Common descent is demonstrable only when causes are known
Bear in mind, throughout, that common descent is a distinct concept from the mechanism of natural selection acting on random variation. Edge of Evolution, 64
In the abstract, the quote above is true. It is in reality that Behe’s constant resort to the contingencies of “naturalistic” heredity, while denying “naturalistic” contingencies in adapatation, fails utterly and completely, both on the ground of consistency and because he is unable to differentiate between the causes of various effects. If he is unable to constrain “design,” as he most certainly is not able to do (indeed, he takes pains to try make his claims of design unfalsifiable), then he cannot constrain anything else in the history of life. If “…anything might have been designed” (DBB, 193)–including mutations which are directed (a favorite claim in EoE)–then we have no reason to believe that the evidence of common descent was not also designed, and produced by miracle.
Yet he does believe observable causes are responsible for similarities:
Like the sequence analysts, I believe the evidence strongly supports common descent. DBB, 176
Unsurprisingly, where the actual “naturalistic” causes are unknown, whether in “design models” or in “atheistic models,” such certainties have not been obvious or accepted. A philosopher such as Buffon could propose that life arose to fit “internal molds,” which shaped organisms into set patterns. Paley states that “This similitude, surely, bespeaks the same creation and the same Creator” (Natural Theology, chap. 25).
One might suppose that Behe has more cause to believe in common descent than Paley did, however. Well, yes, that is true, both in the huge amount of evidence which indicates what is expected of common descent, and at least as importantly, because we understand the mechanisms of both conservation and of non-conservation of genetic information in organisms. The processes of preservation and of change are inextricably tied together within biology, never mind the fact that the concepts are different (the processes themselves are occasionally separable, such as during the early part of abiogenesis). That is, we understand how genetic information is preserved both by reproduction and by natural selection, and we know that because we understand the limits of change imposed by (roughly) the neo-Darwinian model of evolution.
Paley credited God for similarity because he could not conceive of how morphology (which is about the only type of evidence that he had) could be preserved as a “general plan,” yet so thoroughly modified. Darwin explained this, which is why he and most modern biologists have understood the evidence of common descent to implicitly support the known causes of organism modification. For, if there is nothing that accounts for the differences between frogs and humans, how are the similarities going to be accounted for via common descent? We have to understand similarities and differences under the same model, and we do so by understanding them all to be due to common descent as modified by mutation plus natural selection (plus other known processes).
Once one believes that an unobservable and unpredictable (in the probabilistic sense of the word) process, or processes, is responsible for the “design” of organisms, how can one possibly determine which aspects of organisms were not poofed into existence? A rat might as easily be descended from, or designed from the template of, an octopus or a petunia, if we are not paying attention to the actual mechanisms of stability and of change. The only apparent reason why Behe accepts the accidents of heredity, and not the evidence of accident in adaptation, is because he wishes his god to be responsible for the latter and not for the former. This goes back to the fact that Behe has absolutely no means of independently observing design in life in an entailed manner, discussed here.
The evidence that life evolved in a process involving natural selection is precisely the evidence of accident and contingency found in life. Two such crucial contingencies are the accidents of heredity and of mutation, and, aside from effects of the filter of natural selection, that is largely what we see in life (I write “largely” because causal regularities exist apart from natural selection and descent). The accidents of heredity are accepted by Behe as causal, even though any accepted meaning of the term “intelligent design” implies that such accidents would not predominate in life as they do–we filter out many undesirable accidents whenever we adapt designs. Then he wants “design” to hide underneath the accidents of mutation, and to be indistinguishable from them, except probabilistically.
Such a position must be called “incoherent,” at least if we are being charitable. The filter of intelligence involves rationality, planning, and the correction of defective accidental characteristics, wherever these occur. We accept that a filter quite different (if with some similarity in output) from intelligence produced life precisely because neither accidents of heredity nor of mutation characterize intelligent activity to any great degree, while they are unquestionably predicated of any unguided natural selectionist evolution involving the sorts of organisms we recognize.
I am writing this now because just one day previously I wrote a post about all of the evidence of evolution in the eukaryote flagellum, one of Behe’s “examples” of “irreducibly complex” systems. I noted there that Behe would accept the evidence of common descent, but would deny that it indicates that it evolved by the mechanisms by which we say it evolved, rather claiming that it had to be designed. That, however, is an absurd notion on his part, for the terms “intelligence,” “design,” and “intelligent design” do not even refer to processes adopting the contingencies of heredity and mutation that we observe in life. “Evolution,” and “evolution by natural selection,” by contrast, do refer to processes including such observed accidents and limitations. We simply match up cause to effect to conclude that eukaryotes’ flagella evolved (with no poofs).
So of course it is true that “common descent” and “natural selection” are separate (at least separable) concepts. In science, though, we do what Behe and other IDists do not, which is to combine the two concepts in order to constrain these concepts as they actually (empirically) do pertain to life.
Because Behe does not follow science at all in the area of origins, we are at a loss to understand how his god of the miracle mutations is in any way preferable to, or more scientific than, the belief that some god simply spoke all of life into existence a few thousand years ago, complete with the evidence predicted for organisms that have evolved without any guidance of intelligence.
This is part of a series of posts that I am combining into one long post, which may be found at Darwin’s Black Box.