Science in Christian Perspective

BIOLOGY
Irving W. Knobloch, Ph.D.

The Role of Mutation in Evolution: Before one should attempt to discuss such a topic one should, perhaps ' define the term "mutation". Two definitions are used currently. One restricts the term to changes in the protein molecule known as a gene. The other definition includes not only these gene changes but any change in the individual chromosomes or in the set or sets of chromosomes in a cell. Such changes might include deletions, inversions and doubling of chromosomes.

DeVries publicized mutations with work on the Evening Primroses although such sudden appearances of new forms had been noted in other organisms earlier and had been tern-led "sports". Although DeVries' mutants are now thought by most biologists to have been hybrids,* it must be said that his work gave .impetus to a neglected field of inquiry.

In this necessarily brief discussion we shall restrict ourselves to the role, of gene or point mutations in evolution. To prove that a mutation of this kind has occurred is really quite a difficult task, for two reasons. One reason is that a large number of organisms, if not all, are quite heterozygous for many characters and one must eliminate the effects of crossing and recombination in determining if a point mutation has taken place. Another difficulty concerns itself with the frequency of chromosome doubling and rearrangements in organisms. Polyploidy, for example is extremely common in plants (30-35% in angiosperms according to G. L. Stebbins-Variation and Evolution in Plants). New species arising by either crossing or by polyploidy cannot be logically credited to point mutations. Thomas Hunt Morgan once wrote (Scientific Basis of Evolution) that "a point mutation may be said to be known as such only when it has been traced to a definite locus in a known chromosome". Hagedoorn (Relative Value of the Processes Causing Evolution) believes that it is next to impossible to prove the fact that a real (gene) mutation has occurred.

If one were to ask a large number of educated laymen (or even teachers) to name the most important method of species formation, one would probably find that a significant number would name "mutation." It is not known what these people understand by the term "mutation" but it is doubtful if many of them have ever heard of an alternative method of speciation. Most of the public think that genes are quite unstable and that mutations are going on at a great rate. This statement of course is not true.

Not only are the laymen mesmerized by the word ,'mutation" but scientists as well. A recent article on mutations in bacteria pointed this! The environment is ruled out by clever experimentation and the writer then claims that the new forms have arisen by mutation and the inference is that it is point mutation. No mention is made of the possible contributions of methods of speciation other than gene changes. The difficulty of proving a gene or point mutation has been mentioned above.

It might be advantageous to inquire as to the importance of mutations. Several scientists will now be quoted. It is to be understood that while these statements are on the cautious or negative side the writers, no doubt believe in mutation to a greater or less degree. The purpose of these quotations is to show that there may be somewhat of difference of opinion among scientists in regard to the importance of the point mutation as a powerful factor in speciation.

"Although a great many species have been studied, it must be admitted that most of them are not in a ,mutating' condition. Thus if mutation is not a general phenomenon, it can have but slight significance as a means of species formation" Arthur W. Haupt, Fundamentals of Biology, McGraw Hill Book Co., N. Y., 1928.

"Mutation changes one gene at a time; simultaneous mutation of masses of genes is unknown. On the other hand, species differ from each other usually in many genes; hence, a sudden origin of a species by mutation, in one thrust, would demand a simultaneous mutation of numerous genes." Theodosius Dobzhansky, Genetics and the Origin of Species, 2nd Ed., Columbia Univ. Press, 1941.

"It may, in short, be stated that no mutation has ever occurred in the progress of genetic work which is fully viable and behaves as a dominant to the wild-ty pe condition. That any have given rise to changes which could be of survival value in nature appears highly doubtful". E. B. Ford, Mendelism and Evolution, Dial Press, N. Y., 193L

"It is true that thus far nobody has produced a new species or genus etc. by macromutation. It is equally true that nobody has produced even a species by the selection of micromutations. In the best-known organisms, like Drosophila, innumerable mutants are known. If we were able to combine a thousand or more of such mutants in a single individual, this still would have no

An article by Dr. C. P. Martin of McGill University, Canada (A Non-geneticist Looks at Evolution, American Scientist 41 (1) :100-106, (953) touches on some of the points mentioned above. Dr. Martin concedes the possibility of gene mutations but he asserts that they are largely pathological in their effect. He might also have mentioned the fact that most mutants cannot compete successfully with their "wild" progenitors, that the viability of many mutants is low and that the majority of mutations produce only slight effects rather than large "jumps". One might also say that even in the case of genes known to be unstable (i.e. the lavender a gene of Delphinium ajacis), the change when it occurs, is from the recessive to the dominant and usually f rom the mutant type to the "wild" type. He does not feel that the "facts" of genetics establish the mutation-selection theory beyond all doubt. Dr. Martin is probably a neo-Lamarckianist (use and disuse). Lamarckianism has always been an attractive theory and many thousands of attempts have -been made to prove the inheritance of acquired characteristics, a necessary part of the theory. Environmental effects are of course not inherited, according to the experiments, unless the genes are changed in some way. This is quite difficult to do because of the inherent stability of the gene (although chromosomes themselves may be changed or destroyed). The present reviewer cannot refrain from hypothesizing that when once the plasmagenes are understood, they may be found to be more amenable to environmental pressure than the nuclear genes.

One of the troublesome aspects of the natural selection hypothesis of Charles Darwin is the frequent and unpleasant discovery of characters which would be difficult or relatively impossible to acquire by natural selection. Dr. Martin mentions one, the distal flexure line in the palm of the hand. He asserts that geneticists would plead caution in denying the usefulness of this character-one cannot say whether a structure is useful or not as it may have a hidden or unsuspected use. Religious people invoke the same argument in pleading for the "hidden" usefulness of some vestigial structure. I do not wish to decry the argument in either case as it may, on occasion, be a perfectly valid one. I found Dr. Martin's paper quite interesting.

A good deal more could and should be said on the subject of mutation. In summary, I would like to make it very clear that I regard gene mutation as a very logical and possible occurrence but I do not think that it is, in view of the stability of the gene, as important a factor in speciation as its proponents contend. I would also like to emphasize that there are other methods of speciation such as polyploidy and hybridization and that a species cannot truthfully be said to "inutate" unless these other possibilities are eliminated. Some may refer me to the thousands of research papers dealing with mutations in many organisms. My position here would be that some of these justifiably refer to point mutations but in many cases the claims are dubious because the other variables in speciation have not been considered. A well-known geneticist recently told me that point mutations are assumed to have occurred after all other possibilities have been eliminated. This, I would say, is a fair statement.