Sir Harry Kroto, Nobel laureate and rigorous defender of chemistry, revealed last week that he is leaving Britain for the US. Like many scientists, he fears his research funding here will dry up once he reaches retirement age this year. Is 65 the end of the road for science? ask Anna Fazackerley and Steve Farrar.
When the celebrated evolutionary biologist John Maynard Smith turned 65 his colleagues paid him the traditional retirement honour of editing a collected volume of his scientific papers. The trouble was that 15 years later he had written so many more that they had to start a new volume.
"He had worked flat out from 65," explained Paul Harvey, head of zoology at Oxford and co-editor of the two collections. "He had a clear-thinking mind and it was all very simple for him. He loved to sit in his armchair and talk about science - that was his favourite position up until he died."
Last week, it emerged that another Sussex old-timer, the Nobel prizewinning chemist Sir Harry Kroto, was leaving the UK for a lucrative research position at Florida State University.
The fact that 64-year old Sir Harry was headhunted will come as no surprise to many in academia. Not only does he have a sparkling CV, but there is also no official retirement age in the US. As long as a senior scientist is performing well and bringing in the research contracts, age cannot legally be an issue.
Freeman Dyson, the 80-year old British physicist best known for his work in quantum electrodynamics, remains an important figure at Princeton University. On paper, he retired as professor of physics at the Institute of Advanced Studies ten years ago, but in reality he has never left.
Professor Dyson still has an office at the university and a place at the academic lunch table. "I am very privileged," he said. "My life is my association with the people here."
This desire to keep going is typical among many world-class scientists, who have clearly not entered into research simply to pay off their mortgage or to fund the family holiday.
At the age of 100, Ernst Mayr, Alexander Agassiz professor emeritus of zoology at Harvard University, continues to write books and debate scientific ideas.
Colleagues say that he is frustrated by the physical side-effects of old age: his daughter had to take away his car keys a couple of years ago after a minor collision and he is now confined much more to his home.
But, according to James Hankel, director of the museum of comparative zoology that Professor Mayr used to run, "his mind is still razor-sharp".
He added: "For some, such as Professor Mayr, the ability to contribute to a field doesn't stop simply because they have reached a certain age. They have such an intellectual passion for what they are doing that to a certain extent it is what keeps them young."
Many of these older scientists refuse to blow their own trumpets - Professor Dyson describes himself as more of a "historical monument" than a groundbreaking scientist - but they often have an important impact on others in university.
Professor Hankel explained: "I love having Ernst Mayr here. He is inspirational to the students. Having figures who can talk about leading biologists of 50 or 60 years ago and give you personal anecdotes is invaluable."
Similarly, many personal recollections of Maynard Smith, posted on the Sussex University website after his death in April at the age of 84, focus on inspirational group discussions with him over beer and chips in the Swan pub.
But persuading excellent scientists to retire at 65 may be counterproductive in other more tangible ways, especially if their best research is yet to come.
The work that won Cambridge University theoretical physicist Sir Nevill Mott his Nobel prize in 1977 was done after his retirement in 1973, although some believe his earlier work merited a separate award. He famously switched from field to field, yet never lost his ability to ask the right questions and intuitively seek out pertinent answers. He continued writing scientific papers up until his death in 1996 aged 90.
Abe Yoffe, emeritus reader in physics at Cambridge's Cavendish laboratory, shared a room with Sir Nevill in the first 14 years of his "retirement". He recalled a brilliant scientist with an insatiable hunger for research.
"People's minds don't just stop when they reach retirement age," Dr Yoffe said. "Nevill kept solving problems and people kept speaking to him because of his ideas."
At the Medical Research Council's Laboratory of Molecular Biology in Cambridge there has been something of a tradition of great scientists refusing to quit the lab on their 65th birthdays.
Max Perutz, founder and long-time director of the LMB, like many others, chose to take on retired worker status until he died, aged 83. In that time he published more than 100 scientific papers, reviews and commentaries, and was a constant source of inspiration and encouragement to other scientists and students.
Richard Henderson, the current director of the LMB, said: "We had Max for 18 years after his retirement and he was very valuable to us throughout.
"Not least, he always retained his ability to ask the obvious question at the end of a lecture, the sort everyone else was too embarrassed to attempt."
Aaron Klug maintains a small group at the LMB, where he won his Nobel prize in 1982. Last year, at the age of 77, he published a key paper in Nature about the structure of transcription factors.
Professor Klug said: "I'm known here as the retired worker. But you have to show that you are doing something useful. There is pressure to make way for younger people so you are in tough competition."
Three other LMB Nobel laureates - Francis Crick, Sidney Brenner and Cesar Milstein - likewise refused to bow out of science politely simply because they had hit their mid-sixties.
The notable exception was double Nobel laureate Fred Sanger. On his retirement, aged 65, he told his colleagues at the LMB that they were wrong to imagine that he would find it difficult to stay away from the laboratory.
He explained that he could and would now pursue ambitions that had previously been denied him by the pressure of his scientific career, namely to build a boat and grow roses.
Dr Henderson noted that only between 5 and 10 per cent of his laboratory's scientists chose to stay on after retirement, but this number often included some of the finest scientific minds.
"Once a scientist has done some really groundbreaking, innovative work, they are never again satisfied with derivative work and are therefore constantly looking for the next golden nugget," he said. "When they get up in the morning the only thing they can think about is their science."
Sir Richard Peto, who has spent decades collaborating with the inspirational 92-year old epidemiologist Sir Richard Doll, agrees that a true passion for science is impossible to shake off.
"The obsession with science comes from a delight in beauty. The results themselves can be really beautiful," he said.
Behind the scenes, many UK academics are worried about what Sir Harry Kroto's departure says about opportunities in the UK for those not ready to swap their scientific mission for a carriage clock.
Dr Henderson reacted angrily to the news, insisting that Sir Harry should have been given the incentive to do his research in the UK. "If he had been here, at the LMB, we would certainly have allowed him to take on students, a lab and technicians," he said.