Organismic vs. Cosmic Design Arguments: Limitations of Intelligent Design, Papers of Engineering

Download Organismic vs. Cosmic Design Arguments: Limitations of Intelligent Design and more Papers Engineering in PDF only on Docsity! (an earlier version appears in W. Mann (ed.), The Blackwell Companion to Philosophy of Religion, 2004) The Design Argument Elliott Sober1 The design argument is one of three main arguments for the existence of God; the others are the ontological argument and the cosmological argument. Unlike the ontological argument, the design argument and the cosmological argument are a posteriori. And whereas the cosmological argument can focus on any present event to get the ball rolling (arguing that it must trace back to a first cause, namely God), design theorists are usually more selective. Design arguments have typically been of two types – organismic and cosmic. Organismic design arguments start with the observation that organisms have features that adapt them to the environments in which they live and that exhibit a kind of delicacy. Consider, for example, the vertebrate eye. This organ helps organisms survive by permitting them to perceive objects in their environment. And were the parts of the eye even slightly different in their shape and assembly, the resulting organ would not allow us to see. Cosmic design arguments begin with an observation concerning features of the entire cosmos – the universe obeys simple laws, it has a kind of stability, its physical features permit life and intelligent life to exist. However, not all design arguments fit into these two neat compartments. Kepler, for example, thought that the face we see when we look at the moon requires explanation in terms of intelligent design, as did Newton when he considered the fact that the planets circle the sun in the same direction and in the same plane . Still, the common thread is that design theorists describe some empirical feature of the world and argue that this feature points towards an explanation in terms of God’s intentional planning and away from an explanation in terms of mindless natural processes. The design argument raises epistemological questions that go beyond its traditional theological context. As William Paley (1802) observed, when we find a watch while walking across a heath, we unhesitatingly infer that it was produced by an intelligent designer. No such inference forces itself upon us when we observe a stone. Why is explanation in terms of intelligent design so compelling in the one case, but not in the other? Similarly, when we observe the behavior of our fellow human beings, we find it irresistible to think that they have minds that are filled with beliefs and desires. And when we observe nonhuman organisms, the impulse to invoke mentalistic explanations is often very strong, especially when they look a lot like us. When does the behavior of an organism – human or not -- warrant this mentalistic interpretation? The same question can be posed about machines. Few of us feel tempted to attribute beliefs and desires to hand calculators. We use calculators to help us add, but they don’t literally figure out sums; in this respect, calculators are like pieces of paper on which we scribble our calculations. There is an important difference between a device that we use to help us think and a device that itself thinks. However, when a computer plays a decent game of chess, we may find it useful to explain and predict its behavior by thinking of it as having goals and deploying strategies (Dennett 1987b). Is this merely a useful fiction, or does the machine really have a mind? And if we think that present day chess-playing computers are, strictly speaking, mindless, what would it take for a machine to pass the test? Surely, as Turing (1950) observed, 1 it needn’t look like us. In all these contexts, we face the problem of other minds (Sober 2000a). If we understood the ground rules in this general epistemological problem, that would help us think about the design argument for the existence of God. And conversely – if we could get clear on the theological design argument, that might throw light on epistemological problems that are not theological in character. What is the Design Argument? The design argument, like the ontological argument, raises subtle questions about what the logical structure of the argument really is. My main concern here will not be to describe how various thinkers have presented the design argument, but to find the soundest formulation that the argument can be given. The best version of the design argument, in my opinion, uses an inferential idea that probabilists call the Law of Likelihood. This can be illustrated by way of Paley’s (1802) example of the watch on the heath. Paley describes an observation that he claims discriminates between two hypotheses: (W) O1: the watch has features G1 ... Gn. W1: the watch was created by an intelligent designer. W2: the watch was produced by a mindless chance process. Paley’s idea is that O1 would be unsurprising if W1 were true, but would be very surprising if W2 were true. This is supposed to show that O1 favors W1 over W2; O1 supports W1 more than it supports W2. Surprise is a matter of degree; it can be captured by the concept of conditional probability. The probability of O given H -- Pr( O│H) -- represents how unsurprising O would be if H were true. The Law of Likelihood says that we can decide in which direction the evidence points by comparing such conditional probabilities: (LL) Observation O supports hypothesis H1 more than it supports hypothesis H2 if and only if Pr(O│H1) > Pr(O│H2). There is a lot to say on the question of why the Law of Likelihood should be accepted (Hacking 1965, Edwards 1972, Royall 1997, Forster and Sober 2001); for the purposes of this essay, I will take it as a given. We now can describe the likelihood version of the design argument for the existence of God, again taking our lead from one of Paley’s favorite examples of a delicate adaptation. The basic format is to compare two hypotheses as possible explanations of a single observation: (E) O2: the vertebrate eye has features F1 ... Fn. E1: the vertebrate eye was created by an intelligent designer. E2: the vertebrate eye was produced by a mindless chance process. We do not hesitate to conclude that the observations strongly favor Design over Chance in the 2 Paley (1802, p. 179) says, is intelligent design. This is because the alternative explanation is that the direction of our eyes and the direction of our gait were determined by chance, which would mean that there was only a 1/4 probability that our eyes would be able to scan the quadrant into which we are about to step. I construe the concept of chance in a particular way. To say that an outcome is the result of a uniform chance process means that it was one of a number of equiprobable outcomes. Examples in the real world that come close to being uniform chance processes may be found in gambling