Evolution and diversity of life
Does the theory of evolution explain the diversity of life?
The answer you may receive to the question posed above will differ greatly depending on who you ask. Evolutionary theory is a vast and far-reaching body of ideas, buttressed by huge amounts of careful scholarship, and offers immense explanatory power. For most biologists, Theodosius Dobzhansky’s statement1 that “nothing in biology makes sense except in the light of evolution” is literally true. Though most biologists do not study evolution directly, they work within a framework of ideas that supposes all living organisms are united by common descent; because they assume common descent to be true, they work as if it were so. However, a minority of biologists, ourselves included, perceive some major gaps in the evolutionary paradigm, which in our view call into question its ability to explain the full diversity of life.
Evolution depicts the diverse assemblage of living things via an “evolutionary tree” (figure 1), which postulates that all species are united by a branching pattern of descent from a common ancestor. This ancestor, thought to have formed spontaneously from nonliving materials, forms the root of the tree. Various lines of its descendants form the different branches, all the way out to the twigs (not shown) that represent species – living or fossil. Each major evolutionary change or innovation is represented by a new branch on the tree. The whole tree is held together by its roots and major branching points. Those points will be the focus of this essay.
The root of the tree
A whole set of significant gaps in explanatory power can be found at the tree’s base – in a biogenesis, or the forming of life from nonliving materials. The first postulated step in a biogenesis is the production of simple organic molecules (for example, amino acids) from inorganic materials. Although these molecules have been synthesized, the conditions required are not plausible on an early earth. The next step is polymerization – the linking of the small molecules together. While a few natural conditions allowing polymerization have been found, none help form the precise, complicated sequences characteristic of molecules in living cells. The gap between what random polymerization processes can be shown to produce and the simplest living cell is enormous.
Another feature characterizing living things is the ability to reproduce detailed copies of themselves, which in turn are also able to reproduce. This highly-complex process involves a whole suite of different molecules, all interacting with one another in a precisely-directed way. However, the entire complicated system of molecules is required in order for the cell to be able to copy itself. If any part of the chain of interacting molecules is missing, the entire process fails, and the cell cannot function or reproduce itself. This fact has long been recognized as a formidable challenge for the evolutionary theory of the origin of life.2
Looking beyond the molecules themselves to the organized structure of the cell, we see that living things are extremely complex, ordered systems with specific architecture. Many cellular components are essentially molecular machines, with interacting parts functioning in ways similar to human-designed machines.3 Just as the structure of an automobile is not inherent in the basic properties of metal, plastic, and paint, neither is the structure of living cells inherent in the properties of the molecules of which they are made. Instead, cells are “built” in specific ways, with the complicated patterns and combinations of materials required to carry out their functions.
The cell must constantly work to maintain its internal environment and keep itself in a functional state. The DNA (an acid containing the instructions necessary for the functioning of all living organisms) stores detailed information for how this is done and how all cell functions are carried out. However, such information is not inherent in the structure of DNA, either. Much as the sentiments expressed in a sonnet do not arise spontaneously from properties of the alphabet, the cell’s information had to be put there by some means outside of what can be found in the properties of DNA itself. The lack of a naturalistic source for this information represents another important gap in the theory of abiogenesis. Thus, the lack of a credible explanation for life’s origin leaves evolutionary theory with no known root for the evolutionary tree (see figure 2).
The major branches of the tree
We will next explore the attachment of major branches to the evolutionary tree. While evolutionary models attempt to explain how evolutionary information can arise incrementally by a combination of random mutation and natural selection, these models work best for rearranging information that is already present, such as may occur with species changing gradually over time. This is analogous to variations along the branches of the evolutionary tree.
The models quickly encounter huge and growing probability problems when attempting to explain how random changes could have produced large amounts of the new, specific, and complex information needed for originating life or producing an inherently new and different kind of creature.4 However, this is precisely what would be needed to produce a new branch on the tree. Attempts at an explanation have been made, such as exaptation (using existing parts for a new and different purpose than their original function).5 However, these explanations do not reveal how the original function developed in the first place, or what directs the parts to come together in a new way to perform some other function. No doubt much more research will be done on this question in the future.
Another hurdle for explaining the diversity of life via the evolutionary model is based on the structure of chromosomes. Chromosomes are composed of DNA, a very long, linear molecule. Genes, which contain the information necessary for cell function, are sequences lined up like sentences along the DNA strands. Occasionally, a gene is accidentally duplicated, producing an extra copy. The mutation/selection model of evolution posits that random small changes (mutations) in the DNA of the extra gene copy slowly accumulate. If these differences provide a benefit, they will be favored by natural selection. Over time, the model suggests that these small changes can produce a gene that performs a new function radically different from the original one.
