Moss - What genes cant do - 2003, страница 5

While we must assume thisteleological principle as our point of departure, that of life-forms asNaturzwecke, or organizational ends (purposes)-unto-themselves, wemust, says Kant, nevertheless strive to account for them as far as possible in the only explanatory mode at our disposal, that of mechanisticanalysis.

Whereas the proponents of the preformationism-epigenesisdebate foundered in a largely fruitless effort to explain the source of thisorganization, Kant’s principal programmatic recommendation thereafterwas to take the fact of a purposeful organization as a heuristic given andproceed to explain its workings mechanistically.So if in investigating nature we are to avoid working for nothing at all, then, injudging things whose concept as natural purpose does undoubtedly have a basis(i.e., in judging organized beings), we must always presuppose some originalorganization that itself uses mechanism, either to produce other organized formsor to develop the thing’s own organized form into new shapes (though theseshapes too always result from the purpose and conform to it).

(Kant, Critiqueof Judgment).Kant found in the Göttingen scientist Johann Friederich Blumenbach anapproach to reconciling the conflict between purposeful organization andmaterial mechanism very much akin to his own. Blumenbach had been,as were many other eighteenth century intellectuals (Lenoir 1980), highlytaken with the discovery of regeneration in the fresh water polyp. Theability of the polyp to regenerate an amputated part exhibited for Blumenbach a kind of organizational urge, or Trieb. But of special interestto Blumenbach was the observation that the regenerated part was alwaysGenesis of the Gene11smaller than the original. What this suggested to him was that the “organizational urge” was a material phenomenon susceptible to physical dissipation. Blumenbach hypostatized a special inborn Trieb, or urge, whichhe specified as a Bildungstrieb, or formative urge.

What Blumenbachunderstood by the Bildungstrieb was neither some (Platonic) soul superimposed on matter nor merely the sum result of the individual parts ofan organism. It was rather a force which resulted from the peculiarorganization of a living being as a whole. It was thus inseparable fromthe parts but not reducible to them. Kant said of Blumenbach:Yet by appealing to this principle of an original organization, a principle thatis inscrutable to us, he leaves an indeterminable and yet unmistakable shareto natural mechanism. The ability of the matter in an organized body to [takeon] this organization he calls a formative impulse [Bildungstrieb] (Critique ofJudgment).And in a later writing Blumenbach states that just because we can’texplain the mechanism by which the Bildungstrieb is brought aboutthat does not hinder us in any way whatsoever, however, from attempting toinvestigate the effects of this force through empirical observations and to bringthem under general laws (quoted in Lenoir 1982).6Conception of the Keime und AnlagenHow does one go about empirically characterizing a Bildungstrieb?Can a research program be focused around an organizational forcewhich must always already be taken as a given? Kant found the key toapproaching this problem in his observations of the apparent kinship ofvarious species suggestive of the relationship of various organisms to acommon archetype and thereby the possibility of identifying some mechanism which leads from one type to another.

The pursuit of a comparative anatomy, for Kant, could become a means for finding some unifyingprinciples of nature that would reveal something about the productionof organized beings. Observing gradations in the form and complexityof living taxa, Kant suggested that “an archeologist of nature” couldconceive of nature producing a less complex organized being with thepotential to give rise to progeny that “became better adapted to theirplace of origin and their relations to one another.” (Kant, Critique of12Chapter 1Judgment). Kant famously referred to this speculation as a “daringadventure of reason.” He even considered the possibility of a chain ofcommon descent extending all the way from aquatic animals and marshanimals to land animals, but he dismissed this hypothesis on empiricalgrounds.

Adequate evidence—intermediate forms, for example—simplywas not available to support it. Still, Kant considered the transmutationof taxa within some limited range, based on the heritable influence ofthe existential conditions of organisms on their generative stock, to behighly plausible (Critique of Judgment).Blumenbach, a formative influence on a whole generation of turn-ofthe-century biologists at Göttingen, was the principal conduit for aKantian-inspired research program. The strategy of seeking to elucidatethe principles by means of which new life-forms are produced from some“purposefully” organized germ has been described as that of teleomechanism (Lenoir 1982). The idea that whole branches of the animalkingdom, such as vertebrates, were derived from some common stock ofadaptive potential indeed proved to be a very powerful heuristic for triggering new research programs.

