364 THE GROWTH OF THE 'ORIGIN OF SPECIES.' 



a part in the great scheme of nature, one is apt to wonder 

 why a distinct species should have been created." 



A comparison of the two editions of the 'Journal' is in- 

 structive, as giving some idea of the development of his views 

 on evolution. It does not give us a true index of the mass 

 of conjecture which was taking shape in his mind, but it 

 shows us that he felt sure enough of the truth of his belief 

 to allow a stronger tinge of evolution to appear in the second 

 edition. He has mentioned in the Autobiography (p. 68) 

 that it was not until he read Malthus that he got a clear view 

 of the potency of natural selection. This was in 1838 — a 

 year after he finished the first edition (it was not published 

 until 1839), and five years before the second edition was 

 written (1845). Thus the turning-point in the formation of 

 his theory took place between the writing of the two editions. 



I will first give a few passages which are practically the 

 same in the two editions, and which are, therefore, chiefly of 

 interest as illustrating his frame of mind in 1837. 



The case of the two species of Molothrus (1st edit. p. 61 ; 

 2nd edit. p. 53) must have been one of the earliest instances 

 noticed by him of the existence of representative species— a 

 phenomenon which we know (' Autobiography,' p. 68) struck 

 him deeply. The discussion on introduced animals (1st edit. 

 p. 139; 2nd edit. p. 120) shows how much he was impressed 

 by the complicated interdependence of the inhabitants of a 

 given area. 



An analogous point of view is given in the discussion (1st 

 edit. p. 98 ; 2nd edit. p. 85) of the mistaken belief that large 

 animals require, for their support, a luxuriant vegetation ; the 

 incorrectness of this view is illustrated by the comparison of 

 the fauna of South Africa and South America, and the vege- 

 tation of the two continents. The interest of the discussion 

 is that it shows clearly our a priori ignorance of the condi- 

 tions of life suitable to any organism. 



There is a passage which has been more than once quoted 

 as bearing on the origin of his views. It is where he dis- 

 cusses the striking difference between the species of mice on 



