organisms as natural purposes

772 D.M. Walsh / Stud. Hist. Phil. Biol. & Biomed. Sci. 37 (2006) 771–791

0. Introduction

Kant’s third critique, in particular the ‘Analytic of the teleological power of judgment’,famously introduces a tension between our conception organisms and our understandingof the natural world as governed by unified mechanical law. Organisms, Kant tells us, are‘natural purposes’ and as such are subject to teleological explanation. We account for thenatures and capacities of their constituent parts and processes by appeal to those purposesof the organism that they fulfill. At the same time, organisms are natural entities subject tomechanical laws. Mechanical laws give us complete scientific explanations of all the phe-nomena of the world and concedes no irreducible explanatory role to goals or purposes.The tension gives rise to Kant’s famous ‘Antinomy of the teleological power of judg-ment’—roughly, that organisms both must be and cannot be judged to be wholly the prod-ucts of mechanical processes. The tension Kant articulates regarding organisms as naturalpurposes is as germane today as it ever was. Organisms really do have the astonishingproperties by which Kant identifies them as natural purposes. Moreover, scientific expla-nation, today just as in Kant’s time, is cast in the mechanical mode. The tension ought tosurvive in contemporary biology, perhaps not as an antinomy, but nevertheless as a gen-uine challenge to the adequacy of our conception of the biological world.

My objective here is to draw to the attention of contemporary biology (and philosophyof biology) the relevance of Kant’s conception of organisms as natural purposes. Kant’sproblematic may have been largely forgotten by contemporary biology, but it has strongresonances with issues that are only now beginning to attract biologists’ attentions—self-organization, the ‘emergent’ properties of organisms, their adaptability, their capacity toregulate their component parts and processes. I do not attempt to persuade biologists toadopt the critical philosophy. Indeed there is a question whether it is consistent with mod-ern day naturalism.1 I do claim that Kant’s ‘Critique of the teleological power of judg-ment’ offers a particularly vivid articulation of the challenge raised to any theoreticalbiology by the nature of organisms, a challenge encapsulated in the ‘Antinomy of the tel-eological power of judgment’. I contend that contemporary biology has (inadvertently)embroiled itself in an analogous antinomy, one of teleological explanation. Recentresearch on organismal development suggests that biological phenomena cannot be whollyexplained unless we consider organisms as both mechanical and purposive entities. I wouldlike to suggest, however, that biologists have the conceptual resources, without recourse tothe critical philosophy, to reconcile the mechanical nature of biological processes with thefact that the conception of organisms as natural purposes has an ineliminable explanatoryrole to play.

1. The Antinomy of the teleological power of judgment

An organism, according to Kant, constitutes a functional unity whose parts and pro-cesses contribute to its development, sustenance and reproduction, indeed whose parts seemto exist in the form they do precisely because they fulfil these roles. Organisms are distin-guished by three diagnostic features: (i) self-organization: the growth and interaction of partsis evidently caused by the organizational structure of the organism as a whole and is directed

1 See John Zammito’s discussion (2006).

D.M. Walsh / Stud. Hist. Phil. Biol. & Biomed. Sci. 37 (2006) 771–791 773

toward the attainment of a viable adult form; (ii) self-reproduction: each organism is capableof securing the existence of other such organisms similar in structure and function; (iii) andself-nourishment (McLaughlin, 2000). During its ontogeny, Kant tells us, an organism

2 All(2000)

first processes the matter that it adds to itself into a specifically-distinct quality,which the mechanism of nature outside of it cannot provide, and develops itself fur-ther by means of a material which, in its composition, is its own product. (Kant,2000, p. 371)2

The constituent parts and processes of a living thing are related to the organism as awhole by a kind of ‘reciprocal causation’.

The essential definition Kant offered of : : : organic form : : : was that of the recipro-cal interrelation of parts as means to ends, and consequently, of the priority of thewhole over the parts in the constitution of the entity. (Zammito, 1991, p. 218)

The definition of an organic body is that it is a body, every part of which is there forthe sake of the other (reciprocally as an end, and at the same time, means). : : : Anorganic (articulated) body is one in which each part, with its moving force, necessar-ily relates to the whole (to each part in its composition). (Opus postumum, quoted inGuyer, 2005, p. 104)

I would provisionally say that a thing exists as a natural end if it is cause and effect ofitself. (Kant, 2000, p. 371)

The self-motivating, self-forming capacities of organisms, the reciprocal dependence ofpart on whole and whole on parts, the supple goal-directed, compensatory capacities char-acteristic of organismal development, these, Kant tells us are all essential to our concept ofan organism to think of an organism qua organism is to think of it as a purposive entity.Moreover, an organism’s purposes are immanent in it; they are not extrinsic purposes, likethose of artifacts. Hence, organisms are natural purposes.

Organized beings are thus the only ones in nature which : : : must nevertheless bethought of as possible only as ends, and which thus first provide the objective realityfor the concept of an end that is not a practical end but an end of nature, and therebyprovide natural science with the basis for a teleology : : : (Ibid., pp. 375–376)

Kant’s concern about this conception of organisms is that while it is obligatory—wecannot take ourselves to be studying organisms qua organisms unless we consider themas natural purposes—it seems to put the defining features of organisms beyond the ambitof scientific explanation.

For Kant all genuine explanation is mechanical. To explain mechanically the propertiesof a naturally occurring entity, one cites the properties of its parts that determine thewhole. His conception of scientific explanation appears to conform to what C. D. Broadhas called ‘Pure Mechanism’, according to which, there is:

: : : (a) a single kind of stuff, : : : (b) a single fundamental kind of change, : : : (c) a sin-gle elementary causal law, : : : and (d) a single and simple principle of composition,

citations from the Critique of judgement are taken from the translation by P. Guyer & E. Matthews, Kant. References give the pages in the Akademie edition.


according to which the behaviour of any aggregate of particles, or the influence ofany one aggregate on any other, follows in a uniform way from the mutual influencesof the constituent particles taken by pairs. (Broad, 1925, p. 45)

On the one hand, the functional unity of an organism can be explained in the mechan-ical mode; an organism is a causal consequence of the capacities of its parts. But, on theother hand, the parts themselves seem to be the effects of the structural and functionalunity of the organism. Consequently, we cannot account for the nature of organisms bymere mechanical explanation alone:

: : : it is quite certain that we can never adequately come to know the organizedbeings and their internal possibility in accordance with merely mechanical principlesof nature, let alone explain them; and indeed this is so certain that we can boldly saythat it would be absurd for humans even to make such an attempt or to hope thatthere may yet arise a Newton who could make comprehensible even the generationof the a blade of grass according to the natural laws that no intention has ordered;rather, we must absolutely deny this insight to human beings. (Kant, 2000, p. 400)

This tension between the requirement to conceive of organisms as natural phenomena,explicable in the mechanical mode, and the requirement to think of them as purposive enti-ties whose natures defy mechanical explanation, is articulated in ‘The Antinomy of the tel-eological power of judgment’:

The first maxim of the power of judgment is the thesis: All generation of material things

and their forms must be judged as possible in accordance with merely mechanical laws.

