The Genetic Effects of Radiation

It is unrealistic to suppose that all sources of man-made radiation should be abolished. The good they do now, the greater good they will do in the future, cannot be abandoned. It is, however, reasonable to expect that the present Nuclear Test Ban Treaty will continue and that nations, such as France and China, which have nuclear capabilities but are not signatories of the Treaty will eventually sign. It is also reasonable to expect that X ray diagnosis and therapy will be carried on with the greatest circumspection, and that the use of radiation in industry and research will be carried on with great care and with the use of ample shielding. A film badge (left) and a personal radiation monitor (right) record the amount of radiation absorbed by the wearer. These safety devices, worn by persons working in radiation environments, are designed to keep a constant check on each individual’s absorbed dose and to prevent overexposure. 44 As long as man-made radiation exists, there will be some absorption of it by human beings. The advantages of its use in our modern society are such that we must be prepared to pay some price. This is not a matter of callousness. We have come to depend a great deal for comfort and even for extended life, upon the achievements of our technology, and any serious crippling of that technology will cost us lives. An attempt must be made to balance the values of radiation against its dangers; we must balance lives against lives. This involves hard judgments. Those working under conditions of greatest radiation risk—in atomic research, in industrial plants using isotopes, and so on—can be allowed to set relatively high limits for total radiation dosages and dose rates that they may absorb (with time) with reasonable safety, but such rates will never do for the population generally. A relative few can voluntarily endure risks, both somatic and genetic, that we cannot sanely expect of mankind as a whole.[9] From fruit fly experiments it would seem that a total exposure of 30 to 100 rads of radiation will double the spontaneous mutation rate. So much radiation and such a doubling of the rate would be considered intolerable for humanity. Some geneticists have recommended that the average total exposure of human beings in the first 30 years of life be set at 10 rads. Note that this figure is set as a maximum. Every reasonable method, it is expected, will be used to allow mankind to fall as far short of this figure as possible. Note also that the 10-rad figure is an average maximum. The exposure of some individuals to a greater total dose would be viewed as tolerable for society if it were balanced by the exposure of other individuals to a lesser total dose. A total exposure of 10 rads might increase the overall mutation rate, it is roughly estimated, by 10%. This is serious enough, but is bearable if we can convince ourselves 45 that the alternative of abandoning radiation technology altogether will cause still greater suffering. A 10% increase in mutation rate, whatever it might mean in personal suffering and public expense, is not likely to threaten the human race with extinction, or even with serious degeneration. The human race as a whole may be thought of as somewhat analogous to a population of dividing cells in a growing tissue. Those affected by genetic damage drop out and the slack is taken up by those not affected. If the number of those affected is increased, there would come a crucial point, or threshold, where the slack could no longer be taken up. The genetic load might increase to the point where the species as a whole would degenerate and fade toward extinction—a sort of “racial radiation sickness”. We are not near this threshold now, however, and can, therefore, as a species, absorb a moderate increase in mutation rate without danger of extinction. On the other hand, it is not correct to argue, as some do, that an increase in mutation rate might be actually beneficial. The argument runs that a higher mutation rate might broaden the gene pool and make it more flexible, thus speeding up the course of evolution and hastening the advent of “supermen”—brainier, stronger, healthier than we ourselves are. The truth seems to be that the gene pool, as it exists now, supplies us with all the variability we need for the effective working of the evolutionary mechanism. That mechanism is functioning with such efficiency that broadening the gene pool cannot very well add to it, and if the hope of increased evolutionary efficiency were the only reason to tolerate man-made radiation, it would be insufficient. The situation is rather analogous to that of a man who owns a good house that is heavily mortgaged. If he were offered a second house with a similar mortgage, he would have to refuse. To be sure, he would have twice the number of houses, but he would not need a second house since he has all the comfort he can reasonably use in his first 46 house—and he would not be able to afford a second mortgage. What humanity must do, if additional radiation damage is absolutely necessary, is to take on as little of that added damage as possible, and not pretend that any direct benefits will be involved. Any pretense of that sort may well lure us into assuming still greater damage—damage we may not be able to afford under any circumstances and for any reason. Actually, as the situation appears right now, it is not likely that the use of radiation in modern medicine, research, and industry will overstep the maximum bounds set by scientists who have weighed the problem carefully. Only nuclear warfare is likely to do so, and apparently those governments with large capacities in this direction are thoroughly aware of the danger and (so far, at least) have guided their foreign policies accordingly. 47 SUGGESTED REFERENCES Books Radiation, Genes, and Man, Bruce Wallace and Theodosius Dobzhansky, Holt, Rinehart and Winston, Inc., New York 10017, 1963, 205 pp., $5.00 (hardback); $1.28 (paperback). Genetics in the Atomic Age (second edition), Charlotte Auerbach, Oxford University Press, Inc., Fair Lawn, New Jersey 07410, 1965, 111 pp., $2.50. Atomic Radiation and Life (revised edition), Peter Alexander, Penguin Books, Inc., Baltimore, Maryland 21211, 1966, 288 pp., $1.65. The Genetic Code, Isaac Asimov, Grossman Publishers, Inc., The Orion Press, New York 10003, 1963, 187 pp., $3.95 (hardback); $0.60 (paperback) from the New American Library of World Literature, Inc., New York 10022. Radiation: What It Is and How It Affects You. Ralph E. Lapp and Jack Schubert, The Viking Press, New York 10022, 1957, 314 pp., $4.50 (hardback); $1.45 (paperback). Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, General Assembly, 19th Session, Supplement No. 14 (A/5814), United Nations, International Documents Service, Columbia University Press, New York 10027, 1964, 120 pp., $1.50. The Effects of Nuclear Weapons, Samuel Glasstone (Ed.), U. S. Atomic Energy Commission, 1962, 730 pp., $3.00. Available from the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402. Effect of Radiation on Human Heredity, World Health Organization, International Documents Service, Columbia University Press, New York 10027, 1957, 168 pp., $4.00. The Nature of Radioactive Fallout and Its Effects on Man, Hearings before the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy, Congress of the United States, 85th Congress, 1st Session, U. S. Government Printing Office, 1957, Volume I, 1008 pp., $3.75; Volume II, 1057 pp., $3.50. Available from the Office of the Joint Committee on Atomic Energy, Congress of the United States, Senate Post Office, Washington, D. C. 20510. Genetics, Radiobiology, and Radiology, Proceedings of the Midwestern Conference, Wendell G. Scott and Evans Titus, Charles C. Thomas Publisher, Springfield, Illinois 62703, 1959, 166 pp., $5.50. Articles Genetic Hazards of Nuclear Radiations, Bentley Glass, Science, 126: 241 (August 9, 1957). Genetic Loads in Natural Populations, Theodosius Dobzhansky, Science, 126: 191 (August 2, 1957). 48 Radiation Dose Rate and Mutation Frequency, W. L. Russell and others, Science, 128: 1546 (December 19, 1958). Ionizing Radiation and the Living Cell, Alexander Hollaender and George E. Stapleton, Scientific American, 201: 95 (September 1959). Radiation and Human Mutation, H. J. Muller, Scientific American, 193: 58 (November 1955). Ionizing Radiation and Evolution, James F. Crow, Scientific American, 201: 138 (September 1959). Motion Pictures Radiation and the Population, 29 minutes, sound, black and white, 1962. Produced by the Argonne National Laboratory. This film explains how radiation causes mutations and how these mutations are passed on to succeeding generations. Mutation research is illustrated with results of experimentation on generations of mice. A discussion of work with fruit flies and induced mutations is also included. This film is available for loan without charge from the AEC Headquarters Film Library, Division of Public Information, U. S. Atomic Energy Commission, Washington, D. C. 20545 and from other AEC film libraries. The following films were produced by the American Institute of Biological Sciences and may be rented from the Text-Film Division, McGraw-Hill Book Company, 330 West 42nd Street, New York 10036. Mutation, 28 minutes, sound, color, 1962. This film discusses chromosomal and genetic mutations as applied to man. Muller’s work in inducing mutations by X rays is described. These three films are 30 minutes long, have sound, are in black and white, and were released in 1960. They are part of a 48-film series that is correlated with the textbook, Principles of Genetics, (fifth edition), Edmund W. Sinnott, L. C. Dunn, and Theodosius Dobzhansky, McGraw-Hill Book Company, 1958, 459 pp., $8.50. Mutagen-Induced Gene Mutation. The narrator of this film is Hermann J. Muller, who won a Nobel Prize in 1946 for his work in the field of genetics. The measurement of X-ray dose in roentgens and the dose required to double the spontaneous mutation rate in Drosophila and mice are discussed. The magnitude and meaning of permissible doses of high-energy radiation are discussed. Other mutagenic agents (ultraviolet light and chemical substances) are discussed, concluding with comments on the importance of gene mutation in the present and future. Selection, Genetic Death and Genetic Radiation Damage. The narrator of this film is Theodosius Dobzhansky, the coauthor of this booklet. Genetic death is discussed in detail, as are examples of how genetic loads are changed subsequent to radiation exposure. While it is generally agreed that the great majority of mutants are harmful when homozygous, more evidence is needed about the beneficial and detrimental effects of mutants 49 when heterozygous. In the case of sickle cell anemia, heterozygotes are adaptively superior to normal homozygotes. This makes for balanced polymorphism, by which a gene is retained in the population despite its lethality when homozygous because of the advantage it confers when heterozygous. Gene Structure and Gene Action. The lecturer of this film is G. W. Beadle of Cornell University. The Watson-Crick structure of DNA is discussed in terms of mutation. Several tests of the chain separation hypothesis for DNA replication are described (experiments with heavy DNA, radioactive chromosomes, and the replication of DNA in vitro). This working hypothesis is presented: The coded information in DNA is transferred to RNA, which serves as a template for polypeptide synthesis. PHOTO CREDITS Dr. Asimov’s photograph by David R. Phillips, courtesy Chemical and Engineering News Page 4 James German, M.D. 6 Bausch & Lomb, Inc. 12 James German, M.D. 20 Indiana University 24 Robert C. Filz, Air Force Cambridge Research Laboratories 25 J. K. Boggild, Niels Bohr Institute, Copenhagen University 26 Brookhaven National University 28, 31 Herman Yagoda, Air Force Cambridge Research Laboratories 41 Oak Ridge National Laboratory Footnotes [1]For more detail about cell division, see Radioisotopes and Life Processes, another booklet in this series. [2]This is more commonly known as “Mongolism” or “Mongolian idiocy” though it has nothing to do with the Mongolian people. [3]Actually, all waves have some of the characteristics of particles and all particles have some of the characteristics of waves. Usually, however, the radiation is predominantly one or the other and little confusion arises under ordinary circumstances in speaking of waves and particles as though they were separate phenomena. [4]For more about this subject, see Radioisotopes in Industry and Radioisotopes in Medicine, companion booklets in this series. [5]For more about this subject, see Fallout from Nuclear Tests, another booklet in this series. [6]For details on somatic effects of radiation, see Your Body and Radiation, a companion booklet in this series. [7]Estimated average exposures to the gonads, based on 1963 report of Federal Radiation Council. [8]One thousandth of a rem. [9]Nevertheless, it should be