One day in July 1958, François Jacob squirmed in a Paris movie theater. His wife, Lise, could tell that an idea was struggling to come out. The two of them walked out of the theater and headed for home.

“I think I’ve just thought up something important,” François said to Lise.

“Tell!” she said.

Her husband believed, as he later wrote, that he had reached “the very essence of things.” He had gotten a glimpse of how genes work together to make life possible.

Jacob had been hoping for a moment like this for a long time. Originally trained as a surgeon, he had fled Paris when the Nazis swept across France. For the next four years he served in a medical company in the