216 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 4 



during 5 or 6 generations. Thus, for the first time, he announced, 

 a progressive series of mutations had been called forth by a common 

 environmental factor. If this work of Jollos is confirmed, it may 

 well be the most important discovery made as yet regarding the 

 meth(xl and cause of evolutionary mutation. Plough and Ives (1934) , 

 who have this month [April 1934] announced the results of their 

 repetition of the experiments of Goldschmidt and Jollos, find that 

 six times as many mutations occur in the heated lines as in the con- 

 trols, but while this proves that increased temperature is a fruitful 

 source of mutations there is so far no confirmation that these muta- 

 tions are directed. Indeed, Plough and Ives expressly deny that 

 there is any indication of orthogenetic mutations in their experi- 

 ments. 



Hitherto the great objection to the mutation theory of evolution 

 has been that mutations are so generally regressive and that they 

 lead nowhere. The only method of meeting this objection has been 

 to rely upon natural selection to eliminate vast numbers of useless 

 mutations and to preserve the few useful ones and thus slowly to 

 build up the marvelous combinations of useful adaptations that all 

 organisms possess. But there are many indications in the living 

 world that evolution has proceeded in certain directed lines, some- 

 times even farther than was useful, as for example in the enormous 

 size of body and weight of armor of certain dinosaurs and titano- 

 theres, and many zoologists since Eimer have insisted that " ortho- 

 genesis ", or directed evolution, is a necessity. If directed mutations 

 can be caused by some common environmental factor, as Jollos 

 suggests, it would solve one of the major difficulties of the mutation 

 theory. Osborn in particular has emphasized the necessity of 

 definitely directed variations in a series of publications during the 

 past 40 years, the last of which has just been published (1934). He 

 originally called this principle " definite variations " and later 

 " rectigradations." More recently he has stressed the necessity not 

 only of directed mutations but, much more, of useful and progressive 

 mutations in any explanation of evolution. This principle of the 

 origin of the fittest, as contrasted with the survival of the fittest, he 

 calls " aristogenesis " (1933, 1934). 



Goldschmidt has recently (1933) emphasized the importance of 

 certain embryological processes in evolution. He concludes that 

 genes control development partly by influencing the velocities of 

 certain reactions, and he suggests that by changing the differential 

 growth rate at an early stage a perfectly new evolutionary line could 

 be started. This suggests a speculation which I advanced before 

 this Society in 1903, and published in greater detail in 1905, regard- 

 ing the origin of major groups, or phyla, of the animal kingdom. 



