BBC News science reporter
The increase in life expectancy enjoyed by many societies is a triumph of modern science.
Our understanding of the human body and how to repair it when it breaks down have continued to push "old age" into the distance - and researchers intend to keep pushing.
But the claims made by Dr Aubrey de Grey, a scientist at the University of Cambridge, UK, that lifespan can be increased by over 1,000 years, have proven too much for some; and a dispute has now broken out within the gerontology community.
The argument, which has been played out through academic journals, and most recently at a "life extension" conference, has culminated in the unusual step of a cash prize on offer for anyone who can disprove de Grey's science.
Difficult science
Dr de Grey's claims for long life centre on SENS (Strategies for Engineered Negligible Senescence); essentially, strategies to prevent and cure ageing.
SENS is based upon repairing the molecular and cellular damage that accumulates throughout life; so as to prevent age-related illness and frailty.
It focuses on addressing seven different types of cell damage, including mutations to chromosomes and mitochondrial DNA, and cell loss. He argues that once these can be fixed or prevented, the sky's the limit for lifespan extension.
His assertions have made headlines around the world, but some gerontologists are not convinced that the science behind SENS is sound, and they spoke openly about their views at the Tomorrow's People International Conference on Life Extension and Enhancement held at Oxford University.
"Aubrey is trying to generate enthusiasm for a commitment and programme that, in a sense, sidesteps the practical challenges that the science faces," explained Professor Tom Kirkwood, co-director of the Institute for Ageing and Health, University of Newcastle.
"There are really big challenges and we are all aligned in hoping that we can harness the science to improve and extend quality of life, but it doesn't serve any useful purpose to try to extrapolate so far beyond the immediate challenges."
Most scientists, and I was among this group, took the position that any sort of response to de Grey was just feeding the fire.
Twenty-eight scientists working in the field took the step of submitting a rebuttal to a paper published by Dr de Grey in the journal EMBO Reports in 2005.
The strongly worded paper says that: "Each one of the specific proposals that comprises the SENS agenda is, at our present state of ignorance, extremely optimistic...
"A research programme based around the SENS agenda... is so far from plausible that it commands no respect at all from within the scientific community."
Professor Richard Miller, associate director of the Geriatric Centre at the University of Michigan, US, told the BBC News website that he became involved with the rebuttal because he felt it was important to have on record that so many gerontologists felt that the ideas were without merit.
"I wrote the article and we sent it around to 30 or so of our colleagues, expecting that only half would sign it, because scientists really do not like to take a public position in opposition to someone that they know.
"I was amazed that we found no-one who refused on the grounds that they agreed with Aubrey; a couple of people said they didn't want to sign anything about his work because they didn't want to draw attention to it. We got 28 people who astonishingly were willing to say in public that they had evaluated the science and had found it to be worthless."
Money challenge
In response to this and other objections from the scientific community to SENS, Dr de Grey has fought back by launching the "SENS Challenge" in the Technology Review magazine of the Massachusetts Institute of Technology.
"It's essentially an offer of $20,000 (£11,000) to anyone who can write a demolition of my ideas that are sufficiently powerful to demonstrate that not only are they wrong but they are so wrong that they are unworthy of learned debate," explained De Grey to the conference delegates.
"This is open to anyone who has credentials in molecular biology of any sort, and the important thing about it is that it is judged by a review panel."
I think we will hopefully be able to get some means to make a significant impact on processes of ageing.
Prof Tom Kirkwood
At the conference, Dr de Grey announced that he had a five-person-strong panel to review submissions, including Dr Craig Venter, who led the private effort to decode the human genome, and Dr Nathan Myhrvold, a former chief technologist at Microsoft.
"I essentially felt that it was critical for me to smoke out the opposition," Dr de Grey told the BBC News website.
"I had to move things along to an on-the-record opposition so that people would be forced not simply to say what they thought of these ideas, but why."
So far, there have been very few submissions to the challenge, and none of these from the scientists involved with the EMBO rebuttal.
"Most scientists, and I was among this group, took the position that any sort of response to de Grey was just feeding the fire," said Professor Miller, explaining why he had chosen not to enter the challenge.
But while the debate continues, all involved do agree that life extension is within the realms of possibility for science; but how exactly we do it, how long we can postpone death for, and whether modern society can handle the burden of an increasingly aged population is still being debated.
"I think we will hopefully be able to get some means to make a significant impact on processes of ageing. These will not necessarily result immediately in substantive life extension, but they may change the profile of health that people experience as they go through [old age]. We haven't begun seriously to discus what should be our priorities and how we should develop strategies," explained Professor Kirkwood at the conference.
"Most medical research is done by trying to prevent people dying. And Aubrey says we should simply extend this into ageing. Actually, now, we are in a situation of being able to harness what comes from the basic biomedical research to try to devise a better way to age.
"And if that leads to life extension, that's great. But it's difficult to see the path to make that happen."
Time Challenger Labs International, Inc.
