In my final decade of biology teaching, I began offering an annual end-of-year challenge to my 10th-graders. We finished up with a 12-week study of genetics, and my charge to the students was this: “If you work hard and devote yourself to the study of genetics throughout this unit, you will realize at the end that you have no idea what a gene is.”

There is no consensus on the definition of a gene, yet gene is a term we use, appropriately and effectively, throughout our discourse in biology. What a paradox!? Hans-Jörg Rheinberger and Staffan Müller-Wille have published a book that succinctly and brilliantly addresses this current state of things. Rheinberger is emeritus director at the Max Planck Institute for the History of Science, and Müller-Wille is codirector of the Centre for the Study of the Life Sciences at the University of Exeter.

In 10 brief chapters, the authors take us step-by-step through the meanings of gene from Mendel (who didn't use the term) and Johannsen (who coined it in 1911) to the temporary absolute of Francis Crick's “Central Dogma” (1958) to the foment of today. Throughout the book, they establish as much clarity as possible about each of the specific meanings progressively attached to the word gene.

Seldom have I read something so important, so efficiently detailed, and so well written (great credit is owed to the translator, Adam Bostanci, who brought it from the original German to English). Two chapters cover the 19th-century background to Mendel's classic work, crediting Mendel with “an unrivaled courage to reduce the complexity of the experimental design” (p. 28). The authors quote Johannsen acknowledging, in 1909: “No particular hypothesis is attached to the term gene” (p. 4). The next three chapters take us through to the mid-20th-century Central Dogma relating DNA, RNA, and proteins, detailing first the development of the genotype/phenotype dichotomy, chromosome trait mapping, and early efforts to bridge the divides between genetics, embryology, and evolution. But already, “both in transmission and expression, one-to-one relations between genes and their products turned out to be the exception rather than the rule” (p. 8).

Technologies developed around genetic engineering gave birth to the Human Genome Project, and chapters 7 through 9 open up the resulting crowded can of worms that shows the genome to be much more various, variable, and active than was previously assumed, and much more engaged with epigenetic influences. Along with this genetic engineering revolution came an explosion of metaphors, and “references to ‘copying,’ ‘cutting,’ ‘pasting,’ and ‘editing’ have since become ubiquitous. Today, the metaphorical nature of this terminology is generally no longer obvious even to researchers” (p. 80).

In each instance of a seemingly concrete concept or definition, the authors show how useful that particular vision of the gene has been, and how it has opened up new lines of productive investigation, despite being in the end incomplete or even incorrect. For example, “even if the separation of heredity and development can seem logically absurd … without it one would never have learned how complex the relationship between genotype and phenotype actually turns out to be” (p. 46).

My one criticism of what I believe to be an admirable book is a baffling omission of the statement forecasting a revolutionary new understanding of the genome made by Barbara McClintock in her 1983 Nobel Lecture. The authors cite comparable remarks by Evelyn Fox Keller (2015) and Scott Gilbert (2003), but McClintock framed it elegantly decades earlier: “In the future attention undoubtedly will be centered on the genome, and with greater appreciation of its significance as a highly sensitive organ of the cell, monitoring genomic activities and correcting common errors, sensing the unusual and unexpected events, and responding to them, often by restructuring the genome.”

While taking pains to point out that their book approached obsolescence even while they were writing it, Rheinberger and Müller-Wille bravely summarize their “current” understanding of the behavior of genes: “The agility of the genome in the sense of a versatile ‘cache’ of genetic resources … furnishes an inexhaustible reservoir of developmental plasticity and evolution driven by a complex molecular machinery of movable DNA elements, polymerases, gyrases, DNA-binding proteins, repair mechanisms, and more” (p. 72).

And “with genes, organisms have evolved a unique mechanism that allows them to retain a memory of past achievements, with which they tinker to meet challenges to their future. The relatively loose organization of genes into genomes, always prone to mutation, recombination, and more complex modulations, strikes a balance between rigidity and plasticity that allows organisms to evolve over time” (p. 119). Thus the authors, who so elegantly show that the gene still cannot be defined, nonetheless continue to use the word meaningfully. The paradox persists.

AMANDA L. GLAZE is an Assistant Professor of Middle Grades & Secondary Science Education at Georgia Southern University in Statesboro, Georgia. In addition to science teacher education, she has taught courses in biological sciences for grades 7–12 and undergraduate students over the last twelve years. Her interests include evolutionary biology, science and religion, and the intersections of science and society – specifically where scientific understandings are deemed controversial by the public. Glaze holds degrees in science education from The University of Alabama and Jacksonville State University. Her address is Department of Middle Grades & Secondary Education, Georgia Southern University, PO BOX 8134, Statesboro, GA 30458; e-mail: