HISTORICAL ACCOUNT OF EVOLUTION THEORY 43 



viduals of a species (because the destruction of the less fit does not 

 in itself lead to anything that is new) than on the appearance of new 

 characters and modifications, of old characters that become incorpo- 

 rated in the species, for on these depends the evolution of the 



HYBRIDIZATION AND THE ORIGIN OP SPECIES 



As a consequence of the great interest aroused by Mendel's 

 hybridization experiments the question has arisen as to the role of 

 hybridization hi organic evolution. Certain it is that a vast number 

 of animal and plant races now existing are mixed or hybrid hi nature 

 and are continually splitting up into various Mendelian segregates. 

 How many pure races are there today ? Some authors think that no 

 variable races today are pure. Lotsy goes so far as to claim and 

 attempt to prove that unit characters are fixed and that the only 

 source of variation is hybridization, or amphimixis. Biologists today 

 would not be willing to go thus far with Lotsy, but it seems beyond 

 question that hybridization has played an important role hi the pro- 

 duction of very many groups now living. It is of interest to recall 

 that Linnaeus, though a special creationist, admitted the possibility 

 of the origin of new species by hybridization. 



NEO-MENDELIAN DEVELOPMENTS 



Since the rediscovery of Mendel's paper by De Vries and its perusal 

 by thousands of biologists the world over, Mendelian breeding experi- 

 ments with all manner of animals and plants has been the ruling 

 passion of geneticists. Among the leading neo-Mendelians are Bate- 

 son, Morgan, Castle, Correns, East, Hurst, Shull, Tschermak, and the 

 pupils of these. 



Perhaps the first two mentioned, Bateson and Morgan, have con- 

 tributed most largely to an understanding of the intricacies of the 

 Mendelian operations. Bateson has become so imbued with the idea 

 that all mutations are the result of the loss of factors that he proposes 

 the hypothesis that "evolution has taken place through the steady loss 

 of inhibiting factors," as Morgan puts it. "Living matter was 

 stopped down, so to speak, at the beginning of the world. As the 

 stops are lost, new things emerge. Living matter has changed only in 

 that it becomes simpler." It is quite probable that Bateson, hi pro- 

 posing so radical a view, intended to be taken only half-seriously. 

 Apart from this, his best-known expression of opinion, Bateson is the 



