THE 



AMERICAN NATURALIST 



Vol. LV I. ^ Jninnrnj-Ffhru.inj No. 642 



THE OEIGIX OF VARIATIONS 



SYMPOSIUM AT THE THIRTY-NINTH ANNUAL MEETING OF THE 

 AMERICAN SOCIETY OF NATURALISTS, TORONTO, 

 DECEMBER 29, 1921 



VAEIATION IN UNIPAEENTAL EEPEODUCTION 

 PROFESSOR H. S. JENNIN^GS 

 The Johns Hopkins UNivERSiTr 



Darwinism left the origin of variations the unsolved 

 problem. Give ns inherited variations, it said, and we can 

 explain adaptation, by natural selection. But this was 

 the omission of 99 per cent., if not 100 per cent., of the 

 problem of evolution. Are we in better case to-day? 

 Has the experimental study of genetics given us some 

 solid knowledge of the origin, the causes, of variation? 

 Have we learned that the obvious differences observable 

 everywhere among individuals are the foundations of 

 evolution? Or that they are not? Are slight quantita- 

 tive fluctuations the material out of which evolution is 

 made? Have we discovered that extensive saltations are 

 the steps in evolution? Or that less extensive mutations, 

 qualitative or chemical changes, that may be minute or 

 large, are that by which evolution is constituted? Do we 

 know the origin of such saltations, mutations ? Have we 

 found that the present constitution of the organism pre- 

 determines in some way the course of further change ; or 

 that an elan vital is driving the organism to unfold in a 

 definite way, like a flower; that evolution is ortliogonosis? 

 Do we comprehend the ii.-itni-c and causes of siu'li a ])ush 

 to unfold, and of the diivctioii in which it tends.' Have 

 we found perhaps, as at least one investigator maintains, 