devices -- spinning a roulette wheel, drawing from a deck of cards, tossing a coin. The term “random” becomes more and more appropriate as real world systems approximate uniform chance processes. As R.A. Fisher once pointed out, it is not a “matter of chance” that casinos turn a profit each year, nor should this be regarded as a “random” event. The financial bottom line at a casino is the result of a large number of chance events, but the rules of the game make it overwhelmingly probable, though not certain, that casinos end each year in the black All uniform chance processes are probabilistic, but not all probabilistic outcomes are “due to chance.” It follows that the two hypotheses considered in my likelihood rendition of the design argument are not exhaustive. Mindless uniform chance is one alternative to intelligent design, but it is not the only one. This point has an important bearing on the dramatic change in fortunes that the design argument experienced with the advent of Darwin’s (1859) theory of evolution. The process of evolution by natural selection is not a uniform chance process. The process has two parts. Novel traits arise in individual organisms “by chance;” however, whether they then disappear from the population or increase in frequency and eventually reach 100% representation is anything but a “matter of chance.” The central idea of natural selection is that traits that help organisms survive and reproduce have a better chance of becoming common than traits that hurt. The essence of natural selection is that evolutionary outcomes have unequal probabilities. Paley and other design theorists writing before Darwin did not and could not cover all possible mindless natural processes. Paley addressed the alternative of uniform chance, not the alternative of natural selection.4 Just to nail down this point, I want to describe a version of the design argument formulated by John Arbuthnot. Arbuthnot (1710) examined the birth records in London over 82 years and noticed that in each year, slightly more sons than daughters were born. Realizing that boys die in greater numbers than girls, he saw that this slight bias in the sex ratio at birth gradually subsides until there are equal numbers of males and females at the age of marriage. Arbuthnot took this to be evidence of intelligent design; God, in his benevolence, wanted each man to have a wife and each woman to have a husband. To draw this conclusion, Arbuthnot considered what he took to be the relevant competing hypothesis – that the sex ratio at birth is determined by a uniform chance process. He was able to show that if the probability is ½ that a baby will be a boy and ½ that it will be a girl, then it is enormously improbable that the sex ratio should be skewed in favor of males in each and every year that he surveyed (Stigler 1986, pp. 225-226; see also Sober 200x). Arbuthnot could not have known that R.A. Fisher (1930) would bring sex ratio within the purview of the theory of natural selection. Fisher’s insight was to see that a mother’s 5 mix of sons and daughters affects the number of grandoffspring she will have. Fisher demonstrated that when there is random mating in a large population, the sex ratio strategy that evolves is one in which a mother invests equally in sons and daughters (Sober 1993, p. 17). A mother will put half her reproductive resources into producing sons and half into producing daughters. This equal division means that she should have more sons than daughters, if sons tend to die sooner. Fisher’s model therefore predicts the slightly uneven sex ratio at birth that Arbuthnot observed.5 My point in describing Fisher’s idea is not to fault Arbuthnot for living in the 18th century. Rather, the thing to notice is that what Arbuthnot meant by “chance” was very different from what Fisher was talking about when he described how a selection process might shape the sex ratio found in a population. Arbuthnot was right that the probability of there being more males than females at birth in each of 82 years is extremely low, if each birth has the same chance of producing a male as it does of producing a female. However, a male-biased sex ratio in the population is extremely probable, if Fisher’s hypothesized process is doing the work. Showing that Design is more likely than Chance leaves it open that some third, mindless, process might still have a higher likelihood than Design. This is not a defect in the design argument, so long as the conclusion of that argument is not over-stated. Here the modesty of the likelihood version of the design argument is a point in its favor. To draw a stronger conclusion – that the Design hypothesis is more likely than any hypothesis involving mindless natural processes -- one would have to attend to more alternatives than just Design and (uniform) Chance.6 I now want to draw the reader’s attention to some features of the likelihood version of the design argument (E) concerning how the observation and the competing hypotheses are formulated. First, notice that I have kept the observation (O2) conceptually separate from the two hypotheses (E1) and (E2). If the observation were simply that “the vertebrate eye exists,” then since (E1) and (E2) both entail this proposition, each would have a likelihood of unity. According to the Likelihood Principle, this observation does not favor Design over Chance. Better to formulate the question in terms of explaining the properties of the vertebrate eye, not in terms of explaining why the eye exists. Notice also that I have not formulated the design hypothesis as the claim that God exists; this existence claim says nothing about the putative designer’s involvement in the creation of the vertebrate eye. Finally, I should point out that it would do no harm to have the design hypothesis say that God created the vertebrate eye; this possible reformulation is something I’ll return to later. Other Formulations of the Design Argument, and Their Defects Given the various provisos that govern probability arguments, it would be nice if the design argument could be formulated deductively. For example, if the hypothesis of mindless chance processes entailed that it is impossible that organisms exhibit delicate adaptations, then a quick application of modus tollens would sweep that hypothesis from the field. However much design theorists might yearn for an argument of this kind, there apparently is none to be had. As the story about monkeys and typewriters illustrates, it is not impossible that mindless chance processes should produce delicate adaptations; it is merely very improbable that they should do so. 6 If modus tollens cannot be pressed into service, perhaps there is a probabilistic version of modus tollens that can achieve the same result. Is there a Law of Improbability that begins with the premiss that Pr(O │ H) is very low and concludes that H should be rejected? There is no such principle (Royall 1997, ch. 3). The fact that you won the lottery does not, by