A common argument for the existence of God is known as the “Argument from Design.” The essential argument is, “Where you see design, there must have been a designer.” There are several specific types of perceived design that theists often use in an attempt to demonstrate the existence of a supernatural designer, a.k.a. God, but the two most common are probably the “Fine Tuning” argument and the “Intelligent Design” argument. The first of these argues that there exist numerous quantities in our universe, like the speed of light or the gravitational constant, that could have taken on a wide range of possible values when the universe was formed, and most of those possible values would eliminate the possibility of life. That fact that the universe around us has values for these quantities that seem “fined tuned” to permit the existence of life looks, to such theists, like design. Therefore, the argument goes, there must have been a designer who ensured that these quantities had appropriate values, and that designer is God. This Fine Tuning argument will be the subject of an upcoming essay.
The “Intelligent Design” argument, the subject of the present essay, is one formulation of the argument from design as applied to biology, championed by Michael Behe. In its most common form, certain systems within biology are identified as possessing the quality of “irreducible complexity,” which means that of all of the numerous components of the system in question, a nontrivial subset of them are all necessary for the functioning of the system as a whole. That is, if any one of these components is removed, the system ceases to function. Because, the argument goes, evolution by natural selection proceeds by gradual, undirected modification (through mutation) of existing components, there is no selective pressure until the entire minimal set of components are present and functioning. Therefore, this irreducible complexity is evidence of design, because the accepted naturalistic mechanisms of evolution are incapable of producing such systems, and so they must have been produced by a designer.
The intelligent design argument is currently the most common alternative that is presented by theists to the theory of biological evolution, particularly in the context of the science curriculum in public education. Simply the existence of such an alternative explanation, which is not taught in public schools, seems to justify cries of, “teach the controversy,” and “academic unfairness.”
As regular readers of this blog probably suspect, I have multiple complaints with the Intelligent Design argument. I will divide my complaints into the following categories:
- “Irreducible complexity” isn’t irreducible.
- Intelligent design isn’t science.
- Intelligent design teaches students to stop investigating.
- There is no controversy over evolution.
Let’s dive in, shall we?
“Irreducible complexity” isn’t irreducible
In his book, “Darwin’s Black Box,” Michael Behe defines irreducible complexity as, “A single system which is composed of several interactive parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning.” Behe uses the example of a mousetrap to illustrate this concept. Consider the parts of a common mousetrap: the base, the catch, the spring, the hammer, and the hold-down bar. Removing any one of these components destroys the functionality of the mousetrap. Behe’s claim is that such systems cannot be produced by an evolutionary mechanism, because all of the parts would have had to have evolved simultaneously in order to provide a selective advantage. Such an irreducibly complex system, Behe claims, is clear evidence of external design. Behe then went on to identify several biological examples that he contended are similarly irreducibly complex, including the bacterial flagellum of E. coli, the blood clotting cascade, cilia, and the adaptive immune system.
I will start by examining the mousetrap example, and then later address the specific biological examples that Behe proposed. The mousetrap example misrepresents several aspects of evolutionary mechanisms. It assumes that evolution proceeds by the addition of individual parts, each in their final state. It assumes that evolution never removes parts. It assumes that only the final observed function matters. All of these assumptions are incorrect.
I could go through a detailed hypothetical scenario where, step-by-step, a modern mousetrap could develop by incremental changes, where each change confers a meaningful advantage and thus would be selected for in a natural selection mechanism. But I won’t, because there are many such examples available on the web; I will just link to them:
None of these scenarios (except the last one) suggest that mousetraps actually evolved this way. They are thought experiments that illustrate why Behe’s definition of irreducible complexity is irrelevant to biological evolution by natural selection.
The last of the links above, which traces the actual evolution of mousetraps, calls to mind another argument from design analogy, the so-called watch in the desert argument (to put it simply, if you find a watch in a desert, the natural assumption is that it is a designed object rather than a natural one), and my favorite response to that argument. I’m not going to follow that particular argument up at the moment, but may in the future if there is significant popular demand.
