It was Muller, who brought the Atomic Darwinism indirectly into the light of awarness:
“H.J. Muller estimated that the genetic load accumulated in 8 human generations (∼ 240 years) living under constantly improving medical services with zero mortality rate due to natural selective forces is equivalent to that acquired in a single exposure to 200roentgen (1,8 Sievert) of gamma radiation 2 kilometers from Ground Zero in Hiroshima.” http://arxiv.org/pdf/1301.4299.pdf
All quotes are from:
Our load of mutations by H.J. Muller: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1716299/
And since the death rate is a kind of index of the total damage which the gene occasions, it also follows that, paradoxically, the grade of detriment caused by a gene in the average individual in which it manifests itself is not correlated with the total amount of damage it does in the entire population.
More recently, without at the time being aware of Haldane’s approach to this particular point, the present writer gave a statement of it in terms of the individual mutation, noting that each detrimental mutant gene, no matter how slight its phenotypic effect, produces, on the average, one eventual half-death of a zygote, or what may be termed one genome-death, when it acts as a recessive in causing elimination, and one complete zygote death, i.e. two genome deaths, when acting as a dominant
The use of ionizing radiation and of radioactive materials is increasing and promises to continue increasing to such an extent, both in medical treatment and diagnosis, and in commerce and industry, even without considering military affairs in this connection, that unless more caution is exercised than at present the majority of the population may in each successive generation have its gonads exposed to enough radiation to raise. the mutation rate by a significant amount, such as 25% or 50%
Yet despite the fact that the evidence of a short-term rise in mutation rate is so hidden, the total amount of damage caused to all. later generations by even a moderate rise, confined to one parental generation, would if gathered together be seen to be enormous. Thus only a 25% rise in mutation rate for one generation would, in a population of 100,000,000 per generation whose usual spontaneous rate was only 1 mutant gene in 10 germ cells, cause the eventual “genetic death” of 5,000,000 individuals, scattered throughout scores of generations. It would probably cause, in addition, hundreds of millions to be slightly more afflicted than they would otherwise have been, i.e. to have their viability lowered by an average of some 2 or 3%. These effects are hidden only because distributed over so many generations and because so intermingled with those of other factors. Moreover, once the mutations have been produced, they will take their eventual toll despite all counteracting measures that may hereafter be instituted, short of a consciously directed selection.
Thus, in a population of 100,000,000, a rise of mutation rate of only 0.025, confined to just one generation, would in the course of centuries result in 5,000,000 genetically caused extinctions, and in a vastly greater number of individuals who were detrimentally affected to a slight extent.
Thus, if an average of 100 r were applied to the germ cells of the whole population for an indefinitely long period and finally lowered the equilibrium fitness by 10%, then the application of 100 r to just one generation would have a total genetic effect equivalent to the lowering of the average fitness of exactly one whole generation by, 10% (implying with this an increment of 10% in its genetic deaths). Actually, however, these 10%0 of deaths and these forty (i) times as numerous slight shortcomings would be diluted by being spread out over scores of generations. If then we knew this relationship we should have to put the further question: would the benefits of applying just these particular practices, rather than such substitutes or modifications of them as would nothave thisgenetic effect, be worth so large a price?
We see then that although there is some possibility that the studies in Japan may obtain evidence of the induction of mutations, it is certainly premature to say, as some persons have done, that they will afford a definitive test of the genetic effectiveness of radiation in man. Assertions have in fact been made that if positive results are not found there, this will have a salutary influence in quieting public fears concerning the genetic dangers of radiation. It should therefore be reiterated that existing knowledge is not only enough now to make it more likely that no definitely positive effects will be found than that they will, but also enough to make it quite sure that such failure to obtain positive results would not give valid support for the view, thus far based only on wishful thinking, that the amount of effect is insignificant.
It might be imagined however that the average person would be very unlikely to receive a dose of radiation great enough to raise the mutation rate by 0.025. But it takes a total dose of only about 50 r, when applied to the immature germ cells of Drosophila, to cause this much rise, and only 25 r when applied to mature germ cells. Moreover, the data from mice, although entirely too scanty, do indicate so far as they go that the induced mutation rate in mammals is of the same order of magnitude as in Drosophila. Now 50 r is an amount of radiation that a person’s gonads are not at all unlikely to receive under modern conditions. And the use of radiation is increasing in so many ways that, within a few decades, people whose gonads have not been exposed to this much total radiation, in the entire period from their conception to the time they reproduce, may be comparatively rare. A single fluoroscopic “screening” has been estimated to deliver to the skin about 75′ r, on the average (Martin, 1947), and’although but a fraction of this reaches the gonads it would not take very many such examinations to deliver 50 r to them. Again, an increasing number of women are having their ovaries deliberately treated with 300 r for the purpose of rupturing refractory Graafian follicles, i.e. to induce’ovulation (see for instance Haman, 1947), and the practice of having the testes treated with 500 r for the purpose of delaying the possibility of conception for several years is said to be increasing in popularity among men.
As yet,-there is much resistance to such measures when they are proposed. Indeed, even the “permissible level” of 0.3 r per week which has recently become commonly recognized (but not so commonly followed), and which repre-‘ sents a considerably more cautious standard than the long-accepted “tolerance’ dose” of 0.1 r per day that preceded it, would allow 15 r a year. Hence it would allow delivery of 50 r in the course of only three’ and a third years.
Moreover, since, as previously explained, the human mutation rate is probably not far from its critical level, even mild influences may turn out to be of more significance than has been suspected, in relation to the mutational load of mankind.
For example, if 100 r, applied as an average to a whole populations indefinitely, causes a 10%o lowering of average fitness and a corresponding 10% increment of genetic deaths, then this 100 r applied to the germ cells of just one individual who will later reproduce by an average amount will cause, again on the average, a total lowering of fitness of his descendants equal to the lowering of fitness of one descendant by 010%, and will, correspondingly, give a 10% risk of one genetic extinction, occurring at some unknown point in his line of succession. Nevertheless, if we have thereby raised the level of life of the exposed individual himself to such a degree that the effect, when averaged out over his own lifetime, would amount to more than 10%o, then we were in fact justified-provided we could not have attained this benefit by means that were safer for his descendants. And the same kind of considerations must be the guide in decisions concerning whether or not a given individual should undertake reproduction, when he is known to have certain genetic shortcomings.
Nevertheless, they are numerous enough to be collectively important, in the great majority of individuals, and, untreated, they must lead to the “genetic death,” or extinction, of a sizeable proportion-at least some 20%, to be conservative, of the population. On the other hand, if these weaknesses are mitigated or “cured” and in consequence proceed to perpetuate themselves to a greater degree than before, they must eventually, after very many generations, result in a new equilibrium, in which the population harbors and is being treated for correspondingly more of them than before, and in which there is again, despite all these treatments, just as large a proportion meeting genetic extinction as there was originally. At the same time, the amount of genetically caused suffering short of extinction will also have become comparable with what it had been originally
On the basis of existing data in man, supported by evidence from Drosophila, the total human mutation rate is judged to be probably not less than one newly arisen mutant gene in 10 germ cells, on the average, and not more than one in 2 germ cells.