Its All or Nothing

GERT KORTHOF

If the living world has not arisen from common ancestors by means of an evolutionary process, then the fundamental unity of living things is a hoax and their diversity, a joke.

—Theodosius Dobzhansky (1964)

I wrote this chapter for everyone who believes that it is possible to accept something less than full common descent of all life. In my view, anything less than full common descent leads to both an arbitrary fragmentation of the tree of life and a logically inconsistent theory of descent and also conflicts with the evidence.

Carl Linnaeus, the Swedish botanist who invented the biological nomenclature still in use today, was a creationist. According to Linnaeus, "We count as many species as different forms were created in the beginning" (Mayr 1982, 258). Linnaeus's work and thinking were based on the concept of design by God. Species were fixed, and their systematic relationships reflected the divine plan. Despite his belief in the fixity of species, Linnaeus came to accept varieties within species. These varieties, he thought, resulted from changed conditions. By 1756, at the end of his life, he had concluded that the number of species within a genus might increase. This was not evolution as we know it today; Linnaeus suggested that in the original creation God formed only a single species as the foundation of each genus and left the multiplication of species within genera to a natural process of hybridization (Bowler 1989, 67).

French naturalist Georges-Louis Buffon had defended the fixity of species early in his career, but in 1766, nearly a hundred years before the publi-

Pheasants

Ducks

Dogs

Cats

Horses

Pheasants

Ducks

Dogs

Cats

Horses

Figure 3.1. Basic types in the dynamic creation model. The arrows in the figure depict the creation of various "ground types." After Pennock (2002, 685).

cation of Charles Darwin's (1859) Origin of Species, he accepted the idea that closely related Linnaean species had diverged from a common ancestor. This view is close to what today is called microevolution. Buffon even went so far as to claim that families were created by God. The family possessed fixed characteristics and had no ancestors itself (Bowler 1989, 74).

Today, philosopher Paul Nelson (2001a, 684), who is part of the intelligent-design movement, argues for the creation of basic types (also known as "ground types") stemming from common ancestors. He illustrates those basic types with a figure similar to figure 3.1 (Junker and Scherer 1988). The illustration shows five animal groups: pheasants, ducks, dogs, cats, and horses. Each group is descended from a created common ancestor, which itself has no ancestor. Nelson contrasts a static-creation theory (creation of fixed species) with the dynamic-creation model he favors.

Nelson criticizes Mark Ridley (1985) for displaying only the static fixed-species model and ignoring the modern dynamic-creation model (see figure 3.2). The four publications Nelson uses as evidence for his accusation, including the source of figure 3.1 (Junker and Scherer 1988), postdate Ridley's 1985 book. His criticism is unfair because Ridley could not have known of publications appearing after his own book.

Nelson is not the only creationist proposing this kind of model. Jonathan Sarfati (2000, 38, 39) has a similar model, which he calls "the true creationist orchard." (Its picture looks like an orchard.) According to the model, diversity has occurred within the original Genesis kinds. There are no names

Form Evolution Transforming

Fixed species

Fixed species Plus extinction

Figure 3.2. After Ridley (1995, 1996).

Form Evolution Transforming

Fixed species

Fixed species Plus extinction

Figure 3.2. After Ridley (1995, 1996).

attached to the trees in his illustration, so we can draw no inference as to their taxonomic level. He, too. contrasts his model with the alleged creationist "lawn," where each species is like a blade of grass, separate from all others.

The fixed-species model claims that no new species have been produced since creation, but it allows for extinction. The model is a caricature of cre-ationism, says Sarfati, because it implies that the Genesis kinds were the same as today's species. He claims that the fixed-species model is a straw man for creationism, and Nelson claims that it has not appeared in creationist publications in recent decades. His statement implies that creationists adhered to the fixed-species model in previous decades. It would be interesting to know what insight or fact caused creationists to convert to the dynamic-creation model.

The dynamic-creation model is similar to the model of the creationist Walter Remine (1993). He places, for example, dogs, wolves, coyotes, jackals, and foxes in one systematic group: the Canidae-monobaramin, which matches Nelson's dogs group. Remine defines monobaramin as "a group containing only organisms related by common descent, sharing a common ancestor" (444). Subsequently, he states the inevitable: "Directly created organisms have no ancestor, they are created by the direct action of a designer"

Implications of the Dynamic-Creation Model

The dynamic-creation model (DCM) uses the theological concept of creation as its foundation: "Here, the terminal species are members of basic types, stemming from common ancestors which were themselves created" (Nelson 2001a,

684). Therefore, DCM is basically theology. Nelson could have omitted the word created. He could have used an agnostic formula such as "the common ancestors of families are unknown and cannot be known to science," but he did not. Doing so would have destroyed the beating heart of creation theory.

In this chapter I ignore DCM's theological foundation not because it is a minor detail but because I want to avoid endless discussions about whether or not supernatural interventions are a legitimate part of natural science. I will first explore the biological implications of DCM and then evaluate the model itself.

1. Implications for the taxonomic level of basic types. Although Nelson does not state the taxonomic level of the groups, Siegfried Scherer (1998), the author of the drawing Nelson (2001a) uses, says that the basic types are families: Phasianidae (pheasants), Anatidae (ducks), Canidae (dogs), Felidae (cats), and Equidae (horses). Each basic type contains different genera (for example dog, fox, wolf), and each genus contains one or more species. Thus, families are created, not genera or species.

2. Implications for the number of species originating from basic types. The mini-trees in figure 3.1 show only five to eight species per tree. This misleads the reader: each genus has many more species than are depicted in the figure. The pheasant family consists of 38 genera and 155 species, the duck family 41 genera and 147 species, the dog family 12 genera and 34 species, and the cat family 37 species.

These numbers are tiny in comparison with families of insects. A single beetle family (weevils) contains approximately 65,000 species (Tudge 2000). The supposition that the basic type contains all the information necessary to create all the descendant species is therefore highly implausible. It implies, for example, that the information for 65,000 weevil species was already present in the weevil basic type.

3. Implications for the number of basic types. How many basic types are there? Creationists don't tell us. Until we know, the dynamic-creation model is only a fragment of a theory. If basic types are to capture the million or so species on earth, the model must include thousands of basic types.

4. Implications for the number of interventions. The model includes only one arrow per basic type and thus one supernatural intervention per created basic type. The implication is that the rest of each mini-tree is free of supernatural interventions. If the author acknowledged the existence of additional interventions, he could no longer claim that creation had been at the family level. Indeed, such additional interventions might end up as the special creation of species, part of the static-creation model, which Nelson emphatically rejects. Intelligent-design theorists do not deny the existence of unguided natural processes but claim that not all processes in nature are unguided. Therefore, they do not necessarily object to the idea that the mini-trees are unbroken chains of natural processes.

5. Implications for mutation and natural selection. If creation took place at the family level, then genera and species must have originated in a natural way. How? Since DCM claims that the basic types vary (within boundaries) by microevolutionary processes, the mechanism must be the standard Darwinian mutation and natural selection. These mechanisms produce all the terminal species. In other words, genera and species are created by natural processes as described in the textbooks.

But then it does not make sense to keep talking about guided mutations and the like. Further, it does not make sense to continue objecting to the efficacy of natural selection—to claim that natural selection is not a creative force or that natural selection is a tautology and explains nothing (Nelson 2001b, 128). Finally, a total rejection of the mechanisms creating new species is not compatible with DCM.

6. Implications for the concept of variation. In DCM, species are variations of the basic types, but the use of the term variation is inappropriate. Variation is a phenomenon within species or populations (Strickberger 2000, 657). It is misleading to use the term for the formation of new species complete with reproductive barriers. Reproductive isolation is what keeps species apart. Creationists, however, prefer to use the word variation to express the idea that nothing important has happened since the creation of basic types. The terms basic types and ground types are not found in textbooks. The terms operate together with variation: ground type plus variation. But all are inadequate.

