Lee Silver is a dangerous writer, one given to sweeping generalizations that cannot be trusted. Oh, he's not stupid – he's a professor at Princeton – and he certainly has a quick mind and a sense of humor; the impression that comes through his writing is of someone who might be fun across the dinner table. And he is sharp enough to have recognised at sight that the infamous Dr Richard Seed (the man who proposed to clone people in order to become closer to God and make a lot of money) was "seriously nutty." But he is a fool in the classic sense, to quote the nearest dictionary, of being "a person without common sense or judgement." Or else he is prone to treating his readers as if they were.

Let me give two examples, one within his field, one outside it.

Silver has quite a lot of fun in his book with various bizarre and technically plausible scenarios of parenthood that involve more (and even, on occasion, less) than the traditional two adults. In one of them, an infertile woman called Florence is implanted with an egg donated by her twin sister Gail and fertilized in vitro by Florence's husband Frank. The entire procedure is successful, unlike most such attempts, and a daughter, Fiora, is born. To avoid any possible accusation of unfairness, I shall quote the next paragraph in full, from pages 192–3 of the Bard paperback edition:

Who is Fiora's genetic mother? It's Gail, of course, you would say, since she contributed the egg that developed into Fiora. But, in fact, if Fiora and her birth mother Florence were subjected to DNA fingerprint testing, the results would be quite definitive – they would show, without question, that Florence herself was Fiora's gene-mom. What's going on here?

What's going on here, Professor, is something that might technically be described as bullshit.

Note first the exaggerated use of precision terminology – 'without question' and 'quite definitive' and especially the utterly bogus 'DNA fingerprint testing' – that leads up to the deceptively simple question based on the supposed paradox. Do we smell a rat? You betcha; but that odiferous rodent is no more than the distracting handkerchief waved in front of this particular piece of legerdemain. DNA testing, which has nothing to do with fingerprints though its proponents like to associate it with the aura of accuracy that fingerprint identification carries, is not at present unquestionably definitive; it produces statistical results that are often useful and indeed good enough for practical purposes. If we can say that the odds of a given man being a given baby's father are, say, over a million to one, that's good enough to dismiss a paternity suit; conversely, if Mick Jagger has to pay child support based on similar tests, he probably doesn't have a legitimate complaint; but certainty is not part of the procedure, not yet anyway.

But let's not get distracted. Grant the Professor his over-simplification, assume the accuracy he so excessively claims. He's missing the point.

DNA identification rests on two assumptions: First, that two samples can be shown to be identical, and second that the people from whom the samples were taken (whether specifically for testing or accidentally, as with bloodstains) are genetically unique. Whoops.

An identical twin is not genetically unique. By definition. Silver's definition. (Which is quite possibly incorrect, incidentally, given such details as mutation rates in mitochondrial DNA, which might lead to better tests some time, but we are operating at his chosen level of simplification.) Therefore no such test can ever logically establish identity in this case. It can establish a negative, for example that Fiora's genetic mother is not her first cousin once removed; or it can establish the fact, useless as it is in these circumstances, that Fiora's genetic mother is either Florence or Gail; but it is simply meaningless to ask this test to determine 'without question' which of the twins is the genetic parent.

Put simply, Silver's premise is bullshit.

He rambles on – rather entertainingly – to conclude that "the children of all identical twins will be found to have two genetic mothers or two genetic fathers" which he describes, not unreasonably, as "rather unsettling." Well, yes. Unsettling is one word for it. A more appropriate one might be ludicrous. You would think that a writer who liked to use the reductio ad absurdum, as Silver does, would draw the obvious conclusion; but no. He moves on to discuss a different twin-sister case, in the course of which he blithely asserts that we have learned "that identical twin sisters can both be considered genetic mothers of any child conceived from eggs produced by either woman." We have, of course, learned no such thing.

Forget for a moment the emotionally loaded issue of motherhood. That A is the same as B does not mean that A is B. It only means that I cannot tell the difference between A and B. If I have a set of dining-room chairs and move them in order to sweep the floor, I may put them back in a different order and never know the difference. Have they swapped identities? Of course not, they have merely swapped their location in space. And perhaps not that, since I cannot be sure that I did not put them back in the same order.

Silver acknowledges, since he is not an idiot, that a woman might prefer to have a child develop from one of her eggs rather than from an egg donated by her twin sister, even though her eggs and her sister's eggs are indistinguishable by any imaginable test. "In fact," he asserts, "Rationality has nothing to do with it." (At this point in my reading, I simply had to laugh.)

He knows better. Aside from the fact that it is unlikely that he would miss so obvious a point as that identical twins are different individuals, you can tell from the way his language changes when he draws another conclusion, namely that first cousins related through identical-twin parents "will appear to be half-brothers or half-sisters." The give-away is the word 'appear'. It is accurate; and it does not mean 'be' – if you remove the words 'appear to' from the quoted phrase, its meaning changes. So, what's going on here?

Consciously or unconsciously, Silver is trying to blur the question of parenthood, precisely because some of the technologies he describes and promotes do exactly that. It is in his interest to present difficulties associated with the traditional definitions of motherhood and fatherhood, if only to prepare his audience for more startling concepts associated with cloning and then with the creation of children who are genetically related to no one at all. If you artificially alter the genetic makeup of an embryo, and still more if you introduce an entire artificial chromosome, the child will not have the same kind of relationship to the parents as the one with which we are all familiar. At present it is at least theoretically possible to prove that a given person is not the child of a given pair of parents, simply by demonstrating that the child has genes that can have come from neither parent. In a world of manipulated germlines, this would no longer be true.

