BIOLOGICAL EVOLUTION 63 



The first difficulty is concerning " the absence or rarity of 

 transitional varieties," and his answer is: " As natural selection 

 acts solely by the preservation of profitable modifications, each 

 new form will tend in a fully-stocked country to take the place of, 

 and finally to exterminate, its own less improved parent-form and 

 other less favored forms with which it comes into competition." ^ 

 In discussing the difficulty of explaining neuter insects, Darwin 

 formulates the doctrine of selection on the basis of utility to the 

 species rather than to the individual.^ 



In reply to criticism by Mr. Mivart, Darwin takes issue with all 

 who beUeve in mutations, appealing as usual to experience under 

 domestication.^ 



Instincts are discussed at length and their origin explained in 

 the same way as other useful characters, — by natural selection.* 



We find further contributions to our doctrine of adaptation in 

 Darwin's Descent of Man though here he was preceded by other 

 writers. In this work we are shown how the various mental 

 qualities so highly developed in man have descended or " as- 

 cended " from rudiments to be found in the lower orders.* 

 Emotion, imitation, attention, memory, imagination, reason, 

 the use of tools, even language are thus evolved. All of these, — 

 with many others such as self-consciousness, individuality, 

 abstraction, general ideas, sense of beauty, rehgion, — are the 



* Origin of Species, p. 134. ^ Ibid., pp. 230 f. 



' Ihid., pp. 202 f. Recent experiments by De Vries, Bateson and others, how- 

 ever, indicate to their satisfaction that nature does take leaps, " Natura facit 

 saltum." Cf. Walter, Genetics, chs. IV, VII, and VIII. 



* Ihid., ch. VIII. Professor T. H. Morgan takes issue with his conclusions 

 concerning the development of such instincts as that of slave-holding among certain 

 species of ants. " We must not forget," says Professor Morgan, " that it is not 

 enough to show that a particular habit might be useful to a species, but it should 

 also be shown that it is of sufficient importance, at every stage of its evolution, 

 to give a decisive advantage in the * struggle for existence.' For unless a life and 

 death struggle takes place between the different colonies, natural selection is 

 powerless to bring about its supposed results. And who will be bold enough to 

 affirm that the presence of slaves in a nest will give victory to that colony in com- 

 petition with its neighbors ? Has the history of mankind taught us that slave- 

 making countries have exterminated countries without slaves ? " His conclusion 

 is that the instinct was a mutation and that the species practising it survived 

 because it was not so disuseful as to lead to extermination. 



^ Articulate language, however, is peculiar to man. Descent of Man, p. 52. 