7. Implications for micro- and macroevolution. In at least one textbook (Strickberger 2000, 648), microevolution is defined as changes within species. Macroevolution is evolution above the species level (genera, families, orders, and classes). According to DCM, considerable change—albeit ultimately bounded—may occur after the creation of basic kinds (Nelson 2001a, 684). How much change? Since genera are above the species level, DCM implies macroevolutionary processes.

8. Implications for the rate of evolution. The combination of a 6000-year-old earth and the number of species produced from basic types results in an astonishingly high rate of species formation: 65,000 weevil species in 6000 years amounts to more than 10 species per year.

9. Implications for the origin of humans. An interesting species is absent from figure 3.1. What does the model imply about the origin of humans? In traditional classification systems, humans were a separate family (Homi-nidae). In the modern classification based on molecular data, humans, gorillas, chimpanzees, and orangutans are placed in the family Homi-nidae (Futuyma 1998, 729). If creation were at the family level, traditional classification would result in the comfortable idea that humans were created separately. In the modern classification, a common ancestor of the Hominidae family would have been created, and humans, gorillas, chimpanzees, and orangutans would subsequently have evolved in a natural way.

In both classifications, humans, gorillas, chimpanzees, and orangutans are all in the order Primates, suborder Prosimii, and superfamily Hominoidea. If a protodog could produce a family of 34 species in less then 10 million years, why should a hominoid ancestor not produce chimpanzees, bonobos, gorillas, orangutans, and humans in the same time? The chromosome variation within the hominoid group is much smaller than in Canidae (the dog family). If the genetic distance between wolf and fox were the same as that between bonobo and human, then creationists should conclude that bonobos and humans have common ancestors. Creationists, however, presume that humans are created by the direct action of a designer.

10. Implications for the relative order of appearance in the fossil record. In figures 3.1 and 3.2, the vertical axis is the time axis. In figure 3.1, the branches start at different times; but, remarkably, all basic types start at the same time. Where is the evidence? It contradicts the chronology of the fossil record. Furthermore, the fossil record shows that bacteria, the first eukaryotes, invertebrates, vertebrates, land plants, fishes, birds, mammals, and Homo sapiens did not originate at the same time in the history of the earth.

11. Implications for the absolute times of appearance in the fossil record. The cat family appeared 20 million years ago (Strickberger 2000, 243). The history of the horse family, including the fossil Equidae, starts in the early Eocene, approximately 55 million years ago. Neither absolute time is compatible with young-earth creationism. Moreover, the hypothetical basic types need as much evidence from the fossil record as does any other ancestor in the theory of evolution.

12. Implications for the origin of species. A general implication of the dynamic-creation model is that all end products—that is, all species—are not

(directly) created. Because there are no basic types alive today, no species we now encounter has been created. The beautiful ornamentation of the Argus pheasant, which Darwin (1871, 92) noted "was more like a work of art than of nature," was not created by God but by selection (see items 4 and 5 on this list). The Argus pheasant is a member of the pheasant basic type. If the common ancestor of that group did not possess the eyespots on its tail, mutation and natural selection must have created the eyespots. The stunningly ornamented birds of paradise, the tail of the peacock, the stripes of the zebra, and the human brain have evolved by mutation and natural selection.

Evaluation of the Dynamic-Creation Model mysteries

The dynamic-creation model uses standard neo-Darwinian processes when convenient but also introduces mysteries and fatal inconsistencies. Let's first have a look at the orthodoxy. The mini-trees imply common descent, branching evolution, hierarchical taxonomic levels, origin of new species, natural selection, and mutation. For example, the model explains similarities within basic types (similarities of dogs, wolves, foxes, and coyotes) by common descent.

Additionally, the differences between dogs, wolves, foxes, and coyotes are explained by divergence of the organisms arising from the ancestral basic type. Both facts are reflected in the mini-trees. So far, so good. But then a huge difference from the standard Darwinian explanation arises: in DCM, cats and dogs have an independent origin. In other words, cats and dogs are completely unrelated groups without common descent. That claim destroys the standard (Darwinian) explanation of their similarities.

