SUMMARY 297 



those variations which can be so modified as to 

 be in useful relation to the new environmental 

 circumstances are seized upon by natural selection 

 and, being transmitted, form the foundation of 

 a specific inherited response, no longer dependent 

 upon, though operating in close relation with 

 the primitive response whence originally it 

 sprang. Thus the primordial instinct becomes 

 so organised as to serve a secondary purpose, 

 that of rendering secure a means of access to 

 a certain food supply. In the course of evolu- 

 tion species were bound to arise which, owing 

 to some peculiar conditions, derived greater 

 advantage from living solitary than from living 

 in society. Does it then follow, because such 

 species manifest no inclination to live in society, 

 that the instinct never has played any part in 

 their lives ? Or because the primary purpose 

 has lapsed, does it follow that the secondary 

 no longer exists ? 



Let me recapitulate the principal considera- 

 tions which I have discussed in this chapter. 



Though I have been advancing a theory, and 

 though I have taken much for granted, yet it 

 will, I think, be admitted that both the theory 

 and what has been taken for granted rest on 

 observational grounds. As our starting-point 

 we have a bird whose inherited nature alternates 

 according to the season, and in whose nature we 

 can distinguish two contra-phases — the one to 

 live in society, the other to live solitary. While 

 both have their part to play in furthering the 



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