Design arguments are empirical arguments for God’s existence. These arguments typically, though not always, proceed by identifying various empirical features of the world that constitute evidence of intelligent design and inferring God’s existence as the best explanation for these features. Below I will focus primarily on explaining and criticizing Paley’s watchmaker argument and a contemporary design argument espoused by Michael J. Behe. Later I will discuss a few major misconceptions about evolution. Finally I will allow a great book on evolution to speak for itself.
Paley's Watchmaker Argument
William Paley's watchmaker argument is probably one of the most popular design argument used by proponents of intelligent design. Paley's argument proceeds by identifying what he takes to be a reliable indicator of intelligent design:
Suppose I found a watch upon the ground, and it should be inquired how the watch happened to be in that place, I should hardly think … that, for anything I knew, the watch might have always been there. Yet why should not this answer serve for the watch as well as for [a] stone [that happened to be lying on the ground]?… For this reason, and for no other; viz., that, if the different parts had been differently shaped from what they are, if a different size from what they are, or placed after any other manner, or in any order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it.
There are thus two features of a watch that reliably indicate that it is the result of an intelligent design. First, it performs some function that an intelligent agent would regard as valuable; the fact that the watch performs the function of keeping time is something that has value to an intelligent agent. Second, the watch could not perform this function if its parts and mechanisms were differently sized or arranged; the fact that the ability of a watch to keep time depends on the precise shape, size, and arrangement of its parts suggests that the watch has these characteristics because some intelligent agency designed it to these specifications. Taken together, these two characteristics endow the watch with a functional complexity that reliably distinguishes objects that have intelligent designers from objects that do not.
Paley then goes on to argue that the material universe exhibits the same kind of functional complexity as a watch:
Every indicator of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater and more, and that in a degree which exceeds all computation. I mean that the contrivances of nature surpass the contrivances of art, in the complexity, subtilty, and curiosity of the mechanism; and still more, if possible, do they go beyond them in number and variety; yet in a multitude of cases, are not less evidently mechanical, not less evidently contrivances, not less evidently accommodated to their end, or suited to their office, than are the most perfect productions of human ingenuity.
Since the works of nature possess functional complexity, a reliable indicator of intelligent design, we can justifiably conclude that these works were created by an intelligent agent who designed them to instantiate this property.
Paley's argument is that works of nature and human artifacts have a particular property that reliably indicates design. Regardless of how dissimilar any particular natural object might otherwise be from a watch, both objects exhibit the sort of functional complexity that warrants an inference that it was made by an intelligent designer.
Paley's version of the argument, however, is generally thought to have been refuted by Darwin’s competing explanation for complex organisms. In The Origin of the Species, Darwin argued that more complex biological organisms evolved gradually over millions of years from simpler organisms through a process of natural selection. As Julian Huxley describes the logic of this process:
The evolutionary process results immediately and automatically from the basic property of living matter - that of self-copying, but with occasional errors. Self-copying leads to multiplication and competition; the errors in self-copying are what we call mutations, and mutations will inevitably confer different degrees of biological advantage or disadvantage on their possessors. The consequence will be differential reproduction down the generations - in other words, natural selection.
Over time, the replication of genetic material in an organism results in mutations that give rise to new traits in the organism's offspring. Sometimes these new traits are so unfavorable to a being’s survival prospects that beings with the traits die off; but sometimes these new traits enable the possessors to survive conditions that kill off beings without them. If the trait is sufficiently favorable, only members of the species with the trait will survive. By this natural process, functionally complex organisms gradually evolve over millions of years from primordially simple organisms.
Contemporary biologist Richard Dawkins uses a programming problem to show that the logic of the process renders the Darwinian explanation significantly more probable than the design explanation. Dawkins considers two ways in which one might program a computer to generate the following sequence of characters: METHINKS IT IS LIKE A WEASEL. The first program randomly producing a new 28-character sequence each time it is run; since the program starts over each time, it incorporates a "single-step selection process." The probability of randomly generating the target sequence on any given try is 27 (i.e., 27 characters selected for each of the 28 positions in the sequence) - which amounts to about 1 in (10,000 x 1,000,0006). While a computer running eternally would eventually produce the sequence, Dawkins estimates that it would take 1,000,0005 years — which is 1,000,0003 years longer than the universe has existed. As is readily evident, a program that selects numbers by means of such a "single-step selection mechanism" has a very low probability of reaching the target.