DCM offers no alternative explanation, which introduces a deep mystery. I cannot stress enough how amazing it is that the model cannot answer straightforward questions such as why cats and dogs share characteristics and are placed in the same group, Carnivores, or why pheasants and ducks are placed in a group called birds. Who would deny that cats, dogs, bears, and weasels share Carnivore properties?

Darwinian theory explains their shared properties by a common Carnivore ancestor and explains their differences by divergence since the ancestral lines split. The question about similarities can be repeated for every basic type. Similarities do not stop beyond the boundaries of basic types. The whole Lin-naean classification system unacceptably becomes a mystery in the dynamic-creation model.

Vertebrates t N 7/ t

Vertebrates

Figure 3.3. Basic types and evolutionary groups. Basic types (a) are exclusive, whereas evolutionary groups (b) are inclusive.

inconsistency

Now the logical inconsistency is easy to see. If the similarities and dissimilarities are a good reason for classifying individual organisms into the hierarchical categories, species, genera, and families, and for explaining that pattern with common descent, then why are those reasons not equally valid for higher categories such as orders, classes, phyla, and kingdoms? Why is common descent a good explanation up to the family level and a bad explanation at higher levels?

Even horses and birds share vertebrate characteristics. This pattern of similarities is called the groups-within-groups pattern, or inclusive groups (see figure 3.3b). To return to Nelson's mini-trees: the dogs are a group within the Carnivores group, the Carnivores are a group within Mammalia, the Mammalia are a group within the Craniata, and the Craniata are a group within the Animalia. The logic of inclusive groups makes it impossible to see them as independent groups. Every taxonomic group (except the highest) is included in a higher-level group. There is no such a thing as an independent group.

animal farm

According to DCM, basic types have an independent origin. In other words, they are not connected by common descent. All basic types are equal in the sense that they are equally independent. To paraphrase George Orwell, all basic types are unequal, but some basic types are more unequal than others. Indeed, there are degrees of similarities. Although, for example, three of the basic types—pheasants, ducks, and cats—have an independent origin, creationists cannot deny that pheasants and ducks are more equal than pheasants and cats.

Why do some basic types look similar if they do not have a close evolutionary relationship? Why do some basic types look dissimilar if they do not have a more-distant evolutionary relationship? Why expect any similarities above the basic-type level at all? Any pattern of similarities of basic types is possible. Independent origin is unable to predict a groups-within-groups pattern. Higher-level groups, such as birds, carnivores, mammals, reptiles, fishes, insects, and plants, are not expected or predicted at all by a theory of independent origin. In fact, relations between basic types are in principle unknowable (see figure 3.3a), whereas evolutionary relations between groups become clearer when new information becomes available.

What we can conclude from the dynamic-creation model is that the unity of living things is a hoax and their diversity a joke. Although Scherer (1998, 206) tries to give an empirical definition of the basic type, he in fact does nothing to establish the similarities and degrees of similarity between those types. Every biologist classifies pheasants and ducks in one group, Aves (birds), and explains their similarity by saying that pheasants and ducks have a more-recent ancestor than do pheasants and cats. The explanation of the Linnaean hierarchical classification system collapses if we accept the independent origin of basic types.

plan of creation In Linnaeus's time, the existence of the groups-within-groups pattern was explained as the plan of creation. It was, in reality, an unintelligible fact. Without evolution, nobody could hope for a better explanation; maybe no one felt the need for it. But when a good explanation is available, it is unacceptable to fall back into the mysteries of pre-Darwinian times. Introducing mysteries and inconsistencies and destroying the explanation of all the taxonomic categories above the family level is not exactly scientific progress.

