"The biologists are catching up." That was the reaction of the famously taciturn Paul Dirac, the Nobel-prize-winning physicist, when he attended an exposition on the discovery of the structure of DNA by Francis Crick and James Watson. At the time, physics was the premier science, the one heading deeper and deeper into the nature of matter, while biology was seen, even by many of its own, as little more than list-making, without a fundamental scientific understanding of the structures that govern life.

Almost fifty years later, the biologists have grown more confident, to the point of declaring this the Age of Biology. Nuclear physics changed the world, to the surprise of some of its most distinguished practitioners who thought their research was purely theoretical. Now molecular biology is promising, or threatening, to change our very idea of who we are, and its practitioners are not surprised at all.

Where physics brought us nuclear power (and weapons), molecular biology is facing us with the idea of human genetic modification (though only a distant fear of weapons so far). Both technologies rise directly out of deep scientific research, and both deserve important social discussion before being applied. Nuclear power slipped into use with so little effective opposition that it is often thought that the problems with it – including the cost, the danger and the difficulty of disposing of waste products – were insufficiently addressed at the time. This is not entirely true, but even if it were, no one seems to want to make that mistake again.

So the public pronouncements of prominent scientific supporters of human genetic engineering usually sound very reasonable, even moderate in their approach. They are fully aware of the ethical dilemmas they face, they aver, and constantly call for a widening debate so that our society as a whole can face up to and resolve these vital issues. Certainly, they look to avoid the public relations blunders of the nuclear industry, which is infamous for having promised clean, safe, cheap electricity and having delivered dirty, dangerous and expensive waste. In comparison with the nuclear physicists of the 1950s, the molecular biologists seem thoroughly reasonable and even-handed, do they not?

This is, in fact, a slur on the physicists. And in a peculiar way, a warning for those of us concerned with the headlong rush into uncharted genetic territory.

As is so often the case, the facts are even more interesting than the myth. One single piece of contemporary journalism will serve as a neat example. Newsweek reported on November 2, 1953 that the US "government disclosed it had already launched a project to build a full-scale [atomic] power reactor." This was a government effort "for two important reasons: cost and security. A conventional power plant costs about $75 to $100 a kilowatt to build. An atomic reactor, it has been estimated, will cost at least five or six times that amount. ... Equally important, the U.S. has to stay ahead of Russia" because if the Russians built one first they might lure other countries "(such as Belgium)" ... "into the Red orbit."

In other words, the anti-nuke mantra that the industry was born in secret, as part of the national security state and with no economic rationale is not revisionist history at all, but a clear restatement of the very first press announcement.

What of the notorious claim that nuclear power would produce electricity that was 'too cheap to meter'? The phrase was a godsend for later anti-nuclear campaigners – whoever popularized it belongs in the highest rank of Madison Avenue manipulators – but it was taken seriously out of context. The full sentence is: "It is not too much to expect that our children will enjoy in their homes electricity too cheap to meter, – will know of great periodic regional famines in the world only as matters of history, – will travel effortlessly over the seas and under them and through the air with a minimum of danger at great speeds, – and will experience a lifespan far longer than ours as disease yields and man comes to understand what causes him to age." In other words, it was part of a banal piece of utopian fantasy. Admittedly, the phrase was uttered by the Chairman of the Atomic Energy Commission, Lewis L. Strauss (in an address to the National Association of Science Writers in New York on September 16, 1954), which makes using it as a quote just about defensible as advertising goes, but essentially it has been used as propaganda. And as weapons go, the half-truth is a dangerous one. (I can't resist: not as dangerous as nukes, though.) In this case, it comes back to haunt us with the implication that scientists of today are more realistic about the challenges they face than scientists were fifty years ago.

Technological euphoria did abound in the fifties. There were indeed scientists who claimed that nuclear fusion would be a practical source of electricity by 1975 or even sooner. The prophecy was reported in Time (August 22, 1955) as having been made at the first International Conference on Peaceful Uses of Atomic Energy by the Indian physicist Homi J. Bhabha, who was president of the conference and, according to Time, free to speak because he was "bound by none of the security regulations that so often gag U.S. experts." The July, 1955, issue of Foreign Affairs had in fact already included a long and sober article that recommended research into fusion technology, and by October, 1956, Life was proclaiming that "Atomic Fusion, Not Fission, Will Drive Future machines." No less an expert than Edward Teller (the Father of the H-Bomb) pronounced that "I am quite confident that the controlled thermonuclear reactor can be made."

