440 RADIATION BIOLOGY 



must be so to some extent. Hence, in so far as selective multiplication 

 occurs in regard to the genetic traits involved, it works in a direction 

 antagonistic to the welfare and advancement of the population as a whole, 

 a direction opposite to that taken under primitive conditions. There is 

 evidence that this is occurring in technically advanced communities of 

 all types, ranging from the U.S.S.R. to most democratic countries. This 

 being the case, it follows that under conditions like our modern ones any 

 increase in genetic variability, such as would be brought about by appli- 

 cation of radiation, would hasten the degenerative process. 



The implication is not intended that the social conditions and mores 

 which form the basis for this reversed selection are inseparably bound 

 with the possession and use of the techniques of modern civilization, and 

 that there is therefore an inherent contradiction which will in the end 

 defeat all men's efforts to better their existence. It is theoretically possi- 

 ble, by the voluntary exercise of conscious guidance over reproduction, 

 and only by this means, to regain a beneficial direction for the process of 

 selective multiplication in civilized man. Such a situation is not yet even 

 in sight. If and when it should come about, it would be found that there 

 was already in existence such a plentiful supply of natural variation in 

 all human populations as would for a long time allow biological progress 

 at as rapid a rate as the naturally slow multiplication rate of man would 

 make feasible. Perhaps some day, still later, biological techniques of 

 advanced kinds would make possible radically new forms of genetically 

 selective multiplication, and then an artificial increase invariability could 

 be taken advantage of without paying the higher price of an increased 

 genetic load and increased elimination rate. That bridge cannot be 

 crossed now, however, and it would not be justifiable to form present 

 policies regarding irradiation on the assumption that such changes will 

 come about. For the present, then, and with existing conditions in view, 

 it is a fantastic and dangerous rationalization to imagine that an increase 

 in the human mutation rate, brought about by current radiation practices, 

 will further the biological improvement of mankind. 



23. PRACTICAL APPLICATIONS OF THE ACTION OF RADIATION 

 ON THE GENETIC MATERIAL 



Although, for the reasons given above, it is not practicable to utilize 

 the genetic effects of radiation on man for the purpose of improving his 

 genes, nevertheless, if the conclusion presented on p. 388 be accepted, the 

 chromosome changes caused by radiation, through their very destruc- 

 tiveness to proliferating cells, form the main basis of the great therapeutic 

 usefulness of ionizing radiation. In this way malignant growths can be 

 selectively injured and in some cases destroyed, and overdeveloped parts 

 of some types (such as enlarged thyroids) can be reduced in their size 



