Jerry A. Coyne
Intelligent Design: The Faith That Dare Not Speak Its Name
Intelligent design is not an evangelic Christian thing, or a generally Christian thing or even a generically theistic thing. . . . Intelligent design is an emerging scientific research program. Design theorists attempt to demonstrate its merits fair and square in the scientific world-without appealing to religious authority.
-William A. Dembski, The Design Revolution (2004)
[A]ny view of the sciences that leaves Christ out of the picture must be seen as fundamentally deficient. . . . [T]he conceptual soundness of a scientific theory cannot be maintained apart from Christ.
-William A. Dembski, Intelligent Design: The Bridge Between Science & Theology (1999)
Well, which is it? Is intelligent design (ID) merely a sophisticated form of biblical creationism, as most biologists claim, or is it science-an alternative to Darwinism that deserves discussion in the science classroom? As the two quotations above imply, you won't find the answers in the writings of the leading advocates of ID.
The ambiguity is deliberate, for ID is a theory that must appeal to two distinct constituencies. To the secular public, ID proponents present their theory as pure science. This, after all, is their justification for a slick public-relations campaign promoting the teaching of ID in the public schools. But as is clear from the infamous "Wedge Document" of the Discovery Institute, a right-wing think tank in Seattle and the center for ID propaganda, intelligent design is part of a cunning effort to dethrone materialism from society and science and replace it with theism.1 ID is simply biblical creationism updated and disguised to sneak evangelical Christianity past the First Amendment and open the classroom door to Jesus. The advocates of ID will admit this, but only to their second constituency, the sympathetic audience of evangelical Christians on whose support they rely.
Nevertheless, let us give the ID movement the benefit of the doubt. Let us suppose that ID might indeed be an alternative and superior scientific theory-one that explains the natural world better than Darwinian evolution does. Can such an argument stand up to scrutiny? Is it time for Darwinian evolution to go the way of Newtonian mechanics, as a theory good for its time but ripe for replacement by a new paradigm? No. Not only is ID markedly inferior to Darwinism at explaining and understanding nature but in many ways it does not even fulfill the requirements of a scientific theory.
What are those requirements? A scientific theory isn't just a guess or speculation, it is a convincing explanatory framework for a body of evidence about the real world. A good scientific theory makes sense of wide-ranging data that were previously unexplained. In addition, a scientific theory must make testable predictions and be vulnerable to falsification. Einstein's theory of relativity, for example, received a definitive test (and confirmation) by measurements of the bending of starlight by the sun during a solar eclipse. If a theory can't be tested or falsified, it is not a scientific theory. The theory that God caused the Big Bang, for example, isn't a scientific theory, because (while it may be true) there are no observations we can make to disprove it. When a theory has withstood many tests and made many correct predictions, it becomes a scientific fact, which we can understand as a theory having such strong support that all rational people would accept it. The theories of atoms and of chemical bonds, for example, have graduated from theory to fact. Both could conceivably be shown to be wrong-all the data supporting the existence of atoms might have been deceptive-but it's highly unlikely.
So, how do Darwinism and ID compare when judged against these criteria? Let's start by looking at Darwinism. The modern theory of evolution, called neo-Darwinism in light of 150 years of post-Darwin research, has four parts. Put simply, these are as follows:
First, evolution occurs; that is, living species are descendants of other species that lived in the past.
Second, evolutionary change occurs through the gradual genetic transformation of populations of individuals over thousands or millions of years.
Third, new forms of life arise from the splitting of a single lineage into two, a process known as speciation. This continual splitting leads to a nested genealogy of species-a "tree of life" whose root was the first species to arise and whose twigs are the millions of species living today. Trace back any pair of twigs from modern species through the branches and you will find that they share a common ancestor, represented by the node at which the branches meet.
And fourth, much of evolution occurs through natural selection. Individuals carrying genes better suited to the current environment leave more offspring, causing genetic change in populations over time which improves the "fit" of the organism to the environment. It is this improving fit that gives organisms the appearance of having been well designed for their lifestyles.
These claims don't necessarily stand or fall together. Nevertheless, evidence supporting all four began to accumulate starting with Darwin's 1859 On the Origin of Species and continues to inundate us today. Every bit of information we have gathered about nature is consonant with the theory of evolution, and there is not one whit of evidence contradicting it. Neo-Darwinism, like the theory of chemical bonds, has graduated from theory to fact.