itself, show that there is something wrong with the conjunctive hypothesis that the lottery was fair and a million tickets were sold and you bought just one ticket. And if we randomly drop a very sharp pin onto a line that is 1000 miles long, the probability of its landing where it does is negligible; however, that outcome does not falsify the hypothesis that the pin was dropped at random.7 The fact that there is no probabilistic modus tollens has great significance for understanding the design argument. The logic of this problem is essentially comparative. To evaluate the design hypothesis, we must know what it predicts and compare this with the predictions made by other hypotheses. The design hypothesis cannot win by default. The fact that an observation would be very improbable if it arose by chance is not enough to refute the chance hypothesis. One must show that the design hypothesis confers on the observation a higher probability, and even then the conclusion will merely be that the observation favors the design hypothesis, not that that hypothesis must be true. In the continuing conflict (in the United States) between evolutionary biology and creationism, creationists attack evolutionary theory, but never take even the first step toward developing a positive theory of their own. The three-word slogan “God did it” seems to satisfy whatever craving for explanation they may have. Is the sterility of this intellectual tradition a mere accident? Could intelligent design theory be turned into a scientific research program? I am doubtful, but the present point concerns the logic of the design argument, not its future prospects. Creationists sometimes assert that evolutionary theory “cannot explain” this or that finding (e.g., Behe 1996). What they mean is that certain outcomes are very improbable according to the evolutionary hypothesis. Even this more modest claim needs to be scrutinized. However, even if it were true, what would follow about the plausibility of creationism? In a word – nothing. It isn’t just defenders of the design hypothesis who have fallen into the trap of supposing that there is a probabilistic version of modus tollens. For example, the biologist Richard Dawkins (1986, pp. 144-146) takes up the question of how one should evaluate hypotheses that attempt to explain the origin of life by appeal to strictly mindless natural processes. He says that an acceptable theory of this sort can say that the origin of life on Earth was somewhat improbable, but it cannot go too far. If there are N planets in the universe that are “suitable” locales for life to originate, then an acceptable theory of the origin of life on Earth must say that that event had a probability of at least 1/N. Theories that say that terrestrial life was less probable than this should be rejected. This criterion may look plausible, but I think there is less to it than meets the eye. Suppose only ten lotteries are held in the whole history of the universe and that you have just won one of them. The fact that N=10 does not provide a licence for dismissing any theory about how your lottery worked that says that the probability of your winning was less than 1/10. Some of Hume’s (1779) criticisms of the design argument in his Dialogues Concerning 7 double-6; we should not focus on the logically weaker proposition that a double-6 occurred at some time or other. Relative to the stronger description of the observations, the hypotheses have identical likelihoods. If we apply this point to the criticism of the design argument that we are presently considering, we must conclude that the criticism is mistaken. There is a high probability (let us suppose) that a chance process will sooner or later produce order and adaptation. However, the relevant observation is not that these events occur at some time or other, but that they are true here and now – our universe is orderly and the organisms here on earth are well-adapted. These events do have very low probability, according to the chance hypothesis, and the fact that a weaker description of the observations has high probability on the chance hypothesis is not relevant (see also White 2000).10 If the first premiss in the likelihood formulation of the design argument – that Pr(O * Chance) is very low -- is correct, then the only question that remains is whether Pr(O * Design) is higher. This, I believe, is the Achilles heel of the design argument. The problem is to say how probable it is, for example, that the vertebrate eye would have features F1 ... Fn, if the eye were produced by an intelligent designer. What is required is not the specification of a single probability value, or even a range of such. All that is needed is an argument that shows that this probability is indeed higher than the probability that Chance confers on the observation. The problem is that the design hypothesis confers a probability on the observation only when it is supplemented with further assumptions about what the designer’s goals and abilities would be if he existed. Perhaps the designer would never build the vertebrate eye with features F1 .... Fn, either because he would lack the goals or because he would lack the ability. If so, the likelihood of the design hypothesis is zero. On the other hand, perhaps the designer would want to build the eye with features F1 ... Fn and would be entirely competent to bring this plan to fruition. If so, the likelihood of the design hypothesis is unity. There are as many likelihoods as there are suppositions concerning the goals and abilities of the putative designer. Which of these, or which class of these, should we take seriously? It is no good answering this question by assuming that the eye was built by an intelligent designer and then inferring that the designer must have wanted to give the eye features F1 ... Fn and must have had the ability to do so since, after all, these are the features we observe. For one thing, this pattern of argument is question-begging. One needs independent evidence as to what the designer’s plans and abilities would be if he existed; one can’t obtain this evidence by assuming that the design hypothesis is true (Kitcher 1983; Sober 1999). This objection to the design argument is an old one (see, for example, Venn 1866, pp. 250-251); it is continuous with the precepts of “negative theology,” which holds that God is so different from us and the world we already know about that it is impossible for us to have much of a grasp of what his characteristics are. In fact the basic idea of the criticism of the design argument that I have presented was formulated by Hume. When we behold the watch on the heath, we know that the watch’s features are not particularly improbable on the hypothesis that the watch was produced by a designer who has the sorts of human goals and abilities with which we are familiar. This is the deep and nonobvious disanalogy between the watchmaker and the 10 putative maker of organisms and universes. We are invited, in the