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By Alan C. Love. Worry carries with it a connotation of false concern, as in 'your mother is always worried about you'. And yet some worrying, including that of ...
Metascience (2008) 17:1–26 DOI 10.1007/s11016-007-9159-9

Ó Springer 2008

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MORE WORRY AND LESS LOVE?

Alexander Rosenberg, Darwinian Reductionism: Or, How to Stop Worrying and Love Molecular Biology. Chicago: University of Chicago Press, 2006. Pp. x+263. US$40.00 HB

By Alan C. Love Worry carries with it a connotation of false concern, as in Ôyour mother is always worried about you’. And yet some worrying, including that of your mother, turns out to be justified. Alexander Rosenberg’s new book is an extended argument intended to assuage false concerns about reductionism and molecular biology while encouraging a loving embrace of the two. It collects previously published and newly written material woven together with an overarching narrative: Darwinian theory Ôreductively’ reaches all the way down to the history of macromolecules. Rosenberg sees this as a distinct break with his earlier works (The Structure of Biological Science, 1985; and Instrumental Biology or the Disunity of Science, 1994), where he argued against reductionism conceptualised in terms of Nagelian formal strictures on theory reduction. Ironically, Rosenberg now uses the same argument for reductionism in the context of explanation that he previously used against reductionism in the context of theories: natural selection. The operation of natural selection at the level of macromolecules simultaneously shows that biology is relatively autonomous from physical science and vindicates reductionism – a Darwinian reductionism. Rosenberg frames his analysis in terms of ‘‘biology’s untenable dualism’’, i.e. the joint commitment to physicalism and antireductionism. ‘‘How can you be a physicalist and deny the ‘‘nothing but’’ thesis?... It is this paradoxical state of affairs that makes a perplexing mystery out of the problem of exactly how molecular biology relates to the rest of biology’’ (p. 3). After setting the stage around this puzzle in the Introduction, subsequent chapters unpack

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various elements of the argument. Chapter 1 establishes key distinctions (Ôhow-possible’ vs. Ôwhy-necessary’ and Ôultimate’ vs. Ôproximate’ explanations) in order to Ôreconfigure’ reductionism. Chapters 2 and 3 use molecular developmental biology as an exemplar of this new explanatory reductionism. Here Rosenberg replies to criticisms of genes having a privileged causal role in development and defends the integrity of some contested concepts (Ôgene’, Ôgenetic information’, and Ôdevelopmental programming’). Chapters 4–6 deal directly with natural selection. Rosenberg argues that natural selection undergirds a reductionist biology because natural selection is a fundamental physico-chemical law of nature. Chapters 7 and 8 draw out putative applications for humans in terms of our molecular history with respect to altruism and genetic determinism. Although argued with characteristic force and precision, nagging worries remain. Claims that reductionism has been ‘‘the scientific worldview’s program of research since the 17th century’’ and under its aegis ‘‘more and more phenomena’’... have been shown to be ‘‘nothing but’’ matter in motion are tendentious (pp. 2–3). The historical thumbnails he provides about physics and chemistry do not lay the matter to rest. Before Rosenberg’s specific arguments can be adequately assessed, we need to attend to the framing of his discussion. It is the problematic nature of Rosenberg’s assumptions and core distinctions that justify worry about his reductionism. This critical tactic is preferable because his argument arises from a philosophical strategy that is not universally shared, especially when it comes to the difference between epistemology and metaphysics. Rosenberg’s construal of reductionism as a Ônothing but’ thesis is metaphysical (physicalism) but he often switches over to epistemological language such as Ôtheory’, Ôexplanation’, or Ôresearch program’. This is because he aims to derive conclusions for practical research activity from metaphysical considerations, which in his view is where the real philosophical action lies: ‘‘the dispute is... not epistemic but ontological’’ (p. 179). Unless garden variety biological explanations are replaced by Darwinian macromolecular explanations, we are left with either Ôexplanatory Protagoreanism’, which resists reductionism with the feeble claim that it is impossible because of our cognitive deficiencies (‘‘a claim about biologists, not about biology’’, p. 36), or vitalism returns through the back door.

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The issue is metaphysical: ‘‘[t]he antireductionist needs there to be something in the nature of all truly biological phenomena [i.e. metaphysics] that acts as barrier to reduction’’ (p. 15). The moral is epistemological: pursue macromolecular methodologies and explanations. This strategy contrasts with that of many philosophers of biology who concentrate on comprehending reductionism as a kind of reasoning (i.e. epistemology), and subsequently inquire about its metaphysical implications (if any). Rosenberg’s attempt to make metaphysical concepts do work for biology began thirty years ago when he co-opted the idea of Ôsupervenience’ from Jaegwon Kim to explicate the concept of fitness. It continues here in exactly the same form when he imports Kim’s causal exclusion argument from philosophy of mind to bolster his reductionist thesis. Needless to say, these are not settled matters and should be treated with caution. Three other problematic aspects of Rosenberg’s argument structure can be identified, all of which are required for him to arrive at his conclusion: Claim 1: ‘‘Let us distinguish functional biology from molecular biology’’ (p. 25). This distinction is mapped onto the Ôhow-possible’/Ôwhy-necessary’ explanation distinction in order to facilitate a central inference. Only Ôwhy-necessary’ explanations really explain (see below, Claim 3) and they are only found in molecular biology. Functional biology (‘‘what makes a kind functional is that its instances are the products of an evolutionary etiology’’) only produces Ôhow-possible’ explanations because selection is blind to the variety of causal details and multiple realizations underneath adaptations. But the distinction should be rejected for multiple reasons. First, it sets up an artificial Ôtwo-levellism’ that does not reflect the structure of reasoning and knowledge in biology. Even the problematic institutional division between ÔEcology, Evolution, and Behaviour’ and ÔMolecular, Cell, and Developmental Biology’ cannot recover Rosenberg’s split. Second, this leaves out a considerable amount of biology that is neither Ômolecular’ nor Ôfunctional’. Large swathes of biology are structural, whether molecular or not, and just as relevant to questions of reductionism (e.g. part–whole compositional relations). Third, and related, Ôfunctional’ means far more than Ôevolutionary etiology’ in biological science, which leads us to the next claim. Claim 2: ‘‘To call something a wing is not to describe it in terms of its composition, or structure, but in terms of [its selected effect]...

