The Creation Explanation
|Beliefs and Interpretations of Evidence|
Comparative Molecular Structure and the Theory of Molecular Homology and Molecular Evolution
One of the more recently developed types of evidence adduced in support of evolution comes from the study of amino acid sequences of proteins from different plants and animals, and also the nucleotide sequences of the corresponding genes or chromosomes. It will be remembered from the discussion in Chapter-4 that proteins are long chains of the twenty commonly occurring amino acids arranged in specific sequences which determine the properties of each protein. The fundamental structure of any protein is described by listing the order of the different amino acids in the long chain molecule. Many of the proteins produced in living cells serve as enzymes (catalysts or promoters) for reactions which cells must carry out in the course of the many metabolic processes which make life possible.
In general, each enzyme protein catalyzes a specific reaction or type of reaction in a chain of successive chemical reactions which comprise what is called a metabolic pathway. One such pathway found in plants and animals is that by which the sugar glucose is oxidized to provide energy for cells. The sequence of reactions is quite complicated, and each step requires a specific enzyme. One of these enzymes, cytochrome c, has been extracted from about a hundred different species of organisms, and the sequence of amino acids in the enzyme molecule has been determined for each species. It has been found that the cytochrome c molecule is quite similar for all species of organisms. In particular, there are regions in the protein amino acid chains in which the sequence of amino acids is identical in every cytochrome c. These are apparently parts of the molecule in which a very specific structure is essential for its enzyme activity.
In the other less functional regions of the cytochrome c molecules, some of the amino acid units vary from organism to organism. Dr. Richard Dickerson, then with the California Institute of Technology, analyzed these variations in terms of the average numbers of changes between groups of animals and plants. These numbers were then plotted against the assumed number of years back to the supposed time of evolutionary divergence from common ancestors which led to the groups. A fair straight-line relationship was demonstrated, which is interpreted as evidence for a constant rate of mutational change in cytochrome c with time, and also as evidence that the evolutionary development actually occurred in accordance with Darwinian theory.14
table 7-1. Cytochrome c Amino Acid Sequence14 for positions 62 to 84 in the peptide chains from 38 different species. The segment from positions 70 to 80 is invariant, for it is the heart of the active center of the enzyme molecule. In addition 24 other sites are also invariant. Another 23 sites are occupied by only one or the other of two very similar amino acids used in protein chains.There is no evidence for the evolutionary development of the overall structure of the enzyme nor of the active center and its function of catalyzing vital oxidation reactions in living cells. Thus the evidence supports the view that cytochrome c was designed, not evolved. Symbols for the amino acids, classified by character of side-chains are:
F(phenylalanine), Y(tyrosine)--hydrophobic with a benzene-type ring.
The sequence differences in cytochrome c for different species, as well as similar information for other proteins, have been interpreted by means of computer programs to produce evolution "trees" similar to those produced from fossil data. Such information seems quite persuasive as evidence for an evolutionary history of descent from common ancestors as proposed by Darwin. But does it prove the evolutionary scenario to be a fact of earth history? A number of criticisms can be leveled against this interpretation of the protein sequence data.
1. Is this in principle any different from the arrangement of organisms in a similarity series according to bodily form and structure? The cytochrome c molecules are arranged in a series according to certain variations in amino acid sequence. This is actually a series based on molecular morphology (shape) which does not verify an evolutionary history any more than does a similarity series of outward forms and structure. It is only circumstantial evidence for evolution. That it does supply such circumstantial evidence should not be denied by anybody, but the point here is that it does not supply proof.
2. The invariance of all of the cytochrome c molecules in their critical parts is evidence for intelligent, purposeful design. A certain basic design is essential for the functioning of this vital enzyme in all living things.
3. The data of cytochrome c amino acid sequences yield no evidence for the evolutionary origin of this basic design for the enzyme. The burden of proof is on evolutionary theorists to show how a sequence of intermediate sequences could have existed in which each particular sequence was functioning protein which had a selective value over the preceding one. No such proof exists. Therefore, that such an evolutionary development took place is an assumption.
4. Although, as was explained earlier, the amino acid differences between groups of organisms can in many instances be interpreted in a manner which supports the evolutionary theory, this evidence is, nevertheless, circumstantial. Closer analysis of the data reveals inconsistencies relative to the supposed history of evolution. Table 7-2 shows the number of amino acid changes between pairs of animals in the vertebrate group. When these numbers are divided into the assumed time in millions of years back to the supposed divergence of the ancestors of the members of a pair from some assumed or imagined common ancestor, the result is roughly the time in millions of years required for a change of one percent in the 104-unit amino acid chain of enzyme molecule.
As reported in Dr. Dickerson's article, this time is about 20 million years between groups. The fact that this value is fairly constant between the different groups and over varying estimated time periods is adduced in support of the evolutionary assumptions. But observe in Table 2 that such values within the vertebrate group vary all the way from seven million years to 50 million years for this selected set of pairs. The average value is about 25 million years, but the spread of values is so wide that it can hardly be said that the data offer good support for the theory that the vertebrates are related by evolution and that the rate of change of the cytochrome c molecule was constant with time within the vertebrate group. An alternative conclusion is that the great assumed time never existed after all.
table 7-2. Differences in Vertebrate Cytochrome c
Fundamental to inferring evolution history trees from amino acid sequence data is the assumption that the particular protein used has changed at the same rate in all of the species that are considered. However, in the past few decades a considerable amount of information has been published about substantial differences in the estimated rates of amino acid sequence changes for different species. In other words, the so-called protein evolution "clock" does not appear to run at the same speed for the different species. This invalidates any evolution history tree that is developed from the amino acid different data.