So, enough of the analogies… what about the specific biological systems that Behe claimed to be irreducibly complex? Let’s look at the explanations for the evolution of each that have emerged:
- Bacterial flagella: An active area of research, but one in which several plausiblescenarioshave been proposed. Here are several discussions of the state of the field:
- Blood clotting cascade: Similarly, this is an active area of research, and yet we have realistic evolutionary schemes proposed:
- Cilia: Again, an active area of research which has produced plausible evolutionary scenarios:
- The adaptive immune system: Hopefully you see the pattern by now:
In short, irreducible complexity, by Behe’s definition, has nothing to do with whether the complex system in question could result from an evolutionary process, and the proposed examples of irreducibly complex systems have plausible evolutionary origins that are in the process of being evaluated and refined in the scientific literature.
This last point is a perfect segue into my next objection to intelligent design.
Intelligent design isn’t science
I have a future essay planned where I discuss the nature of science, so I will not go into the full explanation here. However, some aspects of that discussion are central to understanding a key difference between intelligent design and biological evolution. Evolutionary theory makes predictions. For example:
- Evolutionary theory predicts that different sets of characteristics that can be used to generate phylogenetic trees will generate the same trees. They do.
- In 1837, it was observed that pig fetuses had a point where the jawbone detaches to become the bones of the middle ear. An early prediction of evolutionary theory based on this observations was that there should exist a fossil between reptiles and mammals that had two separate jaws bones, one of which was smaller and near the ear. Diarthrognathus was found, supporting this prediction.
- Darwin, based on observing the Madagascar Star orchid, predicted that a moth would be discovered with a tongue between ten and eleven inches long. 41 years later, such a moth was found.
- The first Archaeopteryx fossil had a poorly-preserved head. Later, fossils of Ichtyhornis and Hesperornis were found, where were essentially sea birds, but which had teeth. Early evolutionists predicted that better Archaeopteryx fossils would have teeth. These fossils were found, validating the prediction.
The list really can go on and on. Evolutionary theory is one of the most rigorously-tested scientific frameworks in existence.
Intelligent design, however, makes no positive predictions that can be tested. None. If intelligent design wasn’t responsible for a particular complex system, like the bacterial flagellum, then intelligent design proponents can simply retreat to other systems that they claim to be irreducibly complex. Intelligent design has been formulated in a way that prevents its falsification, and without falsifiability, a field is not science.
Another important feature of science is publication in peer-reviewed journals. Such papers are not merely lab reports outlining what a scientist discovered, they are a critical step in the scientific method. Peer reviewed papers are subjected to intense scrutiny by other scientists to determine if the conclusions claimed are sufficiently supported by the evidence provided. There isn’t a single credible peer-reviewed publication providing support to the intelligent design argument … which shouldn’t be a surprise, since, as I described above, intelligent design makes no predictions.
Creationism, intelligent design, and other claims of supernatural intervention in the origin of life or of species are not science because they are not testable by the methods of sciences. These claims subordinate observed data to statements based on authority, revelation, or religious belief. Documentation offered in support of these claims is typically limited to special publications of their advocates. These publications do not offer hypotheses subject to change in light of new data, new interpretations, or demonstration of error. This contrasts with science, where any hypothesis or theory always remains subject to the possibility of rejection or modification in the light of new knowledge.
Intelligent design is not science.
Intelligent design teaches students to stop investigating
Consider the last example of irreducible complexity that I mentioned that Behe proposed, the adaptive immune system. Intelligent design would have us identify that system as irreducibly complex, and then look for the designer. Evolutionary investigations of the origins of this system, however, leads us to the proposal that variable lymphocyte receptors of a particular type (VLRB) from a lamprey may be a key component in biomedical responses to inflammatory and autoimmune diseases (as was discussed in the last of the links under this heading above). I’ve used this graphic in an essay before, but it seems particularly appropriate here as well.
