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Last year marked more than one 50th anniversary. At New York's Rockefeller Institute in 1944, the culmination of 14 years of work arrived for Oswald Avery. With Colin McLeod and Maclyn McCarty, he had been trying to identify chemically the "transforming principle", the molecule capable of imparting specific and stably inherited changes to the genetic make-up of bacterial cells. By rigorously excluding contamination from their solutions, they showed that the transforming principle, which was almost certainly the genetic material itself, was DNA.

It is a measure of the impact of the discovery that it is now hard for us to remember that this familiar result was, at the time, something of a surprise. DNA, deoxyribonucleic acid, while found in the chromosomes, had been wrongly thought to be too tediously repetitive to carry genetic information. This discovery, perhaps even more than Watson and Crick's discovery of the structure of DNA in 1953, signalled the dawn of a new biology, in which the living world became explicable in terms of information stored in giant organic molecules: nucleic acids and proteins.

A convincing case can be made that the second half of the 20th century will be remembered as the age of molecular biology. A subsequent series of extraordinary technical developments have made the molecular determination of form and function in all living organisms potentially knowable. This includes humans. In the past ten years the molecular basis of the majority of major genetic disorders has been discovered. We have also, through studies of variation in human DNA, found out much about our ancestry and evolution. This process will continue and accelerate as the Human Genome Project, which has among its aims the determination of the entire base sequence of human DNA, is completed. This book is an excellent popular account of the progress of human molecular genetics. After an introduction describing the early years of genetics and molecular biology, subsequent chapters deal with the molecular biological approach to inherited disease, cancer, immunology and the mind. Human molecular diversity reveals the movement of our ancestors from Africa 200, 000 years ago, and allows DNA profiling to be used to identify criminals. The most ambitious of the many goals of the Human Genome Project is to produce, probably by around the year 2000, the complete DNA sequence of a representative of each of the 24 different human chromosomes. ( We have 46 chromosomes, but 44 of these consist of 22 pairs.) The project is thus, for biology, unprecedentedly ambitious in scope. One great asset of The Book of Man is that the human dimension of the research is not lost among the "big science". In particular, the authors, while giving a personal account of the scientists who have made the major discoveries, also remind us of the other individuals in the story - those whose lives have been damaged or ended by genetic disease and those whose lives have been saved or improved because of our increasing knowledge of such disease.

The authors are Professor Sir Walter Bodmer, the director of the Imperial Cancer Research Fund, and himself a major player in the discovery of the molecular basis of genetic disease, and Robin McKie, science correspondent of the Observer. A particularly interesting section is Bodmer's personal account of his research career, ranging from statistical training with Sir Ronald Fisher, to studies of polymorphism in primroses, to the genetics of blood group antigens and of bowel cancer. While written in an accessible style, the book is consistently and remarkably detailed and accurate. The illustrations, however, are weak, being neither intrinsically of high quality nor well linked to the material in the text.

The book is unremittingly, and correctly, upbeat in its description of the impact of genetic knowledge upon our lives. It is hard to make a convincing moral case against any of the approaches described here. There are complicated moral issues which remain, however, the most vexed of which concern confidentiality of genetic information. Under what circumstances, for example, should individuals be told that they carry, or may subsequently express, an inherited disorder? Equally, should health insurance be conditional upon the insured being shown to be free of genetic disease?

The latter question, in particular, relates to other health care issues, reinforcing, for example, the need for a comprehensive national health service, in which access to health care is determined solely on the basis of need. Health care systems based on optional personal insurance operate by spreading risk and are only, at best, coincidentally equivalent in their effects to more just systems. They function only because an equality of contribution irrespective of subsequent treatment results from an equality of risk, but such an equality of risk can itself be undermined by increased knowledge.

Above all else, the book should be read by the large minority whose misgivings about the science of genetics outweigh those about all other sciences. Partly, such fears may understandably be based upon recollections of the failed and ill-conceived eugenic experiments of the early years of this century. More generally, an inexcusable ignorance of and disinterest in the scientific endeavour as a whole can, in the case of human genetics, be aggravated by being coupled to a view that our humanity is belittled by not remaining mysterious.

This is, in short, a fascinating insight into one of the most important stories of human discovery. I would recommend this book wholeheartedly to sixth-form students, to undergraduates in all subjects, and indeed to anyone who wishes to know what science can tell us about ourselves.

John Brookfield is a lecturer in genetics, University of Nottingham.