The second program incorporates a "cumulative-step selection mechanism." It begins by randomly generating a 28-character sequence of letters and spaces and then "breeds" from this sequence in the following way. For a specified period of time, it generates copies of itself; most of the copies perfectly replicate the sequence, but some copies have errors (or mutations). At the end of this period, it compares all of the sequences with the target sequence METHINKS IT IS LIKE A WEASEL and keeps the sequence that most closely resembles it. For example, a sequence that has an E in the second place more closely resembles a sequence that is exactly like the first except that it has a Q in the second place. It then begins breeding from this new sequence in exactly the same way. Unlike the first program which starts afresh with each try, the second program builds on previous steps, getting successively closer to the program as it breeds from the sequence closest to the target. This feature of the program increases the probability of reaching the sequence to such an extent that a computer running this program hit the target sequence after 43 generations, which took about half-an-hour.
The problem with Paley's watchmaker argument, as Dawkins explains it, is that it falsely assumes that all of the other possible competing explanations are sufficiently improbable to warrant an inference of design. While this might be true of explanations that rely entirely on random single-step selection mechanisms, this is not true of Darwinian explanations. As is readily evident from Huxley's description of the process, Darwinian evolution is a cumulative-step selection method that closely resembles in general structure the second computer program. The result is that the probability of evolving functionally complex organisms capable of surviving a wide variety of conditions is increased to such an extent that it exceeds the probability of the design explanation.
Contemporary Versions of the Design Argument
Contemporary versions of the design argument typically attempt to articulate a more sophisticated strategy for detecting evidence of design in the world. These versions typically contain three main elements - though they are not always explicitly articulated. First, they identify some property P that is thought to be a probabilistically reliable index of design in the following sense: a design explanation for P is significantly more probable than any explanation that relies on chance or random processes. Second they argue that some feature or features of the world exhibits P. Third, they conclude that the design explanation is significantly more likely to be true.
As we will see, however, contemporary versions of the design inference seem to be vulnerable to roughly the same objection. While each of the design inferences in these arguments has legitimate empirical uses, those uses occur only in contexts where we have strong antecedent reason for believing there exist intelligent agents with the ability to bring about the relevant event, entity, or property. But since it is the very existence of such a being that is at issue in the debates about God's existence, design arguments appear unable to stand by themselves as arguments for God's existence.
Behe’s Argument from Irreducible Biochemical Complexity
Design theorists distinguish two types of complexity that can be instantiated by any given structure. As William Dembski describes the distinction: a system or structure is cumulatively complex "if the components of the system can be arranged sequentially so that the successive removal of components never leads to the complete loss of function"; a system or structure is irreducibly complex "if it consists of several interrelated parts so that removing even one part completely destroys the system's function" (Dembski 1999, 147). A city is cumulatively complex since one can successively remove people, services, and buildings without rendering it unable to perform its function. A mousetrap, in contrast, is irreducibly complex because the removal of even one part results in complete loss of function.
Design proponents, like Michael J. Behe, have identified a number of biochemical systems that they take to be irreducibly complex. Like the functions of a watch or a mousetrap, a cilium cannot perform its function unless its microtubules, nexin linkers, and motor proteins are all arranged and structured in precisely the manner in which they are structured; remove any component from the system and it cannot perform its function. Similarly, the blood-clotting function cannot perform its function if either of its key ingredients, vitamin K and antihemophilic factor, are missing. Both systems are, on this view, irreducibly complex - rather than cumulatively complex.
According to Behe, the probability of evolving irreducibly complex systems along Darwinian lines is sufficiently small that it can be ruled out as an explanation of irreducible biochemical complexity:
An irreducibly complex system cannot be produced … by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional…. Since natural selection can only choose systems that are already working, if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on.
Since, for example, a cilium-precursor (i.e., one that lacks at least one of a cilium's parts) cannot perform the function that endows a cilium with adaptive value, organisms that have the cilium-precursor are no "fitter for survival" than they would have been without it. Since chance-driven evolutionary processes would not select organisms with the precursor, intelligent design is a better explanation for the existence of organisms with fully functional cilia.
Though Behe states his conclusion in categorical terms (i.e., irreducibly complex systems "cannot be produced gradually"), he is more charitably construed as claiming only that the probability of gradually producing irreducibly complex systems is very small. The stronger construction of the conclusion (and argument) incorrectly presupposes that Darwinian theory implies that every precursor to a fully functional system must itself perform some function that makes the organism more fit to survive. Organisms that have, say, a precursor to a fully functional cilium are no fitter than they would have been without it, but there is nothing in Darwinian theory that implies they are necessarily any less fit. Thus, there is no reason to think that it is logically or nomologically impossible, according to Darwinian theory, for a set of organisms with a precursor to a fully functional cilium to evolve into a set of organisms that has fully functional cilia. Accordingly, the argument from irreducible biochemical complexity is more plausibly construed as showing that the design explanation for such complexity is more probable than the evolutionary explanation.
