Half a century after the discovery of DNA's structure, Onora O'Neill asks if we are being blinded by the sensationalism that surrounds genetic advances

Lurid examples are a mainstay in discussions of new genetic technologies. Enthusiasts and scaremongers fill the columns and the airwaves with hopes and fears about designer babies, genetically modified crops and a pharmacogenetic future. Yet too intent a focus on worst and best-case scenarios may blind us to more urgent ethical questions. Can it really be useful to remind one another incessantly that horrendous things went on under the Nazis, or that some brave new worlds might be based on genetic modification? Or can we take these points as read and attend to less sensational but more urgent ethical questions raised by current uses of genetic technologies?

The favoured themes of enthusiasts and scaremongers are the benefits and harms of using gene therapies and genetic modifications to change or control life forms, human and other. Enthusiasts hope that we will cure illnesses with gene therapies and have babies with chosen and desirable traits, and that agriculture based on genetic modification of plants will end world hunger, reduce use of pesticides and save the environment.

Scaremongers warn us that the same technologies point to doomsday. GM organisms - bacteria or plants, animals or humans - might have unforeseen effects, might proliferate or hybridise and create plagues or environmental damage, and might divide human societies into the "genetically enhanced" and a "genetic underclass".

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A less breathless view of matters might compare incipient technologies and their risks and benefits with established technologies for genetic modification. Genetic modification, after all, is not a recent or unheralded innovation: it is the engine of evolution, the basis for plant and animal breeding and part of the background of many reproductive decisions and much medical practice. Some new technologies offer less than one might think; others are less novel than is often supposed.

For a case that offers less than one might think, consider what is available for those who want to design babies. Couples with known risk of serious single-gene disorders (for example, cystic fibrosis) can have tests and may terminate. Or they can try in vitro fertilisation with embryo selection, in the (slender) hope that an embryo without the damaging gene can be implanted (how different is that from the routine practice of selecting a viable embryo for implantation?). But seeking not to have a child with an anticipated, highly damaging single-gene disorder is a far cry from designing a child. There are no current genetic technologies for choosing characteristics that parents prize, such as intelligence or a happy disposition. This should not surprise us: if a single gene were the basis of these traits, we would have noted their patterns of inheritance long ago, as we did for single-gene diseases such as Huntington's. At present, we don't know much about susceptibility genes or their interactions with environmental factors, and we are many steps away from the designer baby scenario. If one wants a happy and intelligent child, a cheerful home and a good school are better bets.

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For a case that is less novel than is often supposed, consider genetic modification of plants using older and newer technologies. The world is full of successful plants that have achieved genetic modifications that make them taste nasty and have toxic effects on various animals, and of plants that hybridise promiscuously, sometimes with mildly unfortunate results. Traditional technologies run the same risks. The wheat and tares of the Bible are both GM plants. The wheat was produced by human manipulation, by generations of Stone Age men and women, and became the staff of life for countless millions. The tares were a backcross between the wheat they produced and its own wild ancestor, einkorn wheat. Tares occur in grain crops; they are a nuisance, not a catastrophe. The simplistic question "are GM plants good or bad?" is unlikely to have a uniform answer. Some modifications of some plants may be good or bad for some purposes, but we cannot tell which merely by referring to the way a modification was produced (natural plant breeding versus laboratory modification).

Some opponents of genetic technologies think that the "precautionary principle" offers a blanket reason for rejecting new technologies and hence any GM crops produced by using them. There are many formulations of the principle. Some are commonsense recommendations to be prudent and avoid likely harms. These versions invite us to judge whether each proposed innovation is more or less prudent than sticking with current practices.

Other formulations demand that we reject technologies that might have unforeseen bad consequences, regardless of evidence. This may look ethically rigorous, but it isn't. Since it rules out both innovation and sticking with the status quo - either choice might prove harmful - it is of zero practical use. It does not offer farmers, breeders, scientists, policy-makers or the public at large a method for making decisions without attending to the specific evidence for each case. To handle the risks of technical innovation, we need rigorous, evidence-based judgement of cases, caution and no fantasies about a risk-free world.

The genetic technologies in widest use today are not used to modify life forms. They are technologies for obtaining and organising genetic information, mainly DNA information pertaining to individuals. The use of DNA information in medical diagnosis and treatment, and in assisting reproductive decisions, is well known but hardly an everyday affair. Its use by the police, the immigration service, the Child Support Agency, family historians, archaeologists, stockbreeders and others is a larger undertaking. Although these are regulated by statute and data-protection requirements, there are unanswered questions about the ethical adequacy of this regulation.

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Why should we suspect that the use of genetic information obtained from individuals raises particular problems? Some have argued that genetic information is distinctively personal and peculiarly sensitive, even vital to our very identity. Is this true? The phrase genetic identity has a wide currency and sounds important, even foreboding. My suspicion is that the term is used to refer to (and confuse) several matters of differing ethical significance. One (metaphysical?) understanding is that genetic identity is the basis of personal identity. This seems to me false. Genetic make-up is not enough to distinguish persons: identical twins who share their genetic make-up are separate persons. Another interpretation is that genetic identity is not what makes people separate, but is what they share: people share a (sense of) genetic identity with their kin, and may share a sense of cultural identity with other groups. This way of putting it seems to me a misnomer: what we share with kin might be called a sense of genealogical identity: it is a matter of knowing that genes are shared, not of knowing which are shared.

Knowing which genes are shared raises different and difficult issues. Some writers have argued that genetic information is exceptional and should be treated differently from other personal information. They have pointed out that genetic information is familial rather than individual. This is true.

But what should we conclude? Various other sorts of personal information are also familial, including some genetic information not obtained from DNA that is familial but not sensitive, for example, baldness.

Yet even if a general claim that genetic information is exceptional is ill-founded, many uses of genetics raise ethical problems. May I seek DNA information that is as true of my twin as of me without prior consent? If I do, does my twin have a right to know what I discover? Or, alternatively, a right not to know it? Or a right to prevent my seeking the information? What practical content and what arguments could be given to any of these supposed rights? Is there a right to "genetic privacy" (covering what?) and do insurers have a "right to underwrite" that clashes with rights to "genetic privacy"? Does the proliferation of problematic and unargued rights claims in this area mean that we have spotted many questions but few answers? Do these "rights" fall by the wayside when data are not interpreted but used for matching purposes, as by the police and immigration service?

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Other, perhaps even more difficult, issues arise where DNA information obtained from individuals is entered into databases to be linked with information about their health or lifestyle information. Data protection standards are supposed to regulate what is done: either individuals agree to the entry, retention and linkage of their data, or they refuse. In the event of refusal, the information may be used only if irreversibly anonymised. Yet irreversible anonymisation of data prevents data linkage, while individual consent capacities may not be adequate to grasp and consent to such complex uses of such data. If data linkage without consent is ethically unacceptable and data linkage with consent is unattainable, public health records and much health research will be damaged. These are large and topical questions. They need a lot of attention, and might get more if we could tear our eyes away from lurid thoughts about genetic modification.

Onora O'Neill is principal of Newnham College, Cambridge. This piece is taken from a lecture to be given today as one of the 2003 Darwin Lectures organised by Darwin College on the 50th anniversary of the discovery of the structure of DNA.

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