Teller was wrong about that, of course (or at least has been so far and there is not much prospect of change), but he was quite right to insist, in the Time article cited above, that "it is important to emphasize ... the public hazard that might follow a reactor accident ... [Because of leaking radiation] it may be necessary to abandon a watershed and ... make the reactor site itself a forbidden area for years to come." This was before any such plant had been completed, and there is no reason to classify him as an opponent of nuclear power (on the contrary, he remains a strong supporter), though admittedly he may have been angling for more funds for fusion research. But doesn't he sound reasonable?

Of course he does. I disagree with Teller on many issues, including the Strategic Defense Initiative (SDI) of which he is the most prominent supporter, but he is no fool. What he was doing in the 1950s, and continues to do even in his nineties (he was born in 1908), was applying his considerable intellect both to technical problems and to their social impact. In a 1990 interview, he describes his reaction to the first atomic explosion: "The feeling strongest in me at the time, was one of worry. What will happen when this is used in earnest?" He characterized Oppenheimer's famous response to the same event (quoting the Bhagavad-Gita, "I am become death, the destroyer of worlds") as "a remarkable example of the conceit of scientists. The idea that they create something new, the lack of recognition that all they do is find something that is already there. To discover is enough. To create, to be the source of something new, or imply it in any way is, I think, very troubling."

Popular journalism will always simplify; SDI becomes 'Star Wars' and the promise of nuclear energy becomes 'too cheap to meter'. In its own way, this is fair enough – neither of those characterizations is ridiculous, though both have become associated with cartoonish positions of opposition. But it is important to remember two things: first, which proponents of nuclear energy (and, doubtless, human genetic manipulation) often forget, that simplistic slogans are used even by people with deep and subtle reasons for their positions; and second, which opponents often forget, that the other side has deep and subtle reasoning ability too.

The corollary of saying that the nuclear advocates of the fifties were by no means as naive as their critics sometimes seem to think is that the subtleties of the modern molecular biologists do not make them any less dangerous.

Thus, W. French Anderson wrote in Newsweek (December 27, 1999) that "if used unwisely, the genetic engineering of human beings could endanger everything we value – including who and what we are. ... Already the first indications of potential abuse are surfacing. ... If such crucial decisions are left to the marketplace, might we ultimately engineer ourselves to the point where we are no longer human beings? ... Our only protection is to accept clear stopping points." Which might lead the reader to conclude that he was an opponent of these technologies; but it is Anderson who has spearheaded a proposal to investigate 'in utero gene therapy' which blurs the distinction between somatic and germline interventions, some think quite deliberately. The funding request acknowledges that "an occasional vector particle may enter an egg or sperm, thereby resulting in germline gene transfer." In other words, he proposes to breach the "clear stopping point" he himself recommends.

Or consider Gregory Pence, the author of a book titled Who's Afraid of Human Cloning? and a staunch advocate of the idea. Somehow, he managed to get himself quoted as agreeing with, of all people, the Pope, as determined an opponent as there is. Evidently, both of them are concerned about what Pence describes as "the potential it causes for deception, fraud and greed." While I am sure that his concern is real, we should remember that this is the man who, in complete seriousness, compared the selection of a child to the selection of a retriever ("many people love their ... sunny dispositions").

Even Lee Silver, whose frightening book Remaking Eden blithely postulates a future in which humanity fractures into different species (essentially, the haves and have-nots, with wealth translated into genes), worries that we may end up "cell by cell ... surrendering our humanity to the marketplace, bartering ourselves away one gene at a time in pursuit of our own engineered perfection."

Or consider this statement: "This is a matter far too important to be left solely in the hands of the scientific and medical community." As it happens, it was made by James Watson, in 1971, writing about human cloning, but it could easily have been, and indeed with slight variations has been, attributed to any of the prominent scientists concerned with the research. Few of them would have added publicly, as Watson did in 1998, when asked what he would say to the American public about human genetic engineering, "We should say that it's none of their business," though many would take the intermediate position (also from Watson in 1998) that "I think our hope is to stay away from regulations and laws whenever possible."

It was Watson who, as the first Director of the Human Genome Project, insisted on diverting five per cent of the funds to set up a Working Group to consider the Ethical, Legal, and Social Implications of the Human Genome Project (forever known as ELSI, and in some ways diminished thereby). This was clearly a politic move, in that it ensured that to a large extent the parameters of the ethical discussion were set by the people controlling the research. Lori Andrews, a law professor with long experience in reproductive issues, has written scathingly of the reasons for her resignation from ELSI, which by her account was deliberately created "not to set ethical standards but to let the science proceed unimpeded." It may be the greatest example in history of foxes funding chicken-coop-security research, but at a minimum it leaves the uninformed onlooker with the clear impression that the scientists are as careful and dispassionate with the social issues as they are with the scientific ones.

