MICHIGAN ACADEMY OF SCIENCE. 23 



minate origin and this has been confirmed by the subsequent study of thou- 

 sands of teeth in cUfferent orders of mammals. The still more significant 

 fact that this definite and determinate evolution was proceeding independ- 

 ently in a great many different families of mammals did not at the time 

 impress itself so strongly on my mind. 



If molar teeth are found independently evolving in exactly similar ways 

 in such remote parts of the world as Switzerland, Wyoming and Patagonia 

 it is obvious that the process is not governed by chance but represents the 

 operation of some similar or uniform law deduced from the four following 

 considerations: 



Firstly, the teeth differ from all other tissues and organs of the body in 

 being preformed, Tjeneath the gum. Unlike all other organs they are not 

 modified, improved or rendered more adaptive by use; on the contrary, after 

 the first stage of wear, the longer they are used the more useless they be- 

 come. Thus, new structures in the teeth do not first appear as modifications 

 (as distinguished from congenital variations) in the course of the life, as is 

 so often if not invariably the case with new structures in the skeleton. New 

 cusps, folds, crests, and styles are invariably congenital. Thus of all organs in 

 the body the teeth most exclusively and ]iurely represent the current of the 

 stirp, germinal or constitutional evolution. 



The other three considerations do not concern directly the matter in hand. 



In 1905 Osborn proposed the term Rectigradation to express what he had 

 ])re\'iously expi'essed as definite variation. "It embraces changes which many 

 writers have described as orthogenetic, under the supposed law of direct 

 change (u.sually in an adaptive direction) which is termed orthogenesis; these 

 probably are the mutations of Waagen." I cite these to show how close are 

 the various ideas. 



And finally we have Osborn 's search for the ''unknown factor in evolution." 

 In 1891 he wrote "disprove the Lamarckian principle and we must assume 

 that there is some third factor in evolution of which we are ignorant." In 

 1908 he reasserts his position with regard to the law of rectigradation. 



"The law of gradual change in the origin of single characters, measurable 

 at long intervals of time, rests on a vast number of observations," but he is 

 still at sea as to the cause of the change. 



And there Xeo-Lamarckism stands toda}'. Starting with Cope's and 

 Ryder's idea of the development of new structures through strains and 

 .stresses set \\\) in the organism and the preservation of such characters by 

 natural selection it has developed beyond that idea. It admits the origin 

 of characters by use and disuse, directly or indirectly (for even the cusps of 

 molar teeth apjDear at points of the greatest contact or strain); it admits 

 the possibility of the origin of new characters per saltum (iMutation of De 

 ^'ries) but beyond all this it demands the recognition of a factor, not yet 

 clearly understood, which governs the origin and development of hereditary 

 characters without the influence of the environment and even in seeming 

 despite of it. Its chief exponents demand the recognition of a factor which 

 will cause the development of an organism along a definite and perhaps, in 

 some degree, predetermined line through and over difficulties which are by any 

 other theory inexplicable. 