Nevertheless, this more modest interpretation is problematic. First, there is little reason to think that the probability of evolving irreducibly complex systems is, as a general matter, small enough to warrant assuming that the probability of the design explanation must be higher. If having a precursor to an irreducibly complex system does not render the organism less fit for survival, the probability a subspecies of organisms with the precursor survives and propagates is the same, other things being equal, as the probability that a subspecies of organisms without the precursor survives and propagates. In such cases, then, the prospect that the subspecies with the precursor will continue to thrive, leave offspring, and evolve is not unusually small.
Second, the claim that intelligent agents of a certain kind would (or should) see functional value in a complex system, by itself, says very little about the probability of any particular causal explanation. While this claim surely implies that intelligent agents with the right causal abilities have a reason for bringing about such systems, it does not tell us anything determinate about whether it is likely that intelligent agents with the right causal powers did bring such systems about - because it does not tell us anything determinate about whether it is probable that such agents exist. As a logical matter, the mere fact that some existing thing has a feature, irreducibly complex or otherwise, that would be valuable to an intelligent being with certain properties, by itself, does not say anything about the probability that such a being exists.
Accordingly, even if we knew that the prospect that the precursor-subspecies would survive was "vanishingly small," as Behe believes, we would not be justified in inferring a design explanation on probabilistic grounds. To infer that the design explanation is more probable than an explanation of vanishingly small probability, we need some reason to think that the probability of the design explanation is not vanishingly small. The problem, however, is that the claim that a complex system has some property that would be valued by an intelligent agent with the right abilities, by itself, simply does not justify inferring that the probability that such an agent exists and brought about the existence of that system is not vanishingly small. In the absence of some further information about the probability that such an agent exists, we cannot legitimately infer design as the explanation of irreducible biochemical complexity.
Five Major Misconceptions about Evolution
A large part of the reason why Creationist arguments against evolution can sound so persuasive is because they don't address evolution, but rather argue against a set of misunderstandings that people are right to consider ludicrous. The Creationists wrongly believe that their understanding of evolution is what the theory of evolution really says, and declare evolution banished. In fact, they haven't even addressed the topic of evolution. The five propositions below seem to be the most common misconceptions based on a Creationist straw-man version of evolution. If you hear anyone making any of them, chances are excellent that they don't know enough about the real theory of evolution to make informed opinions about it.
"Evolution has never been observed."
Biologists define evolution as a change in the gene pool of a population over time. One example is insects developing a resistance to pesticides over the period of a few years. Even most Creationists recognize that evolution at this level is a fact. What they don't appreciate is that this rate of evolution is all that is required to produce the diversity of all living things from a common ancestor.
The origin of new species by evolution has also been observed, both in the laboratory and in the wild. See, for example, (Weinberg, J.R., V.R. Starczak, and D. Jorg, 1992, "Evidence for rapid speciation following a founder event in the laboratory." Evolution 46: 1214-1220). The "Observed Instances of Speciation" FAQ in the talk.origins archives gives several additional examples.
Even without these direct observations, it would be wrong to say that evolution hasn't been observed. Evidence isn't limited to seeing something happen before your eyes. Evolution makes predictions about what we would expect to see in the fossil record, comparative anatomy, genetic sequences, geographical distribution of species, etc., and these predictions have been verified many times over. The number of observations supporting evolution is overwhelming.
What hasn't been observed is one animal abruptly changing into a radically different one, such as a frog changing into a cow. This is not a problem for evolution because evolution doesn't propose occurrences even remotely like that. In fact, if we ever observed a frog turn into a cow, it would be very strong evidence against evolution.
"Evolution violates the 2nd law of thermodynamics."
This shows more a misconception about thermodynamics than about evolution. The second law of thermodynamics says, "No process is possible in which the sole result is the transfer of energy from a cooler to a hotter body." [Atkins, 1984, The Second Law, pg. 25] Now you may be scratching your head wondering what this has to do with evolution. The confusion arises when the 2nd law is phrased in another equivalent way, "The entropy of a closed system cannot decrease." Entropy is an indication of unusable energy and often (but not always!) corresponds to intuitive notions of disorder or randomness. Creationists thus misinterpret the 2nd law to say that things invariably progress from order to disorder.
