The Darwinian mechanism

The term “Darwinian mechanism” refers, of course, to the menu of relevant natural processes that are presumed by the vast majority of biologists to make biological evolution and common descent possible. Here the key question is, In the judgment of ID advocates, what are the “relevant” natural processes that belong on this list? At minimum, the Darwinian mechanism menu includes genetic variation and natural selection. As Dembski’s expresses it, “The Darwinian mechanism consists of random variation, which provides the raw material for Darwinian evolution, and natural selection, which sifts that material.”

But there may be many more categories of natural processes that have contributed to the success of biological evolution over life’s formational history. Would ID proponents place all of these in the category of Darwinian mechanism? Evidently not. For instance, in their evaluation of the proposition that certain “irreducibly complex” biological structures like bacterial flagella were formed by this mechanism, both Behe and Dembski limit their evaluation to gradual processes only, processes that bring about only minuscule functional improvements (sometimes narrowly constrained to a single function) from generation to generation. According to Behe, for instance, “The key question is this: How could complex biochemical systems be gradually produced?”And in Behe’s book, Darwin’s Black Box, the index listing for “Darwinian evolution” includes the parenthetical clarification “(gradualism).”

In No Free Lunch, Dembski tells us that “The problem, then, is to coordinate the gradual Darwinian evolution of an organism with the emergence of an irreducibly complex system that the organism now houses but did not always possess.”And what about various transformational processes or events that fall outside of a strict gradualism? It seems that they are to be set aside as natural processes that are not relevant to ID’s evaluation of the Darwinian mechanism. “Ideas like coordinated macromutations, lateral gene transfer, set-aside cells, and punctuated saltational events are thoroughly non-Darwinian.”But the real question, it seems to me, is this: Whether or not these and other such events are considered to fall within the bounds of a strict gradualist definition of the “Darwinian mechanism,” are they relevant to the formational history of life on earth? The historical development of novel biotic structures is no respecter of the labels that we might choose to pin on the various factors contributing to their actualization.

Another restriction on the menu of relevant natural processes considered by Dembski as legitimate contributors to the Darwinian mechanism arises from his requirement that scientific explanations regarding evolutionary processes must be causally specific. In Dembski’s words, “Causal specificity means specifying a [natural] cause sufficient to account for the effect in question.”“Lack of causal specificity leaves one without the means to judge whether a transformation can or cannot be effected.”

Full causal specificity is, of course, the goal of all scientific explanations, but it is often very difficult to achieve, especially in the reconstruction of life’s formational history. That’s just a fact of life in evolutionary biology, as well as in many other areas of science. What, then, should biology do? Abandon its search for natural causes? Open the door to hypotheses regarding non-natural causation? Posit the possibility of occasional form-conferring interventions by an unembodied intelligent agent? Yes, says Dembski. In effect, that is the ID proposal. After noting that science - “when biased by naturalism” - tends to restrict its search for explanations to purely natural causes, Dembski argues: “But in the absence of causal specificity, there is no reason to let naturalism place such restrictions on our scientific reasoning.”

I suppose that one could grant the possibility that this last point is technically correct, but one could equally well argue that there are good reasons - scientific, philosophical, and theological - why most of us do find positing the sufficiency of natural causes to be warranted. Regardless of that, however, Dembski introduces a serious problem into his analysis when he takes full causal specificity to be a requirement for natural causes to be relevant contributions to the Darwinian mechanism. Many scientific hypotheses regarding the manner in which various transformational processes may have contributed to the actualization of some new biotic structure might fall short of full causal specificity - even though they may be highly plausible applications of mechanisms that are at least partially understood. When that is the case, the ID approach tends to denigrate them as nothing more than “just-so stories” and to remove them from further consideration.If these scientific hypotheses do not exhibit sufficient causal specificity to allow the computation of a numerical probability for success, then they are likely to be dismissed from ID’s consideration. Only those mechanisms that are now fully understood, it seems, can be placed on the menu of relevant natural processes contributing to the Darwinian mechanism.

What is the net effect of this requirement that only causally specific explanations count as relevant scientific accounts of how certain biotic structures got actualized? I believe it throws the door wide open to false positive claims regarding the need for non-natural explanations. No doubt there are now numerous biotic structures for which science is unable to formulate causally specific (detailed and complete) accounts of their actualization. In the absence of full causal specificity (a quality, incidentally, that ID demands of scientific explanations but not of its own explanations) the ID movement does indeed have opportunity to posit its non-natural, intelligent design explanations as logically permitted alternatives. However, each time a new causally specific scientific explanation for one of these biotic structures is developed, the ID explanation for its actualization immediately becomes superfluous.ID’s insistence that its claims can be refuted only by causally specific scientific accounts stands as an open invitation to false positive claims regarding the need for its appeal to non-natural causes.

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