Science in Christian Perspective
Irving W. Knobloch, Ph.D.
East Lansing, Michigan
The present article will bring to a close the series on evolutionary mechanisms started some time ago. In the previous articles we failed to distinguish between two types of variation. New phenotypes, produced by responses to environmental changes, are of doubtful significance in evolution because of the improbability of ever proving the inheritance of acquired characteristics. Only those variations produced by genotypic change can be of value. The mechanisms producing genotypic change have been discussed in previous articles. It seems appropriate at this point to consider the fate of new genotypes, once they are formed, by referring to natural selection.
When once a new phenotype has originated, it is in immediate competition with the better adapted normal forms. In some cases, the new organisms are able to survive in the same niche with the old; in other cases they do not survive the "struggle for existence": and in still other cases they succeed only if a new type of environment can be provided. In this connection both plants and animals can escape to new habitats by powers of locomotion peculiar to themselves.
Darwin's theory of Natural Selection included variation, struggle for existence, survival of the fittest and a progressive and upward inheritance of favorable variations. He had no clear concept of the causes of variation because of a dearth of genetical and cytological facts in his (lay. His last point was also of doubtful value because in few, if any, cases was he drawing his conclusions from the behavior of species with genes homozygous for a character. Johannsen showed later that selection in material that is homozygous is unavailing. New genotypes must arise if natural selection is to have any value.
A good definition of Natural Selection is hard to find in the literature probably because there is a diversity of opinion about it. It seems to be surrounded by an aura of nineteenth century mysticism. it is spoken of as a "guiding influence" or a-, a "directing force". One view which is attractive to me at the present time is that natural selection is synonymous with "environmental resistance". It is largely the forces of the environment which determine the survival of a new genotype whether the forces are in or from the parent (embryo-sac, uterus, archegonium, gelatinous capsule and so forth) or whether the forces are operative after birth, or germination.
Schmalhausen (Factors of Evoution,-Blakiston Co. 1949 p. 25) says that Natural Selection gradually removes or neutralizes the great majority of all mutations except those that are viable. Irene Manton Problems of Cytology and Evolution in the Pteridophyta) says "Natural Selection acts oppositely to a progressive evolution since it tends to eliminate aberrations and to maintain the stability of the species unchanged". Thomas Hunt Morgan (Evolution and Genetics, Princeton Univ. Press, 1925 p. 26) mentioned tfiat selection either by man or nature cannot create anything new but only make more of a certain type already existing or within the capabilities of the genotype. Harold Blum (Time's Arrow and Evolution, Princeton Univ. Press 1951, p. 193) is of the opinion that Natural Selection has no direct effect upon the genes themselves; the mutation of a gene is (not) guided in the direction of greater fitness. Finally, Michael F. Gaiver (Animal Biology, Harper Bros. 1937, 1). 696) says that "'Natural Selection) can only operate after variations have appeared."
Most biologists agree. however, that Natural Selection (or Environmental Resistance, if you prefer) does operate in many cases and its actions determine which variants will survive and which will die. It is difficult however, to make a universal case out for the operation of selection (environmental resistance) as far as evolution is concerned. The wing of a bird, slowly developing through the ages, as a result of genotypic alteration, would clearly have no survival value. (The rebuttal to this statement is that it would not have it as a wing but the organism might still persist if the developing wing were no hindrance. Later genotypic changes could produce a wing.) Likewise, natural selection falls down for the electric organ of the eel, the trunk of the elephant or the variations found in the thrush family (to niention three oft cited cases).
Others have, however, pointed out newer and more telling arguments against the evolutionary value of Natural Selection. Dodson (Textbook of Evolution, Saunders Co. 1952, p. 113) notes that the synthesis of arginine, an arnino acid, bv the niold Ncitrospora requires seven different oenetical I y-control led enzymes, each on-, useless without the other. He says that he idea that these enzymes should be preserved at the time that they were useless is incomprehensible and that the probability that all appeared simultaneously is also incomprehensible.
One might say then that Natural Selection does "weed out" those genotypes unfitted for a particular environment if the amount of variation exhibited is a "hindrance". On the other hand, certain variants rnay persist because the expression of their variability, while useless, is still not a determining factor in their .struggle for existence.
If one is unable to gather a clear pattern out of the above regarding Natural Selection the fault is partly mine. However, it is also because there is no unanimity among biologists in regard to its (selection's) importance. The authorities quoted will bear witnessto this statement.
Another factor in evolution which must be considered briefly is that of "isolation". Although there are other types of isolation, we shall restrict our few remarks to "geographical" isolation. Islands, niountain tops and deserts are "hemmed in" by types of habitat quite different in nature. Free migration is somewhat, if not entirely, restricted and species tend to interbreed. No doubt this tends to stabilize a population and preserves certain genotypes. Apparently the phenomenon does not produce new genotypes by itself but simply acts in a passive fashion. Birds and insects on islands display striking differences when compared with the most nearly similar forms on a neighboring island. In such cases, well publicized in the literature, it seems reasonable to assume that geographic isolation has preserved genotypic variants on the various islands. A species can thus be said to have evolved into a number of group,-, distinct enough to be called separate species.In stinimary we can say that
1. Only variations (new phenotypes) resulting from changed genotypes are of importance in evolittion.
9 New genotypes can be formed by point mutations chromosome aberrations, polyploidy or by hybridization.
3. Many "species" have undoubtedly been formed in the past and are being formed today by these processes.
4. This proliferation of species is one type of evolution.
The fossil record and present day experiments testify that this type of evolution has gone on and still goes on.
6. Due to certain imperfections in the fossil record, mentioned previously, it is not possible to state finally that this limited type of evolution has gone past the class or order category. Therefore it seems that an assumption of a very high order is necessary to bridge this gap. We do not ridicule those who accept organic evolution in the fullest sense of the words but personally we do not accept the full theory as proven without question.
If one accepts the word "create" in the Book of Genesis one would expect that at least some of the species of plants and animals were created. The Bible does not give a complete category of species. Neither is it reasonable to assume that all present day species were created because of the certainty of genetic changes in organisms.
7. Selective processes may eliminate grossly unfavorable phenotypes. Evidently selection does not always operate because some variations from the " normal" have no selective value. The viewpoint is given that selective processes (or environmental resistance) is neutral in respect to aberrations which do not hinder survival.
8. Isolation of one kind or another promotes inbreeding and the fixation of types. Various genotypes, otherwise in danger of submergence, are thus preserved.
The A.S.A. is now considering bringing together in book form the affiliation's thinking about evolution. Acttiallv the book, if published, would take note oi the centennial celebrating the publication of the "Origin of Species" by Charles Darwin in 1859. Darwin's theory was a contribution to the "modus operandi" of evolution itself. Some parts of Darwin's theory are useful today even when talking about a limited type of evolution (as I have done). Possibly Darwin's greatest service to humanity was the stimulation of research which his book provoked. As long as it was assumed that the Bible taught the fixity of species there was no need for research. Much interesting and useful information flowed from the European scientists about evolution in the years following the "Origin of Species". For this we are grateful.
At the risk of being repetitious, I wish to make it clear that if there is any real weakness in modern scientific thinking about organic evolution it is in the failure of scientists to recognize the two apparent levels of evolution. Tnterphyletic evolution is assumed to be true because of the existence of intraphyletic (lower order) evolution. Everyone must decide for himself whether there is sufficient clear cut evidence to accept one type of evolution on the evidence of the other type.