latter case, to imagine a designer who is radically different from the human craftsmen we know about. But if this designer is so different, why are we so sure that this being would build the vertebrate eye in the form in which we find it?11 This challenge is not turned back by pointing out that we often infer the existence of intelligent designers when we have no clue as to what they were trying to achieve. The biologist John Maynard Smith used to tell the story of a job he had during World War II inspecting a warehouse filled with German war materiel. He and his coworkers often came across machines whose functions were entirely opaque to them. Yet, they had no trouble seeing that these objects were built by an intelligent designer. There are similar stories about archaeologists who work in museums; they often have objects in their collections that they know are artefacts, although they have no idea what the makers of these artefacts had in mind. My claim is not that design theorists must have independent evidence that singles out the exact goals and abilities of the putative intelligent designer. They may be uncertain as to which of the goal-plus-abilities pairs GA1, GA2, ..., GAn is correct. However, since Pr(the eye has F1 ... Fn │ Design) = ∑i Pr(the eye has F1 ... F1 │ Design & GAi)Pr(GAi│Design), they do have to show that ∑i Pr(the eye has F1 ... Fn │ Design & GAi)Pr(GAi│Design) > Pr(the eye has F1 ... Fn │ Chance). I think that Maynard Smith in his warehouse and archaeologists in their museums are able to do this. They aren’t sure exactly what the intelligent designer was trying to achieve (e.g., they aren’t certain that GA1 is true and that all the other GA pairs are false), but they are able to see that it is not terribly improbable that the object should have the features one observes if it were made by a human intelligent designer. After all, the items in Maynard Smith’s warehouse were symmetrical and smooth metal containers that had what appeared to be switches, dials, and gauges on them. And the “artefacts of unknown function” in anthropology museums likewise bear signs of human handiwork. It is interesting in this connection to consider the epistemological problem of how one would go about detecting intelligent life elsewhere in the universe (if it exists). The SETI (Search for Extraterrestrial Intelligence) project, funded until 1993 by the US National Aeronautics and Space Administration and now supported privately, dealt with this problem in two ways (Dick 1996). First, the scientists wanted to send a message into deep space that would allow any intelligent extraterrestrials who received it to figure out that it was produced by intelligent designers (namely, us). Second, they scanned the night sky hoping to detect signs of intelligent life elsewhere. The message, transmitted in 1974 from the Arecibo Observatory, was a simple picture of our solar system, a representation of oxygen and carbon, a picture of a double helix 11 representing DNA, a stick figure of a human being, and a picture of the Arecibo telescope. How sure are we that if intelligent aliens find these clues, that they will realize that they were produced by intelligent designers? The hope is that this message will strike the aliens who receive it as evidence favoring the hypothesis of intelligent design over the hypothesis that some mindless physical process (not necessarily one involving uniform chance) was responsible. It is hard to see how the SETI engineers could have done any better, but one still cannot dismiss the possibility that they will fail. If extraterrestrial minds are very different from our own – either because they have different beliefs and desires or because they process information in different ways -- it may turn out that their interpretation of the evidence differs profoundly from the interpretation that human beings would arrive at, were they on the receiving end. To say anything more precise about this, we’d have to be able provide specifics about the aliens’ mental characteristics. If we are uncertain as to how the mind of an extraterrestrial will interpret this evidence, how can we be so sure that God, if he were to build the vertebrate eye, would endow it with the features we find it to have? When SETI engineers search for signs of intelligent life elsewhere in the universe, what are they looking for? The answer is surprisingly simple. They are looking for narrow-band radio emissions. This is because human beings build machines that produce these signals and, as far as we know, such emissions are not produced by mindless natural processes. The SETI engineers search for this signal, not because it is “complex” or fulfills some a priori criterion that would make it a “sign of intelligence,” but simply because they think they know what sorts of mechanisms are needed to produce it.12 This strategy may not work, but it is hard to see how the scientists could do any better. Our judgments about what counts as a sign of intelligent design must be based on empirical information about what designers often do and what they rarely do. As of now, these judgments are based on our knowledge of human intelligence. The more our hypotheses about intelligent designers depart from the human case, the more in the dark we are as to what the ground rules are for inferring intelligent design.13 It is imaginable that these limitations will subside as human beings learn more about the cosmos and the varieties of intelligence it contains. But for now, we are rather limited. I have been emphasizing the fallibility of two assumptions -- that we know what counts as a sign of extraterrestrial intelligence and that we know how extraterrestrials will interpret the signals we send. My point has been to shake a complacent assumption that figures in the design argument. However, I suspect that SETI engineers are on much firmer ground than theologians. If extraterrestrials evolved by the same type of evolutionary process that produced human intelligence, that may provide useful constraints on conjectures about the minds they have. No theologian, to my knowledge, thinks that God is the result of biological processes. Indeed God is usually thought of as a supernatural being who is radically different from the things we observe in nature. The problem of extraterrestrial intelligence is therefore an intermediate case, lying somewhere between the watch found on the heath and the God who purportedly shaped the vertebrate eye (but much closer to the first). The upshot of this point for Paley’s design argument is this: Design arguments for the existence of human (and human-like) watchmakers are often unproblematic; it is design arguments for the existence of God that leave us at sea. I began by formulating the design hypothesis in argument (E) as the claim that an intelligent designer made the vertebrate eye. Yet, I have sometimes discussed the hypothesis 12 when the argument is formulated nondeductively (Madden and Hare 1968, Plantinga 1979, Rowe 