Another interesting section of Guns, Germs and Steel by Jared Diamond is the section on disease. As I mentioned, the whole of this hefty volume is dedicated to explaining “why different peoples ended up with disparate degrees of power and affluence,” and a big part of the answer relates to disease.
About 95 percent of the population of North and South America was killed by diseases brought by Europeans. Why, Diamond asks, didn’t European traders and conquistadores bring back diseases fatal to Europeans?
The only disease that is even suspected of going from America to Europe is syphilis, and its origin is still a subject of debate. Voltaire has a funny joke about it in Candide (a very funny book) where the bishop got it from the choirboy who got it from the chambermaid who got it from a sailor who sailed with Christopher Columbus — or something like that.
Anyway, Diamond answers this question very systematically, by looking at the microbes’ point of view. “After all,” he writes, “microbes are as much a product of natural selection as we are. What evolutionary benefit does a microbe derive from making us sick in bizarre ways, like giving us genital sores or diarrhea?”
Turns out germs are a lot like corporations with inventive new marketing strategies.
“Microbes evolved to feed on the nutrients within our own bodies, and they don’t have wings to let them reach a new victim’s body once the original victim is dead or resistant.”
“From our perspective, the open genital sores caused by venereal diseases like syphilis are a vile indignity. From the microbes’ point of view they’re just a useful device to enlist the host’s help in inoculating microbes into a body cavity of a new host.”
That nagging cough that you find so annoying is just an effective marketing strategy to launch a cloud of microbes toward prospective new hosts. Other microbes hitch a ride on fleas and ticks. Others contaminate soil and water through human waste.
But the strategy that really takes the cake is the rabies virus which drives a dog victim into a frenzy of biting to transmit the virus in its saliva to other hosts.
Diamond goes on to explain why Europeans and Asians, because they had huge herds of large mammals, developed a collective “evolutionary immunity” as people who were genetically more resistant to the major killers — smallpox, influenza, tuberculosis, malaria, plague, measles and cholera — tended to survive.
Then they also developed immune system responses like the dairy maids who had been exposed to cowpox and were therefore immune to smallpox.
There’s a lot more to it — how some diseases came to be restricted to humans, how epidemics travel around the world — but although the explanation is protracted, it’s all very understandable, even for a dummy like me.