IT IS THE WORK OF A DESIGNER/CREATOR, USING A DESCENT PROCESS

Guided Evolution

While many theists are creationists who accept the occurrence of “microevolution” (that is, an evolution that occurs within a species, such as the evolution of penicillin-resistant bacteria) but deny the occurrence of “macroevolution” (that is, one species evolving from a distinct species), some theists accept the theory of evolution as consistent with theism and with their own denominational religious commitments. Such thinkers, however, frequently maintain that the existence of God is needed to explain the purposive quality of the evolutionary process. Just as the purposive quality of the cumulative-step computer program above is best explained by intelligent design, so too the purposive quality of natural selection is best explained by intelligent design. The first theist is widely known to have made such an argument is Frederick Robert Tennant. As he puts the matter, in Volume 2 of Philosophical Theology, “the multitude of interwoven adaptations by which the world has constituted a theatre of life, intelligence, and morality, cannot reasonably be regarded as an outcome of mechanism, or of blind formative power, or aught but purposive intelligence” (Tennant 1928-30, 121). In effect, this influential move infers design, not from the existence of functionally complex organisms, but from the purposive quality of the evolutionary process itself. Evolution is, on this line of response, guided by an intelligent Deity.

• 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 exhibit P. Third, they conclude that the design explanation is significantly more likely to be true. As we will see, however, all of the 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 a 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 the existence of God, design arguments appear unable to stand by themselves as arguments for God’s existence.

•  The 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 (Behe 1996, 39; emphasis added).

Since, for example, a cilium-precursor (that is, one that lacks at least one of cilium 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 (that is, 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. Design arguments are empirical arguments for the existence of God. These arguments typically, though not always, proceed by attempting to identify various empirical features of the world that constitute evidence of intelligent design and inferring God’s existence as the best explanation for these features. Since the concepts of design and purpose are closely related, design arguments are also known as teleological arguments, which incorporates “telos,” the Greek word for “goal” or “purpose.” Design arguments typically consist of (1) a premise that asserts that the material universe exhibits some empirical property F; (2) a premise (or sub-argument) that asserts (or concludes) that F is persuasive evidence of intelligent design or purpose; and (3) a premise (or sub-argument) that asserts (or concludes) that the best or most probable explanation for the fact that the material universe exhibits F is that there exists an intelligent designer who intentionally brought it about that the material universe exists and exhibits F. There are a number of classic and contemporary versions of the argument from design. This article will cover seven different ones. Among the classical versions are: (1) the “Fifth Way” of St. Thomas Aquinas; (2) the argument from simple analogy; (3) Paley’s watchmaker argument; and (4) the argument from guided evolution. The more contemporary versions include: (5) the argument from irreducible biochemical complexity; (6) the argument from biological information; and (7) the fine-tuning argument.

Table of Contents

1. The Classical Versions of the Design Argument
   1. Scriptural Roots and Aquinas’s Fifth Way
   2. The Argument from Simple Analogy
   3. Paley’s Watchmaker Argument
   4. Guided Evolution
2. Contemporary Versions of the Design Argument
   1. The Argument from Irreducible Biochemical Complexity
   2. The Argument from Biological Information
   3. The Fine-Tuning Arguments
      1. The Argument from Suspicious Improbability
      2. The Confirmatory Argument
3. The Scientifically Legitimate Uses of Design Inferences
4. References and Further Reading

•  The Classical Versions of the Design Argument
•  Scriptural Roots and Aquinas’s Fifth Way

The scriptures of each of the major classically theistic religions contain language that suggests that there is evidence of divine design in the world. Psalms 19:1 of the Old Testament, scripture to both Judaism and Christianity, states that “The heavens declare the glory of God and the firmament showeth his handiwork.” Similarly, Romans 1:19-21 of the New Testament states:

For what can be known about God is plain to them, because God has shown it to them. Ever since the creation of the world his eternal power and divine nature, invisible though they are, have been understood and seen through the things he has made. So they are without excuse.

Further, Koran 31:20 asks “Do you not see that Allah has made what is in the heavens and what is in the earth subservient to you, and made complete to you His favors outwardly and inwardly?” While these verses do not specifically indicate which properties or features of the world are evidence of God’s intelligent nature, each presupposes that the world exhibits such features and that they are readily discernable to a reasonably conscientious agent. Perhaps the earliest philosophically rigorous version of the design argument owes to St. Thomas Aquinas. According to Aquinas’s Fifth Way:

We see that things which lack knowledge, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that they achieve their end, not fortuitously, but designedly. Now whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God (Aquinas, Summa Theologica, Article 3, Question 2).

It is worth noting that Aquinas’s version of the argument relies on a very strong claim about the explanation for ends and processes: the existence of any end-directed system or process can be explained, as a logical matter, only by the existence of an intelligent being who directs that system or process towards its end. Since the operations of all-natural bodies, in Aquinas’s view, are directed towards some specific end that conduces to, at the very least, the preservation of the object, these operations can be explained only by the existence of an intelligent being. Accordingly, the empirical fact that the operations of natural objects are directed towards ends shows that an intelligent Deity exists. This crucial claim, however, seems to be refuted by the mere possibility of an evolutionary explanation. If a Darwinian explanation is even coherent (that is, non-contradictory, as opposed to true), then it provides a logically possible explanation for how the end-directedness of the operations of living beings in this world might have come about. According to this explanation, such operations evolve through a process by which random genetic mutations are naturally selected for their adaptive value; organisms that have evolved some system that performs a fitness-enhancing operation are more likely to survive and leave offspring, other things being equal, than organisms that have not evolved such systems. If this explanation is possibly true, it shows that Aquinas is wrong in thinking that “whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence.”

ment from Simple Analogy

The next important version of the design argument came in the 17th and 18th Centuries. Pursuing a strategy that has been adopted by the contemporary intelligent design movement, John Ray, Richard Bentley, and William Derham drew on scientific discoveries of the 16th and 17th Centuries to argue for the existence of an intelligent Deity. William Derham, for example, saw evidence of intelligent design in the vision of birds, the drum of the ear, the eye-socket, and the digestive system. Richard Bentley saw evidence of intelligent design in Newton’s discovery of the law of gravitation. It is noteworthy that each of these thinkers attempted to give scientifically-based arguments for the existence of God. David Hume is the most famous critic of these arguments. In Part II of his famous Dialogues Concerning Natural Religion, Hume formulates the argument as follows:

Look round the world: contemplate the whole and every part of it: you will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human designs, thought, wisdom, and intelligence. Since, therefore, the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man, though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. By this argument a posteriori, and by this argument alone, do we prove at once the existence of a Deity, and his similarity to human mind and intelligence.

Since the world, on this analysis, is closely analogous to the most intricate artifacts produced by human beings, we can infer “by all the rules of analogy” the existence of an intelligent designer who created the world. Just as the watch has a watchmaker, then, the universe has a universe-maker. VERN BENDER             VERN BENDER     VERN BENDER