What is this evidence? It is immense, so I will just touch upon what Darwin himself presented, though he had only a fraction of the evidence available today. It came from the fossil record, from curious remnants persisting in the anatomy and development of living species, and from biogeography-the geographical distribution of Earth's flora and fauna.
Let's start with the obvious place to look, the fossil record. Even in Darwin's time, there was evidence here supporting evolution, in the sequence of organisms laid down in the rocks. The deepest and oldest sediments show marine invertebrates; fish appear much later, and amphibians, reptiles, and mammals later still. Why should divine creation follow such a path, from the simple to the complex? Yet it is what we would expect with evolution. Darwin also observed that the species inhabiting any region-the living marsupials of Australia, for instance-closely resemble fossils found in the same place. This suggests that the former descended from the latter. We can trace evolutionary changes in lineages through the record: Diatoms grow larger, clamshells get ribbier, horses become larger and toothier, and the human lineage evolves bigger brains, smaller teeth, and greater proficiency at walking on two legs. There are transitional forms, too-but more on those later.
Leaving behind the dead, we also find ample evidence of evolution among the living-relics that the evolutionary biologist Stephen Jay Gould dubbed "the senseless signs of history." They are many: The tooth buds developed in the embryonic stage by birds and anteaters-buds that are later aborted and never erupt-are remnants of their toothed ancestors. The tiny vestigial wings hidden under the feathers of the flightless kiwi attest to its ancestors' ability to fly. Some cave-dwelling animals have rudimentary eyes that cannot see, degenerate remnants of their ancestors' sighted ones. What creator, or guiding intelligence, would give animals such useless tooth buds, wings, or eyes?
Our bodies, too, are a palimpsest of our ancestry. The appendix is a familiar example. Less well known is the bad design of the recurrent laryngeal nerve-a nerve that runs from the brain to the larynx, helping us speak and swallow. In mammals, this nerve doesn't take a direct route but descends into the chest, loops around the aorta near the heart, and then runs back up to the larynx. It is several times longer than it needs to be; in the giraffe the nerve has to traverse the neck twice and so is fifteen feet long-fourteen feet longer than necessary! The added length makes the nerve more susceptible to injury, and its tortuous path makes sense only in light of evolution. We inherited our developmental pathway from that of ancestral fish, in which the precursor of the recurrent laryngeal nerve attached to the sixth of the gill arches, embryonic bars of muscle, nerves, and blood vessels that developed into gills. During the evolution of land animals, some of the ancestral vessels disappeared, while others were rearranged into a new circulatory system. The blood vessel in the sixth gill arch moved backward into the chest, becoming the aorta. As it did so, the nerve that looped around it was constrained to move backward in tandem. Natural selection could not create the most efficient configuration because that would have required breaking the nerve and leaving the larynx without innervation.
Look deeper and you find evidence for evolution buried in our DNA. Our genome is a veritable farrago of nonfunctional DNA, including many inactive "pseudogenes" that were functional in our ancestors. Why do humans, unlike most mammals, require vitamin C in their diet? Because primates cannot synthesize this essential nutrient from simpler chemicals. Yet we still carry all the genes for synthesizing vitamin C. The gene used for the last step in this pathway was inactivated by mutations 40 million years ago, probably because it was unnecessary in fruit-eating primates.
Is this really the best an "intelligent" designer can do? IDers claim that arguments for evolution based on inefficiencies or vestigial structures are unscientific because they supposedly include an unjustified theological assumption that a designer would not create such structures. But IDers are missing the point here. The evolutionary argument is that these imperfections and inefficiencies make sense only if one assumes that evolution has occurred! They comport with creationism only if you believe that the creator deceptively designed all organisms to delude us into thinking that they had evolved.
And finally, what of biogeography? This yields some of the most powerful evidence for evolution. It was Darwin's genius in the Origin to show that the distribution of plants and animals made sense only by assuming that species had evolved and split into additional species. Let's take his argument about the wildlife of oceanic islands-islands that, like the Galápagos and Hawaii, were never connected to continents but arose, bereft of terrestrial life, from beneath the sea. Compared with continents or continental islands, these islands have bizarrely unbalanced flora and fauna-unbalanced in that they are missing or impoverished in many types, while others (especially plants, insects, and birds) are present in profusion, consisting of clusters of numerous similar species "radiations." Hawaii, for example, has no native terrestrial mammals, reptiles, or amphibians but has large radiations of fruit flies and silversword plants. One third of the world's 2,000 species of fruit flies are found on the archipelago, although it makes up only 2 percent of the land on Earth.
