Are twins fated to be problematic pairs? Biddy Passmore finds out. The most worrying thing I ever heard about twins was said when mine were eight weeks old. As I wheeled my beautiful Silver Cross pram across the park, a tiny head at each end, a middle-aged woman stopped me and peered in. “Twins,” she said. “I had twins; and let me tell you they’re a great deal less trouble at this age than they are at 34.” I gazed at her, appalled. How could anybody be more trouble, at any age, than eight-week-old twins? (I was soon to discover the answer to that: six-month-old twins, one- year-old twins, two-year-old twins. . .) What peculiar twinnish hell did her children inhabit that was still troubling them at 34? Of course she may not have meant problems peculiar to twins. She may have meant that her twin children were - separately - going through the common traumas of thirty-somethings: overwork, marriage break-up, stroppy children.

For it is worth pointing out, faced with an anthology that highlights the odd and the extreme, that not all the problems twins have are to do with being twins. Further, that the world is full of perfectly happy and well- adjusted twins who overcome the problems of shared attention, lack of privacy and constant comparison that is their childhood lot.

But the experience of twins is - for want of a better word - unique. As Penelope Farmer writes: “My research as well as my experience have led me to think more and more that we twins really are in some respects wholly peculiar, other beasts.” They are not such rare beasts either; with fertility treatment twins account for about one in 80 births (and medical research suggests that as many as one in five of all conceptions start out as twins but one subsequently gets lost in most cases).

Some twins, Penelope Farmer among them, find the relationship fraught with difficulty. Five years after the death of her (non-identical) twin sister Judith from cancer, she is still haunted by their inability to get on together. There is no more devastating passage in her “autobiographical anthology” than this: “Did my sister and I love each other? I’m afraid so. We might have found life much easier if we hadn’t; for I don’t think we liked each other very much, and even the love was profoundly suspicious Q on my sister’s side anyway. ”

Penelope was the “successful” one: out-going and, in her early years, a better academic performer than Judith, who stayed at home and took a secretarial course while Penelope went off to Oxford. They couldn’t afford to send both away, said her parents. That, she writes, “is the material which weaves itself into twin relationships, transforming love into hate, setting guilt to crush some of the joy in achievement - and resentment to fester on both sides. ”

After her sister died, Penelope the novelist sat down to do in an anthology what one weary reviewer had accused her of doing many times before in her fiction: to look for her identity. She waded through an astonishing number of words: the British Library catalogues alone produced more than 1,400 entries under the headings “twin”, “twins” and “Gemini”.

And as she read and thought about her subject, she found the book turning increasingly into a book about doubles generally, ending with the - for her Q doubly (quadruply?) significant theme of writers as doubles, standing outside themselves as they consider how to turn their experience into words.

She has weeded heroically, if not quite heroically enough. At 470 pages, the anthology is too long and a few entries are of limited interest or literary merit. (Did she really need to include an apercu on his double self from Eric Cantona?) Perhaps the extension of the theme to doubles blurs the focus. But Two makes a fascinating collection, which is by turns academic, moving, funny, disturbing and erotic. The harrowing tale of the “silent twins”, June and Jennifer Gibbons, is here, as are the Kray Twins, their mother’s pride and joy as she wheeled her “two little black-haired dolls” down the Bethnal Green Road. Great writers - Plato, Henry James, Mark Twain - jostle with the more obscure, medical observation with myth.

The sections - headed “Birth and Parenthood”, “Love and Hate”, “Separation and Death” and so on - have illuminating introductions by Penelope Farmer.

One of my favourite entries is a story from New Zealand, told by Penelope Fitzgerald, in which a husband has to deliver his baby daughter before the doctor arrives. He thinks he has thrown the afterbirth out with the waste; only the doctor discovers it isn’t the afterbirth: it is a second daughter.She eventually becomes a successful lawyer while her twin “never got to be anything in particular”. “After that,” writes Penelope Fitzgerald, “the Tanners always had one of those tinplate mottoes hung up on the wall Q Throw Nothing Away. ”