At the core of the teleomechanist perspective is the idea that within the organizational form and structure ofthe germ, which as previously stated must be taken as a given, there isthe potential, the Keime und Anlagen,7 not just for a single organism butof an entire range of related basic forms, or Baupläne, and thus for adaptive modification. Epigenesis follows forth from the Keime und Anlagenof the germ, responding plastically and adaptively to the organism’s conditions of existence. Epigenesis is thus construed as an adaptive processwhich, under conditions of sustained environmental pressure over multiple generations, may give rise to stabilized new forms, that is, to newspecies, which are already preadapted to the environmental pressuresfaced by the preceding generations.8According to the teleomechanist heuristic, expressed by Kant, the possibility of these forms must already be present in the ancestral germ.

Thescope of the teleology here is just that of the adaptive capacity latentin the (“purposefully” organized) germ, an adaptive capacity which isunderstood to be wholly material in nature and amenable to mechanistic analysis. This brand of epigenesis as articulated by teleomechanistswas at once a kind of “generic preformationism” (Lenoir, 1982). WhatGenesis of the Gene13was preformed were not particular traits but rather the possibility-spaceof some universe of life-forms which all share a general developmentalpattern intrinsic to the Keime und Anlagen of the original germ.

Genericpreformationism imposes constraints on possible organismic form but itdoes so on a systematic and architectonic basis and not at the level ofthe individual traits of a specific organism.Rather than foreclose or marginalize the significance of developmental adaptability, the teleomechanist’s generic preformationism gave definition and importance to developmental adaptability.

Indeed, it wouldbe the selfsame principles of ontogenetic adaptation that would also bethe principles of phylogenetic radiation. A clear articulation of a teleomechanistic understanding of the relationship of ontogeny to phylogenywas spelled out by Karl Ernst von Baer, a leading nineteenth-centurybiologist, in his influential four laws of development:1. The more general characters of a large group of animals appear earlierin their embryos than the more special characters.2.

The less general forms develop from the most general forms, and soon, until finally the most specialized form arises.3. Every embryo of a given animal form, instead of passing through theother forms, rather becomes separated from them.4. Fundamentally, therefore, the embryo of a higher form never resembles any other form, but only its embryo.9A depiction of von Baer’s model of the relationship of ontogeny to phylogenetic radiation within a type can be seen in figure 1.1. At the centerof the diagram is T, which represents the entire stock of Keime undAnlagen of the type.

It is not meant to correspond to a particular empirical entity but rather only to a hypothetical construct—the embryological germ prior to any differentiation in the direction of a particulardevelopmental path, i.e., the germ that still possesses the potential of theentire possibility-space of the type. Had circular representations beenused instead of only branching lines and had the size of the circle beenused to represent the amount of Keime und Anlagen, then T would berepresented by the circle with the greatest diameter of any in the figure.From T two lines proceed toward C1 and C2. These lines represent twocontingent developmental trajectories, two pathways in the embryology14Chapter 1Figure 1.1Von Baer’s model of the relationship of ontogeny to phylogenetic radiationwithin a type; see text for details.by means of which all the subsequent organismic forms are derived.

C1and C2 represent the first differentiations from the original stock. Theyrepresent that stage of embryological development common to all themembers of Class 1 and Class 2, respectively. The circles that could bestrepresent the stock of Keime und Anlagen of C1 and C2 would be smallerthan that of T but larger than that of any subsequent circles in the figure.Whereas species S1 through S14 would all pass through the stage C1Genesis of the Gene15common to that class and so could not be distinguished from each otherat that point, they could already be distinguished from species S15through S25, which have already taken the form of C2 common to thedevelopmental pathway of all members of the C2 class.