One problem with this model stems from the fact that most mutations either have little effect or are in fact harmful. These harmful or slightly harmful mutations are likely to be much more common than any rare, beneficial mutation. Some evolutionists have presented mathematical models purporting to show how beneficial mutations can accrue by selection and eventually form new genes. Yet these models rarely account for the fact that each beneficial mutation will be linked to a large number of harmful or meaningless mutations, since they are all part of the same long chain of DNA. Given accepted estimates of ratios of beneficial to harmful mutations, models that take this into account suggest that the rare beneficial mutations will be swamped by the cumulative effect of the many harmful mutations linked to them on the DNA.6
These harmful mutations may be in the same gene or in more distant genes that are nevertheless linked by being on the same chromosome, all of which is usually inherited as a unit. In other words, it is difficult to take many steps forward while you are strongly tied to many other individuals that are taking steps backward. It is true that this linkage is not absolute – genes do have ways of swapping positions and rearranging on the chromosome. Nevertheless, the principle of negative mutations outnumbering positive ones should be true regardless of what portion of the chromosome a gene is in. At the very least, this gene linkage greatly complicates the already formidable barrier to producing genes for new, functional molecules by purely random mutation and natural selection. This linkage issue would be a problem for virtually any new evolutionary feature and would likely apply to many small and large branches on the evolutionary tree.
Artificial selection is another line of evidence providing insights into the problems of producing new branches on the evolutionary tree. Darwin used the analogy of artificial selection to claim that natural selection could accomplish even larger-scale changes, given enough time. But many scientists are skeptical that the small-scale changes observed in breeding experiments, or in nature, are sufficient to explain the differences among major groups of organisms. Can nature produce a horse from a fish using the same kinds of changes we observe from our study of finch beaks or our experience in breeding dogs or chickens? Probably not, irrespective of the amount of time available.7 The problem lies in the need for new genetic information, not merely an increase or decrease in the information that already exists. We can see how a single ancestral species may produce a variety of descendant species adapted to different environments, but the resulting pattern looks more like one small tree in a forest of separate trees than a single tree (figure 3).
Fossils and the evolutionary tree
The fossil record provides another way of assessing the problems of evolutionary branching. One of the most striking features of the fossil record is the abrupt appearance of most phyla (major types of organisms) in a relatively short stratigraphic interval in the Cambrian rock layers. This pattern, known as the Cambrian Explosion, offers one of the most compelling lines of evidence against the evolutionary tree. A large number of phyla and classes of animals found in the Cambrian have no ancestors or links to each other. The pattern is well summarized by the phrase “disparity precedes diversity.”8 In other words, the major differences among living organisms appear earlier in the fossil record than the many varieties with minor differences. No fossil evidence exists showing a gradual divergence over long ages to produce organisms with new body plans.9
Systematic gaps are another feature of the fossil record that does not support evolutionary theory.10 The shortage of transitional fossils is a widely-recognized feature of the fossil record, expressed in the familiar phrase “missing link.” Occasionally one hears reports of the discovery of a previously-missing fossil link, and these discoveries are hailed as evidence of evolutionary connections between different branches of the evolutionary tree. However, the most significant aspect of the problem is that the links are missing in a particular pattern.
We may compare the fossil record of horses and donkeys, for example, with that of clams and crabs. Horses and donkeys are very similar, and one might easily explain a lack of intermediates between them. After all, there might be only two or three intermediate species and therefore little chance of finding a fossil from such a small sample. In contrast, clams and crabs are very different. Following evolutionary theory, the number of fossil links connecting them to a common ancestor should thus number in the thousands. One would logically expect to find many fossils from such a large sample. In fact, the reality is exactly the opposite. There are many species of fossil horses, some of which may be regarded as linking horses and donkeys, while there are virtually no fossils that are believed to link clams and crabs. This is exactly the pattern one would expect if different types of organisms originated independently and varied within limits. Again, the pattern is more like a forest of independent trees than a single evolutionary tree.
A few examples of evolutionary links between higher taxa (or families of organisms) have been proposed, some of which appear quite convincing at first glance. When examined critically, they are not compelling to those with doubts about evolution. One important problem is the sequence in which some of these species appear in the fossil record. The fish-tetrapod fossils provide a good example. Soon after Darwin’s theory was published, scientists began looking for potential evolutionary ancestors for the terrestrial vertebrates.11 Lungfish were the first ancestors proposed, but were deemed too specialized. In the 1940s, the fossil fish
Eusthenopteron was described in detail and became the model of a tetrapod ancestor. Description of the fossil fish Panderichthys in 1980 and Tiktaalik12
in 2006 provided further examples of fossils with combinations of traits intermediate between fish and tetrapods. This fossil sequence has been used to argue that tetrapods evolved from the lobe-finned fish. More recently, however, a fossil tetrapod trackway was found in a layer lower in the strata than the fossil fish purported to be the tetrapod ancestor.13 In evolutionary terms, the purported descendant came before its ancestor – obviously impossible. Thus, it seems some other factor(s) must be at work in producing this fossil sequence.
