268 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



primarily on account of the remarkable property that, once changed, 

 further copies are reproductions of the new kind of gene, and do not 

 return to the old pattern. We now do not need to wait for these muta- 

 tions to occur spontaneously ; we have learned to produce them arti- 

 ficially. The same century which brought us the artificial transmuta- 

 tion of the chemical elements has given us the artificial transmutation 

 of the hereditary elements. X-rays and gamma rays from radium 

 were the pioneer tools, and still are indispensable. Most recently, 

 chemical agents such as mustard gas, formaldehyde, and urathene 

 have been found which accomplish permanent genie alterations. The 

 mechanism of induction of mutations is on the way to being clarified. 

 Undoubtedly the solution of these problems will bring with it insight 

 into the origin of the natural mutations which, uncontrollable at pres- 

 ent, occur all the time in all organisms. It is clear already that these 

 spontaneous mutations are elementary events dependent on accidental 

 phenomena of nature: intrinsic instability of genie molecular com- 

 pounds; unusual exposure of genes to reactive chemicals formed in 

 the cell ; and unavoidable events like natural radioactivity or cosmic 

 irradiation. 



These sources of mutagenic action are part of the forces of the 

 universe. Life pays tribute to them, and harnesses them. The tribute 

 consists in the sacrifice of many changed genes. Since the change is 

 accidental in origin, much more often than not its result is detrimental. 

 The mutated gene will not be suitable to take part in the established 

 paths of gene action, and early death or weakness of the organism 

 will result. This tribute is a tragic reality. While any one gene will 

 mutate only in one out of many thousands of cells, the fact that each 

 cell embodies many thousands of genes means that in each generation 

 very many germ cells have acquired at least one mutated gene not 

 present in their ancestry. In each generation millions of mutations 

 are dumped into a species. Why then its apparent stability? The 

 answer to this question has already been given. The early death or 

 weakness of the individuals who carry the mutations removes the 

 unstabilizers at the same rate as they are produced. 



But not quite at the same rate. A few are harnessed to the yoke 

 of survival. Are those a few good genes in contrast to the great bulk 

 of bad genes ? Molecules and genes are not good or bad by themselves. 

 However, a few changes in the living assemblage of cellular mole- 

 cules will happen to be compatible with continued good function, 

 although the majority will not. The internally compatible new 

 assemblages then will have a chance to be perpetuated. Wliether they 

 will coexist with the original ones, or whether they will replace them, 

 will vary from case to case. Sometimes the new assemblage may 

 thrive in a niche of the environment which had not been occupied 

 before. The existence of thousands of different species in the same 



