234 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



illustrations of this principle and to show that variation is hardly 

 the proper term to apply to rudiments which do not arise in a 

 variable but in a h'xed manner. 



It appears that von Waagen suggested the term " mutation " for 

 immeasurable variations somewhat similar to these. Scott in 1891 

 ('91, p. 388) pursued the idea further in the following striking passage: 

 " These facts at least suggest the possibility that individual variations 

 are not incipient species, but that the causes of transformation lie 

 deeper, and act with more or less uniformity upon large numbers of 

 individuals. It may, perhaps, be the outcome of future investigations, 

 that while variations are generally due to the union of changing hereditary 

 tendencies, mutations are the effect of dynamical agencies operating 



Fie. '214. Superior molars of primates. A, Adapis; B, //yo/woc/us ; C, Xot/iarctus. Showing 



homoplastic cusps, hi/, ml, ps, ins, mtx. 



long in a uniform way, and the results controlled by natural selection. 

 While this may be true, a great many facts must be gathered in its 

 support, before it can be regarded as more than a suggestion." Scott 

 subsequently, in his article " Variations and Mutations," expanded this 

 idea : " Bateson's results, as compared with those of paleontology, confirm 

 this distinction in many significant ways and emphasize strongly the 

 difference between variation and that steady advance along definite 

 lines which Waagen called mutation." This paper in turn is said to 

 have influenced de Yries's recent work, Die Mutationstheorie. 



It is a singular coincidence that the human teeth were selected 

 by both Empedocles and Aristotle to test the "survival of the fittest' 

 versus the purposive or teleological theory of evolution. I pointed 

 out in the papers above referred to (Osborn, '89, pp. 561-566; '90) 

 the significant fact that new cusps of the molar teeth do not appear 

 at random, but at certain definite points; that they are at first so 

 minute that they can barely be perceived, so that it is difficult to 

 theoretically assign them a survival value in the struggle for existence ; 

 that the mechanical or Lamarckian explanation is the only one which 

 can be offered: 1 I laid the chief stress, however, not upon the 

 mechanical explanation, but upon definite or determinate origin, and 

 this has been confirmed by the subsequent study of thousands of 



1 Ryder and Cope confidently advanced the mechanical explanation ; it is not 

 without grave difficulties, owing to the lack of an heredity theory. 



