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total detonations, one can calculate fallout doses to target nations (rather inexactly) and to nontarget nations (more exactly). It is worth emphasizing
that the calculated dose from stratospheric fallout to a nontarget nation located
in the Northern Hemisphere in the zone of heaviest deposition, between latitudes
30° and 60°, amounts to about 10 to 12 roentgens in the case of a 20,000-megaton
war of which 50 to 60 percent is fission. In other words, a nuclear war of such
magnitude that it would suffice to devastate the United States, the U-S.S.R.,
and all of Western Europe, and to kill a majority of the populations of those
countries, would produce fallout that would only equal or slightly exceed, in
terms of its genetic effect upon nontarget nations of the Northern Hemisphere,
what the Genetics Committee of the National Academy of Sciences has recom-
mended as an upper limit for tolerable exposure of the population to manmade
radiation.
What would 10 roentgens of whole body radiation at a low dose rate bring about
genetically, if administered to an entire population? Estimates based on the
so-called doubling dose, a dose of radiation that would double the frequency of
spontaneous mutation occurring from all causes. This concept must be interpreted with great caution. Since different sorts of genetic effects occur spontaneously at different rates, they must each have a different doubling dose. Ifa
particular kind of mutation has a very low spontaneous occurrence, its doubling
dose will be very small; if the spontaneous rate is high, the doubling dose will
be high. For example, in my Drosophila experiment, described above, the
doubling dose for the dominant minute-bristle mutations is 60 roentgens. For
chromosome breaks in the white blood cells irradiated by Bender in freshly
drawn blood the doubling dose is less than 1 roentgen. The only significance of
the doubling dose arises if it is in some way integrated over all types of transmissible hereditary defects, that is, all detrimental mutations, and if it is in
some quantitative way related to the genetic burden of detrimental genes
carried by the population and responsible for the current and future emergence
of genetic defects in individuals. For transmissible gene mutations in most
species that have been studied, the doubling dose falls in the range of 30 to 80
roentgens, with 40 to 60 roentgens more common, One cannot assert positively
that such a value applies to human beings, but there is no reason to suppose
that it does not.
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RADIATION STANDARDS, INCLUDING FALLOUT
§
One would therefore conclude that a 10-roentgen dose to an
entire population might produce one-fourth to one-sixth of the number of
harmful mutations occurring spontaneously per generation. The number of
genetically defective individuals born alive probably amounts to 4 percent of all
births (an estimate somewhat higher than that used in the NAS Committee report
of 1956 and based on the tabulation of specific hereditary traits and their estimated incidences given in the “Report of the United Nations Scientific Committee on the Effects of Atomic Radiation in 1958,” annex H). By a recognized
genetic principle, a doubling of the mutation rate will in time lead to a doubling
of the amount of evident genetic defect in the population. That is, a 10-roentgen
dose to a population might increase the frequency of genetically defective persons
born in that population from 4 to 5 percent or somewhat less. This would not
occur until many generations have passed, and if the exposure were limited toa
single generation the level would gradually drop back again to the original level.
Even if the doubling dose for transmissible defects produced by mutations
turned out to be as low as 10 roentgens, one would not expect the level of genetieally defective births to rise above 8 percent. This frightful, yet nevertheless
somewhat reassuring conclusion about the genetic effects of a major nuclear war
on nontarget nations, even in the Northern Hemisphere, deserves in my estimation to be more widely circulated and appreciated.
Finally, I would like to emphasize a point made in the 1960 report. of the
NAS Genetics Committee respecting the extent of damage in human populations
due to unfavorable mutant genes. The damage is not simply a question of the
frequency of these genes. It also depends on the relative amounts of harm they
do to individuals and to society. As the report states it: “How, for example, does
one measure quantitatively the relative importance of a stillbirth, a feebleminded
child, and a death during adolescence?” Or, one might add, of a death very soon
after conception, when the mother is often unaware that an abortion has occurred? In this connection I can do little more than recommend for study the
thought-provoking appraisal of the question by Prof. Sewall Wright, printed
as an addendum to the report. All members of the committee were not in agreement with Wright in his considerations, but all, I think, are fully agreed that
much study of this sort is needed before we can reach a just appraisal of genetic
damage to a population.
86853-—_62—pt, 1-—-+23
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