Moss - What genes cant do - 2003 (522929), страница 49
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Development, by contrast has been deemed to bethe result of a preset centralized program and so teleological (or “teleonomic”9). Evolution, by virtue of the invisible hand of natural selection,has been deemed to be adaptive. Evolution is thus seen as adaptive butnot teleological, development teleological but not adaptive.The asymmetry of development and evolution during the twentiethcentury was not an historical accident. The processes of life have beendifficult to explain in strict accord with the presuppositions of naturalmechanism (of course this is subject to vary with changes in the perceptions of what counts as natural mechanism).
Darwin provided theschema for a natural mechanism that can explain how the forms of lifecan change over generational time. Increasingly, neo-Darwinists haveattempted to bring all of the ultimate explanatory challenges of life underthe ambit of the Darwinian schema. Taken to the extreme, this has ledto a biological ontology in the form of the theology it sought to replace.The radical dichotomization of development and evolution followedfrom the apotheosis of the (conflationary) gene that became the fundamental ground substance of all life and the basis of life’s intelligibility(and of life’s ability to become intelligible to itself).At the beginning of our new century this dichotomization can nolonger be sustained.
The evidence against this is unmistakable andunavoidable. Development and evolution are not only two sides of thesame coin; they are virtually mirror images of one another. The mechanisms of evolution have become essential to understanding developmentand the mechanisms of development have become essential to understanding evolution.
At the dawn of the new century, no ontological rocksmay properly be left unturned.The symmetry, interpenetration, and interdependence of developmentand evolution can be seen on many levels. New genes (Genes-D) areevolved through recombining exon modules at the DNA level. Geneticdiversity is obtained in development through the recombination (splicing) of exon modules at the RNA level. The de novo recombinationevents that allow the immune system to produce receptors for antigensnever before seen mirrors in miniature the de novo recombination eventsthat have resulted in new genomic architectures that may have beenAfter the Gene197instrumental in the evolution of new species.
The developmental capacities of metazoan life forms are at once the basis of their evolvability.Faucets of variability are deployed ontogentically and by extensionphylogenetically. Variability is mediated by the tribunals of N-many dispersed and distributed decision making nodal points and by on-site, onthe-spot, modular committees. The stability and intelligibility sought forin idealized genes must be rediscovered in the complex dynamics ofprocess. The evolving metaozoan capacity to mediate variability (fromall directions) is the basis of increasingly adaptive ontogenetic plasticity.Modularization underlies the formation of contingent linkages betweenproteins, and between multi-protein complexes.
It promotes increasingcompartmentalization, increasing redundancy and the growing capacityfor exploratory behavior. These properties confer “robustness and flexibility on processes during embryonic development and in adult physiology” and at once “confer(s) evolvability on the organism by reducingconstraints on change and allowing the accumulation of nonlethal variation” (Kirschner & Gerhart 1998). Ontogenetic adaptability and phylogenetic evolvability in the metazoa are reciprocal capacities—two sidesof the same street. Kirschner and Gerhart (1999) focus on how robust,modularized, phenotypically flexible developmental systems allow foreven random point mutations to have evolutionary clout through influence that can be magnified through mediation by the systems of contingent modular interaction. Even random point mutation becomes grist forthe ontogenetic mill.
“The consequences of mutation for phenotypicchange are conditioned by the properties of cellular, developmental, andphysiological processes of the organism, namely, by many aspects of thephenotype itself” (Kirschner & Gerhart 1999). What is true for pointmutations (the likelihood of which are also largely regulated by the interlocking enzyme systems of DNA repair, recombination, translocation,and methylation) can only be at least as true for large-scale genomicreconstructions and indeed for extragenomic variation of any sort, theevolutionary consequences of which are equally subject to phenotypicinterpretation and stable incorporation into reproducible life-cycles.Contrary to the last-ditch efforts of diehard gene centrists, the developmental analysis of evolvability “Devo-Evo” cannot be segregated fromthe evolutionary analysis of development “Evo-Devo” (see Hall 2000).198Chapter 5The decay and demise of the gene as the bedrock of biological explanation and intelligibility will surely bring with it new explanatory challenges.
