432 RADIATION BIOLOGY 



deviation of not quite ± 8. It thus becomes evident that the individuals, 

 although varying from one another somewhat, tend to suffer from com- 

 parable total loads, there being, in most cases, no very large distinction 

 between the person whose disability happens to lead to elimination and 

 the one who escapes it. The genetic extinction, then, is seldom caused 

 by some unusual all-or-none condition or process, but rather by a kind 

 of generalized inadequacy, shared to a considerable degree even by the 

 individuals who escape extinction. There must, to be sure, be certain 

 features — forming a pattern of defect — which are more marked in one 

 case, and others in another, but only in relatively rare cases will a single 

 feature or syndrome greatly predominate in providing the risk of extinc- 

 tion. This situation shows that the figure for elimination rate, no matter 

 whether its true value is more or less than 0.2, does not usually represent 

 some major peril which strikes in occasional spots, but rather, for most 

 individuals of the population, including those who survive genetically, a 

 more or less generalized, continuing handicap, inasmuch as it is com- 

 pounded of so many small moieties acting in different yet cumulative 

 ways. It is in this sense legitimate to regard this figure as representing a 

 a true "average disability," borne in large measure by the great majority 

 of individuals. It is a handicap of the given amount, however, only by 

 comparison with the potential performance of hypothetical individuals 

 free of mutant genes. 



21. MANNER OF INCIDENCE OF RADIATION DAMAGE 

 IN SUBSEQUENT GENERATIONS 



How is the above picture altered when additional mutations are pro- 

 duced by exposure to radiation? Suppose that an entire population had 

 been exposed for one generation to a dose which in the gonads averaged 

 20 r, and that, as Russell's preliminary data on mice indicate, this caused 

 mutations at a frequency of about one-cjuarter of that occurring spon- 

 taneously in man. Taking the spontaneous /x as 0.3 would make an 

 induced frequency of 0.075. If the 0.3 spontaneous mutations of each 

 generation give rise to an elimination of individuals represented by the 

 figure 0.2, as explained above, the additional 0.075 induced mutations 

 would give rise to an approximately proportionate elimination of about 

 0.05. That is, if the given population comprised 100,000 individuals per 

 generation, a total of about 5000 would eventually suffer genetic death 

 by reason of the mutations induced in that one generation, in addition 

 to 20,000 who would suffer genetic death anyway by reason of the spon- 

 taneous mutations that had occurred in the same generation. These 

 5000 induced eliminations, however, hke the 20,000 "natural" ones due 

 to the spontaneous mutations of that particular generation, would be 

 scattered out over scores and even hundreds of generations of descend- 