Moreover, the animals and plants inhabiting an oceanic island are most similar to those species found on the nearest mainland, often despite great differences in habitat. Darwin's clinching point was this: The kinds of wildlife commonly found on oceanic islands are those that could get there easily, carried by winds, ocean currents, or other animals. Clearly, novel species on oceanic islands descend from those that were able to colonize from the nearest mainland and subsequently evolved and speciated on the islands. Only unplanned evolution makes sense of all these observations of island biogeography. No theory of design or creation even begins to explain them.
Darwin had strong evidence for evolution but no direct evidence for natural selection as the process by which it occurs. He relied on logical argument-the existence of variation in populations and its influence on reproductive success, from which natural selection followed inevitably-and on analogy with the artificial selection used by breeders to produce forms as diverse as Chihuahuas and St. Bernards from wolves, and cauliflower and Brussels sprouts from wild cabbage, within a mere 1,000 years or so.
But vast amounts of evidence have accumulated since Darwin's time. Biologists have now observed hundreds of cases of natural selection, beginning with the well-known examples of bacterial resistance to antibiotics, insect resistance to DDT, and HIV resistance to antiviral drugs. Natural selection accounts for the defense of fish and mice against predators via camouflage and for the adaptation of plants to toxic minerals in the soil. And the strength of selection observed in the wild, when extrapolated over long periods, is more than adequate to explain the diversification of life on Earth.
Neo-Darwinian evolution passes with flying colors the test of a scientific theory as an explanatory framework for wide-ranging evidence. What a remarkably elegant theory it is, and what a vast body of evidence it explains! It makes sense of data from fields as diverse as paleontology, biogeography, embryology, anatomy, and molecular biology. The geneticist Theodosius Dobzhansky famously declared, "Nothing in biology makes sense except in the light of evolution." One might add that nothing in biology makes sense in the light of intelligent design.
But can neo-Darwinism make predictions? And is it falsifiable? Yes, and yes again. As a historical science, it cannot be expected to predict the future. But it can, nevertheless, make powerful predictions.
Darwin himself made predictions from his theory. The age of the earth was unknown in his time, but he predicted that it would be old, to allow time for evolution to produce the existing diversity of life. We now know that Earth is 4.6 billion years old. He also predicted that if plants on oceanic islands were descended from those on continents, the seeds of continental plants should be able to survive prolonged immersion in seawater, and he confirmed this prediction with experiments described in the Origin.
Developments in biology after Darwin have served to confirm other predictions of evolutionary theory: For example, in order for natural selection to operate, there must be plenty of heritable variation in wild populations of plants and animals. We now know the source of this variation (a problem that baffled Darwin): mutations in DNA. Research in the past century has uncovered ample genetic variation for nearly every trait in every species studied.
We also now understand that natural selection involves the differential reproduction of genes. That means there should be examples of selection that benefit the genes themselves and not their carriers. Recent studies have thoroughly confirmed this prediction. In the production of eggs and sperm, for example, there is normally a 50 percent probability of each of our two gene copies going into each gamete. But there are some "selfish genes" that kill their partners and so get overrepresented in eggs and sperm. This observation does not follow obviously from the view that organisms were intelligently designed.
1 The Wedge Document, an internal memorandum of the institute, was leaked to the Internet in 1999 and later acknowledged by the institute as authentic. It can be found at http://www.geocities.com/CapeCanaveral/Hangar/2437/wedge.html. It states: "The social consequences of materialism have been devastating. As symptoms, those consequences are certainly worth treating. However, we are convinced that in order to defeat materialism, we must cut it off at its source. That source is scientific materialism. This is precisely our strategy. If we view the predominant materialistic science as a giant tree, our strategy is intended to function as a 'wedge' that, while relatively small, can split the trunk when applied at its weakest points . . . Design theory promises to reverse the stifling dominance of the materialistic worldview, and to replace it with a science consonant with Christian and theistic convictions."