16 July 2007

Wenn nur alle Artikel so unterhaltsam wären...

Auf The Panda's Thumb verweist PvM auf einen Artikel von Forrester und Gross in der Juli-Ausgabe von Trends in Biochemical Sciences [Biochemistry by design. Trends in Biochemical Sciences Volume 32, Issue 7, Pages 301-310]. Wer auch immer Zugriff auf den Volltext hat, sollte sich den durchlesen. Großartig geschrieben. Behe, IC und ID werden in den Boden gestampft, in der Reihenfolge.

Ein paar Ausschnitte gibts auf The Panda's Thumb und hier noch einer von mir:

Behe claims to have identified just such ‘powerful challenges’ [to Darwinian evolution] in the form of IC systems at the subcellular level. By his gloss of Darwinian evolution, these objects cannot have evolved. Ergo, they have to have been designed ‘in one fell swoop’. Unfortunately for the argument, this is immediately recognizable as the logical fallacy of false dichotomy. It is not necessarily true that if ‘Darwinism’ (as he presents it) is wrong, intelligent design must be right. There are, in principle, other theories, neither ‘Darwinian’ nor telic, that could be right, so far as the evidence available at any moment goes. Some philosophers of science never tire of reminding us of this. Behe's false dichotomy and other fallacies like it are given a comprehensive review by Dunkelberg (which is one of many similar reviews that have appeared since 1996) [13].

When the IC argument against evolution surfaced, its logical, factual and scholarly flaws were addressed quickly – not least by scientists (including one of us) who reviewed the book [14] and [15]. Those critiques have had no effect on the enthusiasm of the intended popular audience of the book. Behe's fellow ID-enthusiast, William Dembski, boasts of its continuing 15 000 sales per year [16]. Since 1996, Behe and his ID colleagues have responded to evidence of their gross error either by dismissing it without justification or by offering successive, marginal, re-definitions of ‘irreducibly complex’ [13]. Those changes have not improved the argument, however. Beyond the false dichotomy, it had other flaws at the outset, and those, too, have been neither eliminated nor acknowledged.

Perhaps the basic substantive (rather than formal) flaw is the claim that IC systems or structures cannot have evolved gradually because all their parts (as defined) are necessary for the function, and must therefore have been there from the start. In the IC argument, any precursor system lacking any part would be functionless, and, of course, an evolving system is a system of precursors. In a functionless state, a ‘precursor,’ having no selective value, would fail to survive. This potential argument is not new; it was an early consideration of the Modern Synthesis (of classical evolutionary biology with genetics), first taken up by the eventual Nobel laureate Hermann J. Muller in 1918 [17]. This was in the context of the possible reversibility of evolution. Muller's analysis disposed of the non-evolvability argument very simply; he explained that incorporating an additional, but inessential, step or part to an existing structure or physiological system would be selectively positive so long as the change provided some improvement, however slight. It would thus favor survival. Thereafter, through other well-known processes (e.g. mutational loss of some other part of the now-improved system) that increment of function could become indispensable. The change in the system, that is, its evolution, would then have become irreversible. It would now be, as regards that function and as Behe dubbed it, irreducibly complex.

Entirely plausible processes exist, therefore, that have been long known in genetics, by which small and gradual changes to an initially simple, functional system can (and do) cause its complexity to increase and, at some point, to become ‘irreducible’ (Figure 1). Therefore, IC as Behe defines it is not un-evolvable, either in principle or in practice. Moreover, there is no reason why a currently IC system cannot continue to evolve by the mechanism described. Irreducible complexity and its acquisition (in the context of reversibility) were reviewed by Muller in 1939 [18]. This classic understanding, like others in the literature of evolution and genetics, has perhaps been misunderstood by Behe. (He is, by training and experience, neither an evolutionary biologist nor a geneticist.) In a recent article, Douglas Theobald dealt with this particular flaw in the IC argument and therefore in ID theory – neglect of Muller's mechanism – even in his title: ‘The Mullerian two-step: add a part, make it necessary, or why Behe's ‘irreducible complexity’ is silly’ [19].

