About noon on Feb. 28, 1953, two men burst into their favorite pub, a scruffy spot called The Eagle near their Cambridge University laboratory. As people sipped their beers and forked down shepherd's pie, one of the men gleefully announced: "We have discovered the secret of life."
The scene - which played out 50 years ago this week - is one of the most famous of 20th- century science. It marked the conclusion to an intellectual footrace to find the structure of deoxyribonucleic acid, better known as DNA.
Playing with a crude cardboard model of the DNA molecule, Francis Crick, a 36-year- old Englishman, and his 24- year-old American partner, James Watson, had puzzled out DNA's now-familiar double helix early that day.
Their discovery solved the fundamental mystery of heredity, how everything from eye color to crippling disease can be passed through generations.
A half-century later, historians are still filling in the details of the story behind the discovery and resurrecting old questions about who should get credit. In a tale that turns out to be as twisted as the strands of the double helix itself, the role played by a little-known chemist, Rosalind Franklin, is getting new attention.
In a biography published in October, author Brenda Maddox shows how Franklin's photographs and measurements of the molecule, which Watson and Crick acquired secretly, led them to a Nobel Prize. The book raises anew questions about whether the pair went too far and if Franklin's contributions were adequately recognized.
"Rosalind seemed doomed to remain the invisible woman in many minds, the faceless nurse who hands the surgeon the scalpel," Maddox wrote.
James Dewey Watson and Francis Harry Compton Crick met in October 1951 - and it was love at first sight.
"They apparently fell into a kind of intellectual crush on each other," wrote science historian Horace Freeland Judson in The Eighth Day of Creation: Makers of the Revolution in Biology.
Born in Northampton, England, Crick was known for his nonstop talking and stiletto-sharp intellect. He had little to show for it - only the mines he designed for the British Admiralty during World War II. But his Cambridge colleagues soon learned that he had an annoying way of swooping in and attempting to solve their scientific problems.
Watson, meanwhile, was an eccentric skirt-chaser from Chicago who loped across the manicured Cambridge lawns in untied tennis shoes and shorts - even in the winter. He mumbled and had a bad habit of staring. But he was no intellectual slouch, graduating from the University of Chicago with a degree in zoology at 19.
Both altered their careers after stumbling upon physicist Erwin Schrodinger's book What is Life?, which argued that genes were the essential stuff of life. Nobody really knew what genes were made of, though DNA was one possibility.
The book inspired Crick, at the relatively late age of 33, to abandon physics for biology and pursue a doctorate at Cambridge. Watson, too, had become obsessed with DNA after reading Schrodinger and went to Cambridge with hopes of unlocking the molecule's secrets.
Although the two were officially assigned to other things, unofficially they spent most of their time talking about DNA over tea in Room 103 of the Cavendish Laboratory or over lunch at The Eagle.
"I daydreamed about discovering the secret of the gene," Watson later wrote.
Discovered in 1869, DNA was considered only a bit player in genetics. Scientists thought proteins, which perform most essential tasks in the body, were most likely to be responsible for passing on hereditary traits. DNA appeared to be too simple a molecule to do that.
Among the handful of scientists interested in DNA was Linus Pauling at the California Institute of Technology, a chemist who went on to win two Nobel Prizes. He had an unorthodox approach to solving problems: he liked to build Tinkertoy-like models of molecules, rearranging the pieces until they fit.
Just before Watson arrived at Cambridge, the 50-year-old Pauling had used his toys to pull off a scientific coup, discovering that certain proteins had a corkscrew - or helix - shape.
Some scientists were speculating that DNA also might be helix-shaped. Watson, who saw DNA as the "most golden of all molecules," worried that Pauling might try to find out.
"They saw Pauling as a definite threat," said Robert Olby, a historian of science at the University of Pittsburgh.
In fact, in the fall of 1951, Watson and Crick knew that Pauling was sniffing around for good photographs of DNA.
"We knew what to do: imitate Linus Pauling and beat him at his own game," Watson wrote in his 1968 bestseller, The Double Helix.
The place to which Pauling - and soon Watson and Crick - would turn for photos was King's College in London, where Maurice Wilkins and Rosalind Franklin were taking the world's finest portraits of DNA.