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The Thread of Life: The Story of Genes and Genetic Engineering by Susan Aldridge, Cambridge University Press, 拢16.95/$24.95, ISBN 0 521 46542 7 and Lives to Come: The Genetic Revolution and Human Possibilities by Philip Kitcher, Simon & Schuster, $25, ISBN 0 684 80055 1

I WAS once phoned, the week after the Frankfurt Book Fair, by three different publishers, each urgently seeking an author to write a book on black holes. A quarter of a century later, genetic engineering is the topic every publisher wants on their list. The resulting books vary widely in quality. Most are repetitive, several sensational, a few misleading and some unreasonably partisan.

Anyone looking for a dependable insight into the applications and implications of molecular genetics on what is really happening and what realistically might happen in future, can be directed with confidence towards this complementary pair of books, Susan Aldridge鈥檚 The Thread of Life and Philip Kitcher鈥檚 Lives to Come. With clarity, cogency and surprisingly little overlap, British researcher and science writer Aldridge explains the science of DNA, gene splicing and biotechnology, while American philosophy professor Kitcher focuses on their impact on human disease and human affairs.

One of the delights of Aldridge鈥檚 account is the way she opens each chapter, not with what Peter Medawar termed 鈥渁 resounding banality鈥�, but with a well-considered enticement. 鈥淒NA is a database鈥� introduces a description of gene expression and the genetic code. 鈥淒NA, RNA and proteins are all molecules with a history鈥� draws us into a chapter on evolution and the origin of life. 鈥淭ake a large onion and chop finely. Place the pieces in a medium-sized casserole dish,鈥� is how Aldridge begins her directions for preparing DNA in the kitchen.

Avoiding technical terms wherever possible, she presents her story as a palatable sequence covering DNA and how it works, genetic engineering, and its uses in areas such as plant breeding and pharmaceuticals production. Each chapter is unusually well orchestrated to carry readers from one set of ideas to another. 鈥淐lose-up of the genome鈥�, for example, begins by noting the surprising disparities between the amounts of DNA in different organisms, shows how it is packaged and parcelled, and progresses through linkage and mapping to transposons and the fluidity of the genetic material.

Errors are few but irritating. Malaria is caused by the protozoan Plasmodium, not a virus. Penicillin impedes the formation of, rather than attacks, the cell wall of Gram-positive bacteria. It was Howard Florey, not Ernst Chain, who led the Oxford team that developed penicillin. And it is misleading to state that Fred Hoyle and Chandra Wickramasinghe 鈥渉ave developed the concept of panspermia, life being seeded by microbes falling from cometary dust鈥� when the idea was originated much earlier by Svante Arrhenius.

Aldridge鈥檚 account of the debate about genetic determinism is odd. She illustrates it not with Dean Hamer鈥檚 claims regarding a possible gene associated with male homosexuality, but with Simon LeVay鈥檚 work on apparent differences between the brains of self-declared male homosexuals and those of men assumed to be heterosexual. But LeVay鈥檚 work was not genetic research, it was an anatomical study of brains recovered postmortem. Although such differences could be determined by specific genes, LeVay did not claim this, and other explanations are equally plausible.

Using less technical detail than Aldridge, Kitcher is a trusty guide to the psychological, moral and social issues associated with applying molecular genetics to the conquest of hereditary disease, and in areas such as insurance and employment. But he also dwells upon ways in which the new biology affects how we see our lives, our freedom and our humanity.

Kitcher鈥檚 book has already been praised not only by those who vigorously support the need, in James Watson鈥檚 words, 鈥渢o prevent the births of children condemned by their genes to tragically disabled lives鈥�, but also by those who study science in its cultural context, such as Dorothy Nelkin and Jonathan Beckwith, who are equally concerned about the associated ethical dangers. That alone is a remarkable achievement.