Darwin offered an elegant explanation for the groups-within-groups pattern: common descent. The creation model leaves unexplained or completely mysterious all those similarities that common descent elegantly and consistently explains. Even allowing for creation as a scientific explanation still leaves the pattern of similarities unexplained. The assumption of created ancestors does not lead to specific expectations about the pattern of life on earth such as the groups-within-groups pattern. How could it? "Darwin, after all, banished speculation about the 'unknown plan of creation' from science" (Johnson 1993, 70).

reinventing common descent Scherer (1998) tried to express biological relationships between species by using a new systematic category: basic types. This category does not help to classify organisms belonging to different basic types. To capture the relationships between pheasants, ducks, and all the other birds, we need a basic type called birds, which is the ancestor of all the different basic types of birds. The same holds for all the mammals and all the animals. We need basic types called mammals and animals. To capture the relationships between all forms of life on earth, we need a basic type called life. And that amounts to reinventing common descent. Nelson's and Scherer's basic types are neither "basic" nor "types." Unaware of the boundaries between basic types, mutation and natural selection can go beyond their confines.

darwin's invention

Nelson's criticism of Ridley's illustration is odd for many reasons. The dynamic-creation model contains mini-trees. But the idea to use trees to represent the relations between species is stolen from Darwin and was certainly not invented by creationists: "Darwin, curiously, was the first author to postulate that all organisms have descended from common ancestors by a continuous process of branching. . . . A continuing multiplication of species could account for the total diversity of organic life" (Mayr 1982, 507).

Additionally, the trees in Ridley's illustration have diverging branches, while those in Nelson's illustration are vertical. This means that species are static. The dynamic-creation model is a distortion of common descent. We cannot even say that DCM is halfway toward common descent. Nelson and other intelligent-design theorists are blind to the power and purpose of common descent, which does not explain families but life itself. To limit the scope of common descent to families is like driving a plane on the road and ignoring that it is meant to fly.

New Evidence for Common Descent of Basic Types

So far I have focused on logic and explanatory power, which can be understood without detailed knowledge of genetics and biochemistry. Indeed, Darwin knew nothing about either field, but he understood the logic of evolutionary theory. In 1900, Mendelian genetics was born. Fifty years later, James Watson and Francis Crick published the structure of DNA. Another 50 years later, the complete sequence of the human genome was published. The last event signified the transformation of genetics (the study of individual genes) into genomics (the study of the genome, or the whole gene set of a species).

When scientists started comparing whole genomes of species, startling new evidence for the similarity and common descent of species began to emerge. The DNA sequences of human and mouse, for example, revealed that not only genes but also whole segments of chromosomes of mouse and human are identical. A chromosome segment of roughly 90.5 million DNA bases on human chromosome 4 is similar to mouse chromosome 5. Almost all human genes on chromosome 17 are found on mouse chromosome 11, and human chromosome 20 corresponds entirely to the bottom segment of mouse chromosome 2. A graphical and interactive representation of all the cases of synteny (correspondence of chromosome segments of two different species) of mouse and human can be found at the web site of the Sanger Institute (2002). The maps are based on Simon Gregory et al. (2002).

These special similarities mean that hundreds to thousands of genes are found in the same order in both mouse and human. This is impressive evidence for their common descent. The distribution of genes over chromosomes cannot be explained by biochemical or biological necessity. With the exception of the Y-chromosome and, to a lesser degree, the X-chromosome, no chromosome is dedicated to a special biological function such as digestion, respiration, locomotion, reproduction, or perception. The genes that control those biological functions are distributed over 20 pairs of chromosomes in the mouse and 23 pairs in the human. Consequently, the correspondences between different species cannot be explained by necessity or chance. Historical contingency is the dominant factor that produced the size, shape, composition, and number of chromosomes. Despite the many rearrangements of chromosomes since the human-mouse split, both humans and mice inherited 195 intact, conserved segments from their common ancestor.

In the creation model, human and mouse belong to different basic types. The correspondence of their chromosome segments shows, however, that mouse and human are not basic types but derived types. Similar results are found for cats, seals, cows, horses, and rats. Indeed, while I was working on the final revision of this chapter, Science (13 June 2003) published a special issue devoted to the tree of life. Among the many enlightening topics was the visualization of a tree of life incorporating no fewer than 3000 species (Pennisi 2003). Because of the immense amount of information packed into the tree, it is, the editor noted (not without humor), "best viewed when enlarged to a 1.5 meter diameter" (93).

