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Review: Making Sense of Evolution
Making Sense of Evolution is an ambitious book synthesizing the views of a practicing biologist (Massimo Pigliucci) with those of a practicing philosopher of biology (Jonathan Kaplan). It begins with central concepts in evolution that are referred to throughout the book, and then moves on to such topics as how to measure natural selection, the debate over the units or "levels" of selection, adaptationism, functions, testing adaptive hypotheses in human evolution, and the concept of species.
Readers of Reports of the NCSE may be familiar with Pigliucci's Denying Evolution (2002); however, this book has a very different audience in mind — graduate students and professionals in biology and philosophy of biology. Indeed, laypersons who pick up Making Sense of Evolution based on the title alone are likely to walk away disappointed; it is replete with technical terms from both biology and the philosophy of biology. That being said, the authors do an admirable job in explaining much of the jargon; boxes and diagrams, although occasionally overused (as when they span multiple pages), are extremely helpful in highlighting key points and concepts.
I cannot help but remark that this is exactly the sort of book that creationists exploit, given its stinging criticism of contemporary evolutionary practice. The authors are aware that their words could be taken out of context and misused, but say that they seek to provide a more accurate picture of science as it really is: nuanced and provisional. Although I applaud and agree with this general sentiment — neither philosophers of biology nor biologists should hold back when there are criticisms to be made — in this case the authors are overly critical. Our current evolutionary models and methods are limited in various respects, and Pigliucci and Kaplan are right to point out these limitations. However, they deemphasize the utility of these models and methods. To give one simple example, it is true that some evolutionary models do not work well for making long-term predictions; however, these same models work quite well for short-term predictions. Pigliucci and Kaplan acknowledge this, but suggest that it is long-term predictions that we really care about. Yet that is far from obvious; indeed, it could reasonably be argued that the models of population genetics were intended to apply primarily to short-term predictions, so that the apparent limitation is not really much of a limitation at all. Someone who is not fully conversant with the models and methods in question might get the impression that evolutionary biology is in much worse shape than it actually is, whereas someone who is more familiar with these practices is likely to feel that the full story has not been told.
The picture of contemporary philosophy of biology that emerges is also somewhat misleading. Citations to key sources are spotty, so that a reader who wanted to follow up on the issues would have a difficult time doing so. For example, the view that natural selection is a "force" is introduced without a citation to Elliott Sober, evolution is described as a historical science without citations to Ernst Mayr and Stephen Jay Gould, and underdetermination is discussed without a citation to Pierre Duhem. To anyone who is familiar with the literature, these omissions are almost akin to discussing the development of the theory of natural selection without citing Charles Darwin. More substantively, some of the concepts that are used throughout the book — concepts that are supposed to provide clarification and insight into more complex issues — are unclear and not fully defended. For example, Pigliucci and Kaplan introduce two concepts of fitness, one at the level of individuals and one at the level of ensembles of populations, and, correspondingly, two concepts of natural selection. However, it is unclear why natural selection should not be seen simply as one kind of cause with corresponding effects at the level of ensembles of populations. And again, following the citations will be of little help — in this case, because Pigliucci and Kaplan have misinterpreted the position of the authors credited with developing these concepts, Matthen and Ariew (2002), who hold that natural selection is a statistical summation at the level of populations.
Another central concept, random genetic drift, is similarly ill-treated. We are told that the many biologists who think they are comparing the outcomes of selection and drift are confused, because drift is not a "force," a "cause," or a "process". Yet no argument is given; the authors simply take one definition of drift ("a name we give to certain outcomes that are at a particular place in the statistical distribution of likely outcomes") and point out that on this definition, it makes no sense to talk of drift as a process. But that definition ignores the fact that biologists identify "drift" with a number of biological processes — most commonly, the "random" (or more accurately, "indiscriminate") sampling of gametes in the process of fertilization; in such cases, heritable differences between gametes are causally irrelevant to which gametes are successfully joined (see Beatty 1984 and Millstein 2002, which are cited but not discussed). On this alternative definition, one need not reach the conclusion that generations of biologists are simply confused about what it is that they are doing.
Even though at times I found this book to be a frustrating read — for example, we are supposed to think that it makes no sense to talk of developmental constraints simply because development makes selection possible (as though that which enables cannot simultaneously constrain) — I do think that there is some value in it. In particular, I applaud the authors' joint venture — certainly there is much to gain from collaborations between biologists and philosophers of biology — and their overall theme emphasizing the need for models and methods that reveal the causal processes underlying statistical patterns. We can be so dazzled by our statistical methods that we forget their limitations, and if representing nature is a goal of our science, retooling our models and methods to uncover the causes at work will help us achieve that goal. Nonetheless, conceptual and methodological clarity will have to wait for another day. But then again, this just means that evolutionary biology and its philosophical analysis are ongoing rather than static; this should be no surprise to anyone who is familiar with the true nature of science.
AcknowledgmentsI thank Ayelet Shavit and Vadim Keyser for reading this book with me. My understanding of the issues at stake is very much in debt to their helpful comments and insights.
ReferencesBeatty J. 1984. Chance and natural selection. Philosophy of Science 51: 183–211.
Matthen M, Ariew A. 2002. Two ways of thinking about fitness and natural selection. The Journal of Philosophy 99: 55–83.
Millstein RL. 2002. Are random drift and natural selection conceptually distinct? Biology and Philosophy 17 (1): 33–53.
Pigliucci M. 2002. Denying Evolution: Creationism, Scientism, and the Nature of Science. Sunderland (MA): Sinauer Associates.