376 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



tion is due are evidently changes in the germinal tissues, probably 

 in the manner in which they divide. It is likel}'^ that the occurrence 

 of these variations is wholly irregular, and as to their causation we 

 are absolutely without surmise or even plausible speculation. Dis- 

 tinct types once arisen, no doubt a profusion of the forms called 

 species have been derived from them hj simple crossing and subse- 

 quent recombination. New species may be now in course of creation 

 by this means, but the limits of the process are obviously narrow. 

 On the other hand, we see no changes in progress around us in the 

 contemporary world which Ave can imagine likely to culminate in the 

 evolution of forms distinct in the larger sense. By intercrossing 

 dogs, jackals, and wolves new forms of these types can be made, 

 some of which may be species, but I see no reason to think that from 

 such material a fox could be bred in indefinite time or that dogs 

 could be bred from foxes. 



Whether science Avill hereafter discover that certain groups can by 

 peculiarities in their genetic physiology be declared to have a pre- 

 rogative quality justifying their recognition as species in the old 

 sense, and that the differences of others are of such a subordinate 

 degree that the}^ may in contrast be termed varieties, further genetic 

 research alone can show. I myself anticipate that such a discovery 

 will be made, but I can not defend the ojDinion with positive con- 

 viction. 



Somewhat reluctantly, and rather from a sense of duty, I have 

 devoted most of this address to the evolutionary aspects of genetic 

 research. We can not keep these things out of our heads, though 

 sometimes we wish Ave could. The outcome, as you will haA^e seen, is 

 negative, destroying much that till lately passed for gospel. De- 

 struction may be useful, but it is a Ioav kind of Avork. We are just 

 about Avhere Boyle was in the seventeenth century. We can dispose 

 of Alchemy, but Ave can not make more than a quasi-chemistry. We 

 are awaiting our Priestly and our Mendeleeff. In truth it is not 

 these Avider aspects of genetics that are at present our chief concern. 

 They Avill come in their time. The great advances of science are 

 made like those of eA^olution, not by imperceptible mass improA'e- 

 ment, but by the sporadic birth of ]>enetratiA'e genius. The journey- 

 men follow after him, widening and clearing up, as Ave are doing 

 along the track that Mendel found. 



PART II. 



At Melbourne I spoke of the new knowledge of the properties of 

 hA'ing things Avhich Mendelian analysis has brought us. I indicated 

 how these discoA^eries are affecting our outlook on that old ])roblem 

 of natural history, the origin and nature of species, and the chief 



