The Lost City of the Monkey God

by Douglas Preston

Traditional Indian remedies against illness—sweats, cold baths, and medicinal herbs—were ineffective against smallpox. Indeed, many efforts at healing only seemed to hasten death. In Europe, at its worst, smallpox killed about one out of three people it infected; in the Americas the death rate was higher than 50 percent and in many cases approached 90 to 95 percent. Epidemiologists generally agree that smallpox is the cruelest disease ever to afflict the human race. In the century before it was eradicated in the 1970s, it killed more than half a billion people and left millions of others horribly scarred and blind. It inflicts unbearable suffering, both physical and psychological. It usually starts like the flu, with headache, fever, and body aches; and then it breaks out as a sore throat that soon spreads into a body rash. As the disease develops over the subsequent week, the victim often experiences frightful hallucinatory dreams and is racked by a mysterious sensation of existential horror. The rash turns into spots that swell into papules, and then fluid-filled pustules that cover the entire body, including the soles of the feet. These pustules sometimes merge, and the outer layer of skin becomes detached from the body. In the most deadly variety of smallpox, the hemorrhagic form, called the bloody pox or black pox, the skin turns a deep purple or takes on a charred look, and comes off in sheets. The victim often “bleeds out,” blood pouring from every orifice in the bo...

Humans do not usually catch infectious diseases from animals; pathogens tend to confine their nasty work to a single species or genus. (Leishmaniasis is a striking exception.) But microbes mutate all the time. Once in a while, an animal pathogen will change in such a way that it suddenly infects a person. When people in the Near East first domesticated cattle from a type of wild ox called an aurochs, a mutation in the cowpox virus allowed it to jump into humans—and smallpox was born. Rinderpest in cattle migrated to people and became measles. Tuberculosis probably originated in cattle, influenza in birds and pigs, whooping cough in pigs or dogs, and malaria in chickens and ducks. The same process goes on today: Ebola probably jumped to humans from bats, while HIV crashed into our species from monkeys and chimpanzees. Alongside the domestication of animals, humans in the Old World began settling down in villages, towns, and cities. People lived together in much denser numbers than before. Cities, with their bustle, trade, filth, and close quarters, created a marvelous home for pathogens and an ideal staging ground for epidemics. So when diseases migrated from livestock to people, epidemics broke out. Those diseases found plenty of human fuel, racing from town to town and country to country and even crossing the oceans on board ships. Biologists call these “crowd diseases” because that’s exactly what they need to propagate and evolve. Epidemics periodically swept through Eur...

In the New World, on the other hand, no big-time diseases seem to have leapt from animals into the human population. While the Americas had cities as large as those in Europe, those cities were much newer at the time the Spanish arrived. People in the New World hadn’t been living in close quarters long enough for crowd diseases to spring up and propagate. Native Americans never had the opportunity to develop resistance to the myriad diseases that plagued Europeans. This genetic resistance, by the way, should not be confused with acquired immunity. Acquired immunity is when a body gets rid of a pathogen and afterward maintains a state of high alert for that same microbe. It’s why people don’t normally get the same illness twice. Genetic resistance is something deeper and more mysterious. It is not acquired through exposure—you are born with it. Some people are born with greater resistance to certain diseases than others.