They treat their Nobel prize winners rather differently in the US. Over here, you're lucky to get an invitation for a glass of sherry with the vice-chancellor before you scuttle back to your cramped office to fill in a few more speculative grant applications. But 45 years after winning the Nobel prize - along with British scientists Francis Crick and Maurice Wilkins - for discovering the structure of DNA, James "Jim" Watson is still regarded in America as quasi-royalty.

At 79, Watson no longer gets involved in hard-graft science. He quit his last high-profile job as head of the Human Genome Project in 1992 after falling out with Bernadine Healy, the newly appointed director of the National Institutes of Health, over the patenting of gene sequences. His main functions as chancellor of the Cold Spring Harbor Laboratory (CSHL) - the Long Island non-profit, private research institute - are to press the flesh with the great and the good to extract research cash, and to keep a beady eye on the Watson school of biological sciences.

But even as a figurehead, Watson is a celebrity. He's a regular on the global conference circuit, and his opinion is often sought by politicians - though recent, and possibly future, presidents won't necessarily like what he has to say about them. "Bush is just a disaster, and the Clintons worry me. They get their truths from social scientists, not scientists. I'm a little afraid of their friends."

Around Cold Spring Harbor, Watson is spoken of in hushed tones by everyone from the security guard at the front entrance to leading academics; but then no one raises their voice much above a whisper at Cold Spring Harbor.

When Watson first came to Long Island in the late 1940s, as research assistant to Salvador Luria, a future Nobel winner himself, CSHL was just a couple of ramshackle buildings with a few wooden outhouses. "We didn't really come to do any serious science," he says. "We came to talk, and to escape the intense heat of the Indiana summer. We did a few experiments, but no one cared much whether they worked or not." These days, CSHL looks more like a five-star hotel complex, nestling on the manicured hills of Long Island's north coast and overlooking a secluded cove stuffed with yachts.

Buy property

The tastefully wood-panelled office in the main building has the feel of a Silicon Valley millionaire's HQ, and the only truly distinguishing feature of the room is the framed Nobel citation on the wall behind the desk.

Everything else is expensive but a wee bit bland; everything apart from Watson himself, that is. Throughout his life, Watson has made few concessions to anyone or anything and, even though he is a committed liberal, political correctness has never featured anywhere on his list of priorities. Least of all today.

"You should always use your Nobel prize money to buy property," he laughs. "My share [$6,000] went as a down-payment on a house in Cambridge, Massachusetts."

"I thought you spent it on paintings," I reply. Watson is well-known for an art collection that includes works by Paul Klee and André Derain.

"Oh no," he says, "the money for them came from royalties from my textbook, The Molecular Biology of the Cell. It earned me about $20,000, the equivalent of an entire year's academic salary."

Like many Americans, Watson is upfront about money. He's pleased to have done well for himself, not just for the trappings, but for the freedom of not being hard up. His parents struggled financially during the Depression, and Watson has always kept one eye on the cash flow while the other was on the science. "I appreciated being rich," he says, "because it allowed me to study in Paris and Geneva. Francis [Crick] twice had to pawn his typewriter to fund his research."

Watson is equally candid about his limitations. At school in Chicago and at college in Indiana, his grades were more often Bs than As. So how come he went from being a rather average student to one of the two men credited with making a key scientific discovery of the 20th century?

"I never had an exceptional mind - I certainly wasn't in the same league as Francis," he says. "I think I've succeeded more by learning what needed to be done next, and getting help in getting it done. I was just very focused and impatient."

This isn't the academic's traditional first resort of false modesty. Self-deprecation isn't part of his make up: he prides himself on telling things straight. And it's probably this, as much as anything else, that has got so many colleagues' backs up over the years. He strips away the mystery of the scientific process and reduces it to an everyday story of hard work, ambition, opportunism and complex human relationships.

And relationships didn't come much more tricky than those involved in the decoding of the structure of DNA. For Watson, it is just another modern morality tale, albeit one that should be told with some exaggeration and good humour to make it more interesting for everyone else. Watson had been working on phages - bacterial viruses - when a meeting with Wilkins in Italy, at which the English scientist talked about his X-ray diffraction data for DNA, persuaded him to change tack. Watson hooked up with Crick at the Cavendish lab in Cambridge and the rest is history: the two men determined the double-helix solution for DNA.

Watson and Crick never enjoyed the easiest of relationships. "I wanted to start my book [The Double Helix] with the sentence, 'I've never seen Francis in a modest mood' but the lawyer wanted me to change it to 'seldom'," Watson laughs.

"Francis sometimes lacked a sense of humour. I also wanted to call the book 'Honest Jim', but Francis didn't get the joke; he thought it implied a dishonesty. At times, he was a little more square than I thought; he had this enormous laugh, but not always when the humour involved himself."

No big deal

Crick might not have been best pleased with Watson's assessment of his career. "Francis knew he wasn't in the same league as the great physicists and, as the great age of nuclear physics had passed, he moved to biology, which offered more interesting objectives and was less crowded."