Silver came up with an intriguing little puzzle, if you enjoy pseudo-philosophical wrangling, but he chose one whose implications seem to fit his pre-existing world-view. To demonstrate how the way an example is presented and discussed can have an effect on the conclusions drawn, let us return to the vexed relationships of Florence, Frank, Gail and Fiora, and construct a different scenario – one that requires no technological difficulties at all.

Assume that Frank is having an affair with Gail, while married to Florence, and that he impregnates both women at essentially the same time. (Who knows what about whom I leave to the reader's imagination, since it is irrelevant to this particular tale.) Both give birth in hospital, on the same day, to baby girls who, not surprisingly, look rather similar. They are half-sisters, with the same father and different mothers; this seems incontrovertible. Alas, there is a mix-up (again, I leave the details unspecified), so no one is exactly certain which baby is whose. The question becomes, is this baby Fiora, the daughter of Florence, or is she Fiora's half-sister? Were the mothers not twins, or were the father not the same, it would probably be possible to run four or five DNA tests and conclusively establish which girl went with whom; but in this case ...

Presented this way, a very similar scenario focuses attention not on the issue of who is the genetic mother, but on the issue of the limitations of DNA identification testing. I like this one better; it suits my skepticism about the technology. But I would, wouldn't I? That's why I chose it.

It would surely be unfair to say that Silver's response to the difficulty of assigning Fiora and her half-sister to the appropriate mother would be: It doesn't matter. (Rationally, that is.) Still, let us examine the logic of this proposition. They are newborns, not identical but with the same genetic inheritance; either of them could theoretically have been the genetic result of mixing Frank's genes with those of either mother. What the heck, no one will know the difference ... Actually, there is considerable evidence that they will, though being newborns they cannot yet express it – they have developed in different wombs, hearing different maternal voices, absorbing different nutrients, and so on. Their environments, in other words, have already acted to distinguish them, and no sane person (Silver likes that phrase) would deny that they are in fact already different individuals, and even if each would be raised well by her aunt, each deserves to be raised by her mother. The reason for even mentioning this is to point up the absurdity, at the extreme, of such an exclusive form of genetic determinism.

But that is precisely what Silver is invoking in his example – identity is strictly a matter of genetic endowment. The basis of his absurdity is the view that 'mother' is a synonym for something like 'person from whom an X-chromosome may logically have been derived' ... and so on, and so absurdly forth. Of course genes are important, and of course there are significant issues at the margins of the term 'motherhood', as there have have been ever since there have been adoptions, let alone surrogates, donors and all the paraphernalia of modern reproductive technology. So what? That a term is imprecise at the edges of definition does not make it meaningless. Red can fade to pink or deepen to purple, and either will cause difficulties of definition, but we can still agree that something red is indeed red. Something dangerous is happening when a Professor as fluent and authoritative as Professor Silver tries to convince us that redness is an outmoded concept, too variable to be understood in the normal way. He's trying to set us up.

It's bad enough that he tries to sway his readers to view the genetic future with his own relish for change. It gets worse when he attempts to place the future he anticipates in a social and economic context. And the jig is up in the very first of the Notes at the back of the book.

In the main text, he asserts, boldly and right up front, that parents have an absolute right to manipulate their children's genes however they wish. In support of which, he states that "American society, in particular, accepts the rights of parents to control every other aspect of their children's lives from the time they are born until they reach adulthood."

So much, I suppose, for compulsory education. So much for minimum working ages. So much for parental abuse laws. So much for ... oh, come on, he cannot be serious. Can he?

Well, in the Notes, he concedes that "America is unique among Western countries in the paramount contribution that parents are expected to make in determining how their children should be raised." (I'd go further and say that Silver's 'America' is a unique theoretical construct that bears no significant relation to the United States with which the rest of us are familiar.) "In most other [sic] industrial countries, society as a whole takes primary responsibility for the socialization and upbringing of its children. Citizens of these countries would have greater legitimacy in arguing for control over the individual use of reproductive technologies."

Hang on a minute. Let us remind ourselves that this man is not an idiot. So what on earth is he doing writing this kind of twaddle?

He is trying to ensure that the regulation of human germline genetic modification is non-existent or utterly ineffective. To this end, he is trying to prevent all argument about what the regulations should be by asserting that no such regulations are legitimate. It is a glorious end-run against every kind of governmental intrusion into any activity whatsoever. You almost have to admire his nerve. Strip away the big words and what you get is: I wanna do this to my kid; it's a free country; you can't stop me.

Well, he might as well throw in the towel on that one. Since, however, he bases his entire book on this absurd foundation, and since there are a number of libertarians in this field who make his positions look moderate and sensible, we'd better spell it out.

First, as even Silver admits, once you accept that society in general – that is, in practice, the government in all its various forms – has a right to make important decisions about the upbringing of children, then you have "greater legitimacy" for stopping people from manipulating their children's genes. And society does assert that right. Therefore members of society do not have an absolute and unquestionable right to genetically modify their children. Society may decide to regulate this activity, or it may not, but the idea of regulation is legitimate.

Looked at from my perspective, this means we can stop the production of 'designer babies'. Looked at from something closer to his, it means that the 'inevitability' of which he speaks is no such thing.

Silver and his ilk may try to weasel around the phrases 'primary responsibility' and 'paramount contribution' to suggest that there is a difference in principle between the American and the European and other foreign attitudes to this issue, but really that distinction is meaningless. There probably is a tendency towards interventionism in Europe and a tendency towards individualism in the U.S., but the difference is largely if not entirely one of degree. Does he believe the English have abolished private schools? That there are no religious minorities in Europe? That, as an American, he may choose to beat his children without risk of being dragged into court and having them taken from him? Of course not. No sane person ...

Now, this doesn't mean the argument is over. What it means is, it can start.