Fossil whales provide another example of a proposed evolutionary series. Several fossil mammals have been found that are claimed to be whale ancestors.14 These fossils show combinations of traits unlike anything living today, and seem to show a trend of increasing similarity to whales. However, none of these fossil species is believed to be ancestral to any other known species, living or fossil. If one wishes to determine whether these fossils were part of an evolutionary lineage or were separately created, one must consult some explanatory theory, since the evidence is quite incomplete. An evolutionist could accept them as the result of evolution, while a creationist can look for another explanation, such as separately-created kinds, or the result of some unknown factor such as is illustrated in the tetrapod example in the previous paragraph.
In summary, although most scientists would say that evolution is adequate to explain the diversity of life, in our view it falls far short of that goal for several reasons. These include the lack of an information source for new forms, linked harmful mutations swamping beneficial ones, fossil disparity before diversity, and systematic gaps in the fossil record. Collectively, these observations show that the evolutionary tree is imaginary, and that the pattern of nature is more accurately illustrated by a “forest” of trees that represent independent-created lineages. We believe that evolution cannot explain the origin of life, the origin of any major new form, or even the development of major new structures within an existing form. Therefore, it cannot explain the broad diversity of life we see today. To us, the evidence inherent in the structure of life itself is compelling evidence that “in the beginning, God created” a diversity of “kinds.”
David L. Cowles (Ph.D., University of California, Santa Barbara) studied metabolism of deep-sea species. After teaching at Loma Linda University for fourteen years, he moved to Walla Walla University in 2001. E-mail: email@example.com.
L. James Gibson (Ph.D., biology, Loma Linda University) is director of the Geoscience Research Institute, with major interests in historical biology and the relationship of creation and science. He is also editor of the journal Origins. Site Web: http://www.grisda.org
- T. Dobzhansky, “Nothing in biology makes sense except in the light of evolution,” American Biology Teacher 35 (1973): 125–129.
- M.J. Behe, The Edge of Evolution (New York: Free Press, 2007), p. 320; D.L. Overman, A Case Against Accident and Self-Organization (Lanham, Maryland: Rowman and Littlefield Publishers, 1997), p. 244.
- First proposed by S.J. Gould and E.S. Vrba, “Exaptation – a missing term in the science of form,” Paleobiology 8 (1982): 4–15.
- J.C. Sanford, Genetic Entropy and the Mystery of the Genome (Waterloo, New York: FMS Publications, 2008), 232; the effect is known as “Muller’s Ratchet.”
- J. Valentine and D. Erwin, “Interpreting Great Developmental Experiments: The Fossil Record,” in Development as an Evolutionary Process, R.A. Raff and E.C. Raff, eds. (New York: Alan R. Liss, Inc., 1985), pp. 95, 96.
- See S.J. Gould, Wonderful Life: The Burgess Shale and the Nature of History (New York: Norton, 1989), p. 49.
- D. Erwin, J. Valentine, and J. Sepkoski, “A comparative study of diversification events,” Evolution 41 (1988): 1183.
- M. Denton, Evolution: A Theory in Crisis (Bethesda, Maryland: Adler and Adler, 1986), pp. 191, 192.
- See J.A. Clack, Gaining Ground: The Origin and Evolution of Tetrapods (Bloomington, Indiana: Indiana University Press, 2002), pp. 68–77.
- E.B. Daeschler, N.H. Shubin, and F.A. Jenkins, “A devonian tetrapod-like fish and the evolution of the tetrapod body plan,” Nature 44 (2006): 757–763.
- G. Niedzwiedzki et al., “Tetrapod trackways from the early middle devonian period of Poland,” Nature 463 (2010): 43–48.
- See, for example, C. de Muizon, “Walking with whales,” Nature 413 (2001): 259, 260.
2. S.C. Meyer, Signature in the Cell: DNA and the Evidence for Intelligent Design (New York: HarperCollins Publishers, 2009).
3. M.J. Behe, Darwin’s Black Box (New York: Free Press, 1996).
This article was originally published as part of a compilation, Understanding Creation: Answers to Questions on Faith and Science, edited by L. James Gibson and Humberto M. Rasi (Nampa, Idaho: Pacific Press Pub. Assn., 2011). Used by permission.