Michael Behe

Not all intelligent-design advocates are like Nelson. Michael Behe (1996) claims to accept the common descent of all life: "I believe the evidence strongly supports common descent" (176). He has since repeated that statement: "I dispute the mechanism of natural selection, not common descent" (Behe 2001b, 697).

Behe's position is puzzling. He does not say why he accepts common descent. The two quotations are nearly all he has to say about it. Perhaps he does not realize the consequences of his statement. Common descent of life means that all life on earth is physically, historically, and genetically connected. It means that life is one unbroken chain of ancestors and descendants. It means that every organism inherited all its genes from the previous generation (with slight modifications). And that includes irreducibly complex systems. (See chapters 4 through 6 in this book.)

Every supernatural intervention is a violation of common descent because it means that a new irreducibly complex system was not inherited from the parents of the individual in which that system first appeared. We could not say, "I inherited all my chromosomes from my parents, except an irreducibly complex system on my X-chromosome, which has a supernatural origin." Equally, Behe cannot claim that common descent is true except when irre-ducibly complex systems appear. Common descent does not allow for that kind of exception because that implies a violation of the laws of genetics. Genetics is the most exact and well-established discipline in biology. Hundreds of thousands of genetic experiments have been done since the birth of classic Mendelian genetics (1900) and the birth of molecular genetics (1953). An irreducibly complex system has never suddenly appeared, whereas the kinds of mutations necessary for evolution have routinely been observed.

Phillip Johnson

Phillip Johnson is one of the leaders of the intelligent-design movement. His opinion about common descent is stated most clearly in his well-known Darwin on Trial (1993): "[Creationists'] doctrine has always been that God created basic kinds, or types, which subsequently diversified. The most famous example of creationist microevolution involves the descendants of Adam and Eve, who have diversified from a common ancestral pair to create all the diverse races of the human species" (68).

This is an intriguing passage for several reasons. It suggests that humans are a basic kind and were created as such. By switching from basic kind to microevolution, Johnson avoids explicitly stating that humans are a basic kind and thus created but strongly suggests that they are. If that is the case, then Johnson's idea of basic kinds is more restricted than is Nelson's dynamic-creation model. Johnson's example of basic kind is at the species level and implicitly affirms that the meaning of microevolution is "change within a species."

If this is Johnson's view, then by implication all species are created, and microevolution is allowed to create only minor modifications within species. Whatever the definition of basic kinds (be it on the species or family level), microevolution by definition produces no new species. Any creation model that ends up with more species than the number of species it started with needs a natural mechanism to produce new species. Creating new species is macro-evolution, according to the textbooks, but it is very difficult for a creationist to admit that he or she accepts macroevolution.

We can see that Johnson would love to believe in the special creation of humans:

We observe directly that apples fall when dropped, but we do not observe a common ancestor for modern apes and humans. What we do observe is that apes and humans are physically and biochemically more like each other than they are like rabbits, snakes, or trees. The ape-like common ancestor is a hypothesis in a theory, which purports to explain how these greater and lesser similarities came about. The theory is plausible, especially to a philosophical materialist, but it may nonetheless be false. The true explanation for natural relationships may be something much more mysterious. (67)

An intriguing passage. Now Johnson states that the hypothesis that apes and humans share a common ancestor is plausible but may be false. He fails to make clear whether he accepts or rejects common descent and why. To state that a scientific theory may be false is nothing new: all scientific theories may be false. Certainly the idea that the true explanation for relationships may be mysterious is not a solid reason to reject common descent. With humor, Johnson remarks that "descent with modification could be a testable scientific hypothesis" (66).

But suggesting a mysterious cause for natural relationships is not "a testable scientific hypothesis." I fail to see what philosophical materialism has got to do with it. Johnson does not propose a nonmaterialist explanation. He evidently does not like the hypothesis of common descent but is unable to find good reasons to reject it and fails to present an alternative. This is science by personal preference.

William Dembski

William Dembski, the mathematician of the intelligent-design movement, published his main works after Johnson and Behe did. He is less specific, however, about common descent than are creationists like Nelson and more ambivalent about the correctness of common descent than is Michael Behe.