However, they neglect the fact that life is not a closed system. The sun provides more than enough energy to drive things. If a mature tomato plant can have more usable energy than the seed it grew from, why should anyone expect that the next generation of tomatoes can't have more usable energy still? Creationists sometimes try to get around this by claiming that the information carried by living things lets them create order. However, not only is life irrelevant to the 2nd law, but order from disorder is common in nonliving systems, too. Snowflakes, sand dunes, tornadoes, stalactites, graded river beds, and lightning are just a few examples of order coming from disorder in nature; none require an intelligent program to achieve that order. In any nontrivial system with lots of energy flowing through it, you are almost certain to find order arising somewhere in the system. If order from disorder is supposed to violate the 2nd law of thermodynamics, why is it ubiquitous in nature?
The thermodynamics argument against evolution displays a misconception about evolution as well as about thermodynamics, since a clear understanding of how evolution works should reveal major flaws in the argument. Evolution says that organisms reproduce with only small changes between generations (after their own kind, so to speak). For example, animals might have appendages which are longer or shorter, thicker or flatter, lighter or darker than their parents. Occasionally, a change might be on the order of having four or six fingers instead of five. Once the differences appear, the theory of evolution calls for differential reproductive success. For example, maybe the animals with longer appendages survive to have more offspring than short-appendaged ones. All of these processes can be observed today. They obviously don't violate any physical laws.
"There are no transitional fossils."
A transitional fossil is one that looks like it's from an organism intermediate between two lineages, meaning it has some characteristics of lineage A, some characteristics of lineage B, and probably some characteristics part way between the two. Transitional fossils can occur between groups of any taxonomic level, such as between species, between orders, etc. Ideally, the transitional fossil should be found stratigraphically between the first occurrence of the ancestral lineage and the first occurrence of the descendent lineage, but evolution also predicts the occurrence of some fossils with transitional morphology that occur after both lineages. There's nothing in the theory of evolution which says an intermediate form (or any organism, for that matter) can have only one line of descendents, or that the intermediate form itself has to go extinct when a line of descendents evolves.
To say there are no transitional fossils is simply false. Paleontology has progressed a bit since Origin of Species was published, uncovering thousands of transitional fossils, by both the temporally restrictive and the less restrictive definitions. The fossil record is still spotty and always will be; erosion and the rarity of conditions favorable to fossilization make that inevitable. Also, transitions may occur in a small population, in a small area, and/or in a relatively short amount of time; when any of these conditions hold, the chances of finding the transitional fossils goes down. Still, there are still many instances where excellent sequences of transitional fossils exist. Some notable examples are the transitions from reptile to mammal, from land animal to early whale, and from early ape to human. For many more examples, see the transitional fossils FAQ in the talk.origins archive, and see http://www.geo.ucalgary.ca/~macrae/talk_origins.html for sample images for some invertebrate groups.
The misconception about the lack of transitional fossils is perpetuated in part by a common way of thinking about categories. When people think about a category like "dog" or "ant," they often subconsciously believe that there is a well-defined boundary around the category, or that there is some eternal ideal form (for philosophers, the Platonic idea) which defines the category. This kind of thinking leads people to declare that Archaeopteryx is "100% bird," when it is clearly a mix of bird and reptile features (with more reptile than bird features, in fact). In truth, categories are man-made and artificial. Nature is not constrained to follow them, and it doesn't.
Some Creationists claim that the hypothesis of punctuated equilibrium was proposed (by Eldredge and Gould) to explain gaps in the fossil record. Actually, it was proposed to explain the relative rarity of transitional forms, not their total absence, and to explain why speciation appears to happen relatively quickly in some cases, gradually in others, and not at all during some periods for some species. In no way does it deny that transitional sequences exist. In fact, both Gould and Eldredge are outspoken opponents of Creationism.
"But paleontologists have discovered several superb examples of intermediary forms and sequences, more than enough to convince any fair-minded skeptic about the reality of life's physical genealogy." - Stephen Jay Gould, Natural History, May 1994
"The theory of evolution says that life originated, and evolution proceeds, by random chance."