1979). Suppose it is suggested that the amount of evil that exists favors the hypothesis that there is no God. Within the framework of likelihood inference, there are two quantities we must evaluate: What is the probability that there would be so much evil, if the universe were produced by an all-powerful, all-knowing, and entirely benevolent God? And what is the probability of there being so much evil, if the universe were produced by mindless natural processes? Once again, if the ways of God are sufficiently mysterious, we will not be able to evaluate the first of these likelihoods (Wykstra 1984). Theists who agree with this judgment about the problem of evil should agree with my criticism of the argument from design. And atheists who agree with my criticism of the design argument should desist from pressing the argument from evil as a proof that there is no God. I earlier considered an objection to my critique of the design argument that involves augmenting the design hypothesis; I now want to consider another objection, one that involves diminishing the observations we need to explain. Instead of considering a detailed description of the features that the vertebrate eye possesses and demanding to know what the hypothesis of intelligent design predicts about those features, perhaps we should focus on the following less specific fact about our world – that it contains intelligent life. Assuming that God is all- knowing, all-powerful, and entirely benevolent, won’t it be clear that Pr(the universe contains intelligent life│ God created the universe) is high? An omnipotent being can do anything that is possible, so God clearly has the ability to create intelligent life. And as for his goals, doesn’t his benevolence entail that he will want to create intelligent life? A proper reply to this objection must await our discussion of the fine-tuning argument and the concept of observation selection effects. But before we turn to that topic, I want to consider how the design argument as I have presented it is related to Darwinian evolutionary theory. The Relationship of the Organismic Design Argument to Darwinism Philosophers who now criticize the organismic design argument often believe that the argument was dealt its death blow by Hume. True, Paley and the authors of the Bridgewater Treatises (in which the design argument was formulated again and again with respect to a seemingly inexhaustible list of observations) wrote after Hume’s Dialogues were published. Nonetheless, for the philosophers I have in mind, the design argument after Hume was merely a corpse that could be propped up and paraded. Hume had taken the life out of it. Biologists often take a different view. For them, Hume’s skeptical attack was not the decisive moment; rather, it was Darwin’s development and confirmation of a substantive scientific explanation of the adaptive features of organisms that really undermined the design argument (at least in its organismic formulation). Philosophers who believe that a theory can’t be rejected until a better theory is developed to take its place often sympathize with this point of view. My own interpretation coincides with neither of these. As indicated earlier, I think that Hume’s criticisms largely derive from an empiricist epistemology that is too narrow. However, seeing the design argument’s fatal flaw does not depend on seeing the merits of Darwinian theory. The Likelihood Principle, it is true, says that theories must be evaluated comparatively, 15 not on their own. But for this to be possible, each theory must make predictions. It is at this fundamental level that I think the design argument is defective. Biologists often present two criticisms of creationism. First, they argue that the design hypothesis is untestable. Second, they contend that there is plenty of evidence that the hypothesis is false. Obviously, these two lines of argument are in conflict. I have already endorsed the first criticism; I now want to say a little about the second. A useful example is Stephen Jay Gould’s (1980) widely read article about the Panda’s thumb. Pandas are vegetarian bears who have a spur of bone (a “thumb”) protruding from their wrists. They use this device to strip bamboo, which is the main thing they eat. Gould says that the hypothesis of intelligent design predicts that pandas should not have this inefficient device. A benevolent, powerful, and intelligent engineer could and would have done much better. Evolutionary theory, on the other hand, says that the panda’s thumb is what we should expect. The thumb is a modification of the wrist bones found in the common ancestor that pandas share with carnivorous bears. Evolution by natural selection is a tinkerer (Jacob 1977). It does not design adaptations from scratch; rather, it modifies pre-existing features, with the result that adaptations are often imperfect. Gould’s argument, I hope it is clear, is a likelihood argument. I agree with what he says about evolutionary theory, but I think his discussion of the design hypothesis leads him into the same trap that ensnared Paley. Gould thinks he knows what God would do if he built pandas, just as Paley thought he knew what God would do if he built the vertebrate eye. But neither of them knows anything of the sort. Both help themselves to assumptions about God’s goals and abilities. However, it is not enough to make assumptions about these matters; one needs independent evidence that these auxiliary assumptions are true. Paley’s problem is also Gould’s.16 Anthropic Reasoning and Cosmic Design Arguments Evolutionary theory seeks to explain the adaptive features of organisms; it has nothing to say about the origin of the universe as a whole. For this reason, evolutionary theory conflicts with the organismic design hypothesis, but not with the cosmic design hypothesis. Still, the main criticism I presented of the first type of design argument also applies to the second. I now want to examine a further problem that cosmic design arguments sometimes encounter.17 Suppose I catch 50 fish from a lake, and you want to use my observations O to test two hypotheses: O: All the fish I caught were more than 10 inches long. F1: All the fish in the lake are more than 10 inches long. F2: Only half the fish in the lake are more than 10 inches long. You might think that the Likelihood Principle says that F1 is better supported, since (1) Pr(O│ F1) > Pr(O │ F2). 