DESCENT WITH CHANGE 383 



These afford a wealth of opportunities for alterations in the germ 

 plasm and so for the appearance of new characters in organisms. 

 Indeed the significance of fertilization, which, of course, is at the 

 basis of hybridization, can hardly be overemphasized at this point. 

 It provides new combinations not only of established germinal 

 factors but also of such mutations as occur, and so affords oppor- 

 tunity for relatively rapid germinal change. (Figs. 167, 189, 196.) 



True it is that mutations seem to be infrequent in comparison 

 with non-inheritable changes of somatic origin, nevertheless it 

 must be borne in mind not only that somatic changes are more 

 readily apparent, but also that the majority of the mutations 

 which occur lead to a decrease in vitality or even to death. This 

 is to be expected, for a random change in a highly complicated 

 mechanism such as a living organism, which has long survived 

 in a severely competitive environment, is far more apt to upset 

 than to improve the nicety of its internal and external adaptation ; 

 natural selection is conservative unless a changing environment is 

 presenting new conditions to be met. 



Relatively little information is available in regard to the basic 

 factors that induce mutations, but we have seen that recent ex- 

 perimental work indicates that environmental factors, such as 

 irradiation, etc., acting directly on the genetic complex are not 

 without influence — mutations have been produced. Indeed it 

 seems probable that both external and internal environmental 

 conditions, particularly the new cellular environment of the genes 

 following hybridization, are potential inducers of genetic change 

 and so of new variations at the disposal of natural selection. How- 

 ever, when all is said, we are far from any appreciation of the 

 physico-chemical changes in the germinal material itself that are 

 responsible for the new characters. Characters may emerge that, 

 at least, are not recognizable as the computable or additive result 

 of newly associated genes — the expressions of the genes may 

 change, new properties may emerge — "emergent evolution." But 

 witness the properties of water that emerge from a certain associa- 

 tion of hydrogen and oxygen ! 



One may well inquire whether geneticists in their extensive ex- 

 periments during the past two decades have succeeded in 'creat- 

 ing' a new species. And the answer is largely determined by one's 

 concept of a species — a problem we have already discussed. It is 

 fair to say that some biologists hold that new species have been 