There is probably no other statement which is a better indication that the arguer doesn't understand evolution. Chance certainly plays a large part in evolution, but this argument completely ignores the fundamental role of natural selection, and selection is the very opposite of chance. Chance, in the form of mutations, provides genetic variation, which is the raw material that natural selection has to work with. From there, natural selection sorts out certain variations. Those variations which give greater reproductive success to their possessors (and chance ensures that such beneficial mutations will be inevitable) are retained, and less successful variations are weeded out. When the environment changes, or when organisms move to a different environment, different variations are selected, leading eventually to different species. Harmful mutations usually die out quickly, so they don't interfere with the process of beneficial mutations accumulating.
Nor is abiogenesis (the origin of the first life) due purely to chance. Atoms and molecules arrange themselves not purely randomly, but according to their chemical properties. In the case of carbon atoms especially, this means complex molecules are sure to form spontaneously, and these complex molecules can influence each other to create even more complex molecules. Once a molecule forms that is approximately self-replicating, natural selection will guide the formation of ever more efficient replicators. The first self-replicating object didn't need to be as complex as a modern cell or even a strand of DNA. Some self-replicating molecules are not really all that complex (as organic molecules go).
Some people still argue that it is wildly improbable for a given self-replicating molecule to form at a given point (although they usually don't state the "givens," but leave them implicit in their calculations). This is true, but there were oceans of molecules working on the problem, and no one knows how many possible self-replicating molecules could have served as the first one. A calculation of the odds of abiogenesis is worthless unless it recognizes the immense range of starting materials that the first replicator might have formed from, the probably innumerable different forms that the first replicator might have taken, and the fact that much of the construction of the replicating molecule would have been non-random to start with.
(One should also note that the theory of evolution doesn't depend on how the first life began. The truth or falsity of any theory of abiogenesis wouldn't affect evolution in the least.)
"Evolution is only a theory; it hasn't been proved."
First, we should clarify what "evolution" means. Like so many other words, it has more than one meaning. Its strict biological definition is "a change in allele frequencies over time." By that definition, evolution is an indisputable fact. Most people seem to associate the word "evolution" mainly with common descent, the theory that all life arose from one common ancestor. Many people believe that there is enough evidence to call this a fact, too. However, common descent is still not the theory of evolution, but just a fraction of it (and a part of several quite different theories as well). The theory of evolution not only says that life evolved, it also includes mechanisms, like mutations, natural selection, and genetic drift, which go a long way towards explaining how life evolved.
Calling the theory of evolution "only a theory" is, strictly speaking, true, but the idea it tries to convey is completely wrong. The argument rests on a confusion between what "theory" means in informal usage and in a scientific context. A theory, in the scientific sense, is "a coherent group of general propositions used as principles of explanation for a class of phenomena" [Random House American College Dictionary]. The term does not imply tentativeness or lack of certainty. Generally speaking, scientific theories differ from scientific laws only in that laws can be expressed more tersely. Being a theory implies self-consistency, agreement with observations, and usefulness. (Creationism fails to be a theory mainly because of the last point; it makes few or no specific claims about what we would expect to find, so it can't be used for anything. When it does make falsifiable predictions, they prove to be false.)
Lack of proof isn't a weakness, either. On the contrary, claiming infallibility for one's conclusions is a sign of hubris. Nothing in the real world has ever been rigorously proved, or ever will be. Proof, in the mathematical sense, is possible only if you have the luxury of defining the universe you're operating in. In the real world, we must deal with levels of certainty based on observed evidence. The more and better evidence we have for something, the more certainty we assign to it; when there is enough evidence, we label the something a fact, even though it still isn't 100% certain.
What evolution has is what any good scientific claim has--evidence, and lots of it. Evolution is supported by a wide range of observations throughout the fields of genetics, anatomy, ecology, animal behavior, paleontology, and others. If you wish to challenge the theory of evolution, you must address that evidence. You must show that the evidence is either wrong or irrelevant or that it fits another theory better. Of course, to do this, you must know both the theory and the evidence.
These are not the only misconceptions about evolution by any means. Other common misunderstandings include how geological dating techniques work, implications to morality and religion, the meaning of "uniformitarianism," and many more. To address all these objections here would be impossible. But consider: About a hundred years ago, scientists, who were then mostly creationists, looked at the world to figure out how God did things. These creationists came to the conclusions of an old earth and species originating by evolution. Since then, thousands of scientists have been studying evolution with increasingly more sophisticated tools. Many of these scientists have excellent understandings of the laws of thermodynamics, how fossil finds are interpreted, etc., and finding a better alternative to evolution would win them fame and fortune. Sometimes their work has changed our understanding of significant details of how evolution operates, but the theory of evolution still has essentially unanimous agreement from the people who work on it.If you wish to truly understand how evolution works, read this book: