The argument is essentially the same as the one concerning the danger to the individual. The tests are responsible for 0.001 or 0.002 roentgens per year to the human reproductive cells. This is equivalent to approximately 0.05 roentgen per generation. Most of this radiation is due to gamma rays from Cs¹³⁷ which has been deposited on the ground or absorbed in the body. The number of mutations caused by this radiation is to be compared with the number of natural mutations. Some of the natural mutations are caused by heat and chemicals. Some are due to background radiation, to cosmic rays or to gamma and beta rays emitted by natural radioactive substances in or near our bodies. Our best estimate is that 10 per cent of the natural mutations are due to the background radiation. Over a period of one generation the background radiation dosage to the human reproductive cells is approximately five roentgens. Assuming a simple proportionality between dosage and the number of mutations, it follows that fifty roentgens would be required to induce a number of mutations equal to the total number of natural mutations (from background radiation and all other causes). That is, fifty roentgens is a “doubling dose.” The atomic tests are therefore increasing the number of mutations by about 0.05 ÷ 50, which is 0.1 per cent. This kind of increase in the rate of mutations would certainly not seem to be a serious reason for worry. Actually the number of mutations from the tests is very small even compared to geographical and altitude variations in the natural radioactivity. The Inca empire existed for many generations in the high country of Peru. The people of Tibet have been exposed for generation after generation to the greater cosmic ray intensity which bombards them through a thinner layer of atmosphere. These people have been exposed to much greater additional radiation than anything which is caused by atomic tests. Yet genetic differences have not been noticed in the human race or for that matter in any other living species in Peru or Tibet. We are certainly talking here about questions which may strike hard on some individuals but which from the point of view of the community or race are not serious. It has been often repeated that all mutations due to radiation are harmful. There is every reason to believe that mutations due to radiation are not different in kind from other mutations. Should we then seriously believe that all mutations are harmful? That most of them are is admitted. If all of them were indeed always harmful, we must deny the simplest facts of evolution. There will be some who maintain that the human race is not capable of improvement. Such an argument is irrefutable. It is also unreasonable. What cannot be further improved is perfect, and not many people will maintain that our species can claim perfection.