Recently re-broadcast by PBS, “Spillover” explains the science behind how viruses like Corona, Zika, SARS and Ebola are transmitted from animals to humans – often with devastating results. In the last half-century the number of spillover viruses has quadrupled, costing countless lives. Typically, people learn about outbreaks as sudden disconnected flare ups. But these viruses have much in common: where they come from, how they maim and kill, and how they can be controlled.

Here’s something you won’t find on ancestry.com: Your inner ear comes from the jawbone of a prehistoric fish. Your skin and hair can be traced to a shrew-like mammal that lived around165 million years ago. As for your trick knee — well, you can thank your primate ancestors for that.

It took more than 350 million years for the human body to take shape. How did it become the complicated, quirky and amazing machine it is today?

Diseases that were largely eradicated in the United States a generation ago – whooping cough, measles, mumps – are returning, in part because nervous parents are skipping their children’s shots. VACCINES – CALLING THE SHOTS takes viewers around the world to track epidemics, explore the science behind vaccinations, and shed light on the risks of opting out.

It’s a mystery on a global scale: five times in Earth’s past, life has been nearly extinguished, the vast majority of plant and animal species annihilated in a geologic instant. What triggered these dramatic events? And what might they tell us about the fate of our world?