Adam Lively on the history of sexual knowledge in Britain. Historians are anxiously self-conscious these days, acutely aware of the “textuality” of their subject-matter and of the ways in which they are interpreting not facts but “discourses”. Traditions are shown to have been invented, and national histories are as likely as not to begin with stories not of invasion and conquest but of the creation of the concept of “the nation”.

But even the most textual-minded historian has to recognise the at least limiting role of geography, for example, on national history. The historian of “old age” or of “death” may be dealing with cultural concepts,the occasions of societal ritual and self-expression, but these occasions are also facts of our existence as flesh-and-blood bodies.

The case of sex is an extreme one. Our culture is so saturated in sexual metaphor and imagery - and, conversely, our attitudes towards the sex act itself so culturally mediated - that it is now inconceivable to regard sex simply as a natural function of the body. In their Introduction to The Facts of Life, Roy Porter and Lesley Hall enthusiastically endorse that pioneer of the historian of “discourses”, Michel Foucault: “Sexuality was produced by the production of the knowledge about it . . . The sexual is such a complex and contested domain, mightily charged with associations and emotions, norms and values, that the terms in which it is posited determine the entity itself. Sex advice books are thus continually creating and reinventing the object they are purporting to discover, depict and even legislate for.”

Thus sexologists are not merely writing about sex; they are writing sex itself. Sexuality is a matter of texts, not biology. This is an extreme position to take, and it is not one that Roy Porter and Lesley Hall stick to throughout their book. While the focus of their study is what scientists, doctors, campaigners, quacks and government officials have described (or, as often as not, prescribed) as sexual behaviour, they acknowledge that in reality there may have been an enormous discrepancy between these prescriptions and what has actually gone on between the sheets over the centuries.

The real world of sexual activity is very largely a closed book to historians. As Roy Porter and Lesley Hall point out, because of prevalent taboos and reticence (even within the medical profession), those who have written frankly about sexual matters, such as Havelock Ellis, Edward Carpenter and Marie Stopes have typically been marginal or eccentric figures. And in interpreting sexual texts, the historian must be aware that they could be read in ways quite contrary to the authors’ stated intentions.

For example, a persistent theme of the literature from the early 18th century right through into the 20th century is a dire warning against the dangers of “onanism” or masturbation. But as Roy Porter points out, the authors of anti-masturbation tracts were painfully (or perhaps in some cases cynically) aware that their writings could be used as guides or stimuli to the very practice they were condemning.

Roy Porter and Lesley Hall are sensitive to the charge of “Whiggism” sometimes levelled at sexual history as it has been written since the 1960s, of portraying a triumphal progress from Victorian repression to contemporary liberation. When it comes to sexual “enlightenment”, more can sometimes mean less. For example, while in broad terms confirming the popular view of a contrast between a bawdy 18th century and a more reticent 19th, The Facts of Life also shows how it was in the 18th century that the image of the woman as glamourised and cosmeticised “sex object” was born. Such feminist perspectives are implicit throughout the book, but it is frustrating that Roy Porter and Lesley Hall don’t bring the book up to the present with a discussion of the debates between libertarians and anti-pornography feminists. The mid-17th century is a logical starting point, with the explosion of popular literacy and print culture, but 1950 seems by contrast arbitrary. The book somewhat peters out at the end.

Roy Porter writes so many books - his London; A Social History has been getting glowing reviews - that one wonders when he finds time to sleep. It has to be said that The Facts of Life slightly has the feel of something thrown together from research materials rather than thought through from beginning to end. In addition to the lack of a guiding thesis,there is a certain amount of repetition. It should also be said that anybody buying this book for flippant reasons is likely to be disappointed.The scholarly notes and bibliography alone consume over a hundred pages. (Alan Rusbridger, a previous author in this field with A Concise History of the Sex Manual, 1886-1986 is given a rap over the knuckles for facetiousness.) But in among the academic rhetoric and Foucauldian theory there is a wealth of fascinating and often very funny material. It’s always slightly suspect when critics protest too loudly that they find pornography and other sexual writing tedious and repetitive. The truth - as the many writers quoted in this book have well understood - is that almost anything written on the subject of sex has an intrinsic interest.