Some human diseases are caused by microbes that have become infectious through evolutionary accidents. They didn’t evolve to infect us, and to reproduce at our expense. Instead, they evolved to fend off competitors or predators or to survive in harsh environments. And by coincidence, the adaptations that help gained make them better at harming our health. For example, a thick coat that stops a microbe from being digested by hungry amoebae might also protect it from our immune system.

This is the coincidental evolution hypothesis, and it’s the subject of my new feature in Aeon. Check it out.

When microbes aren’t killing us, we are largely oblivious to them. So, we construct narratives of hosts and pathogens, heroes and villains, us