Humans get along pretty well with most microbes. Which is lucky, because there are a lot more of them in the world than there are of us. We couldn't even live without many of them. But a few hundred have evolved, and are still evolving, to exploit our bodies in ways that can make us really sick. These are the microbes we call germs. Think plague, flu, HIV, SARS, Ebola, Zika, measles.
This is a series is about where germs come from. In this first of three episodes, we see what our early encounters with germs may have been like — and how germs first got the upper hand.