The second maxim is the antithesis: Some products of material nature cannot bejudged as possible according to merely mechanical laws (judging them requires an

entirely different law of causality, namely that of final causes). (Ibid., p. 387).

2. Sub-organismal biology

Contemporary biology has responded to the problem posed by the natural purposive-ness of organisms by the simple expedient of ignoring it. There is a general thought now-adays that biology has no need of teleological thinking. There are a couple of reasons. Thefirst is that the project of contemporary comparative biology is substantially different fromthat of Kant’s time. The second is that the range of explanatory resources available tobiologists has expanded significantly. These reasons both derive from the influence ofDarwin.

Darwin’s most significant achievement was the understanding that biology’s two greatexplananda—the fit of organisms to their conditions of existence and the diversity oforganic form—are both the consequence of a single mechanical process, natural selection.That process is not to be found occurring within organisms, but within populations. Selec-tion causes populations to change their constitution over time, which in turn realizes theincrease in both the adaptedness and diversity of organisms. Darwin’s theory of selectionchanges the explanatory project of biology from that of explaining the natures of organ-isms by appeal to some principle immanent in organisms themselves to one of explainingthe nature of organisms by appeal to a causal process occurring within populations. The


problematic features of organisms that impelled Kant to identify them as ‘natural pur-poses’—the exquisite integration of organisms, their adaptive plasticity, their self-organiz-ing capacities—are simple causal consequences of change in population structure wroughtby natural selection. This line of thought led Michael Ghiselin to proclaim Darwin’s tri-umph over teleology: ‘he developed a new way of thinking that allows us to dispense alto-gether with that metaphysical delusion’ (Ghiselin, 1993, p. 483) and occasioned ErnstMayr’s insistence that ‘Darwin had solved Kant’s great puzzle’ (Mayr, 1988, p. 58).

Darwin’s theory is explicitly structured according to the mechanistic model (Cornell,1986; Hull, 2003). Darwin took Herschel’s Preliminary discourse (1987) as the canonicalsource on the proper conduct of scientific enquiry. Herschel, in turn, held Newton’smechanics and Lyell’s geology as paradigms of the scientific method. Herschel was partic-ularly impressed with (what he took to be) the insistence by Newton and Lyell on vera

causae explanations. A vera causa explanation, according to Herschel, invokes only thoseprocesses as causes that can be directly observed. Moreover, they must be observable inde-pendently of the effect to be explained. The degree of effect of a true cause must vary with thedegree of the cause itself. Darwin prided himself on the conformance of his theory of naturalselection to Herschel’s methodological precepts. Variation and struggle for existence aredirectly observable in a population, quite independently of their influence on populationchange. They are sufficient to cause population change. The rate of change in a populationis proportional to the degree of variation in a population and the severity of the struggle.Thus, in Darwin’s ‘entangled bank’ all its various organisms, ‘: : : so different from eachother, and so dependent on each other in so complex a manner, have all been producedby laws acting around us’ (Darwin, 1972, p. 462). Darwin’s theory is a strictly causal,mechanical one. Natural selection allows us to assert the thesis of the antinomy and pre-scind from the antithesis.

It does so only if those features of organisms that so impressed Kant have no indispensableexplanatory role to play in biology. As John Cornell expresses it: ‘To reject Kant’s argumentwe would have to ‘‘explain away’’ the organism’ (Cornell, 1986, p. 408). This is precisely whatmuch of contemporary biology has undertaken to do. Current evolutionary biology is largelydirected toward the study of how supra-organismal entities—populations—change as aresult of the causal powers of sub-organismal entities—replicators. The most thoroughand provocative exponent of the sub-organismal nature of biology is Richard Dawkins:

Evolution is the external and visible manifestation of the survival of alternative repli-cators : : : Genes are replicators; organisms : : : are best not regarded as replicators;they are vehicles in which replicators travel about. Replicator selection is the processby which some replicators survive at the expense of others. Vehicle selection is theprocess by which some vehicles are more successful than others in ensuring the sur-vival of their replicators. (Dawkins, 1982, p. 82)

Organisms are mere middlemen in evolution, a sort of interface between the organism-building activities of replicators and the selecting role of the environment. Their salientcharacteristics, and indeed their very existence, are to be explained by appeal to the causalcapacities of replicators.

The integrated multi-cellular organism is a phenomenon which has emerged as aresult of natural selection on primitively independent selfish replicators. It has paidreplicators to behave gregariously. (Ibid., p. 264)


There are good reasons why replicators, rather than organisms, enjoy this privilegedposition. They play a distinctive unifying role in our account of evolution.

Evolution comprises three constituent processes: inheritance of traits, ontogeny oforganisms and change within populations. Replicator biology offers us an elegant accountof how these three processes taken together lead to the fit and diversity of organisms. (i)Inheritance: Evolution requires variation in heritable traits. Replicators, we are told, arethe units of inheritance. They are the only entities that are both copied within parentsand transmitted from parent to offspring in reproduction. (ii) Ontogeny: Development,according to the sub-organismal view, is simply the implementation of a developmentalprogram, the expression of phenotypic information encoded, or programmed, in the repli-cators (e.g. Maynard Smith, 2000). Organisms may be what are selected, but replicatorsbuild organisms. (iii) Population Change: Evolution by natural selection occurs when pop-ulations change their structure as a consequence of the differential survival and reproduc-tion of organism. But not just any old change in population structure counts asevolutionary change, only changes in the relative frequency of replicators. Indeed naturalselection is usually defined as changes in replicator frequencies that result from the differ-ential contribution of replicators to survival and reproduction (Bell, 2000). Replicators,then, are the only entities that take part in all the constituent processes of evolution—inheritance, ontogeny and population change—and whose activities unite these processesinto the process of evolution.

Replicator biology also furnishes a ready explanation of the adaptiveness of evolution.The adaptedness of organisms is the result of the accretion of adaptive (that is, selected)replicators. Fitness-promoting replicators are assembled by selection into integrated suitesof traits (Ayala, 1970). The appearance of biological design is the consequence of an iter-ated process of the introduction of variant replicators, their recombination and selection.

Here again, the influences of Pure Mechanism run deep. Sub-organismal biology’s pro-prietary processes and explanations are mechanical, one and all. The properties of organ-isms are explained by appeal to the capacities of their parts. The parts of organism(replicators) have an explanatory and ontological primacy over the whole.

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Replicators exist. That is fundamental. Phenotypic manifestations of them : : : maybe expected to function as tools to keep replicators existing. Organisms are huge andcomplex assemblages of such tools : : : (Dawkins 1986, p. 263).

The success of sub-organismal biology depends upon replicators having the sort ofeffects that in Newton’s words should ‘esteem them in the highest’ (Newton, 1963, p.398) There are basically three: (i) Constancy of quality: The role of replicators requires thateach replicator has a reasonably constant, or predictable, phenotypic effect across con-texts. Replicators ground the inheritance of phenotypes only if their effects are reliablyconstant across different organisms, i.e. across associations with different replicators; (ii)Constancy of quantity: The fitness consequences of a trait must be reasonably constantacross contexts. Were this not the case evolution by natural selection could not be cumu-lative.3 (iii) Independence: The constancy of phenotypic effect across contexts requires thatreplicators exert their effects on phenotype more or less independently of one another.4

Kauffman (1995) on the conditions for populations of organisms to adapt on smooth, multiply-peakedapes.her (1930) makes the independence assumption explicitly.


The effects of individual replicators on an organism’s phenotype are thus decomposable.The degree of similarity of organism is a function of the degree of similarity in their repli-cators. Given the enormous number of replicators in each organism, it more or less followsfrom (i)–(iii) that the effect of each replicator on fitness is on average small. So, the adverseeffect of new mutant replicators will generally be minimal. Taken together these conditionstell us that organisms are, in Broad’s terminology, ‘resultant’ effects of the capacities oftheir replicators. Replicators are vera causae of organisms (at least in Herschel’s sense).5

Two further conditions must be met by replicators if populations of them are toundergo adaptive evolution. Lewontin has dubbed these ‘continuity’ and ‘quasi-

independence’:

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By continuity we mean that very small changes in character result in very smallchanges in : : : reproductive fitness. Neighborhoods in character space map intoneighborhoods in fitness space. : : : By quasi-independence we mean that there exista large variety of paths by which a given character may change, and : : :, a non-neg-lible proportion of these paths will not result in countervailing effects of sufficientmagnitude to overcome the increase in fitness from the adaptation. (Lewontin,1978, p. 247)

Populations of replicators certainly meet these conditions. Because replicators provideus with mechanical explanation for both the natures of organisms and the process of evo-lution, there should be no residual temptation to teleology (Cummins, 2002).

Sub-organismal biology has its detractors. Most attempts to dislodge it from its privi-leged position in biology involve pointing out the degree to which the above assumptionsare violated (for example, epistasis) or that the adaptation promoting power of replicatorselection is curtailed (Amundson, 2001; Gould & Lewontin, 1979). Another strategy is toargue that replicator biology’s claim to comprehensiveness is ill deserved. Replicators arenot the only units of inheritance. Acquired morphological traits, behaviours, culturallytransmitted capacities can all be inherited and selected without replication (Boyd & Rich-ardson, 2004; Jablonka & Lamb, 2005; Mameli, 2004). Nor are sub-organismal replicatorsthe sole determinants of phenotype; the control of development is distributed throughoutthe organism/environment system (Griffiths & Gray, 2001; Oyama, 1985; Oyama, Grif-fiths, & Gray, 2001; Moss, 2002). These are important checks against what appears to havebeen an almost uncritical embrace of sub-organismal biology in the late 20th century. Nev-ertheless, sub-organismal replicators do play an important causal role in inheritance, evenif they are not the only things that do. They often correlate strongly with both fitness andphenotype. They are at least important difference makers in the development of a widerange of phenotypes. So, wholly comprehensive or not, replicators have a central explan-atory role to play in contemporary biology.

The pressing question, one that contemporary biology has largely declined to broach, is‘what conditions secure the capacities of replicators to act in this way’? A tempting answeris that replicators possess these remarkable capacities by their natures. A tradition inau-gurated by Max Delbruck maintains that the startling stability of DNA and its capacityto make high-fidelity copies are inherent in the structure of the genetic material; theseare what make life possible. A starkly different answer, one that seems just recently to

er McLaughlin has pointed out to me how far short replicators fall as genuine Newtonian vera causae.


be gathering some empirical support, is that replicators have their remarkable capacitiesbecause of the capacities of the organisms of which they are a part.

3. Organismal biology

Against the tide of sub-organismal mechanism of the 20th century biology, a few biol-ogists, for example Waddington (1957) and Schmalhausen (1949), continued to stress thesignificance of features of entire organisms for our understanding of biological processes(Sarkar & Gilbert, 2000). The features of organisms as natural purposes were consideredof particular significance: ‘ you cannot even think of an organism : : : without taking intoaccount what variously and rather loosely is called adaptiveness, purposiveness, goal seek-ing and the like’ (Von Bertalanffy, 1969, p. 45). Organicism is once again getting a hearing,at least among some biologists, due to the recent resurgence of interest in organismaldevelopment.

The most explanatorily significant feature of organisms is their plasticity. Plasticity,according to Mary Jane West-Eberhard (2005a, 2003) is ‘a universal principle of all livingthings’. It consists in ‘: : : the ability of an organism to react to an internal or external envi-ronmental input with a change in form, state, movement, or rate of activity’ (ibid., p. 33).West-Eberhard’s account of plasticity is strongly reminiscent of Kant’s description of thedistinctive features of organisms. Plasticity consists in the adaptive capacity of organismsto regulate their developmental sub-systems in order to build and maintain a stable, work-ing organism.

The plasticity of organisms is pivotal in adaptive evolution. Plasticity engenders robust-ness, the capacity to maintain viability by making compensatory, adaptive changes to phe-notype. This in turn endows organisms with a broad ‘phenotypic repertoire’; an organismis capable of producing any of a wide range of stable phenotypic outcomes. According toWest-Eberhard plasticity and the phenotypic repertoire of organisms are the principalcauses of adaptive evolution. On this view, adaptive evolution proceeds in two stages—phenotypic accommodation followed by genetic accommodation—both of which dependupon the plasticity of organisms. West-Eberhard defines phenotypic accommodation as‘the immediate adaptive adjustment of phenotype to the production of a novel trait or traitcombination’ (ibid., p. 147). She defines genetic accommodation as ‘adaptive evolutionthat involves gene-frequency change’ (West-Eberhard, 2005b, p. 6544).

