f6o THE DOCTRINE OF DESCENT. 



selection in the strict Darwinian sense is inapplicable. 

 Two species of butterflies, differing only in a few specks 

 or pencilings, or the notches on the wings, are in 

 our estimation of perfectly equal physiological value ; 

 they are morphological species. Weismann sets up 

 the proposition that " the colouring and penciling of 

 the upper surface of the wing in butterflies are to be 

 regarded as purely morphological characters, excepting 

 in cases of mimicry and protective uniform colouring," 

 He shows also by other examples that, " under certain 

 circumstances and within a comparatively small range, 

 new as well as morphological characters may be estab- 

 lished by the effects of isolation only." The inapplica- 

 bility of natural selection to the evolution of purely 

 morphological variations was first pointed out by 

 Nageli.'*^ With reference to this subject, Darwin with 

 magnanimous modesty observes : " I now admit, after 

 reading the essay by Nageli on plants, and the remarks 

 by various authors with respect to animals, more espe- 

 cially those recently made by Professor Broca,^° that, in 

 the earlier editions of my ' Origin of Species,' I probably 

 attributed too much to the action of natural selection 

 or the survival of the fittest. I have altered the fifth 

 edition of the * Origin ' so as to confine my remarks 

 to adaptive changes of structure. I bad not formerly 

 sufficiently considered the existence of many structures, 

 which appear to be, as far as we can judge, neither bene- 

 ficial nor injurious, and this I believe to be one of the 

 greatest oversights as yet detected in my work." ^^ 



We are disposed to think that the oversight with 

 which Darwin charges himself is not so great, as it is 

 here a question of the more indift'erent species, not affect- 