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Biology ‘‘taxonomizes’’ the phenomena in which it interests itself functionally, not structurally’’ (pp. 18–19). It is hard to know what to say about this claim other than that it is prima facie simply false. Few biologists would recognise Rosenberg’s picture of individuation because structural considerations are prevalent in descriptions of biological kinds. Many examples can be adduced: cell individuation via shape (e.g. columnar), bone individuation based on shape (e.g. pelvis [basin]), muscle individuation using location (e.g. brachialis [pertaining to the upper arm]), and anatomical units (e.g. head). Generalizations based on these structural categorizations are greatly narrowed if individuation must occur functionally because the functions of these structures vary tremendously. Judgments of homology in comparative biology explicitly individuate structures apart from function and would be vitiated otherwise. There is more to function in biology than Rosenberg is prepared to accept (cf. Wouters, 2003), and far more to biology than function. Claim 3: ‘‘Explanations need laws or something like them... the absence of laws is a serious problem for biological explanation’’ (p. 135). Rosenberg’s commitment to nomothetic explanation is a cornerstone in his argument for Darwinian reductionism. It is what gives the Ônecessary’ in Ôwhy-necessary’ explanations from molecular biology, which is sadly out of reach to functional biology’s Ôhowpossible’ explanation sketches. For this reason, natural selection explanations at the level of macromolecules are more complete and adequate accounts of biological phenomena. And, because the principle of natural selection is a non-derived physico-chemical law, biology remains largely autonomous from physics and chemistry. But Rosenberg’s rejection of Kitcher’s unification account of explanation and any account of Ôinexact laws’ (e.g. Jim Woodward’s Ôinvariance under intervention’) is not really convincing. The only genuine law in biology for Rosenberg is the principle of natural selection, so real explanation in biology must always invoke it (if only implicitly). Many will object to this conception of the principle of natural selection but another reason to worry is that it relies on the problematic understanding of function and individuation already discussed. Also, Rosenberg’s view of how biological explanation works leaves most biologists not offering explanations. This is poignant for biologists using Newtonian mechanics to explain biological phenomena. (Functional morphologists, who taxonomise their elements of research structurally, routinely treat aspects of

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animal morphology in terms of physical concepts, such as the application of a force or load to an appendage to understand the dynamics of locomotion). Most worrisome is the counterintuitive consequence that a macromolecular level selection explanation of a long extinct population from billions of years ago is causally relevant to and justifies an individual level selection explanation for an extant population (cf. p. 194ff). All three of these claims are emblematic of the fact that biological concepts are not what motivate Rosenberg. This also can be observed in his treatment of examples and the narrow cross-section of disciplines from which he chooses them. First, one is often frustrated with his interpretation of the biology, such as his discussion of Drosophila wing formation (p. 49). Rosenberg claims the gene ‘‘wingless builds wings’’ and that it has this name ‘‘because of those effects which were selected by the environment to provide wings’’. He overlooks the fact that wingless also plays a critical role in patterning the cuticle of embryos. And what about cleopatra and glass-bottom boat? Second, the heterogeneity of reasoning in molecular and evolutionary biology is irrelevant to Rosenberg. Large portions of evolutionary research not falling under Rosenberg’s definition (‘‘evolution means the Darwinian mechanism of blind variation and natural selection’’, p. ix) do not matter and never make an appearance. His assertion that ‘‘nothing in the laboratory has arisen to suggest impediments to the research program of reductionism’’ (p. 7) is contentious when some molecular biological researchers apparently recognise such impediments: ‘‘Our results suggest that the cellular responses induced by multiplex protein kinase inhibitors may be an emergent property that cannot be understood fully considering only the sum of individual inhibitorkinase interactions’’ (Kung et al., 2005, p. 3587). Diffusing justified worry requires agreement on the nature of what is in question. Rosenberg’s primary interest is in metaphysics rather than epistemology; he sees his philosophical task as hunting Ôghosts in the machine’. Many philosophers of biology take epistemology to be the primary domain of analysis, especially because biological reasoning is so heterogeneous; functional ascriptions are diverse; and explanation occurs without universal, exceptionless laws. Rosenberg demurs. But this implies that the disagreement does not concern the argument but rather what we should be

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arguing about. And this is certainly something that implies more worry and less love. Department of Philosophy University of Minnesota Minneapolis, MN USA By Ingo Brigandt Darwinian Reductionism develops a novel variety of explanatory reduction (as opposed to classical theory reduction), arguing that biological explanations can be complete (why-necessary rather than how-possible explanations) only if they invoke laws operating at the physical, macromolecular level. This novel notion of reduction is intended to make room for reductive explanations despite the existence of multiple realizations. Rosenberg forcefully argues that previous discussions in the philosophy of biology have ignored important metaphysical considerations, yet his own metaphysically driven account ignores relevant epistemological and scientific issues. Rosenberg rightly attempts to restructure the reduction vs. antireduction debate, but at the same time he discards points on which everyone has agreed – reductionists and antireductionists alike. He sensibly does not spend much space rehearsing well-known arguments for and against antireductionism, but when mentioning antireductionist positions Rosenberg creates straw men, such as the tenet that antireductionists deny that biological facts supervene on physical facts (p. 20), e.g. by assuming that the spatial distance of cells is not a physical property (p. 84). Many philosophical ideas and claims about biology put forward are controversial; and Rosenberg does not provide support for many of his claims that are not generally accepted by those working in the relevant fields. To my mind, the structure of his overall account is unclear. Rosenberg introduces a whole set of arguments for reductionism that reinforce each other but are logically independent, and the discussion neither presents these as independent arguments, nor gives a clear and consistent account of their relation. Some of his claims (pp. 22, 132) explicitly locate the main argument for reductionism in the first half of the book (Chap. 23). On this account, the second part (Chaps. 4–6) addresses some remaining issues, the idea being that since the main argument in the first half presupposes the

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theory of natural selection, this theory has to be reduced to the molecular level in the second part. However, as far as I can tell, whenever Chaps. 2 and 3 invoke natural selection, it is actually never in those parts of the discussion where Rosenberg argues for reductionism (selection is mentioned when making seeming concessions, yet it is emphasised that these do not affect reduction). This argument in the first part consists in the claim that recent successes in developmental genetics shows that development is the execution of a genetic program. Many philosophers and biologists believe that this is false; and Rosenberg’s discussion is too brief to provide convincing support for his interpretation, also ignoring some relevant previous philosophical accounts of the same material (e.g. Laubichler and Wagner, 2001; Robert, 2004). At other points of the book, however, Rosenberg suggests that his main argument is to be found in the second part of the book (pp. 20, 41, 152, 177). This argument for reductionism rests on the status of natural selection and is thus at the heart of Darwinian Reductionism. It turns out to not depend on the earlier discussion at all. Chapters 4–6 suggest that there are three options: (1) natural selection is not a physical process but ontologically emergent, in which case antireduction is vindicated; (2) natural selection is a physical process derivable from physical laws, which implies reduction; and (3) natural selection is a basic, underived physical law, which also vindicating reduction (p. 182). Most of Rosenberg’s discussion is targeted at showing that Option 3 obtains. Note that none of these options – focusing on evolutionary theory – makes reductionism dependent on the nature of explanations in experimental biology, such as molecular, cellular and developmental biology. In contrast, previous debates between reductionists and antireductionists have taken the issue to turn on facts about experimental biology. Rather than discussing Rosenberg’s argument for natural selection being a basic physical law, I focus on how this relates to reduction. First, antireductionists in philosophy of biology are not vitalists but non-reductive physicalists. Thus, they assume that any biological process is also a physical process, which shows that Options 2 and 3 do not entail reduction. Rosenberg thinks that non-reductive physicalism is simply not a viable metaphysical position, and to support this view he appeals to Jaegwon Kim’s (1998) prominent Ôexclusion argument’ against non-reductive physicalism about mental phenomena (which has been effectively criticised; see

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Marras, 2007). Showing that non-reductive physicalism is metaphysically impossible would provide a sufficient argument for reduction, but this would be an argument independent of the status of natural selection and thus of most ideas in Darwinian Reductionism. Rosenberg does not defend Kim’s argument or reply to standard objections – he only presents the argument ‘‘briefly’’ (p. 180) – so in the end it is just another, independent argument. Second, recall that Rosenberg devotes so much effort to showing that natural selection is a basic physical law because the pivotal idea of Darwinian Reductionism is that reductionism is true if and only if selection is a physical process (p. 20). His argument for linking the status of selection with the truth of reduction is based on the assumption that all biological kinds are individuated in terms of their function, where Ôfunction’ means an entity’s selected effect – an idea repeated like a mantra throughout the book (pp. 19, 25, 30, 40,...). Because every Ôkind’ in biology, including molecular and experimental biology, is individuated in terms of its selection history, any description and explanation involves reference to natural selection: ‘‘since Dobzhansky’s dictum is literally true, every proximate explanation in biology is implicitly ultimate, every such explanation includes an implicit commitment to the theory of natural selection’’ (p. 20). Thus, an explanation from experimental biology is fully reductive only if the presupposed principle of natural selection is in fact physical-molecular. In line with his view that all biological kinds are selected-function kinds, Rosenberg maintains that taxa are individuated in terms of their function; yet it is surely uncontroversial that taxonomists classify in terms of phylogeny. His example is Ôamphibian’, though Rosenberg does not explain what he takes the function of amphibians to be that unites them as a kind, or what the function (selected effect) of a whole organism is, as opposed to the function of a part (p. 139). Despite his tenet that ‘‘every biologically interesting structure is labelled by the term that expresses its selected effect’’ (p. 137), the orthodox view within biology is that morphological structures are individuated phylogenetically in terms of homology, and their names are non-descriptive proper names (e.g. Ôhyoid’). Rosenberg makes the same problematic claim about genes and biochemical structures (p. 20). He is right that some gene names, e.g. wingless (p. 49), are derived from their phenotypic function (though in this case it is a simple causal-role, not a selected-effect

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function), but it is unclear what he would make of such names as spa¨tzle and sonic hedgehog. At one point, Rosenberg quotes a long passage from a molecular biology textbook describing the mechanism of DNA replication. The explanation proceeds in terms of structure, activity and causal-role function, without presupposing any evolutionary idea. Yet Rosenberg asserts that ‘‘[t]he PNS [principle of natural selection] haunts the entire discussion’’ (p. 156). The conventional wisdom among biologists and philosophers of biology is that kinds in biology (even within evolutionary biology) are for the most part individuated in terms of structure, common ancestry, activity, or causal-role function, and only rarely in terms of selected effects (Griffiths, 2006). Parts are individuated in terms of selected effect function in studies of convergent evolution and processes such as mimicry. Unless Rosenberg can provide support for the idea that all biological kinds are selected-function kinds, the implications of his assumption about biological kinds for his project are severe. Given that individuation schemes used by scientists are the basis for descriptions, generalizations, and explanations, Rosenberg’s discussion does not reflect how theorizing and explanation proceed within experimental biology. Thereby the account misses an issue that has been central to the reduction debate. The more immediate implication is that Rosenberg’s main discussion about the status of selection (Chaps. 4–6) is irrelevant: since not all kinds in experimental biology are individuated in terms of selected effects, it is not the case that all statements in experimental biology make implicit reference to natural selection. This undermines Rosenberg’s pivotal assumption that reduction is true if and only if selection is a physical process. It is laudable that Rosenberg attempts to go well beyond past philosophical accounts by devising a novel notion of reduction. Still, quite independent of the merits of his particular arguments, at this point in the debate is it really relevant to devise more arguments for either reductionism or antireductionism? While explanations in experimental biology often appeal to several levels of organismal organization at the same time, Rosenberg still perpetuates the dichotomy between Ôbiological explanations involve the higher level only’ and Ôexplanations involve the molecular level only’ (when construing antireductionists somewhat erroneously as endorsing a two-level picture, where an alleged Ôbiological’ level cannot be reduced to a Ôphysical level’; pp. 7, 12, 26). What I take

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to be the more fruitful task for future philosophical study is to try understanding how biologists can investigate several levels of organization jointly and put forward explanations where molecular factors shed light on higher-level features and vice versa. Department of Philosophy University of Alberta Edmonton, Canada By Karola Stotz Rosenberg’s latest opus identifies a dilemma faced by all anti-reductionists, and indeed most of biology and philosophy of biology, and recommends his new ÔDarwinian reductionism’ as a remedy. This dilemma is the ‘‘untenable dualism’’ of rejecting reductionism while retaining a commitment to physicalism, a situation that Rosenberg argues ‘‘must catastrophically shift to vitalism’’ (p. 21). According to Rosenberg, antireductionists reject reductionism and the hegemony of molecular biology because they think that Ôultimate’ explanations in terms of evolution by natural selection are in principle irreducible. They are irreducible because selection is blind to a variety of causes with similar effects, which ensures the multiple realizability of all adaptations. Problematically though, anti-reductionists still attempt to hold on to some version of the physicalist’s Ônothing but’ thesis: ‘‘There are no non-physical events, states, or processes, and so biological events, states, and processes are Ônothing but’ physical ones’’ (p. 25). Rosenberg’s remedy is simple: Darwinism can be reduced to the macromolecular level and therefore fulfils the reductionist requirement, but also represents an irreducible chemical process and so assures biology its autonomous status. To put it in Rosenberg’s own terms, the Ôhow possible’ explanations of Ôfunctional biology’ (everything but molecular biology) are reduced to the Ôwhy necessary’ explanations of (Darwinian) reductionism. Both the diagnosed dilemma and the prescribed remedy rely on problematic assumptions. There are other reasons why people embrace anti-reductionism. Not only is there more to evolution than the statistical process of natural selection, but there is more to functional biology than evolutionary biology and there is more to the Ôfunctional’ in functional biology than selected effects. Most importantly, though, in my view there are different kinds of reductionism than Rosenberg’s metaphysical one, and there is more to