But Watson sees no reason to get precious about these things. He sees nothing wrong with ambition and, in any case, he reckons solving the structure of DNA wasn't quite the big deal it has often seemed since. Rather it was just the final, incremental nail in a series of experiments and, if they hadn't done it, then someone else inevitably would. They were just lucky to be in the right place at the right time.

Whatever the tensions between Crick and Watson, they were nothing compared with those between the other key players. "Neither Francis nor I had the courage to call Maurice to say that we'd solved his problem," Watson says. "John Kendrew [another member of the Cavendish laboratory] thought it best if we called him to say we had something that might interest him. Maurice looked at the model, and knew it probably had to be right. We invited him to put his name to the paper we were writing for Nature, but he phoned from London to say he would be publishing a separate paper in the same issue."

Watson muses: "He said in his autobiography that it was his biggest mistake not to have put his name on the paper. But he realised he hadn't done it. Just as we realised that if he hadn't shown us the X-ray photo and talked honestly about the data, we would never have been in the game. But that was fair play. Everyone was glad when he was later cited as part of the Nobel prize. No one thought about Rosalind [Franklin], because she was dead."

Conveniently so, many have argued, as each Nobel prize has a maximum of three citations. Franklin was a British scientist who died in 1958 and who many believe was never given due credit for her part in the discovery of the structure of DNA, either in her lifetime or since. How does this square with Watson's commitment to fair play?

He smiles. "Rosalind is my cross," he says slowly. "I'll bear it. I think she was partially autistic." He pauses for a while, before repeating the suggestion, as if to make it clear that this is no off-the-cuff insult, but a considered diagnosis. "I'd never really thought of scientists as autistic until this whole business of high-intelligence autism came up. There is probably no other explanation for Rosalind's behaviour.

"She showed great insensitivity to Wilkins. It [DNA] was his problem and she just thought she could take it from him. She was clueless. John Randall [the British physicist who led the King's College team that included Wilkins and Franklin] told her DNA was going to be her thing and [she] took it from Maurice. But fair play should never have allowed Rosalind to do it. So she was either not a nice person, or just clueless. I think clueless. When you knew her, she wasn't nasty; just awkward.

He adds: "Francis didn't think Rosalind was a great scientist. That was Francis at his most honest. The truth was she couldn't think in three dimensions very well."

The assessment is not meant to be as damning as it sounds. Rather, it is Watson just doing what he always does: telling it as he sees it, not least because he doesn't attach the same stigma to mental illness as others do. For Watson, it's just a genetic condition, similar to heart disease. "I've no time for the Steven Rose types, who argue that schizophrenia is caused by the stresses of capitalistic society," he says. "I've hated them for years. I've seen the failure of the environmental approach in a very personal way. My wife and I have a schizophrenic son. We didn't want to accept this for 30 years, so we put him under great pressure when we shouldn't have. He just wanted to be looked after, and we didn't respect that. We tried to make him independent."

Stupid gene

Watson's insistence on the primacy of nature over nurture in genetics has got him into trouble in the past; he has been quoted as saying there is a gene for stupidity and genetic screening would allow us to cure the problem. He feels no reason to back down, merely to qualify. "I wasn't talking about people with a slightly below-average IQ," he points out. "I was talking about the bottom 10% who have severe learning difficulties. If someone's liver doesn't work, we blame it on the genes; if someone's brain doesn't work properly, we blame the school. It's actually more humane to think of the condition as genetic.

"For instance, you don't want to say that someone is born unpleasant, but sometimes that might be true. If you accept that people are the products of evolution, then you have to have an open mind to the truth. Unfair discrimination exists whether we like it or not; I wouldn't have married a gum-chewing vegetarian. Ultimately, we'll help the people we discriminate against if we try to understand more about them; genetics will lead to a world where there is a sympathy for the underdog."

It's not always easy to follow the internal logic of Watson's scattergun stream of consciousness, or to work out which bits he really means and what he's just saying because he's on a roll and enjoying being provocative. But he does have a strong sense of self and, when the chips are down, he's usually to be found on the side of the angels. As head of the Human Genome Project, he took on Craig Venter's rival efforts to privatise gene sequences and, if the matter has yet to be resolved, it hasn't been lost. "Eventually, the Supreme Court will have to adjudicate that it's not good for human health," he shrugs.

Curiously, though, there is no mention of Venter, or his company, Celera, in his idiosyncratic new memoir, Avoid Boring People. "The book was long enough as it was," he smiles, "and I didn't think it would be enhanced by what I said about him." Though that doesn't stop him here. "Craig wanted to patent his sequences, but it made no sense. So I said, 'You shouldn't patent something a monkey could do.' I think that got to him, because at our next meeting he turned up in a monkey suit."

Watson has never claimed to have been the best scientist of his generation. But he's done some good science, he's worked with brilliant minds, he's made friends and enemies in equal measure. And he's enjoyed doing it. "Regrets?" he muses. "Nah. Imagine if I'd married some of the women I asked. It would have been a disaster. You know what? I'd quite like them to make a funny movie out of my book."

And who would play you?

"Sacha Baron Cohen."

Choosing to be diplomatic for the first time in two hours, he declines to say who would play Crick.

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