The Quarterly Review of Biology WHAT IS WRONG WITH INTELLIGENT DESIGN?

This article reviews two standard criticisms of creationism/intelligent design (ID): it is unfalsifiable, and it is refuted by the many imperfect adaptations found in nature. Problems with both criticisms are discussed. A conception of testability is described that avoids the defects in Karl Popper’s falsifiability criterion. Although ID comes in multiple forms, which call for different criticisms, it emerges that ID fails to constitute a serious alternative to evolutionary theory. O striking difference between the intelligent design (ID) position and earlier forms of creationism is that ID is often formulated as a comparatively modest claim. For example, Young Earth Creationism denied that human beings share common ancestors with other species while affirming that God was the designer of organisms and that life on earth is at most 10,000 years old. ID, at least when stated in a minimalistic form, is officially neutral on these three claims (Behe 1996, 2005). The single thesis of what I will call mini-ID is that the complex adaptations that organisms display (e.g., the vertebrate eye) were crafted by an intelligent designer. Scientists have challenged Young Earth Creationism by pointing to compelling evidence for common ancestry and ancient life forms. These challenges do not touch mini-ID. Does that mean that mini-ID is well supported by evidence? This question about the evidential status of mini-ID differs from the psychological question of why it was developed. Although the rest of this paper will address the first query, a few comments are in order with respect to the second. ID proponents often make assertions that go beyond mini-ID’s single claim. 4 Volume 82 THE QUARTERLY REVIEW OF BIOLOGY For example, they often affirm that the intelligent designer they have in mind is supernatural ( Johnson 1991; Dembski 2002),and most deny common ancestry (Davis and Kenyon 1993; Dembski 1999). Why, then, do proponents of ID think that mini-ID is so important? After all, it leaves out so much. One reason is that versions of creationism that mention a supernatural being have a Constitutional problem—U.S. courts have deemed them religious, and so they are not permitted in public school science curricula. ID proponents hope that mini-ID can avoid this objection. In addition, mini-ID has the advantage of expressing an idea to which all creationists subscribe; it thus presents a united front, allowing the factions to stop squabbling and to face their common enemy. Although mini-ID is modest in what it asserts, ID proponents have high hopes for what it will achieve. According to the Discovery Institute’s “Wedge Strategy” (available at http:// www.antievolution.org/features/wedge.html), which was leaked on the internet in 2001, “[d]esign theory promises to reverse the stifling dominance of the materialist worldview, and to replace it with a science consonant with Christian and theistic convictions.” The Discovery Institute is the flagship ID think tank, and the “Wedge Strategy” is its political manifesto. So much for questions about religious motivation and political context (Forrest and Gross 2004). What about the evidence? The “No Designer Worth His Salt” Objection Many biologists take the fact that adaptations are often imperfect to provide a decisive objection to creationism and to mini-ID. Charles Darwin presents this type of argument (Burkhardt et al. 1993:224). More recently, Stephen Jay Gould(1980) made the objection famous in his discussion of the panda’s thumb. The “thumb” is a crude spur of bone that enables pandas to laboriously strip the bamboo they eat. Gould contends that if a truly intelligent designer had built the panda, the panda would possess a far more efficient device for preparing its meals. Biologists have cited other examples, but the conclusion drawn is the same—since no designer worth his salt (Raddick 2005) would produce the many imperfect adaptations we observe in nature, creationism is false. This criticism concedes that creationism is testable. In addition, it assumes that the designer, if he existed, would have wanted pandas to have a more efficient device for stripping bamboo. Creationists have a reply to this criticism. How does Gould (or anyone else) know what God (or some unspecified designer) would have wanted to achieve in building the panda (Nelson 1996; Sober 2005)? This is a good reply by creationists, but it is one that invites an entirely different, but equally serious, criticism of ID. Popper’s Falsifiability Criterion If imperfect adaptations do not demonstrate that the mini-ID claim is false, perhaps the right criticism is that this statement cannot be tested. But, what does testability mean? Scientists often answer by using Karl Popper’s concept of falsifiability (Popper 1959). According to Popper, a hypothesis is falsifiable precisely when it rules out a possible observational outcome. Popper understood “ruling out” in terms of deductive logic; a falsifiable statement is logically inconsistent with at least one observation statement. Popper further suggested that falsifiability provides a demarcation criterion, separating science from nonscience. Popper’s account entails that some versions of creationism are falsifiable, and hence scientific. Consider, for example, the hypothesis that an omnipotent supernatural being wanted everything to be purple, and had this as his top priority. Of course, no creationist has advocated purple-ID. However, it is inconsistent with what we observe, so purple-ID is falsifiable (the fact that it postulates a supernatural being notwithstanding). The same can be said of other, more modest, versions of ID that do not say whether the designer is supernatural. For example, if mini-ID says that an intelligent designer created the vertebrate eye, then it is falsifiable; after all, it entails that vertebrates have eyes. An even more minimalistic formulation of ID is also falsifiable; the statement that organisms were created by an intelligent designer entails that there are organisms, which is something we observe to be true. March 2007 5 WHAT IS WRONG WITH INTELLIGENT DESIGN? Probability Statements Are Not Falsifiable In addition to entailing that many formulations of ID are falsifiable, Popper’s criterion also has the consequence that probability statements are unfalsifiable. Consider the statement that a coin has a 50% probability of landing heads each time it is tossed. This statement is logically consistent with all possible sequences of heads and tails in any finite run of tosses. Popper attempted to solve this problem by expanding the concept of falsification. Rather than saying that H is falsified only when an observation occurs that is logically inconsistent with H, Popper suggested that we regard H as false when an observation occurs that H says is very improbable. But how improbable is improbable enough for us to be warranted in rejecting H? Popper thought that there was no objectively correct answer to this question; the choice of cut-off is a matter of convention (Popper 1959:191). Popper’s idea has much in common with Ronald Fisher’s test of significance (Fisher 1959). According to Fisher, if H says that an observation O is very improbable, and O occurs, then a disjunction is true—either H is false or something very improbable has occurred. The disjunction does follow, but it does not follow that H is false, nor does it follow that we should reject H. As many statisticians and philosophers of science have recognized (Hacking 1965; Edwards 1972; Royall 1997), perfectly plausible hypotheses often say that the observations have low probability. This is especially common when a probabilistic hypothesis addresses a large body of data. If we make a large number of observations, it may turn out that H confers on each observation a high probability, although H confers on the conjunction of observations a tiny probability. If Fisher’s test of significance fails to provide a criterion for when hypotheses should be rejected, it also fails to describe when a hypothesis is falsifiable. Perhaps Popper’s f-word should be dropped. The fact that Popperian falsifiability fails to capture what testability is does not mean that we should abandon the latter concept. Rather, a better theory of testability is needed. Testing Is Comparative To develop an account of testability, we must begin by recognizing that testing is typically a comparative enterprise. If ID is to be tested, it must be tested against one or more competing hypotheses. Creationists now single out evolutionary theory as their stalking horse. Before 1859, the competing theory was the vaguer idea of “chance”—that a mindless random process is responsible for the complex adaptations we observe. The details of these alternative hypotheses do not matter to the problem at hand, but they contribute an insight into the kinds of observational consequences that a formulation of ID needs to have if it is to be tested against its competitors. For example, if mini-ID says that an intelligent designer made the vertebrate eye, and this claim is to be tested against the claim that chance produced the vertebrate eye, we must discover how these two hypotheses disagree about what we should observe. Since both entail that vertebrates have eyes, the observation that this is true does not help. We need to find other predictions that mini-ID makes.