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physicalism than several varieties of the Ônothing but’ thesis. I will be particularly concerned with these last two assertions. Rosenberg claims that the main reasons for embracing antireductionism belong in the realm of politics, religion, and ethics, as well as the defence of turf and funding. The only exception is the already mentioned argument from Dobzhansky’s dictum that Ônothing in biology makes sense except in the light of evolution’ and the multiple realizability of biological kinds. I do not think this is fair to the leading adherents of anti-reductionism in philosophy of biology (e.g. Kitcher, 1984; but see also Dyke, 1988; and the physicists quoted below). A more extended discussion of Rosenberg’s distinction between epistemic and ontological reductionisms would also have been helpful, as many of these theorists would question his suggestion that anything short of metaphysical reductionism is philosophically uninteresting. Most importantly, Rosenberg neglects to discuss the many forms of emergence (weak, strong, trivial, and nontrivial), and the various different commitments to reductionism that go along with them. The book defines the reductionistic program of molecular biology as the belief that all biological phenomena must in principle be fully reducible to the scientific laws recognised by physics and chemistry: there is nothing more to biological facts than the interaction of the macromolecules that bring them about. Here Rosenberg implicitly refers to metaphysical reductionism. At another place we are informed that biological explanations need to be ‘‘improved, corrected, strengthened, made more accurate and adequate, and completed’’ by molecular biology (p. 4). This statement, however, translates the former into biological practice and therefore refers to epistemological reductionism, which includes methodological and explanatory reduction, and is not just, as Rosenberg suggests, a matter of practical limitations on our ability to carry out reductions. However, without an understanding of the difference between methodological and explanatory reductionism that refers to different investigative and explanatory strategies, Rosenberg is unable to accept that a biologist may value molecular research and understanding while at the same time seeking a full explanation that includes different levels of explanation. Hence her explanation would be non-reductionistic (instead of anti) while still grounded in molecular biology and other physical laws that provide the necessary but not sufficient condition for the emergent phenomenon accounted for in the explanation. But Rosenberg

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will not recognise that there are other dimensions to non-reductionism beyond the multiple realizability caused by natural selection. In that case a variety of underlying causes have the same effect, but there are opposite cases, in which the same macromolecules have different effects due to their recruitment into different networks. It is exactly the latter difference between molecular and cellular functions of molecules that creates problems for reductionist research strategies. The way in which the same molecules can function differently in different networks points toward concepts such as organization, emergence, autonomy, self-organization, and complexity, none of which are mentioned in the book, but which are important for any discussion of reduction. Rosenberg’s demand for a reductionistic biology rests on the central metaphysical thesis of physicalism and the claim that nonreductionistic biology is incompatible with physicalism. Physicalism according to Rosenberg is the assumption that all worldly phenomena are nothing but matter in motion. In contrast, the more apt term Ômatter plus organization’ would make it immediately understandable how even physicists can reconcile physicalism with a non-reductionist stance. There is more to physics than reduction to quantum mechanics, relativity theory and an elusive Theory of Everything. According to the physicist George F. R. Ellis, true complexity is the emergence of higher levels of order from, but to a large degree independent of, the underlying low-level physics. Order implies higher-level systemic organization that has real effects on the behaviour of the parts at the lower level. Organised matter has unique properties. In the same vein the Nobel laureates and Stanford professors of physics Phillip W. Anderson and Robert B. Laughlin both independently challenge the prevailing reductionist strategy of modern science. While the former argues on the basis of the principle of symmetry breaking that ÔMore is different’, the latter asserts that laws and theories follow from collective behaviour, not the other way around. If we try to analyze things too closely, we risk not understanding how they work on a macro level. Laughlin and David Pines claim that ‘‘the triumph of the reductionism of the Greeks is a pyrrhic victory: We have succeeded in reducing all of ordinary physical behaviour to a simple, correct Theory of Everything only to discover that it has revealed exactly nothing about many things of great importance’’. They point to higher organizing principles in nature, e.g. the principle of

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continuous symmetry breaking, localization, protection, and selforganization, that are insensitive to and independent of the underlying microscopic theory of everything and often solely determine the generic low-energy properties of stable states of matter (quantum protectorates) and their associated emergent physical phenomena. However, to [many physical] scientists the idea is considered dangerous and ludicrous, for it is fundamentally at odds with the reductionist beliefs central to much of physics. But the safety that comes from acknowledging only the facts one likes is fundamentally incompatible with science. Sooner or later it must be swept away by the forces of history... The central task of theoretical physics in our time is no longer to write down the ultimate equations but rather to catalogue and understand emergent behavior in its many guises, including potentially life itself. We call this physics of the next century the study of complex adaptive matter’’ (Laughlin and Pines, 2000, pp. 28, 30).

