THE EVOLUTION OE BIRDS. 



11 



posed to be a case of the survival of the fittest. In the first place, one cannot imagine 

 any purpose for which the diminished size of the wing could render the species more fit ; 

 and, in the second place, the species did not survive. 



That protective and sexual selection have played an important part in hastening the 

 evolution of species is all but universally admitted ; but their influence has probably been 

 spasmodic, and, when dealing with so-called fortuitous variation, even if we admit the 

 possibility of its surviving the swamping effects of interbreeding, comparatively slow — 

 spasmodic, because it could only operate during periods when there was a struggle for 

 existence ; slow, because the variations from which selection could be made might be in 

 any direction, and only those in a favourable direction could be used. On the other hand, 

 the modification of species caused by use or disuse would be constantly in operation (as 

 long as the inherited habit continued), and always in a definite direction, whether the 

 conditions of existence were such as to warrant the application to them of the term struggle 

 or not. 



If we admit that the inherited habit, which impels a. bird or other animal to use or 

 disuse any organ, is the most important factor in the modification of individuals — one 

 which, if it is continued for a sufficient number of generations, produces a modification 

 of the species — we have only shifted the difficulty one stage backwards. What is the 

 cause of the difference in the habits of one species from another ? In other words, 

 assuming the various species to have had a common ancestor, what is the cause of the 

 change in the habits of birds or other animals ? If men and birds be descended from 

 a common vertebrate ancestor, it is probable that the causes of the change of habits in the 

 one are more or less similar to those which have operated in the case of the other. Why 

 are the French a thrifty race ? and why are the English and the Russians spendthrifts ? Is 

 it because the former nation is more intelligent than the two latter,, and has seen the great 

 advantage to be derived from thrift ; and has practised this- virtue, and left as a legacy to 

 its children the priceless gift of a hereditary habit of thrift ? Or is it because the superior 

 intelligence possessed by the Englishman, and the command of abundance of food enjoyed 

 by the Russian, have rendered the acquisition of the habit of thrift unnecessary ; whilst 

 the poor Frenchman has been literally starved into his thrifty habits in the bitter struggle 

 for existence, aggravated by centuries of cruel misgovern men t ? If the hereditary habits of 

 the most highly developed animals are derived less from intelligent choice than from the 

 inexorable law of the survival of the fittest in the struggle for existence, we may fairly 

 agree with Darwin that Natural Selection is after all a very potent factor in the modification 

 of the descendants of most species. 



When Darwin uses the expressions accidental, fortuitous, or spontaneous variation, 

 he does not mean that the variations are due to chance or accident. Science does not 

 admit the existence of chance 1 . Every apparently accidental variation is due to a definite 



1 " I have hitherto sometimes spoken as if the variations * * * had been due to chance. This of course 

 is a wholly incorrect expression, hut it serves to acknowledge plainly our ignorance of the cause of each 

 particular variation." (Darwin, ' Origin of Species,' 5th edition, p. 165.) 



c2 



Action of 

 Natural Se- 

 lection. 



Inherited 

 habit. 



Change of 

 habits. 



Importance 

 of Natural 

 Selection in 

 modifying 

 habits. 



Definite 

 variations. 