If we as a society want to have a chance of solving complex problems, we need to train the next generation of researchers to keep digging so that they push the boundaries of what we understand and what we can do. We need to train the next generation of citizens to value such investigation. “God did it” kills forward progress.
There is no controversy over evolution
As I discussed above, intelligent design isn’t science, and evolution is (I will have a more detailed essay discussing evolution soon). Evolution is the theoretical framework that makes all of the biological and ecological sciences comprehensible. The evidence for it is overwhelming. There is no evidence for intelligent design. Period.
Many of my readers will dispute those claims based on what the creationist propaganda states, and I welcome a discussion of them. But, this creationist propaganda is just that… propaganda. From a scientific perspective, the theory of biological evolution is as likely to be correct as is the theory of a spherical earth. Anyone who tells you otherwise either doesn’t understand the science or is lying.
I will give a brief breakdown of the argument here, though this will be expanded on in my later, more-detailed essay on evolution. There are three fundamental “length scales” covered by biological evolution. There is microevolution, which describes the variation in expressed traits within a population. There is macroevolution, which describes how the variation in expressed traits within a population can lead to speciation events, or the separation of a population into separate, non-interbreeding populations, and how this in turn can lead to large-scale variation in species. And finally there is common descent, which describes the common ancestry of all life on earth through phylogenetic analyses. (Please note, that the origins of life are not discussed here… that is not the theory of evolution, but a different theory known as abiogenesis.)
There is direct evidence that microevolution happens. The theories of reproduction with inherited traits, mutation, natural selection, and genetic drift explain how microevolution happens. These theories make quantitative predictions that are tested in laboratories daily. The results of these theories provide clear benefits such as an understanding of antibiotic resistance in bacteria and predictive animal husbandry.
There is direct evidence that macroevolution happens (there are numerous examples of speciation events that have been observed in the laboratory and in the wild). There are theoretical models here as well that describe how speciation occurs and how it can lead to extremely divergent species. Punctuated equilibrium is one particular example of such a theoretical model.
There are multiple types of indirect evidence for common descent, including the phylogenetic trees generated by genetic analysis, common trait analysis, and the fossil record. What is particularly remarkable is that all of these independent types of evidence produce strikingly similar phylogenetic trees. The parsimony among the evidence acquired by these quite different techniques is itself striking evidence in favor of the accuracy of common descent. Evolutionary theory, on this scale, explains how common descent happened. There is no serious scientific argument that it happened. Any discussions in the scientific literature that may sound to a nonscientist like controversy are about how it happened. And in large measure, that question has been answered; common descent by the inheritance of traits, mutations, natural selection and genetic drift, and speciation events are the core of the answer. Yes, some details are still being worked out, but the core is so well explained, so well tested, that there is no controversy at all about it.
While science isn’t a popularity contest, there is an amusing story that illustrates just how overwhelming the scientific support for biological evolution is. The Discovery Institute announced that over 700 scientists had expressed support for intelligent design as of February 8, 2007. In response to this, the National Center for Science Education responsed with a “light-hearted” petition called “Project Steve.” In it, only scientists named Steve or some variation (Stephen, Stephanie, Stefan, etc.) who support biological evolution were allowed to sign. The result was that nearly twice as many scientist Steves support biological evolution as do all scientists who support intelligent design. This is not a scientific survey in any sense, but it does serve to illustrate how overwhelming the disparity is between the two sides.
Where does this leave us?
It’s pretty simple. Intelligent design isn’t science, biological evolution is, and the degree to which there is agreement on this point is so overwhelming that contentions that there is a “controversy” that should be taught are laughable. Further, teaching otherwise seriously damages our students’ ability to compete with students trained in other countries.
So this example of the argument from design has failed to provide convincing evidence of a designer, because non-sentient processes are plausibly responsible for the diversity and complexity of life that we observe in the natural world. There are still other places where a designer could be lurking, such as the original appearance of life or in cosmological fine-tuning (both of which I will address in future essays), but biological diversity and complexity isn’t where he can be found.