Recent discoveries in genetics have called into question traditional conceptions of the gene. The Concept of the Gene in Development and Evolution does an excellent job of bringing together philosophers, historians, and biologists to answer the question, What is a gene? Some of the essays in the collection are devoted to recounting the discoveries that have challenged the ‘classical concept of the gene,’ while others offer proposals for reconceptualizing the gene in the light of recent findings. This volume does not address a very wide range of issues in genetics. Hot topics such as genetic engineering, gene therapy, and cloning are never mentioned. The volume is sharply focused on the concept of the gene.

The essays in this collection are aimed primarily at philosophers of biology, historians of biology, and biologists engaged in highly abstract reflection on their discipline. The book is not intended to introduce students or interested readers to important facts about genetics or genetic explanation. I highly recommend the book to philosophers of biology. Like other books in the series "Cambridge Studies in Philosophy and Biology," it seems to be required reading for anyone in that field. I don’t, however, recommend the book to anyone who is not a specialist in the philosophy of biology.

The historical essays include Jean Gayon’s "From Measurement to Organization: A Philosophical Scheme for the History of the Concept of Heredity," which provides a very readable survey of the major conceptions of heredity during the last one and a half centuries. Michael R. Dietrich, in "From Gene to Genetic Hierarchy: Richard Goldschmidt and the Problem of the Gene," reviews the case of a prominent but controversial geneticist who, from the 1930s to the 1950s, attacked the classical notion of the gene and tried to formulate a more sophisticated, functional view of the gene. Frederic L. Holmes, in "Seymour Benzer and the Definition of the Gene," surveys of one of the earliest interactions between classical genetics and the new molecular interpretation of the genetic material based upon the DNA double helix. Scott Gilbert, in "Genes Classical and Genes Developmental," describes the discovery of the first ‘developmental gene’-a gene responsible for turning undifferentiated cells into muscle tissue.

According to Peter Beurton ("A Unified View of the Gene, or How to Overcome Reductionism"), many molecular biologists are now claiming that ‘gene’ is just a word-that the facts are too complicated and the concept too simplistic for it to pick out any well-defined object in the world. While some scholars suggest ways to redefine the concept of the gene in light of the new findings, others (e.g., Hans-Jörg Rheinberger in his contribution, "Gene Concepts") urge scholars to give up on the definitional project altogether.

Thomas Fogle ("The Dissolution of Protein Coding Genes in Molecular Biology") argues that many scholars do not take seriously enough the conceptual difficulties raised by recent discoveries in genetics. He shows that most proposals for dealing with problematic cases are ad hoc and not generalizable. In opposition to the now rejected ‘one gene-one trait’ view, Sara Schwartz ("The Differential Concept of the Gene") defends a ‘many-many’ view that understands genes in terms of the difference a change in a gene makes to a difference in phenotype.

Fred Gifford, in "Gene Concepts and Genetic Concepts," shows that the concept of a genetic trait is as difficult to pin down as the concept of a gene. All phenotypic traits are genetic in the uninteresting sense that genes have something to do with their being what they are. But it is difficult to say what more is required for a trait to count as genetic. Evelyn Fox Keller ("Decoding the Genetic Program") criticizes the common but misleading notion that there is a ‘genetic program’ for development contained within DNA. DNA, she claims, is more like the data upon which instructions act rather than a set of instructions itself. Michel Morange, in "The Developmental Gene Concept," reviews some of the puzzles raised by developmental genes and James Griesemer ("Reproduction and the Reduction of Genetics") advocates reducing genetics to development, thereby reversing the traditional direction of explanation.

Since a small set of empirical findings forms the backbone of the entire volume and since these facts are tremendously interesting, I will briefly summarize them.

The common view of genes is that they are localized sections of DNA that code for certain phenotypic traits of organisms. The discovery (in the 1960s) of highly repetitive sequences of DNA challenged this view. Although such sequences have well-defined locations, they have no functions. Since they are not transcribed or translated and do not give rise to proteins, they do not fit the classical definition of a gene. However, since mutations in repetitive sequences can affect the expression of other genes, it seems unwarranted to exclude them from the class of genes.

The discovery of overlapping genes in the 1970s called into question any simple identification of a gene with a location on a sequence of DNA. One sequence of DNA may be part of two distinct but overlapping coding sequences and may be read in the construction of two distinct proteins. Even more challenging was the discovery in the 1940s that some pieces of DNA lack a constant location at all. These mobile units move around actively in the genome, modifying the expression of adjacent genes.

In the 1970s it was discovered that some genes-"genes-in-pieces"-do not consist of continuous stretches of DNA. Such sequences of DNA are made up of both coding sequences ("exons") and noncoding sequences ("introns"). When an RNA transcript is formed from this kind of DNA, the introns are excised and the exons are spliced together to form the coding sequence for a protein. Such genetic information, then, is not straightforwardly localized but is spread throughout the genome. Genes-in-pieces also manifest the phenomenon of alternative splicing, in which different samples of exons are spliced together from the same sequence of DNA at different stages in the organism’s development. It becomes quite difficult to say whether there is just one gene that is manifest differently or whether each combination of exons constitutes a distinct gene.

Another significant event was the discovery of ‘developmental genes’-genes which regulate the behavior of other (‘structural’) genes that code for proteins. Because developmental genes do not code for any structural product, they don’t fit the classical concept of a gene. But they seem to be genes nonetheless.

The essays in this collection did not convince me that these recent discoveries raise serious conceptual difficulties. It should be unsurprising that biological concepts must be given functional rather than structural definitions. Although I found The Concept of the Gene in Development and Evolution to be sometimes tedious to read, it seems to a solid contribution to the history and philosophy of biology.

James Beebe is currently a doctoral candidate in philosophy at Saint Louis University. He is working on issues in naturalized epistemology and the philosophy of cognitive science.

Categories: Genetics, Philosophical