16 However, you then discover how I caught my fish: (A1) I caught the fish by using a net that (because of the size of its holes) can’t catch fish smaller than 10 inches, and I left the net in the lake until there were 50 fish in it, knowing that there are at least 50 fish in the lake that are larger than 10 inches. This leads you to replace the analysis provided by (1) with the following: (2) Pr(O│ F1 & A1) = Pr(O │ F2 & A1) = 1.0. Furthermore, you now realize that your first assessment, (1), was based on the erroneous assumption that (A0) The fish I caught were a random sample from the fish in the lake. Instead of (1), you should have written Pr(O│ F1 & A0) > Pr(O │ F2 & A0). This inequality is true; the problem, however, is that (A0) is false. This example, from Eddington (1938), illustrates the idea of an observational selection effect (an OSE). When a hypothesis is said to render a set of observations probable (or improbable), ask yourself what assumptions allow the hypothesis to have this implication. The point illustrated here is that the procedure you use to obtain your observations can be relevant to assessing likelihoods.18 One version of the cosmic design argument begins with the observation that our universe is “fine-tuned.” That is, the values of various physical constants are such as to permit life to exist, and if they had been even slightly different, life would have been impossible. McMullin (1993, p. 378) summarizes some of the relevant facts as follows: If the strong nuclear force were to have been as little as 2% stronger (relative to the other forces), all hydrogen would have been converted into helium. If it were 5% weaker, no helium at all would have formed and there would be nothing but hydrogen. If the weak nuclear force were a little stronger, supernovas could not occur, and heavy elements could not have formed. If it were slightly weaker, only helium might have formed. If the electromagnetic forces were stronger, all stars would be red dwarfs, and there would be no planets. If it were a little weaker, all stars would be very hot and short-lived. If the electron charge were ever so slightly different, there would be no chemistry as we know it. Carbon (12C) only just managed to form in the primal nucleosynthesis. I’ll abbreviate the fact that the values of these physical constants fall within the narrow limits specified by saying that “the constants are right.” A design argument can now be constructed, one that claims that the constants’ being right should be explained by postulating the existence of an intelligent designer, one who wanted life to exist and who arranged the universe so that this 17 that there are two stages at which a bias can be introduced. There is first the process by which the system described by the hypotheses under test generates some state of the world that we are able to observe. Second, there is the process by which we come to observe that state of the world. This two-step process occurs in fishing and fine-tuning as follows: Composition of the Lake → Contents of the net → We observe the contents of the net Origin of the Universe → Constants are right → We observe that the constants are right The OSE in the fishing example arises in step 1; the OSE in fine-tuning crops up in step 2. Leslie (1989, pp. 13-14, 107-108), Swinburne (1990a, p. 171), and Van Inwagen (1993, p. 135,144) all defend the fine-tuning argument against the criticism I have just described. Each mounts his defense by describing an analogy with a mundane example. Here is Swinburne’s rendition of an example that Leslie presents: On a certain occasion the firing squad aim their rifles at the prisoner to be executed. There are twelve expert marksmen in the firing squad, and they fire twelve rounds each. However, on this occasion all 144 shots miss. The prisoner laughs and comments that the event is not something requiring any explanation because if the marksmen had not missed, he would not be here to observe them having done so. But of course, the prisoner’s comment is absurd; the marksmen all having missed is indeed something requiring explanation; and so too is what goes with it – the prisoner’s being alive to observe it. And the explanation will be either that it was an accident (a most unusual chance event) or that it was planned (e.g., all the marksmen had been bribed to miss). Any interpretation of the anthropic principle which suggests that the evolution of observers is something which requires no explanation in terms of boundary conditions and laws being a certain way (either inexplicably or through choice) is false. First a preliminary clarification – the issue isn’t whether the prisoner’s survival “requires explanation” but whether this observation provides evidence as to whether the marksmen intended to spare the prisoner or shot at random.22 My response takes the form of a dilemma. I’ll argue, first, that if the firing squad example is analyzed in terms of the Likelihood Principle, the prisoner is right and Swinburne is wrong – the prisoner’s survival does not allow him to conclude that Design is more likely than Chance. However, there is a different analysis of the prisoner’s situation, in terms of the probabilities of hypotheses, not their likelihoods. This second analysis says that the prisoner is mistaken; however, it has the consequence that the prisoner’s inference differs fundamentally from the design argument that appeals to fine-tuning. Each horn of this dilemma supports the conclusion that the firing squad example does nothing to save this version of the design argument. So let us begin. If we understand Swinburne’s claim in terms of the Likelihood Principle, we should read him as saying that 20 (L1) Pr(the prisoner survived │ the marksmen intended to miss) > Pr(the prisoner survived │ the marksmen fired at random). He thinks that the anthropic principle requires us to replace this claim with the following irrelevancy: (L2) Pr(the prisoner survived │ the marksmen intended to miss & the prisoner survived) = Pr(the prisoner survived │ the marksmen fired at random & the prisoner survived) = 1.0. This equality would lead us to conclude (mistakenly, Swinburne thinks) that the prisoner’s survival does not discriminate between the hypotheses of Design and Chance. To assess the claim that the prisoner has made a mistake, it is useful to compare the prisoner’s reasoning with that of a bystander who witnesses the prisoner survive the firing squad. The prisoner reasons as follows: “given that I now am able to make observations, I must be alive, whether my survival was due to intelligent design or chance.” The bystander says the following: “given that I now am able to make observations, the fact that the prisoner is now alive is made more probable by the design hypothesis than it is by the chance hypothesis.” The prisoner claims that he is subject to an OSE, while the bystander says that he, the bystander, is not. Both, I submit, are correct.23 I suggest that part of the intuitive attractiveness of the claim that the prisoner has made a mistake derives from a shift between the prisoner’s point of view and the bystander’s. The bystander is right to use (L1) to interpret his observations; however, the prisoner has no business using (L1) to interpret his observations since he, the prisoner, is subject to an OSE. The prisoner needs to replace (L1) with (L2). My hunch is that Swinburne thinks the prisoner errs in his assessment of likelihoods because we bystanders would be making a mistake it we reasoned as he does.24 The basic idea of an OSE is