The process, as envisaged by West-Eberhard, goes as follows. A mutation or environ-mental change, or change in development produces a new phenotype through phenotypicaccommodation. The organism responds to the new circumstances by the production of anovel phenotype. Given the phenotypic repertoire of organisms, there is latent genetic anddevelopmental variation in a population for the production of any particular phenotype.The introduction of a novel phenotype exposes this variation. Some gene combinations ordevelopmental structures may underwrite more robust, reliable or efficient ways of pro-ducing a novel adaptive phenotype. The effect is that the threshold for the developmentof the trait is lowered (Waddington, 1957). Recombination and selection of these develop-mental and genetic variants occurs. The consequence is evolution—change in geneticstructure of the population—as a consequence of the developmental plasticity of organisms.

There are two important features that distinguish this conception adaptive evolutionfrom the version offered by replicator biology. The first is that it is a property of organ-

isms—their plasticity—that explains why evolution is adaptive. The second is that novel


adaptive phenotypes are not caused by changes in replicator frequency, as the sub-organ-ismal model has it. On the contrary, adaptive novelties, brought about by plasticity oforganisms, cause changes replicator frequencies.

Without developmental plasticity, the bare genes and the impositions of the environ-ment would have no effect and no importance for evolution. (West-Eberhard, 2005b,p. 6544)

3.1. Modularity of development

The key to the adaptive plasticity of organisms lies in the architecture of development:development is modular. Developmental modules have two defining features, their inter-nal structure and their mutual dissociation.

The integrated internal structure of modules makes them robust; they are capable ofproducing their characteristic output despite the vagaries of their contexts, and despitechanges to their structure (von Dassow & Munro, 1999). Gene modules offer a vivid exam-ple. To the extent that genes exert control over phenotype it is not through individualgenes working in isolation; genetic control of development is exerted through suites (mod-ules) of genes working in concert. Genetic modules are characterised by complex regula-tory feedback relations among the module components. One significant consequence isthat gene modules exhibit a significant degree of robustness. The function of a modulecan withstand the loss or malfunction of one or more of its component genes. Conse-quently, each gene module produces its characteristic output across an enormous rangeof conditions (Gibson, 2002; von Dassow et al., 2000). This buffering also turns gene net-works into evolutionary capacitors (Bergman & Siegal, 2002). Gene networks are capableof producing novel stable products in novel circumstances (Greenspan, 2002).

The dissociation of modules—the nature of the regulatory relations among them—exerts another kind of phenotypic effect. The repertoire of a developmental module, therange of its capacities taken in isolation, is considerably greater than the range of its real-ized effects. Typically each module is capable of producing any number of a large array ofstable outputs (Von Dassow et al., 2000). Which of its capacities is manifested on a par-ticular occasion is determined by the context in which the module finds itself. Modules arearranged in interacting hierarchies. Typically, each module directly influences and is influ-enced by other modules (but not many).

The plasticity of development not only permits the adaptability of organisms, it alsosecures continuity, quasi-independence and high fidelity of replication, those conditionsnecessary for replicators to act as they are required to do by the precepts of our mecha-nistic replicator biology. Continuity is caused by the buffering (or ‘canalization’) broughtabout by the modular structure of development causes continuity. It guarantees that agene, or gene network, will have similar phenotypic effects across contexts, its broad phe-notypic repertoire notwithstanding. The robustness of development produces phenotypesthat are remarkably constant despite the enormous amount of underlying genetic variationwithin the population, and the unpredictability of environments. Furthermore, ontoge-netic buffering enables organisms to consolidate the developmental roles of genes; theactions of genes become ‘routinised’, locked into the production of particular phenotypes(Newman & Muller, 2001). Genes (replicators) may exert phenotypic control during devel-opment and ensure the reliable inheritance of phenotypes, but only because the entire


organism exerts regulative control over the activities of genes. As a consequence of thebuffering of development, genetic differences between individuals are largely dampedout. Each replicator, then, has a minor effect on overall organismal fitness.

The modular structure of development also promotes the quasi-independence of replica-tors. Those genes with discernible phenotypic effects will tend to be strongly dissociatedfrom the effects of others because of the modularity of development (West-Eberhard,2005b). Modularity quarantines one part of the phenotype against the deleterious effectsof changes to their parts. ‘Phenotypic accommodation reduces the amount of functionaldisruption occasioned by developmental novelty’ (West-Eberhard, 2003, p. 147). In secur-ing the conditions necessary for the stability of organisms, the plasticity of development,also puts into place the requisite conditions for replicators, genes, to serve as units ofinheritance, phenotypic control and as units whose change in relative frequencies is a markof adaptive evolution. The marvellous capacities of genes may be not so much a pre-req-uisite for the evolution of organisms as a consequence of the evolution of organisms.

The regulation of gene action by organisms seems also to be crucial in ensuring the highfidelity of replication. Gene replication is highly fallible, but replication errors are activelyrepaired by the regulative processes of the cell (Fox Keller, 2000, p. 32). Robert Hayneswrites:

The stability of genes now is seen to be more a matter of biochemical dynamics, thanof molecular ‘statics’ of DNA structure. The genetic machinery of the cell providethe most striking example known of a highly reliable, dynamic system built from vul-nerable parts. (Haynes, 1988, p. 577)

Wagner (2005) claims that the robustness of DNA is a highly evolved adaptation of organ-isms. Newman and Mueller surmise that ‘ : : : the correlation of an organisms form with itsgenotype, rather than being a defining condition of morphological evolution, is a highly

derived property’ (Newman & Muller, 2001, p. 576).

3.2. Organismal and sub-organismal biology

The organism-centred conception of evolutionary biology gives us a radically differentperspective on the processes of development, inheritance and adaptive evolution from thatafforded by sub-organismal biology. According to organism-centred biology it is an irre-ducible property of organisms as wholes that explains the processes of development, inher-itance and adaptive evolution. This is not to insist that replicators do not play a role. Genesreally are (among) the units of inheritance. Replicators (genes) really do exert phenotypiccontrol (along with myriad other developmental resources). Evolution does consist, inter

alia, in the change in gene frequencies in a population. On the organism-centred view,the capacities of organisms, by which Kant identifies them as natural purposes—theirself-organization, self-regulating, goal-directed capacities—constitute the ground for thepossibility of sub-organismal, replicator biology. Replicator biology articulates (some of)the mechanisms by which organisms achieve their capacities. We should see organismaland sub-organismal biology as, in some sense, complementary.

