One of biology’s wilder facts is that we’re all family. You and me, sure, but also me and a mushroom. Triceratops shared genes with you. So does the virus that makes you cough, and a rosebush. Bacteria left us on the tree of life around 2.7 billion years ago, but the wet world they came from is still ours: One code runs all of life. The same proteins that imprint memories in your neurons, for example, do so in octopi, ravens, and sea slugs. This genetic conservation means tricks from one species can be hijacked. If you stick a jellyfish gene in a monkey, it’ll glow green.
IN THE SUMMER OF 1984 the senior scientists of Cetus Corp., a Berkeley biotech company, found themselves in a bind. One of their employees, a promising young scientist named Kary Mullis, had dreamed up a technique to exponentially replicate tiny scraps of DNA. He called it polymerase chain reaction (PCR), and if it worked it would change the world and likely earn Cetus a mountain of money. The only problem was Mullis was an interpersonal wrecking ball.