That even individual cells can coordinate a multitude of highlycontingent and quasi-independent decision making processes meritssome measure of explanatory humility. An example of a growingresearch program that may shed light some light at this level is that whichfollows from the realization that the nucleus also contains its own filamentous matrix. The scaffolding of the nuclear matrix may, along withhistone modification (Forsbeng & Bresnick 2001, Rice & Allise 2001,Jenywein & Allis 2001), provide the means of coordinating the decisionsof ad hoc transcription and splicing committees (Berezney et al.
1995).But the nuclear matrix can be no new fundamental ground substance,no new ontological bedrock. A nuclear matrix may provide the on-thespot, at-the-time solution to certain problems of decision making coordination, yet like its reflection in the cytoplasm, a nuclear matrix is itselfthe modularly variable product of a contingent dynamic history.It may well prove to be the case that as the newly ontogenized understanding of evolution becomes more truly secular, our understanding oflife (and perhaps of matter in general) will yet become more sacred.
Afterthe (conflated) gene, it is the living organism, an active agent of its ownadaptive ontogeny and evolvability, that is once again poised to moveback into the ontological driver’s seat.NotesChapter 11. “Shibboleth” is defined as a catchword or formula adopted by a party or sect,by which their adherents or followers may be discerned and those not their followers may be excluded.2. The quote, from Brandon (1990), is not meant to suggest that this authoris particularlary culpable; rather, it is meant as a general illustration of whathad been taken as a point of departure for the earliest generations of AngloAmerican philosophers working in the philosophy of biology.3. See especially Aristotle’s Parts of Animals and also his Generation of Animals.4.
For historical discussions of the continuity of Darwin’s work and ideas withthe ontogenetic tradition see M. J. S. Hodge (1985) and Robert J. Richards(1992).5. See Maturana, H. and Varela, F. (1973).6. Blumenbach’s comment can be understood in more than one way. Richards(2000) argues that Blumenbach never understood the Bildungstrieb as a “heuristic idea” in a Kantian sense but rather was understanding it in a Newtonianfashion as an empirical force, the cause of which would always remain hiddenand ultimately unknown.
Blumenbach quoted Ovid in this regard—“causa latet,vis est notissima” [the cause is hidden, the force is well recognized]. Blumenbachacknowledges, following Kant’s commendation of him, that the Bildungstriebbrings together the mechanistic with the teleological, but Richards suggests thatBlumenbach neither adhered to Kant’s view nor even necessarily quite understood it.
Lenoir interprets Blumenbach as an “emergent vitalist” who see thevital force, the Bildungstreib as emerging from the organization of matter (whichin Kantian fashion we must take as a given), but Richards argues that forBlumenbach it is the Bildungstrieb which is meant to explain the origins of livingorganization.7. Keime was routinely used as the German translation for the French “germes.”Expressing the preformationist ideas of both Bonnet and von Haller, i.e., as200Notes to pages 12–42preformed parts, it should not be confused with the “emboîtment” model of preformed whole miniatures.
Anlagen, which derives from the German word legenmeaning “to lay out,” is translated as “organizational layout” or “disposition.”Kant is the first to bring the words Keimen and Anlagen together in this technical usage, first in his 1775–1777 discussions of race and then in a passage ofA66 of the First Critique of 1781 (Sloan, 2001). In these texts the meaning ofKant’s use of Anlagen is that of a native structuring capacity or aptitude whichbrings an epigeneticist sense to the more preformationist connotation of Keime(Sloan, 2001).8.
This teleomechanistic model of evolution in which ontogenetic adaptationis playing a driving role is reincarnated in the twentieth century in the nameof Baldwinism and Waddington’s “genetic assimilation” (see Gottlieb 1992). Inchapter 3, I refer to the possibility that the dynamics of chromosome marking mayprovide a mechanistic basis for ontogenetically driven evolutionary adaptation.Lamarck of course provided another nineteenth-century model, butthe label “Lamarkianism” having become a term of derision amongst neoDarwinist has served mostly to polarize and to obfuscate real biological questions.9.
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