So the causal capacities of sub-organismal units and the capacities of organisms as nat-ural purposes have ineliminable, mutually dependent explanatory roles to play even incontemporary biology. Developmental biology explains the purposiveness of organisms


by appeal to the causal capacities of sub-organismal parts and processes, genes, geneticand developmental modules. This is a strictly mechanical form of explanation. But we can-not explain the capacities of sub-organismal components without appeal to the ways inwhich organisms construed as natural purposes control and regulate them. This is a decid-edly unmechanical, teleological form of explanation.

We have something very like Kant’s ‘Antinomy of the teleological power of judgment’,recast in explanatory terms. We might call it the ‘Antinomy of teleological explanation’:

Thesis: All biological phenomena must be explainable in accordance with merely

mechanical laws.

Antithesis: Some biological phenomena cannot be explained according to merely

mechanical laws only (explaining them requires the teleology of natural purposes).

This is no cause for rejoicing; an antinomy is a sign of something gone wrong. I believe,though, that we can consistently hold both the thesis and antithesis. But some work needsto be done. The thesis and antithesis look like formal contradictions, so they cannot beconsistent, unless there is some equivocation in their respective use of the terms. I thinkthere is an equivocation on the notion of explaining biological phenomena: biological phe-nomena can be explained severally or collectively. Mechanism, or some contemporary var-iant, may be able to explain of each organism, how the causal powers of its constituentparts combine to produce the organism in question. But mechanism alone may fall wellshort of explaining why the kinds of organisms that actually exist do so, or why organis-mal structure is so regular. Natural purposes, I shall argue, explain biological regularities.I take this challenge up in Section 5. But first we need to set aside the Kantian convictionthat natural purpose is inimical to mechanical law.

4. Natural purpose

Kant’s strategy for resolving the ‘Antinomy of the teleological power of judgment’ isprobably unavailable to the modern day naturalist wishing to resolve the revised antinomyof explanation (Zammito, 2006). Available or not, it is not clear that Kant’s approachwould be particularly palatable to the modern day naturalist, for a couple of reasons.The first is Kant’s conviction that purposiveness cannot be demonstrated to be an objec-tive feature of the world. Nevertheless, Kant insists, we must treat teleology and mecha-nism alike as regulative principles, guiding discursive thought (Guyer, 2005;McLaughlin, 1990). The second is Kant’s insistence that teleology does not figure in gen-uine explanation: all explanation is mechanistic. A contemporary naturalist committed tothe revised antinomy should first attempt to demonstrate that the phenomenon of organ-isms as natural purposes is an objective, natural phenomenon, consistent with the rule ofmechanical law. The naturalist should then proceed to show, if possible, that natural pur-pose has the same explanatory credentials, as does mechanism. This section and the nextattempt to demonstrate these things in turn.

One of Kant’s reasons for denying that teleology is an objective feature of the naturalworld is the inconsistency he perceives between the purposiveness of organisms and thenature of matter. A mechanical explanation, according to Kant, demonstrates that thephenomenon to be explained is wholly a consequence of the nature of matter. But organ-isms are self-organizing and self-building, and matter, by its nature, is inert.

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However, the possibility of a living matter (the concept of which contains a contra-diction, because lifelessness, inertia, constitutes its essential characteristic), cannoteven be conceived : : : (Kant, 2000, p. 394)

The choice of inertia as the constitutive property of matter, of course, is no accident.Kant is affirming Newton’s first law. Indeed, Kant reinterprets Newton’s law of inertiaas one that holds that all changes in matter have extraneous (external) causes (Watkins,2001). If Newton’s first law articulates the nature of matter, then matter could not beself-moving, self-organizing or self-building.

Kant’s argument has strong resonances with a conundrum raised by Erwin Schrodinger(1944) in his classic essay What is life?. Living things, according to Schrodinger, embody aparadox. They appear not to be consistent with the most basic principle of physics, and yetthey must be. Whereas for Kant the fundamental principles of physics were embodied inNewton’s laws, for Schrodinger they are enshrined in thermodynamics. The materialworld inexorably moves toward a state of maximum entropy—disorder. The distinctivefeature of organisms, however, is that they spontaneously build order and actively main-tain it. In metabolism they convert unstructured matter into highly structured, organicmaterials. In the process, they concentrate and store energy. Organisms are radically neg-entropic.6 Self-organizing matter is as problematic for Schrodinger as it is for Kant.

Although the paradoxes have similar forms, Schrodinger’s resolution is starkly differentfrom Kant’s. Schrodinger points out that organisms do not, in fact, violate the second lawof thermodynamics. The second law applies to closed systems in which energy is neitheradded nor lost. The tendency to increase in entropy is a global property of such systems.So long as closed systems as a whole increase in entropy, open sub-systems may consistentlydecrease in theirs. How do systems decrease entropy locally with systematic regularity? Insystems far from thermodynamic equilibrium, where significant energy gradients occur, itmay well be that the most efficient way of dissipating energy is to build ordered structures todo the job. The marvellous order of convective (Benard) cells provide an illustrative exam-ple. Heat applied to the underside of a pan containing a thin layer of oil will set up a dense,stable arrangement of hexagonal convective cells (Benard cells) of uniform size. Thisorganization is robust; if perturbed it will return to its stable configuration. The explanationof this phenomenon is that this configuration is the most effective means for dissipatingenergy from the bottom of the layer of fluid to the top. These structures are ‘negentropic’,but they do not violate the second law. In Schrodinger’s phrase, they ‘pay their debt to thesecond law’ by greatly increasing the entropy around them. Schrodinger concludes, rathertriumphantly, that the self-organizing, self-regulating features of living things do not vio-late the laws of thermodynamics. The spontaneous construction of stable, ordered struc-tures is to be expected in systems far from thermodynamic equilibrium. Rather thanviolating the second law of thermodynamics either, self-organization is predicted bythermodynamics.

