The 20th century’s greatest biological breakthrough was announced unceremoniously on Feb. 28, 1953, when British scientist Francis Crick (on right, above) winged into the Eagle Pub in Cambridge, England, and declared that he and his younger U.S. partner, James Watson, had “found the secret of life.”
That morning Watson had sketched out how four chemical bases paired to create a self-copying code at the core of the double-helix-shaped DNA molecule, heredity’s master switch. In their more formal one-page paper in the journal Nature, they noted the significance of their discovery in a famously understated sentence: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” But they were less restrained when asking Watson’s sister to type up the paper for them. “We told her,” Watson wrote in his account of their discovery, The Double Helix, “that she was participating in perhaps the most famous event in biology since Darwin’s book.” Another woman played a more significant role: X-ray diffraction images taken by British scientist Rosalind Franklin helped the two men describe the double-helical structure of DNA and spark an ongoing biological revolution.
This entry is excerpted from the new TIME book The 100 Most Influential People of All Time, which profiles spiritual icons, leaders, explorers, visionaries and cultural titans throughout human history. Available wherever books are sold and at time.com/100peoplebook