5. As has been pointed out by Colin Patterson of the British Museum, in many instances the species differences in protein amino acid sequences contradict the expectations based upon the currently adopted evolution tree.16 For example, of the 143 amino acids in a-hemoglobin, two reptiles, viper and crocodile, 5.6% are the same, whereas crocodile and chicken share 17.5%, but viper and chicken share 10.5%. Thus we have two reptiles seemingly more closely related to a bird than to each other. Patterson also notes for a-hemoglobin that man and crocodile share 7.7% of the same amino acids, crocodile and bird 7.7%, but man and bird have the same amino acids in 14.7% of the positions on the protein chain. Perhaps the correct explanation lies in design. Birds and man are both highly endothermic(i.e., maintain high body temperatures different from their environment) and burn energy rapidly. Similarities in their hemoglobin molecules which carry oxygen in the blood would be expected on the basis of the origin by intelligent creation.
6. As explained by Hoyle and Wickramasinghe, the computer-built evolution trees constructed from amino acid difference data require the assumption that evolution actually occurred.17 It is a fact that the evolution trees constructed from fossil data and homology in living species all place all species, extinct and living, out on the ends of the outer twigs. The intermediate fossil and living species needed to provide data for construction of the trunk, main branches, and larger twigs are all missing. But the trunk and the branches are built into the tree by assuming that the evolutionary history did in fact take place. In the case of the amino acid evolution tree, large numbers of mutations to make many changes in the protein amino acid sequences must be assumed in order to build the trunk and branches into the tree. But fewer changes must be assumed between similar types of plants and animals. That is, the little clumps of similar creatures on the tree have more proteins showing fewer differences. But one need not assume an evolutionary history of mutations to explain these data. After all, it is not unreasonable that similar organisms designed to live in somewhat similar environments or have similar functions should have protein molecules which are more similar to each other than to those of species with much different living conditions. Finally, as Hoyle and Wickramasinghe point out, the number of random mutations required to create the hemoglobin molecule by chance in the first place would require a greater time that the supposed evolutionary age of the universe.
7. In his 1986 book, Evolution: A Theory in Crisis, Michael Denton has presented the most telling criticism of evolutionary trees based on protein sequence data.18 He analyses the percentage differences between the cytochrome c molecules of different organisms to show that each group of organisms is equally isolated from any other particular group Table. 7-3 illustrates this fact.
table 7-3. Percent amino acid sequence divergence between cytochrome C2 in Rhodospirillum rubrum and various eucaryotic cytochromes.
(Adapted by permission from Denton.19)
From the data in table 7-3 it is evident that the amino acid sequence of the cytochrome c2 molecules of all of the species in all of the groups of organisms are equally isolated from that of the bacterium Rhodospirillum rubrum. Thus there is no basis in this data to indicate that any group is intermediate between other groups. All are equally isolated from all other groups. This data supports the biblical record of creation of each "kind" separate from all other "kinds."
8. The metabolic pathway involving cytochrome c is only one of many which are found widely distributed throughout all living things. This almost universal distribution of identical or very similar chemical systems in plants and animals is taken to be evidence for genetic relationship and therefore as evidence for evolution of all life from common ancestors. Believers in creation, on the other hand, take this as evidence for a common Creator of all life Who used a common set of basic metabolic patterns with adaptations to meet the needs of each creature.
9. the differences found in the less critical portions of the enzyme molecules from different creatures may be explained in several ways. They may be the result either of initially created differences or of random, neutral mutations, or of both.
10. The overall picture is complicated by the discovery in recent years of various metabolic pathways which are alternatives for the more common pathways. These and other surprising variations in the cell chemistry of many organisms are often difficult to explain from the evolutionary point of view. They offer no difficulty, however, for the creation model of origins. Such variations illustrate an apparently unlimited intelligence as the source of a vast number of working life systems which are designed to participate successfully in a complex biosphere which man is really only beginning to understand.
14. Estimated from various data in Alfred Romer's Vertebrate Paleontology, 3rd Edition (Univ. of Chicago Press, 1966).
15. Patterson, Colin, Address at American Museum of Natural History, New York, 5 Nov. 1981. Transcript in the files of author.
16. Hoyle, Sir Fred, and Chandra Wickramasinghe, Evolution From Space (Simon and Schuster, New York, 1981), pp. 13-33, 82-88.
17. Denton, Michael, op. cit. (ref. 8), pp. 274-307.
18. Ibid., p. 280.
19. Klotz, John W., Genes, Genesis and Evolution, 2nd edition (Concordia Publishing House, St. Louis, 1970), pp. 145-154; Davidheiser, Bolton, Evolution and Christian Faith (Presbyterian and Reformed Publishing Co., Nutley, NJ, 1969), pp. 240-255.