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|The Idea of Homology
There are many similarities(as well as differences) between a chimpanzee and a human. does this mean that shrews, chimps and people evolved from a common ancestor, but that the lines leading to chimp and man separated from each other more recently than the time the shrew line branched off from the line leading to primates(monkey, apes and humans)? This idea is called "homology." It has two elements: the comparative anatomy of different animals or plants, and the assumption that evolutionary descent from common ancestors is a fact. This concept of homology, which is an interpretation of comparative anatomy in accord with the assumption that evolution is a fact, is the great classical evidence for evolution!
Another Interpretation of Comparative Anatomy
There is, however, another interpretation of the different assumption, i.e., that creation is a fact. this interpretation sees among living creatures about thirty basic structural plans. these basic types appear with variations for specific life styles and environments to make up the several million species both living and extinct. Careful study consistently shows each species to have a set of characters which make it highly adapted for certain environments and life styles. Thus the facts of biology point persuasively to the existence of the Creator and to the intelligent, purposeful designs which He has wrought. There is, therefore, no proof for evolution from the data of comparative anatomy. Indeed, the concept of homology is beset by many difficulties, and the actual data is equally well or perhaps better explained under the concept of special creation by a Creator using sets of basic designs which are modified for specific needs
Difficulties with Homology
As was pointed out above, one element of homology is the assumption that evolution is a fact. but it was shown in creation essays 4, 6 and 7 that there is no scientific explanation for the evolutionary origin of new kinds of plants of animals, nor is there a demonstrable biological mechanism for the origin of new kinds of plants or animals, nor is there a testable scientific theory of evolutionary change to "create" complex new biological designs. Also, the fossil record does not document the formation of new complex designs by gradual evolution. Neither can evolution from one kind to another be observed in nature or in the laboratory. Consequently, when one examines the data of comparative anatomy, the guiding assumption of creation is a satisfactory scientifically as that of evolution.
One problem with homology is the fact that numerous similarities among species cannot possibly be interpreted to mean descent from a common ancestor. These are said to be the result of "convergent evolution." Thus there are many similarities between the eyes of octopus and man, but they are not believed to be inherited from a common ancestor. As another example, hemoglobin molecules occur not only in vertebrate animals, but also in yeast, the mold, Neurospora, and in the root nodules of beans. Haemoglobin occurs in some species of every major category of life except sponges, coelenterates(jelly fish, etc.) and protochordates (mostly worm-like marine creatures having a limited nerve chord, which are supposedly ancestral to vertebrates which have hemoglobin). It is obvious that this distribution of hemoglobin does not fit with the idea that similarities indicate common descent, for nobody could believe that humans inherited their hemoglobin molecules from yeast. And independent evolution of hemoglobin in so many different species appears highly improbable.
Another serious problem for homology relates to how characters are inherited. Supposedly, inherited genes control inherited characters. Thus it would be reasonable to assume that homologous characters are controlled by homologous genes. these would be genes that control similar characters, but which have slowly evolved, changing with time, so that the inherited characters are also changed. thus the front appendages of reptiles, mammals, birds and humans are said to be homologous. Therefore, they must be controlled by homologous genes. The fact is, however, that it has been proved in many cases that homologous structures are not produced by homologous genes! In the vertebrates the embryo is constructed of a large number segments that can be numbered, starting at the heads end. Surely particular segments develop under the control of particular genes. We would reasonably assume the same for any particular structure, such as the front leg. Yet we see in the diagram that the same for any particular structure, such s the front leg. Yet we see in the diagram that in six different vertebrates which allegedly inherited their front legs from a common ancestor, the front legs as well as the rear legs develop from entirely different groups of segments from species to species. Thus if the front legs (or rear legs) of these different creatures have been inherited from a common ancestor through evolution, we have the incredible idea that the job of producing the legs is, by evolution, passed slowly back and forth from group to group of different genes, which are themselves gradually changing to accomplish this fantastic juggling act. In his 1971 monograph, Homology, An Unsolved Problem, Sir Gavin de Beer, one of the truly great embryologists of this century, posed the question for evolutionary theory which still is unanswered:
But if it is true that through the genetic code, genes code for enzymes that synthesize proteins which are responsible(in a manner still unknown in embryology) for the differentiation of the various parts in their normal manner, what mechanism can it be that results in the production of homologous organs, the same 'patterns,' in spite of their not being controlled by the same genes? I asked this question in 1938, and it has not been answered.
