More Denton: Another review of Denon's new book (Introduction)

by David Turell , Friday, May 27, 2016, 00:19 (3103 days ago) @ David Turell

Once again an emphasis on the structuralism approach to evolutionary theory: - http://potiphar.jongarvey.co.uk/2016/05/14/denton-emergence-and-common-descent/ - "I might add (because Denton doesn't stress it) that structuralism - the idea that much of biological form depends on lawlike constraints, rather than adaptive contingency - was the prevalent theory of evolution, in the form of orthogenesis, at the time when Darwinism was found wanting in explanatory power at the beginning of the twentieth century. It was only the Neodarwinian Synthesis that rehabilitated Darwinism, and it was the hegemony of that Synthesis within western biology that not only wrote the case for structuralism out of science, but virtually out of history as well. - *** - "Denton's structuralism is a well-argued return to the reality of essentialism in biology: there are indeed true discontinuities between taxa that simply cannot be explained by natural selection. If so, then Aristotle was actually observing nature more accurately than we have for the last century or so, in our dogma that all life is a continuum of contingently changing components. Because these discontinuities constitute some of the most significant features of living things, they radically relativise the significance of natural selection. To a large extent, selection becomes the tinkerer that merely fine-tunes microevolution, whereas what Denton argues to be natural laws of emergence are what paints the grand picture of life. - *** - "Denton actually quotes from Darwin himself: that the features that we highlight to construct the nested heirarchies used to support common descent are by their very nature those farthest removed from adaptive selection. To take his first example, the pentadactyl vertebrate limb (extensively studied by Owen), the whole point is that it has remained universal amongst the whole vertebrate clade for 400 million years, despite every adaptational exigency to which it has been turned from flying or swimming or digging holes to writing books. It cannot possibly, then, be evidence for Darwinian evolution. Indeed, Denton points out that the very existence of a nested heirarchy is evidence against Darwinian processes as the major player in evolution, for change without direction ought to lead to taxonomy without patterns. - "Denton himself considers that pentadactyly, and similar examples, constitute good evidence for common descent itself, but I should remind you that the nested heirarchy was formerly, by those like Linnaeus, considered telling evidence for the special creation of every possible species by God. - *** - "If there are emergent laws of form, as Denton argues, then gradualism is no longer a requirement in evolution. He consistently argues that the evidence from the fossil record, taxonomy and much genetics is that the important changes were relatively, at least, saltational. Let me run with that for a moment, commencing with an example that seems fairly well established: the saltational acquisition of mitochondria by eukaryotes through Lynn Margulis' suggestion of a fusion of two disparate forms of life. Whatever further adjustments arose by adaptation through that assumed saltation, there was a profound discontinuity between the two pre-existing lineages and the resulting clade of eukaryotes. - *** - "let us suppose that emergent laws explain some of Denton's other examples, such as the necessarily sudden (and yet horrendously complex) extrusion of the nucleus from the mammalian erythrocyte, the evolution of the theropod feather or, indeed, that pentadactyl limb. Or ORFan genes. Or turtle anatomy… or the phenomenon of developmental systems drift. Such discontinuities have no known, and in most cases no conceivable, adaptive origin. They arose de novo - and perhaps they even arose more than once in different lineages, as some examples of “convergent evolution” suggest. In such cases (a majority, in fact, of taxon-defining features), not only do we have no clear knowledge of the ancestors in which they occurred, but it doesn't appear to matter much anyway. - *** - "Meanwhile, I'll just ask you to consider whether the obsession of biology with common ancestry would have any purpose whatsoever if the day came when Darwinian gradualism were finally concluded to have only secondary importance for the origin of the species." - Comment: If Darwin evolution was truly at random why the fixed patterns from the beginning of Pentadactyl forms? Note my bold. It all looks like saltation of complexities. This review fits my point of view exactly.