Will we be the authors of our lives?

You and I came by our personal sets of genes the same way as humans always have, through some nifty cellular reshuffling and our parents' response to the dictates of assortative mating. But suppose some future person has at least a subset of their genes consciously chosen. Will they come to see life and their place in it in a fundamentally different way?

This is a deep aspect of what is becoming established as one of the great 21st-century questions, perhaps even the question: what will become of Homo sapiens if we decide to alter our own genes and so, insofar as genes influence such things, reshape human nature? It is a daunting question, but it is encouraging the way the emerging discussion is engaging some serious thinkers. Even in Britain, the genetics arena gives cause for hope that "public intellectual" is not an oxymoron. In Germany, Jürgen Habermas' main contribution has been a long lecture delivered at Marburg in 2001 titled "The debate on the ethical self-understanding of the species". The Future of Human Nature now gives us this lecture in translation, together with responses to critics, and topped and tailed with the texts of two other briefer lectures on broader topics. In his own country, Habermas has been caught up in controversy with fellow philosopher Peter Sloterdijk, whose as-yet untranslated views on the topic caused a media stir a few years ago. But as he does not mention this anywhere in the book and Polity Press has not stirred itself to fill in any of this important context, this slim volume must be considered on its merits.

Habermas' answer to the question of the significance of genetic design is that it would be a profound change. So much he shares with many other commentators. As he puts it, biosciences and technologies do not just expand the possibilities for action, "they enable a new type of intervention. What hitherto was 'given' as organic nature, and could at most be 'bred', now shifts to the realm of artefacts and their production."

But his development of the implications of this now-commonplace observation is much more novel. It has echoes of Francis Fukuyama's argument for an essentialist notion of human nature and an Aristotelian concept of rights in his recent Our Posthuman Future . But it uses a rather different framework. As you might expect, this is Habermas' own theory of communicative action and its derived notion that people engaged in moral action or discourse must have the capacity to be themselves. For Habermas, that means that each individual must be able to see him or herself as the author of their own life history, and treat others on the same basis.

It is this that is compromised by the suggestion that someone's genes might be chosen in advance according to another's intentions. The designer denies the designed the right to endorse or repudiate their project and "changes the initial conditions for the identity formation of another person in an asymmetrical and irrevocable way".

This avoids some of the problems with simpler objections to unnatural selection, such as Bill McKibben's recent suggestion in Enough that it is a radical assault on autonomy. As Habermas recognises, "the situation of a programmed person does not initially differ from that of a person naturally begotten". The genes do not suddenly become more powerful determinants of phenotype merely by being chosen in advance. Yet it still allows him to follow his intuition that proponents of "liberal eugenics" - who hold that taking a view on one's children's genes, while significant, is no more so than, say, paying for private education, sports, training or piano lessons - are missing something important.

There seems a good deal of force in his contention that the difference lies somewhere in the relation between the designer and the designed, intention and execution. The new subject would also be an object, part of someone else's project. In trying to pin down exactly why this is objectionable, he turns to the idea of "natality" proposed by Hannah Arendt, in which each birth is a new beginning in much more than a merely biological sense. But, as Habermas elaborates it, this idea seems merely another way of stating that there is or could be a radical disjunction between nature and culture.

There are a range of objections to this, which Habermas acknowledges. He is not at all keen on evolutionary arguments, but it is clear that many biologists would not see the distinction Habermas wants to draw as being nearly as clear cut as he believes. It is true, as he emphasises, that human beings, like organic life in general, are grown not made. But the modern view of how they are made makes it harder to maintain that there is anything special about the results. Each individual human genome can be seen as a contingent historical document, simply the record of one set of successful experiments in self-replication. The fact that this has given rise, indirectly, to something we still label "human nature" is also contingent. Future evolution might alter the genetic contribution to human nature and give each member of the species a different set of DNA endowments to reckon with. If humans effect change at this level, it is not immediately clear why this is a radical redefinition of the human situation.

Habermas concedes that there is no single, unanswerable argument to support his misgivings about the possibility of genetic manipulation. And even if his counsel against parental design is accepted, it does not speak against a person modifying their own genes postnatally, as part of the individual's life-project. More fundamentally, he accepts that if a prenatal alteration could increase, rather than reduce, a new person's life choices, the argument against "co-authorship" would fail. His response to this objection seems particularly weak, and involves him in maintaining that enhanced intelligence, for example, could have a host of drawbacks. No doubt, but there is a sporting chance that the benefits would be worth the risk.

Such an enhancement remains speculative, of course, but the issues it poses demand attention. Habermas' thoughtful and self-critical contribution reads like the start of an important conversation about them, but only the start. I hope he has time to offer a fuller treatment soon.

Jon Turney is in the department of science and technology studies, University College London.