When biologist James Watson died on Thursday at age 97, it brought down the curtain on 20th-century biology the way the deaths of John Adams and Thomas Jefferson on the same day in 1826 (July 4, since the universe apparently likes irony) marked the end of 18th-century America. All three died well into a new century, of course, and all three left behind old comrades-in-arms. Yet just as the deaths of Adams and Jefferson symbolized the passing of an era that changed the world, so Watson’s marks the end of an epoch in biology so momentous it was called “the eighth day of creation.”

Do read some of the many Watson obituaries , which recount his Nobel-winning 1953 discovery, with Francis Crick, that the molecule of heredity, DNA, takes the form of a double helix, a sinuous staircase whose

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