^06 MUTATIONS AND EVOLUTION. 



■by analogy, from embryology and radiation studies. He sum- 

 marizes as follows : " A theory of evolution that assumes internal 

 changes chiefly independent of external conditions, i.e., spon- 

 taneously arising, and which proceeds chiefly by a splitting up 

 of and loss of genes from a primitively complex molecular con- 

 dition of the germ plasm, seems best to meet the present state of 

 our knowledge." Prof. Bateson* has remarked: "It is to be 

 inferred that these fractional degradations are the consequence 

 of irregularities in segregation." 



On the view that factorial changes consist of chemical or 

 physical changes taking place in highly complex molecules, it 

 seems more feasible to think of them as proceeding with some 

 degree of regularity or method in place of the irregular haphazard 

 manner so generally accepted. Incidental changes may well occur 

 in such an organic complexity as the factors are deemed to be, 

 and it is probably these which have been mainly studied hitherto; 

 but it may be that they are merely the outposts of determinate 

 changes of a more fundamental character which the germ plasm 

 can undergo. The former may weW be frequent and in many 

 directions, but are of small moment for purposes of evolution. 

 More regular molecular alterations may at times be in progress, 

 and we get the same change slowly taking place throughout all 

 the individuals of a race possessing the same germ plasm, or, 

 as will be sought to show later, an orderly succession of changes 

 all in the same direction. The difficulties and uncertainties in- 

 volved in an analysis of the genetic changes concerned in any 

 continuous retrogressive or progressive change in a character are 

 well set forth by Prof. Morgan in his article, " Evolution by 

 Mutation," already noticed. 



That transformation of a whole race can take place without 

 natural selection being in any way concerned was recognized by 

 Darwin. In the " Origin of Species " (6th ed., p. 27) he re- 

 marks : " There can also be no doubt that the tendency to vary 

 in the same manner has often been so strong that all individuals 

 of the same species have been similarly modified without the aid 

 of any form of selection." Prof. Morgan, in his work, " Evolu- 

 tion and Adaptation," 1903, was also inclined to support the same 

 view where he says (p. 293) : " Equally important for the descent 

 theory is the idea that the same mutation may appear time after 

 time. There is good evidence to show that this really occurs^ 

 and in consequence the chances for the perpetuation of such a 

 form are greatly increased. Delboeuf, who advocated this idea 

 of the repeated reappearance of a new form, has also attempted 

 to show that if this occurs the new form may become estab'ished 

 without selection of any kind taking place — the time required 

 depending upon the frequency with which the new form appears. 

 This law of Delboeuf, de Vries believes, is correct from the point 



* " Science," vol. XL. Aug. 28, 1914. p. 298. 



