Reductionism is a four-letter word, from which all manner of evils are supposed to follow—at least if you believe some of its critics. To be called a reductionist is to be slapped with a term of abuse signaling that one is a crass, unsophisticated epistemic leveler, perhaps suffering from a bad case of physics envy. It wasn't always so. During the heyday of logical empiricism in the philosophy of science (the 1940s and 1950s), “reduction”was considered the summum bonum of a philosophical account of natural science (which meant, in practice, physics). Since the steady rise of the philosophy of biology in the 1970s, however, reduction as a philosophical ideal has been out of favor. In Darwinian Reductionism: Or, How to Stop Worrying and Love Molecular Biology, Alex Rosenberg aims to restore reductionism's good name. He has his work cut out for him.
Alex Rosenberg is the R. Taylor Cole Professor of Philosophy and Biology at Duke University. His previous books in the philosophy of biology include The Structure of Biological Science (Cambridge University Press, 1985) and Instrumental Biology, or The Disunity of Science (University of Chicago Press, 1993). The fulcrum for his latest book is what he considers the “untenable dualism” characterizing much contemporary philosophy of biology. On the one hand, virtually all philosophers of biology are physicalists: They maintain that the universe consists solely of physical things (e.g., matter, forces, etc.). On the other hand, many of these same philosophers reject reductionism: “They hold that the adequacy, accuracy, correctness, completeness of biological theories and explanations need not and in most cases do not hinge on the provision of theories and explanations from physical science that show how biological phenomena are physical” (p. 4). How is this possible? Doesn't physicalism entail reductionism? In his sustained defense of reductionism in biology, Rosenberg aims to force physicalist anti-reductionists to come to terms with their conceptual schizophrenia and to put their philosophical houses in order.
Antireductionists, of course, have principled objections to reductionism. They insist that whereas it is true that all biological processes are physical processes, it is also true that biology has its own unique and distinctive explanatory strategies that cannot be framed without explanatory loss in the terms of molecular biology. For example, the Lotka-Volterra equations embody principles governing the behavior of predator–prey populations that describe systems entirely physical in their constitution, yet the concepts of “predator” and “prey” nowhere appear in the terminology of molecular biology. According to antireductionists, even if there is a sense in which the behavior of the physical systems in question could be explained in terms of the behavior of macromolecules, something important would be lost in such a reduction. Ecology and evolutionary biology, they would argue, are no more reducible to molecular biology than are economics and cognitive psychology. This is not to deny that such disciplines deal with purely physical systems. But it is to be skeptical about the human ability to grasp important generalizations in these domains framed solely in terms of biologically interesting molecules.
In response, Rosenberg argues that molecular biology “completes” evolutionary biology. Why do some moths have eyespots on their wings? In order to misdirect avian predators away from more vulnerable parts of their bodies. These eyespots exist because they provided a selective advantage in the past for individuals of this species. How do the eyespots actually come about in individual moths? Through a complex developmental process involving genes—a process that could, in principle, be spelled out in a molecular biological account.
Rosenberg thus wants Darwinians to love molecular biology. But Darwinians already love molecular biology when it provides a proximate explanation for eyespots on moth wings, and especially when it continues to confirm, and sometimes correct, the phylogenetic conclusions arrived at by systematists attempting to reconstruct the tree of life. What's not to love? On the other hand, if “reductionism in biology turns out to be the radical thesis that ultimate [i.e., evolutionary] explanations must give way to proximate ones and that these latter will be molecular explanations”(p. 43)—that is, if reductionism entails the elimination of evolutionary explanations in favor of explanations framed entirely in terms of macromolecules—then arguably there is less for which to feel genuine affection.
Rosenberg never explicitly identifies the intended readership of Darwinian Reductionism, although in places (e.g., pp. 22, 57) he assumes that molecular biologists are his audience. Nonetheless, biologists will probably find the twists and turns of the subtle argumentation in support of reductionism difficult to appreciate. Likewise, most philosophers are likely to find the molecular biological details throughout the text all but impenetrable. The book will most interest those philosophers of biology who are already well versed in the issues discussed in the book. This is not a large audience.
The question that is thus bound to arise for potential nonspecialist readers is why one should be concerned with any of this. Interestingly, Rosenberg considers the issue of reductionism in biology to have important societal consequences: “A biological science that cannot be systematically connected to the rest of natural science gives hostages to mystery mongering or worse—creationism, ‘intelligent design,' and their new-age variants” (p. ix). Granted, were Darwinian theory either inconsistent with or just systematically unrelated to other relevant areas of science, this would clearly represent a crisis in biology. Indeed, some of the chief arguments against Darwin's theory in the years immediately following its publication centered on its alleged inconsistency with what was then believed about the nature of inheritance and about the age of the Earth. But it is less clear that our inability to “reduce” evolutionary biology to molecular biology, in the sense that Rosenberg deems essential, is critical to rebutting the challenges posed by creationism and its intellectual bedfellows. Arguably, unreduced evolutionary biology has succeeded at this task just fine. Ironically, should Rosenberg be successful in convincing readers that evolutionary biology is grossly deficient in the absence of its successful reduction to molecular biology, he could be providing aid and comfort to just those opponents of Darwinism he appears to be most concerned to combat. And this would be something to worry about.
