Ortmann.] 170 [May 15, 



no formation of species by natural selection, but that the only action of 

 this factor consists in the preserving of existing species.* This opinion is 

 as erroneous as that of Weismann, but in the opposite direction. 



So far, however, Darwin's definition of natural selection, as the sur- 

 vival of the fittest, was not altered, only the efficacy was regarded differ- 

 ently. But recently Pfefferf has given another conception of natural 

 selection, differing from Darwin's. According to the latter, by the 

 struggle for existence the fittest are selected (hence the term "selec- 

 tion "), while all others are destroyed. Pfeffer, however, says that 

 there is no selection of particularly good variations, but the struggle for 

 existence destroys indiscriminately fitted and not fitted individuals, and 

 certainly it destroys all the not fitted. Thus the surviving remainder 

 (according to Darwin's terminology the selected part) consists of a 

 number of good and better individuals, which show a good average. The 

 struggle for existence continued in this way during many generations — 

 destroying all the bad individuals — effects little by little that this good 

 average improves from generation to generation. Pfeffer calls this pro- 

 cess "Transformation of species by sel f- regulation " ("Umwandlung 

 der Arten durch Selbststeuerung "). 



This conception of natural selection differs only slightly from that of 

 Darwin, and one could say, that only the form of expression is different, 

 while the effect in both cases is the same. But we shall see below, that 

 the form used by Darwin is in some respect inferior to that used by 

 Pfeffer, and although Darwin's meaning is nearly the same as that of 

 Pfeffer, we shall have some advantage in accepting Pfeffer's phrase, 

 especially in maintaining, that not the fittest, but good individuals sur- 

 vive, and that the change effected is an extremely slow one. 



Recently I have pointed out,^: that this " transformation of species " is 

 nothing else than the well-known "mutation" of palaeontologists, a 

 term, the differences of which from " variation " are first shown by 

 Waagen and Neumayr, and subsequently most vigorously maintained by 

 W. B. Scott. § These differences are neglected by many zoologists, 

 although the "comparatively lawless and uncontrolled character "|| ol 

 the variations and the "directness of advance towards the final goal "H 

 of the mutations differ strikingly. Scott says :** "While variations are 

 dtie to the union of changing hereditary tendencies, mutations are the 

 effect of dynamical agencies acting long in a uniform way and the results 



* Eiraer {Die Arlbildung und Verwandtschaft bei Schmetterlingen, ii, 1^95, p. 33) uses even 

 the expression : "Inefficiency of Natural Selection" (" Ohnmacht der Naturziiclitung") 



tP.oflfjr, '-Die U.nvvaniling der Arten, ein Verging functioneller Selbstgestaltung,' 

 Verhandl. Naturw. Ver. Hamburg (3) i, 1894. 



X Grundzilge der marinen Tiergeographie, p. 31. 



g Scott, "On Variations and Mutations," Amer. Jour. Sci., 4S, 1894, pp. 355-374. 

 II i. c, p. 370. 



IT^. c, p. 360. 



** This sentence is first given in the paper "On the Osteology of Mesohippus and Lcp- 

 to:iierys," Journ. Morplwl., v, 1891, p. 38S, and repeated l. c, p. 372. 



