Ortmann.] lliD [May 15, 



We cannot say, however, that animals subject to orthogenesis are not 

 at all under the influence of natural selection : the latter must necessa- 

 rily act also upon them, since all injurious variations are destroyed and 

 cannot be transmitted and give cause to orthogenetic mutations. Natural 

 selection does not invariably imply mutation, but often, especially if the 

 external conditions are unchanged, it efi'ects only a preservation of an 

 existing species : by destroying all bad individuals it maintains the good 

 standard of the characters of the survivors, and only if there is any advan- 

 tage in any variation, this standard will be improved in a direction indicated 

 by this advantage. Thus we may say that natural selection gives origin to 

 mutation in a useful direction, but that this mutation is very slow, and 

 often so inflnitesimal, that it amounts almost to nothing, that is to say, 

 only the good standard is saved. This action of natural selection effects 

 besides the general adaptation of each animal form : the surviving indi- 

 viduals comply with the requirements of the surrounding conditions of 

 life. 



We have no reason to look upon natural selection as a factor of minoi 

 importance, as Eimer is inclined to do. Even the preserving of a good 

 standard is all-important. Natural selection is a factor which cannot be 

 left aside, and which is a necessary one in the development of all beings, 

 and it is a grave mistake to abate its value in favor of any other factor 

 cooperating in the formation of species. 



II. Yet the value of natural selection has not only been underrated by 

 some authors, but, on the contrary, it has been overrated, especially by 

 Weissman. The latter believes that natural selection does form species. 

 One can hardly understand on what grounds he is induced to allege this 

 action, and why he even believes that it is the only factor in the formation 

 of species, since he himself accepts Darwin's conception of this factor, 

 namely, that it acts selectively upon the best variations, and destructively 

 upon all the others, thus inducing only a change, a transformation of one 

 existing form or species into one other, but never causing the origin of 

 divergent forms or species. This point is so plain, and so beyond any 

 doubt, that only a great logical mistake, and a complete misapprehension 

 of Darwin's theory on the part of Weismann can explain this error. Yet 

 it is perhaps a little difficult, to say precisely, where the fallacy is hidden, 

 and it would be interesting to examine this point more closely. 



I have no doubt that this wrong interpretation of natural selection is 



p. 254). Weismann's argument as respects this point is the following : Eimer believes to 

 have shown, that there are no advantages for the respective species visible in the uif- 

 lerent colors of the butterflies: but since I (Weismann) have propounded the theory, 

 that all characters are due to natural selection, the latter must have produced these 

 color markings also, and we must assume, that they are or were nevertheless advantage- 

 ous ! Comp. Spencer ( Ttie Inadequacy «f Natural Selection, 1893, p. 49) : " He ( Weismann) 

 practically says: Propound your hypothesis ; compare it with the facts ; and if the facts 

 do not agree with it, then assume potential fulfillment, where you see uo actual fultill- 

 ment," 



