In the book Theistic Evolution, we provide a comprehensive scientific, philosophical, and theological critique of the idea known as theistic evolution. But before we can do that, we will need to define what the proponents of this perspective mean by “theistic evolution” — or “evolutionary creationism,” as it is sometimes now called. Indeed, before we can critique this perspective we will need to know what exactly it asserts. Is it a logically coherent position? Is it a theologically orthodox position? Is it supported by, or consistent with, the relevant scientific evidence? The answer to each of these questions depends crucially on the definition or sense of “evolution” in play. “Theistic evolution” can mean different things to different people largely because the term “evolution” itself has several distinct meanings.

This introductory essay will describe different concepts of theistic evolution, each of which corresponds to a different definition of the term evolution. It will also provide an initial critical evaluation (and conceptual framework for understanding) those conceptions of theistic evolution that the authors of this volume find objectionable. The frameworks in this essay will help readers understand the more detailed critiques of specific versions of theistic evolution that will follow in subsequent essays, and it will help readers to understand how the different critical essays to follow mutually reinforce and complement each other. Both here and in the essays that follow, we will focus most (but not all) of our critical concern on one particular formulation of the concept of theistic evolution — in particular, the one that affirms the most scientifically controversial, and also most religiously charged, meaning of evolution.

Since the term evolution has several distinct meanings, it will first be necessary to describe the meanings that are commonly associated with the term in order to evaluate the different possible concepts of theistic evolution that proponents of the idea may have in mind. It will be shown that three distinct meanings of the term evolution are especially relevant for understanding three different possible concepts of theistic evolution. Yale biologist Keith Stewart Thomson, for example, has noted that in contemporary biology the term evolution can refer to: (1) change over time, (2) universal common ancestry, and (3) the natural mechanisms that produce change in organisms.³ are among the most celebrated examples of microevolution. The observed changes in the size and shape of Galápagos finch beaks in response to changing climate patterns provide another good example of small-scale change over time within a species.

Evolution #2: “Common Descent” or “Universal Common Descent”

Many biologists today also commonly use the term evolution to refer to the idea that all organisms are related by common ancestry. This idea is also known as the theory of universal common descent. This theory affirms that all known living organisms are descended from a single common ancestor somewhere in the distant past. In On the Origin of Species, Charles Darwin made a case for the truth of evolution in this second sense. In a famous passage at the end of the Origin, he argued that “probably all the organic beings which have ever lived on this earth have descended from some one primordial form.”⁴ Darwin thought that this primordial form gradually developed into new forms of life, which in turn gradually developed into other forms of life, eventually producing, after many millions of generations, all the complex life we see in the present.

Biology textbooks today often depict this idea just as Darwin did, with a great branching tree. The bottom of the trunk of Darwin’s tree of life represents the first primordial organism. The limbs and branches of the tree represent the many new forms of life that developed from it. The vertical axis on which the tree is plotted represents the arrow of time. The horizontal axis represents changes in biological form, or what biologists call “morphological distance.”

Darwin’s theory of biological history is often referred to as a “monophyletic” view of the history of life because it portrays all organisms as ultimately related as a single connected family. Darwin argued that this idea best explained a variety of lines of biological evidence: the succession of fossil forms, the geographical distribution of various species (such as the plants and animals of the Galápagos Islands), and the anatomical and embryological similarities among otherwise different types of organisms.

Evolution in this second sense not only specifies that all life shares a common ancestry, it also implies that virtually no limits exist to the amount of morphological change that can occur in organisms. It assumes that relatively simple organisms can, given adequate time, change into much more complex organisms. Thus, evolution in this second sense entails not only change but also gradual, continuous — and even unbounded — biological change.

Evolution #3: “The Creative Power of the Natural Selection/Random Variation (or Mutation) Mechanism”

The term evolution is also commonly used to refer to the cause, or mechanism, that produces the biological change depicted by Darwin’s tree of life. When evolution is used in this way, it usually refers to the mechanism of natural selection acting on random variations or mutations. (Modern “neo-Darwinists” propose that natural selection acts on a special kind of variation called genetic mutations. Mutations are random changes in the chemical subunits that convey information in DNA. Modern neo-Darwinists would also affirm the role of other apparently undirected evolutionary mechanisms such as genetic drift, although such mechanisms are typically thought to be of minor importance in comparison with mutation/selection in generating the adaptive complexity of life.)

This third use of evolution entails the idea that the natural selection/mutation mechanism has the creative power to produce fundamental innovations in the history of life. Whereas the theory of universal common descent postulated a pattern (the branching tree) to represent the history of life, the mechanism of natural selection and random variation/mutation represents a causal process that can allegedly generate the large-scale macroevolutionary change implied by the second meaning of evolution (see above). Since proponents of the creative power of the mutation/natural selection mechanism see it (and other similarly materialistic evolutionary mechanisms) as explaining the origin of all the forms and features of life, this definition of evolution is closely associated with, or encompasses, another definition of evolution.

Evolution #3a: The Natural Selection/Random Variation (or Mutation) Mechanism Can Explain the Appearance of Design in Living Systems apart from the Activity of an Actual Designing Intelligence.

Evolutionary biologists since Darwin have affirmed that the natural selection/variation mechanism not only explains the origin of all new biological forms and features; they have also affirmed a closely related idea, namely, that this mechanism can explain one particularly striking feature of biological systems: the appearance of design. Biologists have long recognized that many organized structures in living organisms—the elegant form and protective covering of the coiled nautilus; the interdependent parts of the vertebrate eye; the interlocking bones, muscles, and feathers of a bird wing — “give the appearance of having been designed for a purpose.”⁵ During the nineteenth century, before Darwin, biologists were particularly struck by the way in which living organisms seemed well adapted to their environments. They attributed this adaptation of organisms to their environments to the planning and ingenuity of a powerful designing intelligence.

Yet Darwin (and modern neo-Darwinists) have argued that the appearance of design in living organisms could be more simply explained as the product of a purely undirected mechanism, in particular the variation/natural selection mechanism. Darwin attempted to show that the natural selection mechanism could account for the appearance of design by drawing an analogy to the well-known process of “artificial selection” or “selective breeding.” Anyone in the nineteenth century familiar with the breeding of domestic animals — dogs, horses, sheep, or pigeons, for example — knew that human breeders could alter the features of domestic stock by allowing only animals with certain traits to breed. A Scottish sheepherder might breed for a woollier sheep to enhance its chances of survival in a cold northern climate (or to harvest more wool). To do so, he would choose only the woolliest males and woolliest ewes to breed. If, generation after generation, he continued to select and breed only the woolliest sheep among the resulting offspring, he would eventually produce a woollier breed of sheep — a breed better adapted to its environment. In such cases, “the key is man’s power of accumulative selection,” wrote Darwin. “Nature gives successive variations; man adds them up in certain directions useful to him.”⁶

But, as Darwin pointed out, nature also has a means of sifting: defective creatures are less likely to survive and reproduce, while those offspring with beneficial variations are more likely to survive, reproduce, and pass on their advantages to future generations. In the Origin, Darwin argued that this process — natural selection acting on random