What does it mean to say that we live in an information age? The description trips easily off the tongues of entrepreneurs, politicians, and journalists, but its application to nearly every aspect of the way we live now, paradoxically, makes it harder to define. How much longer before silicon becomes so omnipresent as to be invisible? Has this already happened? This question is equally important to biologists, for whom the idea of information is now technically and conceptually essential. In a recent essay in the Quarterly Review of Biology, evolutionary biologist John Maynard Smith outlined many of the obvious ways in which terminology related to information has taken its place as the standard vocabulary of biology, including "transcription, translation, code, library, message, editing, and proofreading." [1] And yet, despite its relevance to the development of biological ideas, Maynard Smith argues that information has been underappreciated or ignored by philosophers of biology.

This gap in the history and philosophy of biology has now been closed. In Who Wrote the Book of Life? A History of the Genetic Code, Harvard scientific historian Lily Kay has written an exhaustive account of the elucidation of the genetic code, with an emphasis on the role of information science as a catalyst. This book is, in many ways, a sequel to Kay's previous book, The Molecular Vision of Life: Caltech, the Rockefeller Foundation, and the Rise of the New Biology, which is a fascinating history of the refashioning of biology as a molecular science in the years prior to the discovery of the double helix. The roles of T.H. Morgan, George Beadle, and Linus Pauling may be well known, but Kay also focused her attention on the programmatic role of Warren Weaver, then director of the natural science division of the Rockefeller Foundation, who coined the term "molecular biology" in 1938. In doing so, she makes it clear that the blossoming of molecular biology was not an accident but was, to a great degree, the result of a significant rhetorical and monetary commitment on the part of foundations such as the Rockefeller Foundation to a few visionary scientists who wanted to extend the gains of the physical sciences to biology. Likewise, in Who Wrote the Book of Life? Kay shows how work on the genetic code became enmeshed with the idea of information, in large measure, because of technology associated with what she calls "the industrial-military-academic complex" during the cold war.

Difficult as it is to imagine from our vantage point, heredity was not always considered a problem of information transfer. In his essay, Maynard Smith suggests that the first such reference should be attributed to August Weismann in 1904. Arguing against Lamarckian inheritance of learned behavior, Weismann viewed the possibility that changes in neural connections might simultaneously alter germ cells as equivalent to "supposing that an English telegram to China is there received in the Chinese language." Kay demonstrates that such an informational view of inheritance was quite rare in the first half of the twentieth century. She asks, "What did genes do before they transferred information?" The prevailing view, championed by Linus Pauling, was that of biological and chemical specificity. Pauling, the great pioneer in determining the structure of macromolecules, saw structural specificity as underlying the interactions between biochemical locks and keys - antibodies and antigens, enzymes and substrates. Presumably, this would extend to gene-based inheritance as well.

When and how did specificity yield to the notion of inheritance as a transfer of information governed by a genetic code? Kay outlines the influence of postwar information theorists such as Norbert Wiener, author of Cybernetics or Control and Communication in the Animal, and Claude Shannon, coauthor (with the remarkably influential Warren Weaver) of The Mathematical Theory of Communication. These works, which had clear military applications, were landmarks in the theoretical development of the information sciences. Moreover, their ideas, Kay shows, eventually had a great impact on the key figures in the nascent field of molecular biology in the 1950s and 1960s. Wiener, Shannon, and Weaver dealt with problems of command and control, feedback control, quantitative measurement of information, the encoding of messages in signals, the minimizing of noise in transmitting information, and the differences in transmitting continuous and discontinuous signals. As work on the genetic "code" progressed, this work on information theory provided useful ways to think about the problem of understanding nucleic acids as the molecules of heredity.

Kay makes two general points about the application of information theory to genetics. The first is that information terminology, in the strictly technical sense, was actually ill-suited to serve as a foundation for understanding the mechanisms of heredity and gene expression. After all, from the standpoint of information theory, a nonsensical message and a meaningful message can be equivalent. Clearly, in a biological context, a message must have a meaning (a function). Moreover, the genetic "code" is not really a code, since in the world of cryptography and information science a code operates "strictly on linguistic structures." Rather, nucleic acid codons and amino acids correspond to one another, in the manner of a cipher.

Kay's second point is that, however technically suspect the application of information theory to genetics turned out to be, in practical terms this "failure" was irrelevant. In the effort to understand the relationships between DNA, RNA, and protein, the terminology of information theory (code, transcription, translation, text, etc.) served as a powerful metaphor. Thus, we see Henry Quastler's productive, if somewhat obscure, effort to transform molecular biology into an information science, and George Gamow's speculative proposals on the nature of the genetic code. Then there are the great collaborations of molecular biology, exemplified by Francis Crick and Sydney Brenner theorizing about the flow of information between nucleic acids and proteins and demonstrating experimentally the existence of a non-overlapping, triplet code. Likewise, work by Francois Jacob and Jacques Monod on the importance of feedback mechanisms in the regulation of gene expression was informed by the importance of feedback in cybernetic communication systems. These ideas, Kay demonstrates convincingly, were in the air.

It has to be said that Who Wrote the Book of Life? is not an easy read. As would be expected for a book published by a university press, the target audience is an academic one. Readers should expect to come across more than a few references to "discursive frameworks" and "technoepistemic events." Still, biologists interested in a thorough history and analysis of the origins of the way we think about the science of genetics will be rewarded for their effort. Even those who are reasonably well versed in this history will come across facts and documents that they haven't seen before. For example, Kay includes several tantalizing excerpts from the diaries of genetic code breaker Marshall Nirenberg, showing an active mind on the cusp of a great scientific discovery. Even better, Kay describes work in the late 1960s comparing the Chinese "Book of Changes" - I Ching - to the genetic code. Remarkably, these two systems employ "permutations of four basic elements taken three at a time, producing sixty-four building blocks . . ." The analogy was both misguided (one suspects) and irresistible, gently underlining Kay's point that such metaphors need not be grounded in fact to be powerful spurs to progress.