Integrative and Comparative Biology Advance Access originally published online on September 28, 2007
Integrative and Comparative Biology 2007 47(6):899-900; doi:10.1093/icb/icm097
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Book Review |
Darwinian Reductionism—Or, How to Stop Worrying and Love Molecular Biology. Alexander Rosenberg.
Department of History and Philosophy of Science
University of Cambridge
Free School Lane, Cambridge CB2 3RH, UK
Correspondence: E-mail: us227{at}cam.ac.uk
Darwinian Reductionism—Or, How to Stop Worrying and Love Molecular Biology. Alexander Rosenberg
Chicago and London: University of Chicago Press, 2006. 263 pp. ISBN 978-0-226-72729-5 (cloth) $40.00.
The claim that organisms consist of nothing but physico-chemical matter remained controversial in biology until several decades into the 20th century. Biological physicalism was rejected by neo-vitalists like Hans Driesch. Puzzled, in particular, by the intricacies of development, Driesch endowed organisms with a nonphysical substance, the entelechy. Of course, the days of vital forces are long gone; nowadays physicalism dominates every field in the biological sciences. Whether cells or organs, individual organisms or populations, all biological things are ultimately composed of nothing but physico-chemical things. But does this also mean that all these biological entities can be wholly explained in terms of some basic physico-chemical facts? This question has occupied philosophers of biology for several decades. The issue here is epistemological rather than metaphysical; it pertains to the resources required to explain biological facts, rather than to the nature of biological facts themselves. Antireductionism has emerged as the most popular answer: biological theories and explanations need not be replaced with physical theories and explanations; biology as a discipline is autonomous from physics and chemistry insofar as even the most complex web of physico-chemical explanations is ill suited to replace higher-order biological explanations.
Alexander Rosenberg, a distinguished philosopher of science at Duke University, attacks the antireductionist consensus. According to him, antireductionist physicalism is a philosophically unstable position that should be abandoned in favor of reductionism—and a particularly thorough one at that. For on Rosenberg's view, even natural selection needs to be explained in terms of molecular interactions.
The basic framework of Rosenberg's reductionist physicalism is laid out in the introduction and the first chapter. There, he distinguishes molecular biology from all the remaining fields of biological research, which concern higher-level entities and are subsumed under "functional biology". Employing Ernst Mayr's distinction between proximate and ultimate explanations, Rosenberg argues that the ultimate explanations found in functional biology must be eliminated in favor of proximate explanations generated in molecular biology. That is, explanations appealing to evolutionary history in order to explain, for example, why a butterfly has spots on its wings need to be reconstructed as explanations that, in the end, appeal exclusively to interactions between macromolecules: "reductionism in biology turns out to be the radical thesis that ultimate explanations must give way to proximate ones and that these latter will be molecular explanations." (p 43)
The second and third chapters aim to show that reductionism is already a successful research program in developmental biology. Rosenberg expounds in detail the (somewhat outdated) model of gene expression by Bodnar (1997
) to argue that higher-level developmental phenomena like cell specification and pattern formation can be explained purely in terms of molecular interactions, in particular in terms of differential gene expression. The overall message is that molecular biology reveals complicated webs of molecular interactions that replace or complement concepts such as organizer or positional information. Although Rosenberg rejects the notion of genetic information, he claims that genes literally program the embryo.
One of the most influential objections to reductionism is treated in Chapter 4. Philip Kitcher argued that biology lacks the laws of nature required for reductionist explanations. Rosenberg agrees that there are no laws in biology (except the "principle of natural selection"), only local and transient regularities that are subject to the ever-changing demands of natural selection. But he complains that antireductionists like Kitcher provide no viable account of how biological explanation works without laws. Rosenberg does not discuss the growing literature on mechanistic explanation at this point, which might show a way forward.
Chapters 5 and 6 contain Rosenberg's attempt at reducing the theory of natural selection. He first rejects a recent antireductionist view, according to which the principle of natural selection is as irreducible to the interaction of individuals as the 2nd law of thermodynamics is irreducible to particle interactions. He then proposes that while the principle of natural selection cannot be derived from chemical and physical laws, it is itself a law of chemistry and therefore unproblematic for reductionists. This suggestion is motivated with a thought experiment in which self-replicating molecules compete for combinations of stability and replication that best suit a given environment.
The two concluding chapters aim at making reductionism palatable or even appealing for biologists and philosophers alike. Rosenberg praises the insights and methodological innovations provided by sequence analysis. He focuses especially on applying these techniques to the study of human biological and cultural evolution. Rosenberg also endeavors to diffuse a persistent worry against reductionism, i.e., that it implies genetic determinism. Far from it, he claims: where previously tight correlations between genes and phenotypic effects suggested some form of genetic determinism, the reductionist research program of molecular biology dissolves these correlations into a multitude of independent causal pathways leading to similar outcomes. Rosenberg develops this claim by discussing one of the paradigm examples of a genetically determined disorder, phenylketonuria.
Many of the central theses in "Darwinian Reductionism" would have benefited from more carefully developed arguments. As they stand, claims to the effect that the principle of natural selection is a chemical law, or that all biological entities are categorized with respect to their evolutionary functions, are bound to attract criticism. Furthermore, it seems to me that one of the obvious objections against explanatory reductionism, i.e. that it ignores the explanatorily salient higher-level features in favor of unnecessary detail, is not adequately addressed. Despite these shortcomings, Darwinian Reductionism offers interesting perspectives on, for example, the historically contingent nature of biological generalizations, the role of informational notions, and various antireductionist arguments. And it certainly is an accessible discussion of a central and important topic in the philosophy of biology.
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Bodnar JW. Programming the Drosophila embryo. J Theor Biol (1997) 188::391–445.[CrossRef][Web of Science][Medline]
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