Besides questioning Rosenberg’s idea of the content of physics and hence of physicalism, none of his explanations of the motives of anti-reductionists in biology get much grip on these anti-reductionists in physics. Chapters 2 and 3 attempt to vindicate reductionism through a series of success stories of developmental molecular biology. Rosenberg believes these show that development can be reduced to genetics. However, what they explain is not development but only the role of genes in development. These chapters shed some doubt on the seriousness of Rosenberg’s promise that his reductionism is not about neglecting some causes over others. Gene networks as reproduced in this book are in reality only a convenient shortcut to the elucidation of functional co-dependence of genes. There is no mention that by taking this shortcut they collapse a multi-molecular network of genes, regulatory sequences, gene products, and intra- and extraenvironmental signals to a single dimension. This is deliberate, because it makes the genome appear to constitute a program. The last chapter, whilst hedging against the accusation of genetic determinism through a detailed story of how multiple mutations (Ôgenes’) and environment can cause the Ôsame’ phenotype, also asserts the special role of genes in programming and regulating development and normal functioning. Had Rosenberg presented contemporary knowledge of the time- and tissue-dependent requirements for environmental resources that activate, select, and even create the relevant nucleic acid sequences from the Ôsame gene’, he would have concluded that what appears as a Ôprogram’ is constituted after the fact by a network

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of interactions. Elucidating details about Ônormal’ environments would have shown how much the organism or its parental generation has to invest in order to reliable provide these environmental resources – just as in a self-organised ant colony, agency is located neither in the genome nor the environment but in the organization of all factors in an intricate network. As much as I think that the anti-reductionists have often put forward unconvincing arguments for a hierarchical approach of explanation, Rosenberg’s conviction that reductionism will be the truism of tomorrow is likely to be mistaken. Instead of being Ônothing but’ quantum mechanics and the theory of relativity, physics consists of a hierarchy of laws that emerge out of complexly organised matter. Only when this truth sinks in will the reductionist camp in the life sciences agree to embrace complexity. Cognitive Science Program University of Indiana Bloomington, IN 47406 USA By Daniel Schweitzer Can all biology be reduced to molecular biology? In his latest book Rosenberg attempts to do just that, arguing that that all Ôfunctional’ biology can be reduced to molecular biology. Rosenberg’s radical suggestion is that although there are clearly epistemological limitations to such a project, metaphysically at least, there is no reason why this cannot be achieved. An omniscient God who knew all the molecular facts about Earth would be in possession of a complete account of the entire range of phenomena that the biological sciences encompass. Rosenberg provides a rough definition of reductionism: ‘‘Reductionism is the thesis that biological theories and the explanations that employ them do need to be grounded in molecular biology and ultimately physical science, for it only by doing so that they can be improved, corrected, strengthened, made more accurate and more adequate, and completed’’ (p. 4). I will present an example drawn from developmental biology which will illustrate the possibility of non-reductionist explanations whose explanatory power does not derive from the underlying details of the molecular

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biology upon which it supervenes. Further, this does not involve any appeal to a problematic notion of Ôdownward causation’. Rosenberg distinguishes between two forms of reductionism: (1) epistemic reductionism and (2) ontological reductionism. Rosenberg claims that the former is too weak to capture the dispute between reductionism and anti-reductionism in biology. Indeed, this is correct because the real terms of dispute concerns the status of ontological reductionism. Ontological anti-reductionists claim that a physical approach to biological phenomena would miss certain generalisations that would obtain independently of us. Ontological antireductionists are committed to physicalism (the thesis that all biological facts are fixed by the physical and chemical facts) but they do not agree with the reductionists about the implications of physicalism for explanatory strategies or methodological issues in biology. On Rosenberg’s account, functional explanations persist in biology because we simply do not know or understand all the molecular details and pathways that constitute a particular biological process. Physicalist anti-reductionists disagree. I would argue that Rosenberg subscribes to a problematic notion of explanation in so far as he is committed to the view that all explanations in biology are ultimately causal explanations. But in fact, there are numerous examples of explanations in biology that demonstrate that genuine explanations need not be causal explanations. That is to say, explanatorily relevant information is not always information about causes. For instance, population biologists employ the tools of mathematical modelling. Their models are explanatory and not simply descriptive of the phenomenon under investigation. Consequently, there are explanations in population biology that cannot be explained in terms of the underlying lower level properties of the system. Similarly, as I will shortly show, there are explanations in developmental biology in which the explanatorily salient information cannot be considered to be a property of the underlying molecular structures of the system. Lewis Wolpert’s so called ÔFrench Flag model’ is a developmental explanation which is akin to a dynamical modelling explanation in the case of population ecology. It was formulated in the late 1960s in order to account for some puzzling features of development, including how patterns form in the early embryo as well as providing a potential solution to the problem of size invariance (Wolpert, 1969). In a rather simplistic construal of development,

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the model represents the spatial structure of the embryo by a linear gradient in the concentration of an unspecified substance termed a morphogen, in which the concentration of the morphogen is maintained at the two ends of the embryo by hypothetical sources and sinks. According to this model, a cell in a developmental field ascertains its position by measuring the concentration of the substance at the point in which it finds itself. In this way, the developmental field can be considered to be a Cartesian field. In fact, given a two dimensional field, the concentration of two different morphogens are able to uniquely specify a particular position in the developmental field. The French flag model nicely illustrates the power of so-called non-causal explanations because it is essentially a mathematical model whose explanatory power does not derive from the underlying details at the cellular/molecular level. Such explanations, I believe, may be termed Ôpattern explanations’ because they attempt to explain the emergence of patterns (e.g. segment formation in Drosophila) in virtue of properties of the mathematical model. That is not to say that the model’s success can be evaluated in abstraction of the molecular details. It does, however, entail that there are certain non-causal properties of the model whose explanatory power cannot be accounted for in terms of the model’s ability to track causal properties of the system in question. The French flag model of development has now been refined and superseded by more sophisticated models. But the central insight to be learned from it remains – that there are genuinely non-causal explanations in developmental biology. Modelling explanations need not be causal because they can appeal to the mathematical details of the model instead. One could argue that the very reason that such models are explanatory is because the mathematical details are descriptive in so far as they track causal properties of the system in question. But as is illustrated in the case above, no amount of empirical investigation into the phenomenon of interest, such as a developmental system, will reveal the ultimate explanation. Indeed, no amount of detailed molecular investigation will bring us closer to the truth. A detailed understanding of the molecular pathways involved in a developmental pathway may even distract us from the unifying, mathematical explanation of the phenomenon at hand.

