In both cases, the germs behind the pandemic weren’t especially lethal. Covid-19 and the flu both fall within the normal range of mild infectious diseases. Compared with smallpox and Ebola, they kill only a small percentage of their victims, and their person-to-person transmission isn’t unusual. What sets them apart—what has made them world-wide pandemics—is modern transportation: fast steamships and railroads for the flu, and now jet airplanes for Covid-19.
Of course, there have been a great many “mere” epidemics in human history, diseases that have spread more slowly over large areas, but their effects have been profound. Over the course of recorded history and now in the archaeological record, examples abound of germs producing high death tolls and social and political upheaval, with far-reaching effects on local economies, trade, migration, colonization and conquest.
Will Covid-19 mark the beginning of a transformation in our own era, too? Are we entering an age of pandemics? It is far too early to say, but the long history of germs as agents of historical change can provide needed perspective—and perhaps a window into how Covid-19 and its likely successors may shape our destiny.
Consider first a familiar case: the plague bacterium, which was transmitted from rodents to humans by fleas, and spread from Asia into Europe in the 14th century. The Black Death killed about a third of Europe’s population in the years 1347-51 and recurred with lower death tolls for many decades thereafter.
The Black Death forced landowners to start paying their tenants and to grant them more rights. Its immediate effect on Western Europe’s economy and trade was disastrous. Paradoxically, though, its long-term effect was positive.
By reducing the number of laborers, the Black Death forced landowners to start paying their tenants and to grant them more rights and freedoms. Societies became less rigidly stratified; nuclear families became stronger; and sanitation and quarantines developed to combat infectious diseases.
Tropical diseases have had similarly profound effects. Only after quinine was found to be effective in treating malaria, for instance, could Europeans embark on their colonial conquests in New Guinea and Africa, carving up territories where European settlement had been impossible before.
Why, before quinine, were Europeans unable to establish themselves in New Guinea and Africa, where indigenous peoples had been thriving for hundreds of thousands of years? Because different peoples have different susceptibilities to the same disease—a major theme of medical history. Over thousands of years of exposure to malaria, New Guineans and Africans evolved many forms of genetic resistance through natural selection. Northern Europeans, by contrast, had no history of exposure to malaria, hadn’t evolved any of those genetic protections and hence were unlikely to survive long enough to develop antibodies.
The most lethal, permanent and far-reaching effect of germs in recorded history was to aid the European conquest and extensive replacement of Native Americans, Pacific Islanders and Aboriginal Australians. This was the reverse of what happened in Africa and New Guinea, where local diseases and different susceptibilities enabled local peoples, for a time, to resist European invaders.
Perhaps the deadliest germ that Europeans brought with them was smallpox. The disease killed Europeans too, of course, but through natural selection over thousands of years of exposure, they had evolved partial genetic resistance. They also had acquired immunity by developing antibodies. In the centuries before vaccination was developed, smallpox was widespread in Europe, and almost everyone was exposed in childhood, when some died but most survived and remained immune thereafter.
The long-term effects of Covid-19 remain to be seen. One troubling prospect is that the immunity conferred by the vaccines currently showing most promise will likely last only months or a few years, not a lifetime.
Jerry Lincecum is a retired Austin College professor who now teaches classes for older adults who want to write their life stories. He welcomes your reminiscences on any subject:
jlincecum@me.com