According to evolutionary biologist H. Allen Orr (2002), the intelligentdesign movement usually admits that people, pigs, and petunias are related by common descent. But its leading theorist, Dembski (2002b, 314, 315), does not unconditionally accept common descent. He ignores Nelson's dynamic-creation model and fails to say what, for example, the similarity of apes and humans means:

Darwinism comprises a historical claim (common descent) and a naturalistic mechanism (natural selection operating on random variations), with the latter being used to justify the former. According to intelligent design, the Darwinian mechanism cannot bear the weight of common descent. Intelligent design therefore throws common descent into question but at the same time leaves open as a very live possibility that common descent is the case, albeit for reasons other than the Darwinian mechanism. (315)

Dembski is right to distinguish between common descent of all life and the mechanism of evolution, but he is wrong about the relation between the two. Yes, both are part of Darwinism, but he is incorrect to suggest that natural selection and random variation are the justification for common descent. Darwin would have adopted his theory of common descent on the basis of classification alone. Common descent is inferred from data that are independent of the mechanism of evolution. Common descent itself does not imply anything about the tempo or the gradualness or the relative importance of selection in evolution.

Dembski is determined to undermine the mechanism of evolution. He hopes to debunk common descent as a logical consequence of destroying the mechanism of evolution. Significantly, 150 years after Darwin, Dembski (2002b) still has nothing better to say than a cryptic "time leaves open as a very live possibility that common descent is the case, albeit for reasons other than the Darwinian mechanism" (315). This vague remark is very similar to Johnson's (1993) mysticism: "some process altogether beyond the ken of our science" (155). Remarkably, Johnson had previously stated that "speculation is no substitute for scientific evidence" and that "Darwin, after all, banished speculation about the 'unknown plan of creation' from science" (70). It is too late for mysticism 150 years after Darwin. Biologists have something better: it is called common descent.

Both Johnson and Dembski forget that Darwin did not know about genetic mutations, he did not know Mendelian genetics, and he did not know molecular genetics. The point is that Darwin had sufficient reason to explain patterns of similarities and dissimilarities in the organic world even without knowledge of genetics. The success of Darwin's explanation did not even depend on the specifics of his theory of heredity, which turned out to be wrong. Now that we know that the genetic language of all life (how genes are translated into proteins) is not only similar but also virtually identical in all organisms, we have a magnificent confirmation of common descent.

Darwin could not have foreseen that common descent would receive such dramatic underpinnings. The specific genetic code that all living organisms use to translate genes into proteins could have been dramatically different; no chemical laws that render the current genetic code necessary have been discovered. Each created basic type could have a different genetic code without any physiological or ecological problems (Korthof 2001). Dogs and cats could have different genetic codes. Humans and apes could have different genetic codes. Yet they do not.

Common descent would be best refuted if the most closely related organisms had the most dissimilar genetic codes. (Theoretically, genetic codes can differ in gradual ways.) But all species have essentially the same genetic code. The rare and small variations of the genetic code are superimposed on common descent and follow the pattern of descent with modification. Phyloge-netic trees can be constructed for those variants. The genetic code, which translates genes into proteins, is stored in DNA and subject to mutation. Variant genetic codes have very restricted effects on the organism. Nearly all possible variant genetic codes are destructive for the organism and are subject to strong selection pressure. That explains why variations are rare. Far from being an argument against common descent, as some creationists argue, they offer clues to the origin of the genetic code.

Furthermore, Darwin did not and could not construct the theory of common descent to explain the universality of the genetic code. The universality of the genetic code was discovered more than 100 years after the publication of the Origin of Species. Common descent thus successfully explains a completely new fact about life on earth. All those similarities will not go away, whatever Dembski's claims about the inadequacy of the mechanism of evolution.

In fact, it is extremely hard to come up with a complete and systematic alternative to common descent. Attempts to formulate a naturalistic alterna tive have resulted in severe problems and absurdities. For example, the Senapathy-Schwabe hypothesis of independent origin has even greater problems in explaining the properties of life (Korthof 2002, 2003).

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