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The French flag model provides a framework for conceptualising development in the early embryo – in particular, it was used to understand the phenomenon of spatial regulation in the regeneration experiments conducted during the 1960s. Although the model does not yield specific predictions pertaining to the types or quantities of the molecules needed to carry out the functional roles as specified by the model, it does provide the form of explanation characteristic of mathematical modelling explanations. For instance it specifies that, for the production of a developmental field, one requires a morphogen whose diffusion rate can be calculated by the diffusion equations employed to model the dynamics of the system. In that sense, developmental explanation can be said to motivate research – generating research questions and providing new avenues for research. If it is true that not all the causal details of the developmental system are explanatory, then this has some interesting implications. For instance, if all the underlying molecular details of developmental biology were known, then according to my analysis, there would still be gaps in our understanding. That is, there would still be features of development that would need to be explained. Furthermore, such properties would not be discoverable through experimental investigation alone. As the French flag model illustrates, there are some properties of the system that are not fully captured by a molecular description of the process. By invoking the resources of mathematical modelling, this model is able to explain certain features of a developmental system in virtue of non-causal properties of the system. According to Rosenberg, the explanation provided by the French flag model of development cannot be genuinely explanatory. Explanations are only explanatory when they can be framed in terms of the underlying molecular biology of the system. In the case of developmental biology, we have seen that there are genuinely non-causal explanations that are irreducible. This of course does not commit one to a problematic form of antireductionism: there is nothing anti-physicalist about such a position. However, it does entail the thesis that there are genuinely non-causal explanations in developmental biology whose explanatory power is irreducible. Although Rosenberg’s aim is to understand how biological research is currently practised, I would argue that contemporary developmental biology, rather than simply being dominated by molecular biology, is increasingly recognising the importance of

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modelling type explanations of the sort inspired by the pioneering work of Wolpert. Of course, the French flag model itself is rather simplistic. But it serves to illustrate the power and extent of dynamical explanations in the absence of a complete understanding of how the types of events posited by such models would be realisable in molecular biology. University of Queensland St. Lucia QLD 4072 Australia

Author’s Response By Alexander Rosenberg On putting down On the Origin of Species, Thomas Huxley is reputed to have said, ÔHow stupid of me not to have thought of it.’ On putting down (in all senses of the word) Darwinian Reductionism, the present reviewers must have been muttering ÔHow stupid of him to have thought that!’ Doubtless it was due to a fault of my exposition that none of my reviewers was able to detect the broad strategy of Darwinian Reductionism or How to Stop Worrying and Love Molecular Biology (hereafter DR). So, before turning to a consideration of their more important criticisms, it will be worthwhile stating the line of argument that the book attempts (evidently unsuccessfully) to articulate. DR begins by arguing that the ruling orthodoxy in the philosophy of biology – physicalist antireductionism – must be treated as two claims about the world, and not one claim about the world joined to another claim about our knowledge of it. Physicalism is the thesis that the physical facts fix all the facts, including the biological ones, and it is uncontroversial in the philosophy of biology. If antireductionism were merely the thesis that we don’t yet know the full story of how the physical facts do so, it would be uncontroversially true. If antireductionism were the claim that, owing to epistemic limitations on us, or any sapient agent, we will never know this full story, then it would obviously stands in need of a very much stronger epistemological foundation that no one has yet

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provided and no antireductionist has even gestured at the need for. Be that as it may, many an antireductionist has explicitly denied that theirs is a claim about epistemic limitations. Indeed, they make a positive epistemic claim that biologists can, indeed must, understand and explain biological processes adequately and completely without adverting to the physical facts that fix these processes, for the physical facts that fix the biological ones are explanatorily irrelevant to them. These sorts of claims about biological explanation require an antireductionist metaphysics, which identifies biological kinds, and laws distinct from and irreducible to physical kinds and laws. What is the existence of these kinds and laws but the existence of facts that are not fixed by the physical facts? So understood, physicalist antireductionism is, I argue, echoing the expression of an earlier naturalism in philosophy, an Ôuntenable dualism.’ An antireductionism strong enough to be worth arguing for is a metaphysical thesis about natural kinds and laws – abstract existents – that philosophical nominalists and philosophically unsophisticated scientists cannot take seriously. Perhaps for these reasons biological kinds and laws are sometimes mistaken for the mere predicates and sentences that name these kinds and express the scientific hypotheses that are our best guesses as to what these laws are. When this happens the metaphysical thesis is misunderstood as an epistemic one and the untenable dualism of physicalist antireductionism is not noticed. What we may excuse among scientists who are indifferent to the ontological problem of abstract objects and don’t distinguish sentences from propositions, is not acceptable among philosophers, even us philosophers of science. DR sought to resolve this untenable dualism by showing: (1) that biological explanations require improvements in completeness, precision, and adequacy, which can only be provided by enhancing their grounding in physical science; (2) that some biological processes are only so to be explained; and (3) that apparently distinctive biological concepts, categories, kinds and laws can be shown to be physical in character and hence are no barrier to the reduction contemplated in the first two theses. Reductionism, I emphasised, is a methodological strategy demanded by a metaphysical claim – physicalism, and it must be sharply distinguished from another methodological strategy – eliminativism – with which it is often (and sometimes purposely) confused, according to which

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science needs to move from the bottom up in providing us with knowledge of the world and its processes, since it is the facts at the bottom that fix all the other processes. Eliminativism is so called because its exclusively bottom-up strategy requires that we jettison as unacceptable anything that cannot be immediately and completely grounded in physical theory. Reductionism does not endorse this methodology. Rather it is opportunistic, allowing research to proceed top-down, bottom-up, and from the middle in both directions. It encourages the search for scientific knowledge of the world at whatever level of the organization of the physical facts strikes the scientist as worth studying. It only requires that once some understanding is achieved at any level, it can in principle always be grounded, and thereby almost always enhanced, in more fundamental and ultimately physical processes. Opponents of reductionism are eager to assimilate it to eliminativism, for, so assimilated, reductionism would thereby require us to divest ourselves of a great deal of hard-won scientific achievement, an admonition that no scientist will follow. Here are a couple of examples in the reviewer’s remarks of this sort of misrepresentation of what reductionists hold: ‘‘According to Rosenberg... [e]xplanations are only explanatory when they can be framed in terms of the underlying molecular biology of the system’’ (Schweitzer, p. 23, emphasis added); and ‘‘Rosenberg’s view of how biological explanations work leaves most biologists not offering explanations’’ (Love, p. 6). DR argues for Thesis 1 by showing that evolutionary explanations are by and large Ôhow possible explanations’ and are always strengthened to the degree we can convert them into Ôwhy necessary’ explanations, and that doing so almost always requires that we identify the actual causal chain or mereological route from explanans to explanandum – usually a macromolecular one. DR argues for Thesis 2 by an extended example. It attempts to show that there were no explanations at all in developmental biology before the advent of the macromolecular understanding of embryological development as the articulation of a genetic programme. This argument leads to consideration of several theses advanced by philosophers and biologists who argue against reductionism in developmental biology by denying that the gene has any special function in development or even by arguing that there is really no such thing as the gene. DR argues at length for Thesis 3 that apparently distinctive biological concepts, categories, kinds, and

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laws can be shown to be physical in character because it is on the denial of this thesis that philosophers have advanced the only version of antireductionism strong enough to be worth refuting and plausible enough to be worth believing. Once Thesis 3 has been defended, DR turns to the project of attempting to deal with the motives that so often drive opponents of reductionism to accusations that it is not only a false thesis but a morally dangerous one – dehumanizing in its refusal to countenance causes for socially significant human capacities and behaviours above the genetic. This assimilation of macromolecular reductionism to genetic determinism, which lies behind so much of the attack on reductionism outside philosophy, rests on many errors about biology and mistakes about reductionism that the first seven chapters of DR attempt to uncover. In the final two chapters I attempt to deploy reductionism’s successes in molecular biology to refute this genetic determinism that everyone seems to fear, and so draw the motivational force from antireductionism. Thus we might all stop worrying and learn to love molecular biology. The aim of DR – to articulate a version of reductionism sensitive to so much that the philosophy of biology has revealed about the subject of biology, its methods, theories, epistemology and its relations to the other sciences – appears to have been completely invisible to the four reviewers of the book. None have addressed the problem of Ôuntenable dualism’ broached at the outset of the book and which made the rest of it a necessary undertaking. None argued (though all asserted) that physicalist antireductionism is a perfectly tolerable package of two metaphysical claims or a combination of one metaphysical and one epistemic claim. None diagnosed the evidently puerile mistake that led me to write about a problem not even important enough to attract much attention in their reviews. What a lot of them did fix upon, and attack, was a proposition central to the strongest metaphysical argument for antireductionism: the thesis that most biological kinds are functional in the selected-effects sense of function. Before defending this claim it is important that the dialectical situation be clear. Antireductionism needs some biological fact or other which is beyond the explanatory reach of physical science. In the work of Kitcher, Sober, and other antireductionists this fact is alleged to be the role of natural selection in producing and organizing biological phenomena and thus underwriting their correct, adequate, complete biological explanations. These explanations will

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be autonomous from physical science owing to the irreducibility of the process of natural selection to processes catalogued in chemistry or physics. And of course the more pervasive the process of natural selection is in shaping biological facts, the greater will its presence be an obstacle to reduction. Conversely, the more it can be shown that biological kinds are not selected-effects functional kinds, the easier it should be to reductively explain processes that they subsume. Accordingly, it will make a reductionist’s argument far easier if, as several of my reviewers suggest, there is wide scope for non-selected-effects, Ôcausal role’ functional analysis, description, and explanation in biology. The scope for reduction will be further expanded if structural, morphological, and compositional classifications, generalizations, and theories can be seen to play substantial roles in biology. For then the difficulties that natural selection imposes on the reductionist’s argument will be more limited. And of course if the explanation for biological similarities that homology claims provide are themselves based on such purely physical dimensions, then matters will be proportionately that much easier for anyone like me who seeks to vindicate an approach to the biological that gives explanatory scope to the physical sciences. In DR I invoked Dobzhansky’s dictum for two reasons. The first was that (a) the most powerful arguments for antireductionism employ a combination of the Putnam/Garfinkel Ôsquare-peg, round hole’ argument for the complete adequacy of higher level explanations and the irrelevance of lower level ones, with (b) the claim that natural selection is the indispensable higher level explanatory theory everywhere in biology. The second reason I adopted Dobzhansky’s dictum was my belief that by and large a strong thesis of adaptationism is correct: the biological is carved out from the physical by the operation of natural selection, and this explains the pervasiveness of functional description and analysis in the discipline. As such, I could not adopt my critics’ suggestion that the importance of selected-effect functions is greatly exaggerated in biology. If natural selection Ôcarves nature at the joints’, then it stands to reason that other classifications, say, homological ones, will be isomorphic or extensionally equivalent to functional kinds – if homology carves likewise. Since many of the functional individuations are also embodied in Ôfolk biology’ and long antedate the comparative anatomist’s classificatory projects, their epistemic role in the prior individuation of biologically significant traits is inescapable. It is a

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more vexed question whether selected-effects are constitutively as well as epistemically presupposed by all other biological taxonomies. But it is worth noting that the only domain of biology that is selected-effects function-free are those parts of molecular biology where individuation and explanation can proceed from primary structure – i.e. molecular sequence. Thus, in so far as my reviewers minimise the role of selected effects, their reason for continuing to be resolutely antireductionist is more perplexing, as they have deprived themselves of the only attractive metaphysical argument for antireductionism. But of course my critics are not interested in metaphysics. They, or at least some of them, are just interested in what biologists do, not what, by the biologist’s own lights, they ought to be doing. Thus, Love writes: ‘‘Many philosophers of biology take epistemology as the primary domain of analysis, especially because biological reasoning is so heterogeneous, functional ascriptions are diverse, and explanations occur without universal, exceptionless laws (p. 192–196). It is certainly correct that many philosophers of biology are interested only with what biologists do, their actual claims and actual methods, and not with what the biological facts are and how a conception of them might guide inquiry. But, frankly, I fail to see how the considerations that Love adduces provide any support for this preference as opposed to mine, which also attaches importance to the fit, or temporary lack of it, between biologists’ theory and their self-proclaimed view about the way the world is. I too am of course interested in epistemology. But too much of contemporary philosophy of biology’s epistemological exercises are merely uncritical reports of biology’s recent history, without any inclination to draw methodological morals, or undertake philosophy’s normative epistemological role of assessing the justification of the biologists’ claims. Quoting a molecular biologists’ assertion that ‘‘multiplex protein kinase inhibitors may be an emergent property that cannot be understood fully considering only the sum of individual inhibitor-kinase interactions’’ (Love, p. 185–188, emphasis added) is no argument that protein kinase inhibition is an emergent property. Still less is it an account of whether emergence is an epistemically coherent notion. Nor is it an argument against reductionism to quote from a couple, or indeed a legion, of physicists who write things like: ‘‘the central task of theoretical physics in our time is no longer to write down the ultimate equations but rather to catalogue and understand emergent behaviour in its many

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guises, including potentially life itself. We call this physics of the next century the study of complex adaptive matter’’ (Laughlin and Pines, 2000, quoted in Stotz, p. 484–488). I can’t wait to see what the physics textbooks will look like a hundred years hence. Neither, I suspect, can Steven Weinberg. Worse than merely passages from biologists’ papers that disagree with me is to invoke biological ideas as if they were unknown to me, and ignored in DR, when in fact I had almost fetishised them. Thus Schweitzer Ôintroduces’ the ÔFrench Flag model’ of pattern formation in gene expression as a Ôcounterexample’ to macromolecular reductionism. To begin with, merely asserting that it offers the basis for an argument against reductionism doesn’t constitute an argument against the latter. But additionally, Schweitzer omits to mention the fact that it was my work that introduced Wolpert’s models to philosophical discussion more than a decade ago, and that DR (and not his review of it) contains the first thorough account of the French flag model (along with three other equally important Wolpertian models of genetically controlled pattern recognition), and that there is a sustained argument in the book to show how the model contributes to explanations in a reductionist molecular biology. By contrast, Schweitzer merely asserts that the French flag model ‘‘does provide the form of explanation characteristic of mathematical modeling explanations’’. Is it a quibble to complain that the French flag does not provide the form, but only an instance of mathematical models in pattern formation (for the other instances see DR, Chap. 3)? The really hard epistemological task for philosophers of biology, who like Schweitzer apparently follow Sober in holding that Ônoncausal’ (Schweitzer’s term) mathematical models explain contingent phenomena, is to give an account of how a priori truths can do this, and to show what is wrong with DR’s argument that they can’t. Love and Brigandt separately attribute my arguments for reductionism to Jaegwon Kim and then write them off without even a whisper as to what might be the matter with them. It is certainly true that one page in DR expounds the powerful dilemma of overdetermination vs. competition that Kim lays before antireductionism in the philosophy of mind; and, that page argues, it also vexes biological antireductionism. There is also a long footnote in which Kim’s distinction between higher Ôorder’ vs. higher Ôlevel’ predicates is employed to distinguish reductionism from eliminativism. But philosophers with longer memories than my present reviewers may

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remember that I introduced the notion of supevenience to biology in 1978 (‘‘The Supervenience of Biological Concepts’’ in Philosophy of Science), having stolen it, not from Kim, but from Donald Davidson’s ‘‘Concepts of Supervenience’’, 6 years before Kim’s study. Moreover, my previous work, Instrumental Biology or the Disunity of Science (1994) reflected the belief that, even with supervenience, the only way physcialists could tolerate a metaphysically autonomous biology was to treat it as a useful instrument, a heuristic device, instead of giving biological theory a realist interpretation. As DR makes clear, the step from this instrumental view to a realist reduction of Ôthe biological’, was not due to Kim’s arguments (powerful though I think they are). It is rather owing to a new appreciation of the long insistence, by philosophers like Sober and Beatty, that we take seriously the fact that biology is a historical and terrestrial science, unlike chemistry and physics. As to what might be wrong with Kim’s arguments, all we have is a reference in Brigandt to Marras (1997). In this and other interesting and learned papers, Asonio Marras has argued that Kim’s overdetermination vs. competition arguments against irreducible theories in psychology hinge on a metaphysical assumption about events and property identities that might be challenged: roughly that an event has only one constitutive property, a view of Kim’s that goes back to 1973. I invite those who reject my reductionist conclusions because they reject Kim’s antireductionist arguments to join Marras in the heavy metaphysical lifting. A careful attention to the details of the history of biology or the animadversions of distinguished biologists and less well-known physicists is no substitute for this obligatory philosophical undertaking. On leaving the British Academy debate of 1860 between Huxley and Wilberforce, a lady was heard to say: ‘‘Descended from apes? Let us hope it is not true, but if it is true, let us hope it does not become widely known’’. My reviewer’s reactions seem to have been similar to hers: ‘‘Reducible to molecular biology? Let us hope it is not true, but if it is true let us hope it does not become widely known’’. Center for Philosophy of Biology Duke University Durham, NC, 27708 USA

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REFERENCES Anderson, P. ‘‘More is Different’’, Science 177 (1972), pp. 393–396. Atlan, H. ‘‘Intentional Self-organization. Emergence and Reduction: Towards a Physical Theory of Intentionality’’, Thesis Eleven 52 (1998), pp. 5–34. Davidson, D. ‘‘Mental events’’, in L. Foster and J. W. Swanson (eds.), Experience and Theory (London: Duckworth, 1970), pp. 207–227. Dyke, C. The Evolutionary Dynamics of Complex Systems: A Study in Biosocial Complexity (Oxford: Oxford University Press, 1988). Griffiths, P. E. ‘‘Function, Homology, and Character Individuation’’, Philosophy of Science 73 (2006), pp. 1–25. Kim, J. ‘‘Causation, Nomic Subsumption, and the Concept of Event’’, Journal of Philosophy 70 (1973), pp. 217–236. Kim, J. ‘‘Concepts of Supervenience’’, Philosophy and Phenomenological Research 65 (1984), pp. 153–176. Kim, J. Mind in a Physical World (Cambridge, MA: MIT Press, 1998). Kitcher, P. ‘‘1953 and all that’’, Philosophical Review 93 (1984), pp. 335–373. Kung, C., D. M. Kenski, S. H. Dickerson, R. W. Howson, L. F. Kuyper, H. D. Madhani and K. M. Shokat. ‘‘Chemical Genomic Profiling to Identify Intracellular Targets of a Multiplex Kinase Inhibitor’’, Proceedings of the National Academy of Sciences USA, 102 (2005), pp. 3587–3592. Laubichler, M. and G. P. Wagner. ‘‘How Molecular is Molecular Developmental Biology? A Reply to Alex Rosenberg’s Reductionism Redux: Computing the Embryo’’, Biology and Philosophy 16 (2001), pp. 53–68. Laughlin, R. B. and D. Pines. ‘‘The Theory of Everything’’, PNAS 97 (2000), pp. 28–30. Marras, A. ‘‘Kim’s Supervenience Argument and Nonreductive Physicalism’’, Erkenntnis 66 (2007), pp. 305–327. Robert, J. S. Embryology, Epigenesis, and Evolution: Taking Development Seriously (Cambridge: Cambridge University Press, 2004). Rosenberg, A. ‘‘The Supervenience of Biological Concepts’’, Philosophy of Science 45 (1978), pp. 368–386. Rosenberg, A. Instrumental Biology or the Disunity of Science (Chicago: University of Chicago Press, 1994). Wolpert, L. ‘‘Positional Information and the Spatial Pattern of Cellular Differentiation’’, Journal of Theoretical Biology 25 (1969), pp. 1–47. Wouters, A. ‘‘Four Notions of Biological Function’’, Studies in the History and Philosophy of Biological and Biomedical Sciences 34 (2003), pp. 633–668.