French Anderson warning of potential abuse is precisely analogous to Edward Teller warning of nuclear hazards – both are realists; both know very well, and are willing to admit, that what they propose is not without risk; both consider that they are fully aware of the dangers and competent to assess them. Both, in fact, explicitly accept the right of the public to make policy decisions – and both are willing to work as hard as they can to ensure that the public makes the decision they favor.

That is what all this talk of ethics is about. It is obvious to everyone that human genetic engineering raises ethical issues; only the most obtuse of scientists could fail to acknowledge that, and if they tried they would not be believed. So what they do is to raise the issue and try to persuade us that in raising it they have also settled it.

It took a generation to slow the spread of nuclear power in the US and industry apologists (it is far from dead) are right to complain that some of the arguments made against them are unfair. They always admitted there were difficulties, technical and financial, though they concluded that these could be overcome – it's a bum rap to say they seriously pretended there were no problems. (Which is not to forgive them for the sins some of them did commit.) And at this point overstating the historic case against them may actually backfire; as energy consumption continues to rise, the nuclear lobby will continue to press its case and to point to the falsity of some of the complaints. Which is a straw-man argument with a difference, since the straw man was built by their opponents.

In the case of human germline engineering, it is true that the bogey has been unleashed by Lee Silver (among others). The specter of distinct species of post-humans, or of exacerbated inequality within human society, was raised not by opponents but by supporters of the technology. It is even possible that this was done, in part, out of a cynical desire to create an extreme position from which a 'compromise' could be made; to change the parameters of the debate. Certainly the tenor of editorial comments in mid-2000 suggests that the prospect of 'designer babies' is still extremely repugnant to many people. When, however, a series of incremental changes is proposed – let us simply change this single piece of genetic variation with the intention of, say, trying to eliminate diabetes from the human germline; and this one to reduce the risk of breast or prostate cancer – the molecular biologists are going to say that this is certainly not a case of 'designer babies' and they will point to their carefully crafted public statements to demonstrate how deep is their concern for the issues, and how thoroughly they have thought them through.

They may even claim to be more aware of the social consequences and potential dangers than the nuclear physicists were, and given the way most of us think about the physicists of the 1950s, they may sound convincing. But they would be wrong. What the history of the nuclear industry tells us is not that physicists were naive but that to hear scientists speaking of ethics, technological difficulties, unintended consequences and the like is absolutely no reason to think that they will be deterred from pursuing their goals.

Beware of scientists who claim to support democratic decision-making. What they usually want is cover – a justification to do precisely what they always wanted to do. The rest of us have to scramble to decode their pronouncements in time to stop them.

Biology has indeed caught up – to roughly where physics was fifty years ago. That is, capable of mischief and hopeful of better. We already have genetically modified plants and even the odd animal, since with them we do not worry about mistakes but merely discard them; are people to be next? Something could be done to people, we know that already, but we are not yet assured that what can be done will be predictable or even useful, let alone safe or desirable. Even assuming, as I do not, that the ethical questions can be settled, will that prospect turn out to be as much of a mirage as the idea of harnessing nuclear fusion for the production of electricity?

Nuclear physics has continued to develop, and its theories of time and space grow ever more arcane, but that sudden burst of practical applications in the middle of the twentieth century is looking increasingly like a technological blunder of the first magnitude. Not only do we still have no fusion reactors, we still have no coherent plan for the long-term storage of nuclear waste, we still have an absurd quantity of the weapons, and there still have been no fundamental technological breakthroughs.

What is essential now is that society as a whole be suitably skeptical of the claims of the molecular biologists. Within their field, they operate in a generally pragmatic manner, testing hypotheses and abandoning them if they are disproven. They also speak tentatively, of statistical probabilities and theoretical constructs. Somehow, these caveats frequently get lost when the discussion moves to the practical realm; we have already seen far too many journalistic claims and retractions about the supposed discovery of genes that have specific consequences – homosexuality and breast cancer, to name but two. The authority with which scientists speak of their field to outsiders is all too often an over-simplification only partially justified by the undoubted fact that the laity cannot understand the details or the math; yet on that shaky foundation too many of them build a set of social prescriptions or predictions whose grandiose certainty seduces the unwary.

It seems appropriate to close with a quotation from Edward Teller. He did not always like to follow his own prescription, but that just makes him human – we would be well advised to do as he says, not necessarily as he did: "We scientists are not responsible and should not be responsible for making decisions. But we scientists are uniquely and absolutely responsible for giving information."