Alexander Rosenberg
Until the recent past, most of the history of biology was the pursuit of structures that would explain functions. Having pursued these structures to the natural stopping place of biochemistry and molecular biology, the discipline has neither gone further in its pursuit of structure to physical chemistry, and beyond it to physics, nor has it ceased at a dead end beyond which there are no further biological questions. Instead it has turned around, and now is actively engaged in the search for biological functions of chemically characterized structures.
This volte face is particularly apparent in the study of the genome. In the last decade molecular biologists have learned a great deal about the structure of the nucleic acid polymers that make up the chromosomal material. They have learned, in particular, that sequences of nucleic acids, the bases that compose DNA, adenine, thymine, guanine, and cytosine, recur in repeating series of several different kinds; that very similar sequences can have utterly different effects, that some have no apparent role in the genetic capacities of the DNA. Biochemists have learned that there are split genes, which contain ‘introns’ – intervening sequences that do not code for any protein product, that are snipped out in the messenger RNA; that there are some so-called ‘moderately repeated’ DNA sequences recurring hundreds of times on the same chromosome, and some ‘highly’ repeated DNA-sequences instanced millions of times on the same chromosome; that some genes come in tandem clusters, and others are to be found on more than one chromosome; that there are ‘pseudo-genes’ with base sequences very close to those of functioning genes, but which do not have their structural or regulatory functions; then there are genes occurring only once on one chromosome, in each nucleus, that code for a protein-product in the way we expect genes to do. All this structural information cries out for functional explanation, and much of it for evolutionary, adaptationalist explanation. That is, while some features of the structure of the chromosome are what we might expect, given the role which the genome plays in the heredity and development of individual organisms, other features seem to do nothing for the organism that contains them. For these structures, a different sort of explanation is required, one which explains their presence and persistence, in spite of their neutrality or maladaptive contribution to the survival of the organism containing them. Typically, these explanations too will be functional, identifying features of structurally identified portions of the genome as contributing either to the evolutionary adaptation of the very portion of the DNA itself, or to the evolutionary adaptation of the population in which the organism interbreeds.
Fonte; Rosenberg, A. 1985. In: Fetzer, JH, ed. Sociobiology and epistemology. Dordrecht, Reidel.
