The Shape of Things to Come

Review of Evolution, by Nicholas H. Barton, Derek E. G. Briggs, Jonathan A. Eisen, David B. Goldstein, and Nipam H. Patel. 2007. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY. xiv + 833 pp. Cloth. $100. ISBN 978-0-87969-684-9. An evolutionary perspective now permeates the literature in all of biology, from ecology to molecular biology. Consequently, the scope of evolutionary biology is becoming increasingly broad. This trend presents a serious challenge for teachers of evolutionary biology. Although we can still justify a central role for evolution by citing Dobzhansky’s claim that “nothing in biology makes sense except in the light of evolution,” we can also turn things around and argue that nothing in evolution makes sense except in the light of [all of] biology. Dobzhansky’s claim about the importance of evolutionary biology was based on his belief that structure and function (what things are and how they work) can be fully appreciated only in the context of understanding how they came to be the way they are. What he wrote in his provocatively titled essay (Dobzhansky 1973) was: “Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts, some of them interesting or curious but making no meaningful picture as a whole.” Today, the pile of sundry facts has grown very large, and many of these facts influence directly how we think about the evolutionary process. Dramatic growth in the breadth and depth of biological knowledge has uncovered an array of new structures, functions, and interactions that require explanations of how they came to be. At the same time, our increasingly sophisticated understanding of biological mechanisms allows more complete explanations of the process of evolutionary change. Learning (and teaching) evolutionary biology, therefore, must be an iterative process. As teachers, we can present the broad outlines of variation, inheritance, descent with modification, and natural selection without relying on a detailed knowledge of ecology, behavior, physiology, genetics, or molecular biology. After all, Darwin had no clear understanding of the mechanisms of inheritance, let alone the molecular basis of heredity, and yet he was able to publish a compelling discourse on the fundamental principles of evolution, principles that have endured for 150 years. But to describe the detailed mechanisms that produce adaptation and diversification, we do need an intimate knowledge of all of biology. For example, to explain variation in beak size and shape in Galapagos ground finches, we start with observations of phenotypic variation in natural populations (Lack 1947). We then show that the variation is heritable, demonstrate that patterns of variation depend on presence/absence of presumed competitors for food (seed) resources, record single generation changes in the proportions of birds of different sizes and correlate them with the size spectrum of seed resources, document that changes in beak shape also drive the evolution of song, and finally show that expression patterns of the genes Bmp4 and calmodulin appear to determine aspects of beak shape and therefore may be targets of selection (Boag 1983; Gibbs and Grant 1987; Grant 1999; Podos 2001; Abzhanov et al. 2004, 2006). For a student to fully appreciate this story, which reveals the continuity of thought from Darwin to modern developmental genetics, she must have an appreciation of foraging ecology, competition for limiting resources, trait heritability, role of song in species recognition and mate choice, and how patterns of gene expression are responsible for the