that we must take account of the procedures used to obtain the observations when we assess the likelihoods of hypotheses. This much was clear from the fishing example. What may seem strange about my reading of the firing squad story is my claim that the prisoner and the bystander are in different epistemic situations, even though their observation reports differ by a mere pronoun. After the marksmen fire, the prisoner thinks “I exist” while the bystander thinks “he exists;” the bystander, but not the prisoner, is able to use his observation to say that Design is more likely than Chance, or so I say. If this seems odd, it may be useful to reflect on Sorenson’s (1988) concept of blindspots. A proposition p is a blindspot for an individual S just in case, if p were true, S would not be able to know that p is true. Although some propositions (e.g., “nothing exists,” “the constants are wrong”) are blindspots for everyone, other propositions are blindspots for some people but not for others. Blindspots give rise to OSEs; if p is a blindspot for S, then if S makes an observation to determine the truth value of p, the outcome must be that not-p is observed. The prisoner, but not the bystander, has “the prisoner does not exist” as a blindspot. This is why “the prisoner exists” has an evidential significance for the bystander that it cannot have for the prisoner.25,26 To bolster my claim that the prisoner is right to think that likelihood does not distinguish 21 between Chance and Design, I want to describe a slightly different problem. Suppose that a firing squad always subjects its victims to the same probabilistic process, which has the result that the prisoner before it either survives or is killed. A thousand prisoners who one by one have survived the firing squad are assembled and are asked to pool their knowledge and estimate the value of an unknown probability. What is the probability that a prisoner will survive if the firing squad fires? The standard methodology here is maximum likelihood estimation; one finds the value of the parameter of interest that maximizes the probability of the observations. For example, if a coin lands heads 512 times out of a thousand tosses, the best point estimate of the probability that the coin will land heads when tossed is 0.512. Those who believe that the single prisoner has evidence about his firing squad’s intentions are obliged to conclude that the best estimate in this new problem is that the probability is unity. However, those persuaded that the single prisoner is subject to an OSE will want to maintain that the thousand prisoners are in the same boat. These skeptics will deny that the observations provide a basis for estimation. Isn’t it obvious that testimony limited to survivors provides no evidence on which to base an estimate of the probability that someone will survive?27 And if this is true of a thousand survivors, how can a single survivor be said to know that Design is more likely than Chance? I now turn to a different analysis of the prisoner’s situation. The prisoner, like the rest of us, knows how firing squads work. They always or almost always follow the orders they receive, which almost always are to execute the prisoner at hand. Occasionally, they produce fake executions. They almost never fire at random. What is more, firing squads have firm control over outcomes; if they want to kill (or spare) someone, they always or almost always succeed. This and related items of background knowledge support the following probability claim: (Pf) Pr(the marksmen intended to spare the prisoner │ the prisoner survived) > Pr(the marksmen intended to spare the prisoner). Firing squads rarely intend to spare their victims, but the survival of the prisoner makes it very probable that his firing squad had precisely that intention. The likelihood analysis led to the conclusion that the prisoner and the bystander are in different epistemic situations; the bystander should evaluate the hypotheses by using (L1), but the prisoner is obliged to use (L2). However, from the point of view of probabilities, the prisoner and the bystander can say the same thing; both can cite (Pf). What does this tell us about the fine-tuning version of the design argument? I construed that argument as a claim about likelihoods. As such, it is subject to an OSE; given that we exist, the constants must be right, regardless of whether our universe was produced by Chance or by Design. However, we now need to consider whether the fine-tuning argument can be formulated as a claim about probabilities. Can we assert that (Pu) Pr(the universe was created by an intelligent designer│ the constants are right) > Pr(the universe was created by an intelligent designer)? I don’t think so. In the case of firing squads, we have frequency data and our general knowledge of human behavior on which to ground the probability statement (Pf). But we have neither data nor theory to ground (Pu). And we cannot defend (Pu) by saying that an intelligent 22 Good, I.J. (1967): “The White Shoe is a Red Herrinng.” British Journal for the Philosophy of Science. 17: 322. Good, I.J. (1968): “The White Shoe Qua Herring is Pink.” British Journal for the Philosophy of Science 19: 156-157.. Gould, S. (1980): The Panda’s Thumb. New York: Norton. 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Notes 26 1 I am grateful to Martin Barrett, Nick Bostrom, David Christensen, Dennis Des Chene, Mark Crimmins, Ellery Eells, Branden Fitelson, Malcolm Forster, Daniel Hausman, Stephen Leeds, William Mann, Lydia McGrew, Susanna Rinard, Matthew Seligman, Matthew Smith, Roy Sorenson, Dennis Stampe, Richard Swinburne, Scott Thurow, and Jonathan Weisberg for useful comments. 2 Does this likelihood version of the design argument conflict with the idea that the argument is an inference to the best explanation? Not if one’s theory of inference to the best explanation says that observations influence the assessment of explanations in this instance via the vehicle of likelihoods. 3 In light of the fact that it is possible for a hypothesis to have an objective likelihood without also having an objective probability, one should understand Bayes’ theorem as specifying how the quantities it mentions are related to each other, if all are well-defined. And just as hypotheses can have likelihoods without having (objective) probabilities, it also is possible for the reverse situation to obtain. Suppose I draw a card from a deck of unknown composition. I observe (O) that the card is the four of diamonds. I now consider the hypothesis (H) that the card is a four. The value of Pr(H * O) is well-defined, but the value of Pr(O * H) is not. 4 Actually, Paley does consider a “selective retention” process, but only very briefly. In Chapter 5 (pp. 49-51) he explores the hypothesis that a random process once generated a huge range of variation, and that this variation was then culled, with only stable configurations surviving. Paley argues against this hypothesis by saying that we should see unicorns and mermaids if it were true. He also says that it mistakenly predicts that organisms should fail to form a taxonomic hierarchy. It is ironic that Darwin claimed that his own theory predicts hierarchy. In fact, Paley and Darwin are both right. Darwin’s theory contains the idea that all living things have common ancestors, while the selection hypothesis that Paley considers does not. 5 More precisely, Fisher said that a mother should have a son with probability p and a daughter with probability (1-p), where the effect of this is that the expected expenditures on the two sexes are the same; the argument is not undermined by the fact that some mothers have all sons while others have all daughters. 