324 DARWINISM TO-DAY. 



they incline to regard these conditions as causes. And if it be 

 suggested to them that the results they see may have been achieved 

 by the selection of adaptive variations from among a number of 

 promiscuous variations that are not adaptive, they ask why it is 

 that they do not find evidence of these numerous known adaptive 

 variations in the organs, when one would suppose that, on any 

 hypothesis, except that of definite variation, such forms must have 

 been the more abundant of the two. It is useless to reply to them 

 that the known adaptive variations in each generation were killed off 

 when young, and so, even if fossilised, are practically undistinguish- 

 able ; because they will reply with abundant proof that the adaptive 

 characters chiefly appear in the adult stages of the organism, possibly 

 only in its senile stages, and so are incapable of coming under 

 the action of natural selection during the early undifferentiated 

 stages. How the conversation might continue does not much 

 matter, for it is obvious that it has reached a point beyond which all 

 must be speculation. The facts on which the palaeontologist relies, 

 the facts that Prof. Cope adduces with such wealth of knowl- 

 edge, are strong presumptive evidence in favour of his second 

 thesis, but they are not proof." (Bather, F. A., Natural Science, 

 Vol. X, pp. 40-41, 1897.) 



Prof. Scott, another American palaeontologist, discusses the 

 question of variation in an interesting paper in the American Journal 

 of Science, Vol. XLVIII, pp. 335-374- 1894. The great point made 

 by Prof. Scott is the clear distinction between individual and 

 phylogenetic variation. Individual variation is irregular and not 

 fixed, while "phylogenetic variation," or mutation (in the sense of 

 * Waagen) which is distinguished from individual variation, not 

 by any character of quantity or quality, but by pursuing a deter- 

 minate direction and thus, under control of natural selection, leading 

 to the formation of new species. "Remembering that the signifi- 

 cant fact in the history of a group is not so much the character of 

 its variations at any one stage, as the gradually shifting positions 

 successively occupied by the normal or centre of stability, we find 

 that any mammalian series at all complete, such as that of the 

 horses, is remarkably continuous, and that the progress of discovery 

 is steadily filling up what few gaps remain. So closely do successive 

 stages follow upon one another that it is sometimes extremely 



* The term "mutation" was first used in biology, probably, by 

 Waagen, 1869, in a paper on the phylogeny of an ammonite. In 

 this first use of the word its meaning was a change or modification 

 accomplished during a considerable historic period. Indeed, it had 

 much the meaning of evolution or descent as we use these terms 

 nowadavs. 



