can be directly transmitted from person to person, many tropical diseases are spread via an insect vector. These key intermediaries cannot survive in colder environments and so the diseases are confined within particular climate zones.71 Europeans arriving in Africa possessed no genetic resistance or seasoning to malaria, nor immunity to yellow fever, and quickly died in large numbers. Indeed, the mortality rate from yellow fever in adults who have not been previously exposed to the disease could be as high as 90 per cent.72 Europeans may have had a stark military advantage over the native polities, but they consistently lost against the indigenous microbes. At least to start with, endemic diseases seemed to level the playing field between the native peoples and would-be invaders, serving as a very effective biological deterrent against incursion.
Yet this didn’t prevent European powers from pursuing some of the worst forms of extraction from Africa. A modern map still bears the marks of what European powers considered of value: Pepper Coast, Ivory Coast, Gold Coast, Slave Coast. But the European presence in Africa was limited to a small number of troops and traders in the coastal forts – known as factories – negotiating deals with the local chiefs and overseeing the exploitation of resources from further inland, including the most abhorrent form of extractive practice, the seizing of forced human labour.73
Thus Africa’s endemic disease environment served as an effective firewall, largely keeping out European intruders and preventing the widespread colonisation that had occurred in the Americas and Oceania. European colonisers were able to cling to no more than tiny toeholds along the coastline, and even within the factories the European death rate exceeded 50 per cent every year.74 It was the Portuguese who first established trading posts on the West African coastline in the late fifteenth century, but for the next four centuries or so Africa remained the ‘Dark Continent’, its interior unknown to European eyes. For Europeans, Africa was a death sentence:75 the British referred to the continent as the ‘White Man’s Grave’.76 As late as 1870, very few Europeans dared travel more than a day or two inland from the coast.77 Only in regions where the disease environment was unusually favourable, such as in the very southern tip of the continent around Cape Town, were Europeans able to establish a permanent presence.78
All this started to change from the second half of the nineteenth century. Medical science came to understand the basis of different infectious diseases – by isolating and identifying the microbe that causes each one – and so was better equipped to treat or prevent them. Labs developed new vaccines and, later, antibiotics. Production was increased of natural plant products known to combat diseases, and chemists learned not only how to extract and purify their active compounds, but then to artificially synthesise them in bulk. The ancient relationship between humanity and diseases was being fundamentally transformed, improving the lives of countless millions. But the colonial powers also used these new medical capabilities to extend their reach across the world.
From the early nineteenth century, quinine was used to aid British imperial control over malarial regions of India. In the 1860s, the British smuggled cinchona plants and seeds out of South America to establish plantations in British India and Sri Lanka for their own supply. As powdered quinine tastes extremely bitter, they took to drinking it dissolved in carbonated water with sugar as ‘Indian tonic water’. This was often mixed with gin to help further mask the bitterness and make the medicine more palatable – and so was born the G&T cocktail.79 (Incidentally, quinine is also the compound within tonic water that glows in the dark when illuminated by ultraviolet light, familiar to those sipping G&Ts in a nightclub.) But it was not until the 1880s, with the mass production of high-quality fever tree bark by the Dutch in Indonesia, that the price of quinine began to decline significantly.80
This solved the global quinine supply problem. With the disease barrier that had previously been protecting the continent now crumbling, the gateway opened for colonial expansion into the vast interior of Africa without the abject fear of imminent mortal sickness.81
By the early 1880s, the British had already established a presence on the Guinea Coast and in South Africa, and claimed territory around the eastern coastal ports of Mombasa and Berbera (in modern Kenya and Somalia) to secure their sea route to India. France seized a region along the northern bank of the Congo, and Germany claimed Dar es Salaam (modern Tanzania) as well as parts of Togo, Cameroon, Tanganyika and Namibia.82 In 1884, Otto von Bismarck, the statesman who had united Germany in the previous decade, convened a conference in Berlin to settle disputes between the imperial powers over their territorial claims in Africa – a kind of international diplomatic gentleman’s agreement over divvying up the land grab – which is widely considered as the starting gun for the ‘scramble for Africa’. Rivalry between the powers escalated the feeding frenzy, with each striving to outdo and gain a strategic advantage over the others. They morally justified the exploitation of the ‘Dark Continent’, its population and resources as a civilising mission bringing enlightenment and humanitarianism.83
Within a single generation, virtually all of Africa was carved up by Britain, France, Germany, Italy, Belgium, Portugal and Spain, the borders between them bearing no consideration to geography or ethnic groupings.fn8
The scramble for Africa was facilitated by technological advances in transportation and communication – including steamships, railways and the telegraph – but the crucial development that had enabled Europeans to explore and exploit the African continent were medical countermeasures against the endemic tropical diseases, which until then had made it a death-trap.
So far, we’ve considered the effects of endemic diseases in different parts of the world. We’ll now turn our attention to the raging spread of epidemics through whole populations and see how these sudden, catastrophic jolts of mortality precipitated long-lasting shifts in the affected societies.