The messy processes of evolution through a 40‐year lens

Darwin’s finches are, to say the least, an iconic species for the study of evolution. Starting with Darwin’s own writings through to the pioneering field studies of David Lack, this clade of birds came to symbolize adaptation and the creative force of natural selection. But it is really through the work and writings of Peter and Rosemary Grant that this group has come into sharp focus as a key example of how ecological factors drive evolution in real time: evolution that we can see happening. The stature of this research is due to the interesting birds themselves, and also of course to the quality of the work by the Grants and their collaborators. But, more than that, the scientific community and broader public are so familiar with this story of evolution because of the prolific output from the Grants, with countless peer-reviewed papers and three prior books reviewing their work (not to mention a Pulitzerwinning book about the Grants and their study subjects). With all of this voluminous literature already out there, do we really need one more book about Darwin’s finches? Surprisingly, the answer appears to be “yes.” I say “surprisingly” because I picked up this volume expecting to see the same old material rehashed and retreaded. What I found instead was a synthetic review that used the previous work to draw insightful conclusions about the role of chance events, as well as ecological and social factors, in driving the evolution of broad patterns of biodiversity. The book does not cover the entirety of the Grants’ work on these birds, but instead focuses in on the finches of Daphne Major Island. To be sure, the birds of Daphne Major have been the central focus of work by the Grants, and some of the work on that island has been covered in their other books (particularly research covered in the first five chapters of the present volume). But this book goes much deeper, and with a particular focus on divergence between lineages and the early stages of speciation. It also casts a wide net, in the final chapters seeking to reach broad and general conclusions about evolution and the two processes that determine net rates of biodiversification: speciation and extinction. This book reveals, at a minimum, four important lessons about evolutionary biology. First, evolution happens in real time. This is perhaps the least surprising of the lessons to be gleaned from this book, as it is covered well elsewhere, and indeed the story of drought on Daphne Major causing rapid phenotypic and genotypic evolution in finch beak size has become the textbook example of natural selection and adaptation; every school kid learns this story. Here, though, the Grants expand insightfully on this theme, using nearly a half-century of painstaking data to take the “long view” of evolution (at least on the microevolutionary scale). It shows nicely how selective pressures and the direction of evolutionary change can vary over the course of a few decades, and how that change can be dissected to reveal its underlying causes. Second, this book demonstrates the key role of chance events, along with environmental conditions, in driving evolutionary change. This can be seen in the long-term evolutionary trends of the focal study species, illustrating how two closely related species on the same island, dealing with the same environmental events, can show strongly divergent patterns of evolutionary change over time. But the point is really driven home in the chapters detailing the unexpected arrival of a third species to the island, and the important evolutionary consequences for the two existing finch species through competition-driven selection, introgressive hybridization, and even song learning. The underlying theme here is that evolution is, in the Grants’ own words, “genetically predictable but environmentally unpredictable.” As