Schrodinger contends that the constitutive property of living things is metabolism:organisms maintain their negentropic structures by synthesizing the materials from whichthey are built (cf. Kant, 2000, p. 371). Maturana, Varela & Uribe (1974) appeal to a similarform of self-organization—autopoiesis—in their definition of living things. A living thing is

ese features that Schrodinger took to be constitutive of living things are the very properties of organisms asl purposes that occasioned such disquiet in Kant.


an autopoietic machine—an embodied, self-organizing entity that actively maintains itsstructure. ‘Embodiment’ here means that the machine synthesises the materials out ofwhich it is built (Boden, 2000). Stuart Kauffman endorses this account of the nature ofliving things, and he explicitly invokes Kant’s reciprocity of causes in describing theself-organizing, self-sustaining autocatalytic reactions characteristic autopoietic machines:

7 I th8 Gin

presum

Immanuel Kant : : : saw organisms as wholes. The whole existed by means of theparts: the parts existed because of, and to sustain, the whole. This holism has beenstripped of a natural role in biology, replaced with the image of the genome as thecentral directing agency that commands the molecular dance. Yet an autocatalyticset of molecules is perhaps the simplest image one can have of Kant’s holism.(Kauffman, 1995, p. 69)

Kant and Schrodinger both take metabolism—self-organization and self-building—tobe the mark of an organism. Kant takes these processes to be the mark of purposiveness.Whereas Kant avers that this purposiveness cannot be an objective principle, Schrodingerargues that it can. But Schrodinger locates self-organization as an objective property, notof matter as such, but of an organized system.7

Self-organization has become one of the most fruitful avenues of research in modernevolutionary biology (Camazine et al., 2003). The mechanisms that underwrite self-orga-nization and the capacities of self-organizing systems are becoming increasingly wellunderstood (Heylighen, 2001). Organisms are complex self-organizing systems that existon the ‘edge of chaos’, neither too sensitive to perturbations to be thrown into chaos,nor too resistant to them to be fixed and frozen (Kauffman, 1993, 1995). In such systemsthe whole is the consequence of the causal capacities and activities of its component parts.Yet the capacities and activities of the component parts are the consequences of the adap-tive plasticity of the system as a whole. These systems are both cause and effect of theirconstituent parts. The robust, adaptively plastic, self-organization that marks organismsout as natural purposes is a simple consequence of a natural tendency of matter far fromthermodynamic equilibrium.

Kant errs in his claim that natural purposes are inconsistent with the nature of matter.We can now locate purposiveness as an objective part of the mechanistic, natural world.

: : : teleological behaviour directed toward a characteristic final state or goal is notsomething off limits for a natural science and an anthropomorphic misconceptionof processes which, in themselves, are undirected and accidental. Rather it is a formof behaviour which can be well defined in scientific terms and for which the necessaryconditions and possible mechanisms can be indicated. (Von Bertalanffy, 1969, p. 46)

The thesis of the antinomy is true; organisms as natural purposes are susceptible ofmechanical explanation. But this naturalization of biological teleology does not particu-larly promote the project of resolving the revised antinomy. To the extent that these sys-tems-theoretic, approaches to teleology offer a passably mechanistic explanation ofteleology, at the same time they weigh heavily against the truth of the antithesis.8 What

ank Joan Steigerwald and Peter McLaughlin for help here.sborg (2004), p. 64 n. 47, expresses a similar worry, that naturalizing teleology in this way threatens theed indispensability of organisms as ends.


needs to be shown now is that the antithesis is true, despite the naturalization of teleology:some biological phenomena cannot be explained except by appeal to natural purposes,even though natural purpose itself is mechanistically explicable.

5. Causes, laws and explanations

The concept of a law of nature is ambiguous; at least it is compound. It is used vari-ously to cover two distinct but related concepts: governance and systematicity. By ‘gover-nance’ I mean that the laws of nature govern the occurrences of things. An increasinglyprominent view of laws of nature holds that laws derive from fundamental capacities ofthings, the capacities that constitute their natures. These capacities necessitate their effects.The laws that describe how things with various causal powers are intrinsically disposed toact in virtue of having these powers are the causal laws of nature (Ellis, 2001, p. 206). Thisview of natural law, it would seem, is quite congenial to Kant. Kant’s conception of gov-ernance reflects this idea of laws of nature deriving from the natures of things: ‘: : : the lawsof nature depend upon the natures that things have, and it is these natures that govern theactivities of substances in determining what happens’ (Watkins, 2005, p. 406). By ‘systema-ticity’ I mean that laws of nature are supposed to be manifested as counterfactually robustempirical regularities. Kant appears to assume the systematicity of laws at least as a reg-ulative principle (Breitenbach, 2006). According to Kant the regularities of the physicalworld are to be explained by appeal to the governance of laws that constitute the natureof matter.

Governance and systematicity of law are intimately associated in the Pure Mechanismof Newton, so admired by Kant. The world is regular precisely because it is governed by afew fundamental, systematic laws. Wherever we see an instance of regularity we are enti-tled, according to Newton, to infer the action of a particular law, acting on the same initialconditions. ‘Therefore to the same natural effects we must, as far as possible, assign thesame causes’ (Newton, 1963, p. iii). On the Pure Mechanism model of explanation forany effect e, that instantiates regularity R, the factor that explains e’s occurrence is thesame as the factor that explains its instantiation of R. This has been enshrined in thecanonical concept of explanation throughout much of the 20th century, the DN model.According to the DN model of explanation, to explain an effect, e, is to subsume it undera general law, R, such that R (in conjunction with some initial conditions) entails theoccurrence of e.

Nevertheless, governance and systematicity can be dissociated.9 Natural law does notinvariably issue in systematicity of effects and the systematicity, or regularity, of effectsmay not be the consequence of unity of governing natural law. Chaotic and self-organizingsystems offer interesting illustrations. Chaos theory gives us an example of governance with-out systematicity. Chaotic systems are deterministic. Given the laws of nature and preciseinitial conditions, a given chaotic system will produce its outcome as a matter of nomicnecessity. But the laws governing chaotic systems do not figure in anything like systematicempirical regularities. Chaotic systems are characterised by hypersensitivity to initial condi-tions. A minor variation in initial conditions can result in an enormous difference in

9 Nancy Cartwright (1999), for example, argues that the laws governing the workings of the world are notsystematic, but make up a patchwork of merely local regularities.


outcome. Consequently, for any given chaotic system, if we know the initial conditions andthe laws it is obeying, we get a complete explanation of its evolution. But this gives us noprediction or explanation of what would happen in other counterfactual situations in whichthe initial conditions are even minutely different. Self-organizing systems, on the other hand,offer an example of systematic regularity of phenomena that is not attributable to the unityof governing law. The robustness of self-organizing systems enables them to produce andmaintain a trajectory toward a particular endpoint despite significant differences in initialconditions and perturbations in the process. It is not the unity of law, or of underlyingcauses, that determines the systematic regularity of self-organizing systems; it is somethingelse, a structural property of the system as a whole. Where governance and systematicity peelapart in this way, it is natural to suppose that an explanation of the mechanical causes of aparticular event is not eo ipso an explanation of some regularity (and vice versa).

