Darwin's Black Box: The Biochemical Challenge to Evolution. By Michael J. Behe. New York: The Free Press, 1996.
Autor: Marie I. George, St. John's University, New York
Publicado en: The Thomist, 62, 3 (July 1998), 493-497.
Fecha de publicación: July 1998
Michael Behe has a gift for explaining things, be they complex biochemical processes or key philosophical terms. His clarity along with his scientific competence account for why he succeeded in capturing the attention of major scientific journals such as Nature and the American Scientist despite his opposition to neo-Darwinian orthodoxy. Behe presents a biochemical remake of Paley's argument from design. He maintains that the present inability of neo-Darwinism to explain the origin of complex biochemical systems is due to the very nature of these systems. The failure of neo-Darwinism coupled with the irreducibly complex nature of these systems leads Behe to conclude that the only adequate explanation for them is an intelligent designer.
Behe begins by explaining why Paley's argument needs to be reformulated, that is, why the proper way to determine the adequacy of the neo-Darwinian explanation of evolution is by examining things at a biochemical level. Contrary to Paley, who thought that there was a need to invoke design at the level of gross anatomy to explain organs of extreme perfection, Behe maintains that at that level neo-Darwinism offers a plausible step-by-step account of the origin of such organs. The problem Behe has with neo-Darwinian explanations is that they fail to take in account the underlying biochemistry. He reasons that if the inner workings of something are not understood, if something is a 'black box,' there is no way one can render judgment as to whether the origin of that thing can be fully explained by random changes which accumulated gradually. He proceeds to explain the biochemistry upon which the functioning of one complex organ depends (namely, the eye), making it amply clear that the complexity of the interactions makes it difficult to see how any adequate explanation of their origin could be provided by Darwinian principles. This leads him to conclude: "Now that the black box of vision has been opened, it is no longer enough for an evolutionary explanation of that power to consider only the anatomical structure of whole eyes....Each of the anatomical steps and structures that Darwin though were so simple actually involves staggeringly complicated biochemical processes that cannot be papered over with rhetoric."
Behe devotes a large part of chapter 2 to citing respected biologists who also have difficulties with the versions of neo-Darwinism that insist on the slow accrual of mutations. He then goes on to expose what he finds problematic, by first asking: "What type of biological system could not be formed by "numerous, successive, slight modifications"?" His response is "a system that is irreducibly complex" (39). The definition of this key concept follows: "By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning" (39). He uses the simple example of a mousetrap to illustrate what he means (42, 43): for a mousetrap to function at all the hammer, string, catch, holding bar, and platform have to all be present and assembled in the appropriate way out of appropriate materials. An irreducibly complex system cannot be produced by continuously improving the initial function (which continues to work by the same mechanism), by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition non-functional. Behe further maintains that a system has to be working for it to be retained by natural selection, and thus that "if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop." (39).
Here though, the alternative of coadaptation presents itself: could not the parts of the future organ be performing some other function before they get diverted to the new function? Behe would respond that the initial functional units require an explanation at the biochemical level, and here the Darwinian analysis is bound to run up against irreducible complexity (150-153).
In the second section Behe gives detailed, but easy to follow, explanations of a number of biochemical equivalents of the mousetrap: cilium, blood clotting, the AMP pathway, and B cells. It is unfortunate that we cannot go over the details here, for the strength of the case Behe makes for design cannot be fully appreciated without them. In regard to each case, Behe does two things. First, he highlights the irreducible complexity found within. For example, blood clotting requires a determinate amount of substances activated at the right time an a the right speed. If any factor is missing or if the timing is not right death will ensue. Thus, a mutation which simply produced one of the factors and not the others would either be of non use to the organism, or to the extent it was produced in an unregulated fashion would be liable to be detrimental to it. And there is no reason for a regulatory system to have been retained by selection if it appeared before the apparition of the factors that would need regulating. The need for regulation in biochemical systems poses a seemingly insurmountable obstacle to gradualism.
After manifesting the irreducibly complex nature of specific systems, Behe proceeds to show that in spite of their biological importance, an examination of scientific literature turns up relatively few attempts to explain their evolutionary origins, and the few attempts that are made are generally hopelessly vague and do not face up to the need to account for biochemical complexity. To my mind, Behe successfully make an inductive case that the show of confidence of neo-Darinism in its ability to explain how different life-forms developed really reposes on no explanation, or at least on none that enter into the "black box" and can submitted to scientific verification. While most scientific reviewers do not disagree as to Behe's description of the present state of evolutionary biology, they do insist that the pessimist prognosis Behe gives is premature given the newness of the discipline.
