376 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



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

 in the manner in Avhich the}^ divide. It is likely 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 by simple crossing and subse- 

 quent recombination. Xew 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 Avorld which we 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 tj^pes can be made, 

 some of vs'hich 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 will 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 they ma}'^ 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 opinion with positive con- 

 viction. 



Somewhat reluctantl}^, 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 we could. The outcome, as you will have seen, is 

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

 struction ma}^ be useful, but it is a low kind of work. We are just 

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

 of Alchemy, but we can not make more than a quasi-chemistry. AVe 

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

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

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

 made like those of evolution, not hy imperceptible mass improve- 

 ment, but by the sporadic birth of penetrative genius. The journey- 

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

 along the track that Mendel found. 



PART II. 



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

 hving things which ISIendelian analysis has brought us. I indicated 

 how these discoveries are affecting our outlook on that old problem 

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



