On Time, Being, and Hunger: Challenging the Traditional Way of Thinking Life

Twelve

95 Twelve No subject of biology has caused more “wonder” than development. Is there anything more fantastic, more unbelievably perfect than the process by which a single cell, dividing and multiplying itself, can give rise to a highly complex organism? Almost inevitably, one is led to think that what guides the development of living beings from the fertilized egg to the adult form should be an unifying and internal principle of organization. At the end of the 1950s and the beginning of the 1960s, François Jacob and Jacques Monod’s famous operon model of gene regulation made molecular biologists believe that one of the major genetic secrets concerning development had finally been revealed.1 In the presence or absence of the right chemical signal, control genes give the order to switch on or off certain particular specifications for protein synthesis. Little imagination was then needed to link morphogenesis as well as the genesis of all teleonomical processes to such chemical interactions. The formation of living forms and of living functions would ultimately rest on the stereospecific properties of microscopic molecules. 96 On Time, Being, and Hunger If one analyzes the catalytic or regulatory or epigenetic functions of proteins, one is led to the recognition that each and every one depends—above all— upon the capacities of these molecules for stereospecific association. . . . All the teleonomic performances and structures of living beings are, at least in principle, analyzable in these terms. Assuming this concept to be adequate— and there is no reason to doubt that it is—the remaining step toward resolving the paradox of teleonomy is to give an explicit account of the manner in which stereospecific associative protein structures form and of the mechanisms by which they evolve.2 But detractors did not take long to denounce the scientific hubris implied in such conclusions. Indeed, soon the operon model was revealed as all too simplistic; at most it was applicable to prokaryote cells, and for certain speci fic functions. What is true for bacteria, however, is not necessarily true for elephants. It was soon discovered that development could not be reduced to the simple idea of an unfolding, displaying, informing, preexisting DNA molecule that contained the building plans of the whole organism; in fact, such a view was surreptitiously bringing preformationism back to life in the guise of the genetic program.3 Once again, the thing at stake is revealed to be much more “complex,” and to engage a whole theory of self-organization is fathomable only on the condition of going far beyond the level of molecular analysis. The developmental program consists of, and lives in, the interactive complex made up of genomic structures and the vast network of cellular machinery in which those structures are embedded. It may be that this program is irreducible—in the sense, that is, that nothing less complex than the organism itself is able to do the job.4 Fortunately, however, the problem of development did not dishearten molecular biologists. Several discoveries carried out during the late 1980s and 1990s concerning the genetic basis of development,5 together with a persistent tradition looking for mathematical and chemical models for understanding the interaction of cells in morphogenesis,6 seem to show that the “complexity” in question still may do without the ghost of self-organization, or that the complexity in question is such that it may break with any supposed self-appropriating identity or unity of developmental processes. It is known, for instance, that the cells’ position contributes to the determination of their differentiation and consequently morphogenesis. A group Chapter Twelve 97 of cells differentiated and located at one place of the embryo will determine the formation of arms, while the homologous group of cells located in the opposite place will determine—only by virtue of the difference in position—the formation of legs. At earlier stages of development, one can, for instance, change the position of such groups of cells without affecting the normal development of the organs. How are the position and movement of cells determined? How do the cells “know” their position? How do they know when and where to migrate? When and where will this or that part of their genome be activated? The answer will be found not in the mind of nature, or thanks to the external projection of the experience of our own living body, but in gradients of...