Behe's assumption that there is such a thing as a single function that is permanently and unalterably associated with a particular biochemical system, or with a chemical (or for that matter a morphological) structure, is flawed on several levels. If it were correct in biological reality, there might be some merit in the IC argument, but it is not correct. The functions of biological and biochemical systems, like their parts, have changed continuously in the course of history. An old word to describe this reality was ‘preadaptation’, the supposed ability of a part, although its original ‘function’ was a, to serve alone in, or as an element of, a future, different function, b. This widespread phenomenon, but not its early interpretation, is so important in the history of life that it has been given a new, more carefully chosen name: ‘Exaptation. A character previously shaped by selection for a particular role (an adaptation) (…) later co-opted by selection for a new and still current fitness role’ [20].


So, it is not true that the individual components of biochemical structures or systems – including Behe's own exemplar, the blood-clotting cascade – have no other function than that which he chooses to associate with the putative IC system. Thrombin, for example, has functions, including one in the complement system, other than its central role in clotting. And these functions are credibly interpreted in terms of the evolutionary history of thrombin [21] (Figure 2). Assignment of a single function to any set, especially a large set, of interacting macromolecules is arbitrary. Indeed, the opposite condition – a dense pleiotropy – has emerged in contemporary, systemic genomics and proteomics, especially among regulatory genes [22]. Beyond the error of proclaiming IC un-evolvable, Behe dismisses the demonstrated frequency, in the history of Earth's biota, of gene and whole-genome duplication events, followed by diversification of structure and, eventually, of ‘function’ among the copies so produced. But the combination of exaptation and genetic duplication-divergence, for which a mass of evidence exists, makes the IC argument naïve (see later).
[Quelle: Forrester & Gross, Biochemistry by design. Trends in Biochemical Sciences Volume 32, Issue 7, Pages 301-310]

Sie warnen in ihrem Artikel allerdings auch davor, dass wir uns in Europa nicht auf die relativ große Zustimmung zur Evolutionstheorie verlassen sollten und verweisen u. a. auch auf die bedenklichen Stimmen aus dem Vatikan. Die neuesten Äußerungen des Papstes, Bischof Mixas und nicht zuletzt der hessischen Kultusministerin Karin Wolff geben ihnen recht.

Unsettling signals are coming even from the Vatican, where Cardinal Christoph Schönborn's July 2005 public statement of support for ID, released by the public relations firm of the Discovery Institute, was followed by ambiguous comments from Pope Benedict [81]. Statements from the pope released in April 2007 have not dispelled concerns about this ambiguity [82] and [83].

America's experience should be instructive to scientists and the concerned lay public abroad. In the short term, creationism threatens the already weak public understanding of basic science, thus posing a corresponding, immediate threat to proper science education. In the longer term, once the public understanding of science is sufficiently degraded, the degrading of public support for scientific research could well follow.
[Quelle: Forrester & Gross, Biochemistry by design. Trends in Biochemical Sciences Volume 32, Issue 7, Pages 301-310]


13 Dunkelberg, P. (2003) Irreducible complexity demystified. Talkdesign.org 26 April

14 Gross, P.R. (1996) The dissent of man. Wall St. J. 30 July, p. A12.

15 Various (2006) Behe, Michael .

16 Dembski, W.A. (2004) Irreducible complexity revisited. PCID November.

17 H.J. Muller, Genetic variability, twin hybrids and constant hybrids, in a case of balanced lethal factors, Genetics 3 (1918), pp. 422–499.

18 H.J. Muller, Reversibility in evolution considered from the standpoint of genetics, Biol. Rev. 14 (1939), pp. 261–280.

19 Theobald, D. (2006) The Mullerian two-step: add a part, make it necessary, or why Behe's ‘Irreducible Complexity’ is silly. 21 November.

20 E.S. Vrba, Exaptation. In: M. Pagel, Editor, Encyclopedia of Evolution Vol. 1, Oxford University Press (2002), pp. 338–339.

21 M. Huber-Lang et al., Generation of C5a in the absence of C3: a new complement activation pathway, Nat. Med. 12 (2006), pp. 682–687.

22 C.T. Hittinger et al., Pleiotropic functions of a conserved insect-specific Hox peptide motif, Development 132 (2005), pp. 5261–5270.

81 Peretó, J. (2006) Intelligent design and the assault on science. Eurozine 13 July.

82 Lawton, M. (2007) In new book, pope quoted as seeing no conflict between faith, science.

83 Owen, R. (2007) Pope puts his faith in the Book of Genesis, not Darwin. The Times (Lond.) 13 April.
Catholic News Service 13 April.

0 Kommentare: