Ruth Deech was in sprightly flow on the Today programme on Monday morning: “It is an issue of principle,” the former chair of the Human Fertilisation and Embryology Authority insisted, “that both sexes have a part to play in the bringing-up of children.” Not that she was fighting a lonely corner. The proposal before the House of Lords this week — that not only should IVF clinics be relieved of their obligation to ensure that there are fathers for the babies they create, but that lesbians be able to register their partner's name as co-parent — has outraged many vocal opponents.

Such a change in the law, says Iain Duncan Smith, would “drive the final nail into the coffin of the traditional family”. Because? “Research shows,” says Baroness Deech (she didn't say which research), “that there is a distinct contribution to the upbringing of children made by fathers.” Cardinal Cormac Murphy-O'Connor, in a letter to this newspaper, placed a father within “the natural rights of the child”, while the commentator Melanie Phillips is adamant: “What we know beyond a shadow of a doubt is that children need their fathers.”

Really? Why? What for? And when did anybody last even ask? It might be very nice indeed for a child to have a dad around the house — provided, naturally, that he's the proper kind: the devoted, sober, gentle giant much given to manly rites of passage like the proud purchase of a brace of season tickets to Arsenal. But nice is not the same as need and certainly not as “rights”; further, if the hands-on presence of a father were actually so imperative, our species would have died out in the primordial swamp.

Hunter-gatherers didn't sit around fashioning nappies out of hemp; they were off and away, garnering the means of survival — a function that, by the way, remains the most useful role for a father. Ask any single mother what she most misses about having a man and her answer will be a man-sized salary; it is the absence of that, rather than of the man himself, that makes children go off the rails.

Medieval men thundered off to war for years on end; feudal men (rich) ignored their children until they were adults, feudal men (poor) ignored them until they were fit to work a field. As recently as the beginning of the last century aloofness remained the norm until, just as it started to thaw as an inevitable by-product of the economically driven evolution of the nuclear family — constant presence, shared living space, shared meals and how was school today? — two consecutive generations spent years without fathers, losing them first to the rigours of Ypres and then to the confines of Colditz, often never to return. Children's “needs”, you say? Don't be silly. Such as they were, they were met by women or not at all.

What we now call the “traditional” role of a father is not, in fact, much older than post-Second World War when men, by and large, stopped killing each other and found better things to do, like spending time with their families and discovering that they liked it. By the Seventies they were well stuck in: attending childbirth classes, severing umbilical cords, reading at bedtimes and engaging in show-off man-to-boy bonding.

Again, jolly nice for the kids lucky enough to get full-beam attention. But to turn nice into necessary requires a denial of history as well as of geography — there are still many parts of the world where the bearing and raising of children is entirely the province of women — and, indeed, of nature itself: for every male swan, happy to embrace monogamy and even to squat on a clutch of spring eggs, there is a bull to inseminate a promiscuous dozen, unable to care less for the resulting progeny. Yet both species, rather like our own, seem to truck along quite nicely.

Among opponents to this hot-potato Bill there is a less shrill cabal of those who agree that, as long as adequate provision is made for the physical nurture of children, and as long as there are sufficiently committed female parents, the routine presence of a man might not be important; nevertheless, they say, children should have a “right” at least to know who their genetic father is.

It is a gentler case, but still invites the same questions: really? Why? What for? Medical history is, of course, useful, but IVF clinics already record that. Curiosity would, of course, be assuaged, but that takes us back to the difference between a want and a need, which, frankly, is a modern confusion already over-indulged.

Moreover, if you start invoking “rights” in this debate, this is where you will be forced to end: if it is a child's right to be told his genetic make-up, must it not morally be every child's right? How shall we justify discriminating in favour of the few IVF babies, when the science now exists to compare the DNA of all children with that of the adults raising them? Do not logic and ethics demand that we provide the same knowledge to all children?

Professional estimates suggest that as many as one in twenty children may be living in blissful ignorance of their true paternity — an ignorance usually shared by the “father”, which, biologically, he isn't. Even if it were only as high as one in a hundred, that would still leave 600,000 of us running around not knowing who our real daddies are. Shall we, must we, all be told the truth? Or shall we keep it as a special treat for children born to pushy lesbians who have the effrontery to ask for the discretion that the rest of us take for granted?

On neither count, not knowledge of the man nor of his identity, do this Bill's opponents make reasoned sense. One is left to assume a more likely stance than their claim to be pro-father, which is that they are simply anti-lesbian. It would be easier all round if they would dare to say so.

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