Kant appears to countenance the important distinction between the mechanical explana-tion of regularities and the mechanical explanation of singular occurrences. Some phenom-ena, while explicable mechanistically, are nonetheless ‘contingent with respect to mechanicallaw’ (Breitenbach, 2006; Ginsborg, 2001). One source of this contingency may be that someevents, while wholly explicable causally, are not likely to be regular. An example might be aparticular avalanche or volcanic eruption (chaotic systems in general will have this prop-erty). There is nothing about the general nature of matter that explains the specific detailsof these occurrences. They are highly irregular. What is so puzzling about organisms is thatthey are both so ‘contingent with respect to mechanical law’ and also regular.

Thus when Kant says that we cannot conceive of how unorganized matter left to itsown workings could spontaneously form itself into an organism, his point is that the reg-ularities exhibited by organisms cannot be accounted for in terms of fundamental regular-ities that characterize the behaviour of matter at the most general level (Ginsborg, 2001,p. 245). Biological regularity is not explicable by appeal to mechanical law.

5.1. Difference making

Intuitively, to explain an event is to single out those conditions that make the differencebetween the event’s occurrence and its non-occurrence: to explain is to identify a differencemaker. Typically the relation between the phenomenon to be explained, P, and its differ-ence maker, D, is one of invariance (Woodward, 2000). Invariance is a relation between arange of properties {d1, d2, : : :, dn} that D might possess and a range of properties {p1, p2,: : :, pn} that P might possess. The relation Ædi, piæ is invariant if and only if it is (i) changerelating and (ii) robust. Change relating is meant to capture the idea that a difference in thevalue of di brings about a difference in the value of pi. Robustness is meant to capture theidea that the relation between di and pi is insensitive to a range of other factors extrinsic toÆdi, piæ; as Garfinkel points out ‘: : : an explanation must have a certain amount of stabilityunder perturbations of its conditions’ (Garfinkel, 1990, p. 448). When the invariance rela-tion holds, we can use it answer questions of the ‘what-if-things-had-been-different’ sort(Woodward, 2000).10 To be in a position to answer such a question of some phenomenon,P, is to be able to explain P.

10 We need also to be in the position to answer the question: ‘what would have to be the same for things to workout this way again?’.


The difference making approach to explanation reveals how, for some event or processe, that instantiates regularity R, the explanation of e’s occurrence may differ from theexplanation of e’s instantiating R. An example (misappropriated) from Elliott Sober(1984) illustrates the point. Suppose we observe that all the children in a particular class-room read at the grade three level and want to know why. The appeal for an explanationmay be read in either of two ways. We may want to know of all the children severally whyeach reads at that level. If so we must look to the particular history of each child, and wecite that factor that makes the difference between her reading at the grade three level,rather than some other. Alternatively, we may want to know why the constitution ofthe classroom is such that all the children read at that level. Here we advert to those fea-tures that make the difference between this class having this particular composition ratherthan some other. In Sober’s example, the class is constituted this way because there isselection for reading ability; only those students who can read at the grade three levelare allowed into the class. This is a case in which the occurrence of an event token e—say, Sarah’s reading at the grade 3 level—and e’s instantiating a regularity R—that all chil-dren in the class read at that level—call for different explanations. The occurrence of e andits instantiation of R are sensitive to (stable across) different difference makers.

5.2. Mechanical difference making and purposive difference making

Using the apparatus of difference making we can demonstrate that Kant’s conceptionof organisms as natural purposes deserves a central, irreducible place in the understandingof evolutionary biology. This requires two steps, each of which exploits a distinctive fea-ture of the invariance account of explanation. In the first step, we demonstrate the consis-tency of the thesis and antithesis of our revised antinomy of teleological explanation. Inthe second, we establish the reciprocal causal relation between an organism and its parts.

The first step, resolving the revised antinomy, avails itself of the fact that for sometoken event e that instantiates a regularity R, the explanation of e’s occurrence may be dis-tinct from the explanation of e’s instantiation of R.

Suppose we wish to explain some biological even token e, say the development of somea particular vertebrate’s eye; e is both an effect of local causes and an instance of a partic-ular (heritable and developmental) regularity, R. There will be a complete microstructural,mechanical explanation which cites all the causal factors in the etiology of e, call these col-lectively ‘ci, : : :, ck’. The occurrence of e is counterfactually dependent upon ci, : : :, ck. If ci

had been different, for instance, so would the chain of subsequent events leading to e. Yetci, : : :, ck reliably produces e across a range of extraneous circumstances; ci, : : :, ck is amechanical difference maker for e. As a genuine mechanical explanation, this will demon-strate that the occurrence of ci, : : :, ck necessitates the occurrence of e as a matter of law.

Kant’s conception of mechanistic explanation allows that effects of this sort are suscep-tible, severally, of mechanistic explanations:

: : : the claim that organisms are inexplicable on mechanical laws : : : does not itself

entail that we could never explain the origin of an individual bird as a lawlike con-

sequence of the precise arrangement of matter to be found in an intact egg (as we

might explain the ringing of an alarm clock as a lawlike consequence of its state just

after having been wound up). (Ginsborg, 2001, pp. 242–243)


By the same token, the mechanical explanation of e, by appeal to its causal antecedents,ci, : : :, ck, fails to explain why e instantiates R. At this point, Kant cannot appeal to theidea that purpose plays a role in explaining biological regularities in just the way thatmechanism explains occurrences severally. For Kant, as we have seen, purposiveness isnot an objective feature of the world. Moreover, for Kant, purposiveness does not figurein any genuine natural explanations. But, given the account offered above of purposivenessas a natural phenomenon, and the apparatus of difference making, we can help ourselvesto a solution unavailable to Kant.

Organisms exhibit a startling degree of what Garfinkel calls ‘redundant causality’(Garfinkel, 1990, p. 448). There are many alternative causal paths that an organism canexploit in attaining its stable end state. This is just, of course, a consequence of their plas-ticity. Because of the redundant causality in organisms, R is not counterfactually depen-dent upon ci, : : :, ck. There are many ways to achieve R and if our particular individualhad not taken path ci, : : :, ck to e, plasticity would have ensured some other route tothe instantiation of R. So ci, : : :, ck is not a difference maker for R; plasticity is. So thereare two distinct aspects of our target event e to be explained, its occurrence and its instan-tiation of R, and these are sensitive to different difference makers: the microphysical causesof e and the purposiveness (plasticity) of the organism respectively. Biology, then, has adivision of explanatory labour between the mechanical nature of biological processesand their purposiveness.

