I AM PLEASED TO HAVE an opportunity to respond to Dr. Behe's criticism of my paper, as it gives me an opportunity to elaborate on some aspects of my talk and clarify what I believe are misstatements or misinterpretations of my position. As Dr. Behe has accused me of raising straw men, I could perhaps point to a few of his own. This discussion could perhaps be subtitled, "My straw man can beat up your straw man "
The thrust of Dr. Behe's criticism is that in arguing the validity of Darwinian evolutionary theory, a comparison of the various hypotheses of immune diversity is (1) irrelevant and (2) begs the issue of where the immune system came from, for which he thinks there is at present no adequate answer. Let me address these issues one at a time.
In the first place, I chose this topic because it is restricted enough and sufficiently well investigated to be understandable in the framework of a short presentation. I did not wish to deal with the evolution of the immune system, since it is an extremely complex topic that does not lend itself to a didactic exposition. But since Dr. Behe has brought this up I will be happy to do so.
But first, let us consider his criticism that my analysis of the various hypotheses of immune diversity constitutes a straw man, which I use to buttress my own narrow and unsubstantiated belief in evolutionary dogma. Perhaps we can best do this by turning the argument around.
Say the germ line theory had proven to be true, and say that a mammal contained a huge amount of genetic information coding for millions and millions of different antibody types. Most of this information would never be marshaled, either in the individual's lifetime or the lifetime of the entire species. Say, further, that it were discovered that mammals carried genes that coded for man-made compounds that had been synthesized only this year, and that bore absolutely no resemblance to any naturally occurring compound. Do you think that a creationist would argue that such a system constituted scientific evidence for purpose in biology? And do you think, moreover, he would argue that the existence of genes of no selective value to the individual (or perhaps to the entire species) would suggest that mechanisms other than Darwinian evolution and natural selection guide the development of complex biological system? I leave it to the reader to decide this question.
Dr. Behe points out quite correctly that the enigma of immune diversity was solved using molecular techniques that were not available when the question was formulated. It was not resolved through a deductive process carried out by monks speculating in the confines of their cells in a lonely mountainside monastery. I agree with the statement that immune diversity was never a topic of theological conjecture. My point was that in the early years of the twentieth century there were several competing theories to account for how antibodies were produced. The theory of natural selection predicted that the germ line hypothesis could not possibly have been right, at least in its simplest formulation. This is a characteristic of a good scientific theory; it makes predictions, generates experiments, and drives the field forward.
Dr. Behe accuses me of presenting a biological mechanism and then arbitrarily stating that God wouldn't use it, and therefore God does not exist. Au contraire. My point was that what we know about the immune system gives us no reason to propose any kind of divine purpose or conscious will in shaping it. Clearly God may exist and he may use any means he wishes to shape the universe. Perversely, he may have created the universe ten minutes ago, and everything in it may be placed there simply to confuse and distract us. I certainly don't believe in such a wicked god, and neither does Dr. Behe or anyone else who defends Christian theology. The divine purpose that we are considering here finds its roots in biblical accounts of God and his powers. This God is a knowing, loving deity.
But Dr. Behe's obstruction is typical of anyone who clings steadfastly to the notion that living systems were shaped by a knowledgeable, rational, purposeful consciousness. When one presents a biological system that doesn't tit these criteria, Dr. Behe can always say, "You are trying to put ideas in God's head. Neither you nor anyone else knows what God was thinking when he created living systems."
If there is a rational purpose to life and if Darwinian evolution is inadequate to explain it, then the divine hand that shaped it must have created us in his image and his thought processes must be similar to our own. This is what the God of Christianity is all about. He is not arbitrary. He is not wicked. He is not capricious.
My point is that an inspection of the history of biology shows that, over and over again, theories of life requiring a teleological basis have been found, in the light of modern molecular investigations, to be unnecessary. This realization certainly doesn't argue that God does not exist, but simply that it is unnecessary to propose a divine purpose to explain how living creatures came to their present state of development. But this is precisely where Dr. Behe and I differ. He says that the most important materialistic, mechanistic principle of biology, the theory of evolution, is inadequate to explain the diversity of living systems, and therefore we must evoke divine purpose, and a divine purpose that intervenes on a step-by-step basis.
But to return to Dr. Behe's second criticism of my argument, are there really unresolvable questions concerning how the immune system could have evolved solely through natural selection? Most of Behe's specific points go back to the notion that the evolution of complex systems is impossible because none of the individual components has selective value independent of a complete, integrated whole. But this is a straw-man argument, which implies that unless the system is working flawlessly it won't work at all. Clearly in Dr. Behe's universe there is no Model T on the way from the horse and buggy to the Mercedes.
For instance, Behe says that an antibody molecule by itself would have no selective value for an organism, and therefore it is impossible that the immune system arose through a gradual process of evolution and natural selection. He then goes on to mention that a specific protein, known as complement, must be present in order for immunoglobulin molecules to exert toxicity against foreign invaders; he suggests that without a fully developed complement system antibodies would be of no selective value. But this statement ignores the fact that various primitive complement-like molecules have been identified in invertebrates, which function in a nonspecific manner to protect the organism from foreign invaders. In fact, complement-like molecules have been found in a variety of protostome and deuterostome invertebrates. These molecules are used for triggering phagocytosis (a process by which pathogens are devoured), possibly through the intervention of other molecules known as lectins.
Behe seems oblivious to the evidence that antibodies are members of a class of molecules, the immunoglobulin super family, many of whose members are involved in cell-cell recognition and signaling. In fact, super family molecules of the class known as b-microglobulin exist on the brain of the squid. It has been suggested that the immunoglobulin superclass evolved from a common precursor responsible for mediation of cell signals. Members of the Ig super family are found in the membranes of neurons, indicating that molecules that communicate signals use a common basic plan, modified for individual tasks. Thus a common molecular precursor has been revamped over and over again in the course of evolution. The ancestral immunoglobulin molecule no doubt functioned as a crude recognition molecule, allowing some degree of reactivity against foreign pathogens. From this vantage point we can think of the immune system as being one component of a broad-ranging communication network, occurring throughout the phylogenetic tree and throughout different organ systems within individuals.
It is not known how an internal recognition system became modified in the course of evolution so as to "turn outward" and recognize foreign proteins. But it does not take a great leap of the imagination to conceive of a primitive species that would use immunoglobulin-like molecules for recognition of foreign proteins through a mechanism of broad specificity, eventually developing through natural selection a panel of recognition signals, and then later evolving a broader and broader collection of molecules through gene duplication. Eventually mutations destabilizing some of these recognition genes might appear. These unstable regions might generate a wider range of molecules with a weak affinity for pathogenic organisms.
One can imagine what an advantage an organism would have with this crude proto-recognition system for the identification of foreign marauders, even if it were initially extremely inefficient.
A reasonable idea does not constitute a proof. I have suggested these possibilities simply to illustrate how artificial Behe's argument is, and to emphasize that there is nothing arcane or mysterious about the evolution through intermediate steps to a highly sophisticated biological mechanism. I would have to admit that we really do not know precisely
how the immune system came to be. But Dr. Behe's objection to a Darwinian evolutionary interpretation is precisely what troubles me about the anti-evolutionist stance; because we don't have an ironclad proof of every precise feature of the evolution of the immune system in hand, Behe suggests that we just abandon the whole enterprise and accept a fuzzy and ill-defined teleology as a scientific explanation.
This strikes me as a profoundly unscientific approach that is foreordained to failure.