The leading international science journal Nature has focussed the US presidential election campaign on science by asking both President George Bush and Senator John Kerry for their views on the major issues.
By Paul Reynolds
BBC News Online world affairs correspondent
Both candidates were given 15 questions and asked to confine their answers to a total of 1,500 words. Mr Bush had to be edited as he overran; Mr Kerry kept within the limit.
The most significant difference identified by the magazine was over stem-cell research, with Mr Kerry wanting to go well beyond the quite restrictive policy adopted by President Bush.
This issue is a vital one for American scientists. Many of them feel that their colleagues elsewhere (in the UK, for example) are being given a head-start by more liberal policies.
It is an issue which brings science right up against moral fundamentalism.
But there were differences as well over climate change, the development of a new generation of nuclear weapons, manned space exploration and anti-missile defence.
The major questions:
STEM CELL RESEARCH
In August 2001, President Bush, after agonising about the policy for some time, announced that federal funding would be available for research only into stem-cell lines which existed at that moment. i.e. no new lines could be created.
He argued that to do otherwise would be to violate the integrity of the embryo. In his Nature response, he stuck by this policy. "I am committed to pursuing stem-cell research without crossing a fundamental moral line, and I am the first president to provide federal funding [which came to $216m last year] for human embryonic stem-cell research."
He went on to challenge some of the expectations that such research might lead to miracle cures: "However, stem-cell research is in a very early state and while it may hold great promise we should not overstate the state of science, or politicise these issues..."
Senator Kerry makes much of stem-cell research in his campaign and Nature says that he mentioned it more often at the Democratic convention than unemployment. He is supported by a lobby group backed by 48 Nobel Prize winners.
His answer in Nature therefore called for restrictions to be lifted: "I will lift the ideologically driven restrictions on stem-cell research created by the Bush administration by overturning the ban on federal funding of research on new stem-cell lines, all while ensuring rigorous ethical oversight."
By "ideologically driven restrictions," Mr Kerry meant the influence of the anti-abortion movement.
President Bush outraged much of the world when he withdrew from the Kyoto Protocol. He has since followed more of a national than an international approach.
In his Nature response he accepted that "global climate change is a serious long-term issue" but then challenged assumptions about the effect of greenhouse gases by saying that the National Academy of Sciences "found that considerable uncertainty remains..."
He said: "My administration is now well along in implementing a comprehensive climate-change strategy... I also committed the nation to a goal of reducing American greenhouse-gas intensity by 18% over the next 10 years."
Senator Kerry calls for intentional action but does not in fact commit himself to rejoining the Kyoto accord and speaks in rather general terms only.
"The scientific evidence is clear that global warming is already happening... President Bush rejected the Kyoto Protocol, stubbornly walking away from the negotiating table altogether.
"John Edwards and I (he keeps on mentioning John Edwards in his answers) will take the United States back to the negotiating table while working at home to take concrete steps to reduce pollution..."
So, no target figure came from Mr Kerry, just a commitment to negotiate internationally.
NEW NUCLEAR WEAPONS
The US is currently examining how to build a new generation of so-called mini-nukes. Mr Bush says that this effort will continue because "the evolving security environment requires a flexible and responsive weapons-complex infrastructure", an answer clearly written by an official expert.
It means that the US wants a greater range of nuclear weapons, for example in attacking underground bunkers.
Mr Kerry says flatly that "I would end the pursuit of a new generation of nuclear weapons." So that difference is clear enough.
This is a priority for President Bush who says that "Our policy is to develop and deploy, at the earliest possible date, ballistic missile defences drawing on the best technologies available."
Mr Kerry favours research but "I am not for rapid deployment of missile defence. We should not waste money on deployment at this stage." He therefore does not rule it out but is cautious about its effectiveness.
MANNED SPACE EXPLORATION
Mr Bush appears to have back-pedalled from his "man on Mars" ambition but he still wants man to go back to the Moon. "America will return to the Moon as early as 2015 and no later than 2020 and use it as a foundation for human missions beyond the Moon." He does not mention Mars.
Mr Kerry is sceptical. "There is little to be gained from a space initiative that throws out lofty goals, but fails to support these goals with realistic funding." However, he and John Edwards, he says, will increase funding for a continuation of space exploration.
Here the differences are more to do with the practice of how crops are regulated rather than whether they should be allowed in principle. Neither candidate opposes GM foods.
Mr Bush says it is important that the "regulatory framework keeps pace with science," a hint that it can be too restrictive.
Mr Kerry talks about how important it is to "give government agencies the power to effectively regulate genetically modified food products". And he gives a nod to international concerns by saying that he would work to address these while Mr Bush stresses the role of GM food in "meeting the world's demand for food".
Perhaps the hardest question for the candidates to answer was one about whether Americans should "change their lifestyles and consume less". A "yes" response might have landed them in trouble. So there is a good deal of waffle in their answers to this one.
Mr Bush: "America in a very real sense has changed, not by consuming less but by consuming and producing smarter", by which he means that it is economic growth which makes environmental progress possible.
Mr Kerry, who has a good reputation among environmentalists, takes a not dissimilar overall view: "Time and again, America has met environmental challenges through ingenuity and technological innovation."
But he goes further by saying that "strong leadership" is needed to put public health and environmental interests ahead of the interest of the polluters. There could, therefore, be battles ahead on such issues if he becomes president.