This demonstrates that the thesis of the revised antinomy—that all phenomena (sever-ally) have causal explanations that advert to mechanical law—does not entail the falsity ofthe antithesis—biological phenomena, taken collectively, may have non-mechanical, non-nomic, teleological explanations.

Thesis: All biological phenomena must be explainable [severally] in accordance withmerely mechanical laws.

Antithesis: Some biological phenomena cannot be explained [collectively] according to

merely mechanical laws only (explaining them requires the teleology of natural

purposes).

Taken by itself, however, this resolution of the revised antinomy concedes too much toPure Mechanism, in doing so it falls short of establishing the most important feature ofKant’s conception of organisms as natural purposes. The consistency of the thesis andantithesis, as I have reconstructed them, does not preserve the idea that an organism is‘both cause and effect of itself’. For all it tells us, organisms may be merely effects ofthe suite of component processes. There has been no real gain on sub-organismal biology.

The second step in rehabilitating Kant’s conception of the organism involves demon-strating that the suite of causal processes that actually occurs in the development of anorganism is also (reciprocally) dependent upon the purposiveness of the organism as awhole. This step also exploits the invariance approach to explanation. As we have seen,the component processes of ontogeny are mechanical difference makers for the purposive-ness of organisms. At the same time, the purposiveness of organisms is the differencemaker for the suite of component causal processes. Uniquely in organisms, mechanismand purpose are reciprocal difference makers.

The phenomena of phenotypic repertoire and phenotypic accommodation demonstratethis. An organism has a broad phenotypic repertoire. Each of its component parts can


produce a wide range of developmental outputs. The particular output each part produceson an occasion depends on the regulatory relations of the organism as a whole. In pheno-typic accommodation the component processes of development are altered by the adap-tive, regulatory capacities of the organism as a whole. Should one part of thedeveloping organism be impinged upon by environmental pressure, or mutation, the restof the developmental system of the organism implements compensatory changes in orderto maintain a well functioning, viable organism. ‘Phenotypic accommodation reduces theamount of functional disruption occasioned by developmental novelty’ (West-Eberhard,2003, p. 147). Kant appears to anticipate West-Eberhard’s concept of phenotypic accom-modation, to some degree, in his discussion of how the purposiveness of the organism as awhole regulates the component processes of development: ‘If birth defects occur, or defor-mities come about during growth, certain parts : : : form in an entirely new way, so as topreserve what is there and so produce an anomalous creature’ (Kant, 2000, p. 372).

The important point for our purposes is that the particular suite of causal processes thatactually occur within a developing organism only do so because of their regulation by thepurposiveness (plasticity) of the whole organism. We would have no explanation of whythe mechanisms of development play the causal roles they actually play in the productionand maintenance of a viable organism typical of its kind, without the purposiveness (plas-ticity) of organisms. This may be part of what Kant is adverting to by his claim that theorganism is ‘contingent’ with respect to mechanistic causes (Ginsborg, 2001); that is, ‘: : :that nature, considered as a mere mechanism, could have formed itself in a thousands dif-ferent ways without hitting upon the unity in accordance with such a rule’ [the structure ofa particular organism] (Kant, 2000, p. 360).

There is, then, an invariance relation between the plasticity of the organism as a wholeand the causal powers of its component processes. It is (i) change involving: a change inthe overall structure of the organism would occasion a change in causal properties ofthe components; and (ii) robust: a developmental component has its particular causalpowers despite internal and external perturbations. This invariance relation is the exactreciprocal of the invariance relation between the causal powers of an organism’s compo-nent processes and its plasticity. So, mechanical and purposive explanations in biology aremutually dependent. Each kind of difference maker (mechanical and purposive) has theother kind of difference maker as a difference maker. This is the sense in which organismsare causes and effects of themselves.

6. Conclusion

It goes without saying that the organismal perspective has fallen largely out of favour inpost-Darwinian biology. The very idea of explanation by appeal to the purposes of organ-isms has come to be seen as problematic, ‘a metaphysical delusion’. Besides, orthodoxopinion in contemporary evolutionary biology holds that there is no need to extend toorganisms—much less their purposiveness—an explanatory role if sub-organismal causalmechanisms are explanatorily adequate. To the extent that Kant’s conception of organ-isms as natural purposes has received any consideration from contemporary biology atall, it has been largely dismissed as an irrelevance.

I have attempted to do two things here. The first is to emphasize that the properties oforganisms which, according to Kant, mark them out as natural purposes, areobservable. It does not require immersion in the critical philosophy to see that organisms


are self-organizing, self-building adaptive systems. If recent evolutionary developmentalbiology is to be believed, the purposiveness of organisms is a contributing cause of bothontogeny and adaptive evolution. The second is to carve out an explanatory role fororganismal purposes that is consistent with the modern commitment to mechanism. Here,contemporary biology—and contemporary metaphysics—encounter precisely the problemthat motivated Kant’s ‘Antinomy of the teleological power of judgment’: teleologyappears to be inconsistent with mechanism. Mechanical causes explain; purposes cannot.Moreover, explanation by purpose appears to be otiose. If each natural phenomenon canbe fully explained by adverting to its mechanical causes, there is no unexplained residuefor which purposes are needed.

As I see it, anti-teleological scruples such as these are motivated by the lack of a plau-sible model for how purposes could explain. I have tried to sketch out such a model hereusing the notion of invariance explanation, which yields two results, one fairly specific, theother quite general. The specific result is that there is an explanatory invariance relationbetween the purposiveness of an organism and the causal capacities of its parts thatdirectly mirrors the invariance relation between the causal capacities of an organism’sparts and its overall purposiveness. Purpose and mechanism are reciprocal causes. Giventhat, even if the occurrence of each biological event has a complete mechanical, sub-organ-ismal explanation, it does not follow that there is no explanatory role for the purposive-ness of organisms to play. Purposiveness explains the regularity of these occurrences, andthis is crucial for the understanding what makes adaptive evolution adaptive. The moregeneral result is that, on the invariance model, purpose explains just like any other kindof cause.

Acknowledgements

I wish to thank Peter McLaughlin for comments on an early draft, Marcel Quarfoodfor engaging discussion on these issues, and audiences at IHPST, Toronto and the Con-sortium for the History and Philosophy of Biology workshop in Montreal. I would par-ticularly like to thank Joan Steigerwald, first for the invitation to contribute and thenfor patience and acumen as editor.

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