In chapter 9 Behe addresses the matter of design, which he defines as "the purposeful arrangement of parts" (193). He delineates when it is reasonable to conclude that something has been designed: "For discrete physical systems--if there is not a gradual route to their production--design is evident when a number of separate, interacting components are ordered in such a way as to accomplish a function beyond the individual components. The greater the specificity of the interacting components required to produce the function, the greater is our confidence in the conclusion of design" (194).
Behe then rests his case: "If a biological structure can be explained in terms of those natural laws [biological reproduction, mutation, and natural selection], then we cannot conclude that it was designed. Through this book, however, I have shown why many biochemical systems cannot be built up by natural selection working on mutations" (203, 204). He goes on to admit the possibility that there may be an as-yet-undiscovered natural process that would explain biochemical complexity. However, he sees this about as likely as discovering a Loch Ness monster. A common criticism leveled against Behe's reasoning here is that it is an appeal to ignorance, and one that seems particularly flagrant since it is only fairly recently that genetics is coming into its own.
A still more serious criticism of Behe is that he fails to revamp Paley's argument inasmuch as the (generally understood) deficiency of the latter lies in its presentation of gaps which were supposed to be unfillable by natural causes. This deficiency will not be remedied by exposing other gaps that may in the future be filled. Paley should have invoked a designer (and perhaps did) not to fill in gaps as to secondary efficient causality, but to give an adequate account of the order that he saw in living things. Behe thinks that if neo-Darwinism or some other naturalistic theory can explain an organ or biochemical process, then there is no need to bring in a designer. However, if science were to find explanations for biochemical systems, it would not, by that very fact, exclude the need for a designer in order to reach a complete explanation. After all, the construction of a house depends not only on construction workers, but on an architect. One could further question Behe's denial that the human eye at the level of gross anatomy is a manifest instance of design. He reasons that the dependency of one part upon another is not as critically adjusted as are the factors in biochemical processes; yet the human eye's parts are clearly adjusted not for some minimal functioning, but so that the kind of vision which hallows for reading and the manipulationg of very small objects is possible. Is a modern luxury car less in need of a designer than the minimally functional original Ford?
One could also turn Behe's objection to Paley against him: biochemistry is unable to establish irreducible complexity because it does not reveal the ultimate workings of the black box, since biochemistry itself is a black box ultimately explained by physics.
In chapter 10 Behe examines some of the other reasons that lead to the demise of the argument from design. He astutely notes how some have focused on Paley's poorly chosen examples as a pretext to reject his entire argument (212). He is also to be credited for his response to Hume's supposed refutation of Paley (217). Hume argues that watches and organisms are very dissimilar, and so if watches require a designer, it does not necessarily follow that organisms do. Behe responds that the argument from analogy is valid, for "in order to reach a conclusion based on an analogy, it is only necessary that the deduction flow out of the shared properties." The irreducibly complex watch required an intelligent designer to produce it; therefore an irreducibly complex system also requires a designer.
Does Behe go so far as to deny that new life forms have evolved over time? If there are no natural explanations for the origin of the biochemistry needed for organs (such as the eye) of organisms appearing late in the fossil record, are we not back to special creation of each organism? Behe suggests that perhaps the designer made the first cell containing numerous irreducibly complex systems, most of which were only to be "turned on" many generations later (227, 228). However, one wonder why, if the designer is intelligent enough to make the first cell "loaded," he could not "program" a universe to produce eventually a cell capable of gradually complexifying through generations by natural means? Another objection, raised by the biologist Kenneth Miller, is that if the first cell had many genes turned off, they would not be subject to selection, and thus would tend to accumulate a tremendous number of mutations rendering the irreducibly complex systems inoperable by the time they were needed.
Behe successfully dispels the myth that neo-Darwinism has everything under control in explaining the origin of life and of the various biochemical systems needed for various life forms. He attempts to find theoretical grounds for why such an explanation could never be forthcoming from that quarter. In the end, however, he admits he cannot provide such. He is to be commended for stimulating reexamination of the design argument, as well as for doing a marvelous job of putting before our eyes the design of biochemical system, systems which Darwin and Paley did not even know existed. In the final analysis, however, it seems at very least premature to rest one's case for God's existence on tiny gaps.