It’s a risky world, as we know, but all the more risky because some of the risks keep evolving. Ebola virus and the influenzas can adapt. ISIS can change tactics; Kim Jong Un can do turnarounds. And now experts warn that we have entered the “post-antibiotic era,” during which increasing numbers of people—in the hundreds of thousands—will suffer and die each year from infection by forms of bacteria that were once easily controlled with antibiotics.
The World Health Organization considers antibiotic resistance one of the biggest threats of the 21st century. The World Economic Forum calls it a “potential disaster” for human health and the global economy. Just one such microbial threat, multidrug-resistant Staphylococcus aureus, caused more than 11,000 deaths in the United States in 2011 alone, and that one plus other resistant microbes kill hundreds of thousands of people annually around the world.
How has this happened? By a combination of Darwinian natural selection (hit a population of bacteria with an antibiotic, and the fittest will survive) and an evolutionary mechanism discovered much more recently, a phenomenon so counterintuitive that Charles Darwin didn’t imagine it: horizontal gene transfer. What that means is genes moving sideways across boundaries—between individuals, between species, even between kingdoms of creatures. One researcher in the 1950s dubbed it “infective heredity.” Genome sequencing reveals that such horizontal transfer of DNA has been profoundly important in the history of life, and among bacteria it’s especially common, with particular implications for the spread of antibiotic-resistance genes.