It appears that the claim that evolution explains everything is premature. It should also be pointed out that even the claim that genetically inherited information determines entirely the structure, functions and behavioral traits of living organisms is scientifically premature. Especially it should be pointed out that the claim that genetically inherited information determines entirely the structure, functions and behavioral traits of living organisms is scientifically premature. Current research in the molecular biology of embryonic development in fruit flies and some other species, is revealing developmental pathways in which particular genes and their protein products influence or control fundamental elements of embryonic development and the resulting adult biological structures.
There is still a long way to go, however, before the totality of body plans can be explained by genes and their protein products. The farther this research progresses, the greater is the complexity of embryonic development revealed at the level of molecular biology. And the greater the complexity revealed, the more remote becomes the achievement of a testable scientific theory of its evolutionary origin, that is, of its origin apart from intelligent, purposeful design.
How, then, are similarities between different kinds of creatures to be interpreted? Consider the following question: Why do practically all automobiles have four wheels rather than three or five? Quite simply, experience has shown that four wheels afford the most practical arrangement for an automobile. Therefore, automobiles, while differing in many other respects, are all designed by practical-minded engineers around the four-wheel scheme. Thus it is only reasonable and to be expected that the God of creation would use a practical basic design, for example, for the vertebrates. The basic design framework is a backbone and four limbs, eminently practical and adaptable to many specific variations. This is simply on aspect of an orderly universe which is the result of a systematic plan and design framed and applied by the omniscient and omnipotent Creator.
On a more fundamental level, the similarities between species in cell structure, in the biochemical systems which provide energy and building materials for all species, and in the structure of the basic molecules such as amino, sugar and fat molecules, as well as of the larger protein and nucleic acid molecules, also fit in with the creation model: basic designs are modified for specific applications. There is no more proof that the large, complex molecules in the species are homologous, i.e., that they were inherited from a common ancestor, than there is proof that the much larger anatomical structures are homologous. In all the schemes for supposed molecular evolution there are inconsistencies and also large gaps.
A good example of alleged molecular homology is afforded by the a- and b-haemoglobin molecules of land vertebrates including man. These supposedly are homologous with an ancestral myoglobin molecule similar to human myoglobin. Two a- and two b-haemoglobin associate together to form the marvelous human haemoglobin molecule that carries oxygen and carbon dioxide in our blood. But myoglobin acts as single molecules to transport oxygen in our muscles. Supposedly, the ancient original myoglobin molecules slowly evolved along two paths until the precisely designed a- and b-haemoglobin molecules resulted that function only linked together in groups of four to work in the blood in a much different way under very different conditions from myoglobin in the muscle cells. What we have today in modern myoglobin and haemoglobin molecules are marvels of perfect designs for special, highly demanding tasks. Is there any evidence that intermediate, half-evolved molecules could have served useful functions during this imaginary evolutionary change process, or that any creature could survive with them in its blood? There is no such information. Modern vertebrates can tolerate very little variation in these molecules. Thus, the supposed evolutionary history of the allegedly homologous globin molecules is a fantasy, not science.
We can safely conclude that homology, at every level--body structure, cell structure, biochemical systems, and molecular structure--is an inconsistent and unsatisfactory theory and poor evidence for evolution. Unless, that is, one's philosophy rules out God the Creator. But if one's philosophy includes God the Creator, the facts better support the Genesis record of special creation of the kinds, with provision for limited variation within each kind.
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