THE GENETICS OF GROUPS, FOR GROUP READING
Genetic Structure and Selection in Subdivided Populations. François Rousset. Princeton University Press, Princeton, NJ, 2004. 288 pp. $85.00 (0691088160 cloth).
In the first half of the 20th century, the eminent founders of quantitative population genetics—R. A. Fisher, J. B. S. Haldane, and Sewall Wright—established a foundation of mathematical methods of analysis that, with further development by others, serves researchers so well in our quest to understand how patterns of biological adaptations in time and space, and ultimately speciation events, are generated and maintained by natural selection. Among the other contributors to the development of the field are Gustave Malécot, W. D. Hamilton, John Maynard Smith, Motoo Kimura, Thomas Nagylaki, and Monty Slatkin, all of whose work François Rousset ably reviews and synthesizes in his new monograph on genetic structure and selection in group-structured populations.
In the preface, Rousset opens a section entitled “Assumed Background” by stating, “I assume the reader has some basic interest in population biology and some knowledge of the population genetics of panmictic populations…. I have used only a minimum set of mathematical techniques that are already well-established among population biologists” (p. xv). Lest this lull you into thinking that this monograph is going to be a breeze to read, let me immediately disabuse you of that notion. This book will be tough going for all but a small handful of the leading mathematical population geneticists.
Much background material on the fundamental notions and assumptions underlying the formulation of models in population genetics is either absent or skimmed over in this book. Furthermore, empirical examples that would help illustrate concepts and ground the reader's intuition are absent. The work is like a pictureless recipe book of formulas that can be used to compute the frequencies of genes under selection in structured populations. Thus, the best way to break the back of the material is through participation in a reading group or seminar led by someone steeped in the conceptual foundations of the field and familiar with illustrative empirical examples. The mathematical tools needed to read this book are not beyond the basics of calculus and linear algebra, but the derived formulas presented throughout the text increasingly tax the ability of the noncognoscenti to conceptually interpret their meaning in the context of the common origins (coalescence) of genes found in different subgroups of the population.
In concluding a short introductory chapter, Rousset advises the reader that “this book aims to show how a range of questions can be efficiently addressed using a limited number of concepts and technical tools, and to provide a self-contained account of the basic models of the genetic structure of populations”—an aim that is certainly fulfilled. He further advises that one can either read chapters 3 and 4, reviewing neutral theory of population structure, or jump straight from chapter 2, which covers the basics of influence of selection and drift on changes in allele frequencies from one generation to the next, to chapters 5 and beyond, where the real meat of the book resides.
Chapter 5, followed by the more technical chapter 6, signals the modernity of Rousset's approach by developing an excellent exposition of the dynamical concepts underpinning “evolutionarily stable strategy theory,” an approach introduced by Maynard Smith and his collaborators in the 1970s. This modern treatment is continued in chapter 7, where the ideas of W. D. Hamilton on inclusive fitness, cooperation, and altruism are presented in the mathematical framework developed in the early chapters. Rousset takes considerable care in this chapter to clarify the essential differences between inclusive and direct fitness, as well as unify these two views of selection. Of particular note in this chapter is an insightful diagram (figure 7.2) that clarifies, in the context of Hamilton's famous identity of evolutionarily favored acts (involving costs, benefits, and relatedness of actors and recipients), when such acts should be interpreted as cooperation, altruism, spite, or selfishness.
The remaining four substantive chapters of the book deal with diploid and sex-structured populations (chapter 8), effective population size (chapter 9), and the generalization of the analysis to account for fluctuating (chapter 10) and class-structured (chapter 11) populations. A short chapter offering an overview and perspectives concludes the book.
In the final paragraph of the last chapter, Rousset raises the issue that a common problem in the field of population dynamics (from both an evolutionary and an ecological perspective) is how to make theoretical models simpler. The trap here is that, although we may find more effective ways to encapsulate our understanding of the commonalities of a broad spectrum of processes in relatively simple equations, the ideas behind those equations are neither simple nor easy to master. It takes about six years of slogging through mathematical physics to understand the real implications of the fundamental equations of physics so elegantly represented by a set of symbols that I have seen printed on a T-shirt. In the same way, Rousset has done a fine job of unifying seemingly disparate ideas in population genetics under the rubric of rather compact-looking “gene coalescence” equations. From his concluding statement, it is clear that Rousset would like to make his equations even more compact. But for most of us reading his book, our task is to master the concepts behind the elegant equations presented in Rousset's monograph, if we are to have any hope of keeping up with future developments in the field of mathematical population genetics.