6 Dawkins (1986) makes the point that evolution by natural selection is not a uniform chance process by way of an analogy with a combination lock. This is discussed in Sober (1993, pp. 36- 39). 7 Dembski (1998) construes design inference as “sweeping from the field” all possible competitors, with the effect that the design hypothesis wins by default (i.e., it never has to make successful predictions). As noted above, Paley, Arbuthnot, and other design theorists did not and could not refute all possible alternatives to Design; they were able to test only the alternatives that they were able to formulate. For other criticisms of Dembski’s framework, see Fitelson et al. (1999). 8 Paley argues in Chapter 16 that the benevolence of the deity is demonstrated by the fact that organisms experience more pleasure than they need to (p. 295). He also argues that pain is useful (p. 320) and that few diseases are fatal; he defends the latter conclusion by citing statistics 27 _ (WAP) origin of universe ` constants now are right In contrast, one of the strong anthropic principles assumes the following causal arrangement: (SAP) we exist now 6 origin of the universe 6 constants now are right Even though (WAP) is true and (SAP) is false, both entail a correlation between our existence and the constants’ now having the values they do. To deal with the resulting OSEs, we must decide how to take these correlations into account in assessing likelihoods. 20 This point is worth contemplating by those who think that the intelligent design hypothesis is not required to explain the detailed features of the adaptive features we observe organisms to have, but that the burden is only to address an explanandum that is logically weaker. Can an explanandum be found that is logically weak, but not too weak, so that the design argument is not caught in the snares of an OSE? 21 The fishing and fine-tuning examples involve extreme OSEs. More modest OSEs are also possible. If C describes the circumstances in which we make our observational determination as to whether proposition O is true, and we use the outcome of this determination to decide whether H1 or H2 is more likely, then a quantitative OSE is present precisely when Pr(O * H1 & C) …Pr(O * H1) or Pr(O * H2 & C) …Pr(O * H2). A qualitative OSE occurs when taking account of C alters the likelihood ordering: Pr(O * H1 & C) > Pr(O * H2 & C) and Pr(O * H1) Ý Pr(O * H2) or Pr(O * H1 & C) = Pr(O * H2 & C) and Pr(O * H1) … Pr(O * H2). Understood in this way, an OSE is just an example of sampling bias. 22 There is a third possibility – that the marksmen intended to kill the prisoner – but for the sake of simplicity (and also to make the firing squad argument more parallel with the argument from fine-tuning), I’ll ignore this for most of my discussion. 23 The issue, thus, is not whether (L1) or (L2) are true (both are), but which an agent should use in interpreting the bearing of observations on the likelihoods of hypotheses. In this respect the injunction of the weak anthropic principle is like the principle of total evidence – it is a pragmatic principle, concerning which statements should be used for which purposes. 24 In order to replicate in the fine-tuning argument the difference between the prisoner’s and the bystander’s points of view, imagine that we observe through a telescope another universe in which the constants are right. We bystanders can use this observation in a way that the 30 inhabitants of that universe cannot. 25 Notice that “I exist” when thought by the prisoner, is a priori, whereas “the prisoner exists,” when thought by the bystander, is a posteriori. Is it so surprising that an a priori statement and an a posteriori statement should differ in their evidential significance? I also should note that my claim is that the prisoner’s observing “I am alive” does not permit him to conclude that Design is more likely than Chance. I do not say that there is no proposition he can cite after the marksmen fire that discriminates between the two hypotheses. Consider, for example, the observation that “no bullets hit me.” This favors Design over Chance, even after the prisoner conditionalizes on the fact that he is alive. Notice also that if the prisoner were alive but riddled with bullets, this would not so clearly make Design more likely than Chance. 26 If the prisoner and the bystander talk to each other after the prisoner survives, what new information can the prisoner gather from the bystander’s testimony? I leave the dialectics of this conversation to the reader to explore. 27 The problem is that the survivors know the numerator, but not the denominator, of a fraction that represents the actual frequency of survivors. To see my point, assume that the prisoners have no idea how many prisoners have gone before the firing squad, except that there must have been at least 1000. Parallel assumptions are needed for the fishing example to embody an OSE. 28 The hypothesis that our universe is one among many has been introduced as a possible explanation of the fact that the constants (in our universe) are right. A universe is here understood to be a region of space-time that is causally closed. See Leslie (1989) for discussion. If the point of the multiverse hypothesis is to challenge the design hypothesis, on the assumption that the design hypothesis has already vanquished the hypothesis of chance, then the multiverse hypothesis is not needed. Furthermore, in comparing the multiverse hypothesis and the design hypothesis, one needs to attend to the inverse gambler’s fallacy discussed earlier. This is not to deny that there may be other evidence for the multiverse hypothesis; however, the mere fact that the constants are right in our universe does not favor that hypothesis. 29 As Dennett (1987a, pp. 284-285) observes, human beings have been modifying the characteristics of animals and plants by artificial selection for thousands of years. However, the organisms thus modified were not created by human beings. Recall that I formulated the design argument as endorsing a hypothesis about how organisms were brought into being. This is why the work of plant and animal breeders, per se, does not show that the design argument should be stripped of its theological trappings. 31