PATHOGENESIS

World history through the eyes of microbes.

Bacteria may be microscopic and easy to disregard, writes Kennedy, a professor of politics and global health, but they’re ubiquitous and astonishingly prolific—outweighing humankind, for one thing, by 1,000 times in terms of total mass. However, along with viruses, bacteria shape the fortunes of all life on Earth. It’s hardly news that this includes the course of human history. In 1976, William McNeill’s Plagues and Peoples made a strong case for the radically important role of disease in the rise and fall of civilizations and as a significant force in propelling innovation and warfare. Kennedy’s book is in some ways redundant, but it is well grounded scientifically and draws on recent literature to examine, for instance, the effect of disease on the eventual hegemony of Homo sapiens over other early humans. If “for early humans, the Eastern Mediterranean region must have seemed like a cursed realm, the Paleolithic equivalent of Tolkien’s Mordor,” the arrival of human-borne pathogens into Neanderthal populations must have been even more deadly. Plagues in third-century Rome helped an obscure offshoot of Judaism gain supremacy over pantheistic religions whose gods, by allowing such calamities, were proven weak; without those murderous bacteria, Christianity might never have established itself. Kennedy charts the interaction of climate change with disease—the reappearance, for example, of the bubonic plague after a long absence as the Northern Hemisphere warmed and pest-bearing rodents proliferated, just in time for the Mongol Empire to spread the pandemic through its widespread raids—and he helps puzzle out a long-standing mystery concerning the Columbian conquests: “How do we explain the almost unilateral flow of pathogens from Europe to the Americas?” The answer is nuanced but reveals a great deal about how so many great Native American empires were so quickly subdued.

Of interest to students of world history, with lessons to ponder for our own pandemic-hobbled time.