524 



EVOLUTION OF BIRDS 



xviii. 8- 



viduals whose constitution differs from the mean of the race, enabling 

 them to pioneer. It is not certain to what extent individual birds are 

 able to 'adapt themselves' in this way to new habitats. Probably the 

 majority of the members of any population are limited by their 

 structure and behaviour pattern to a rather narrow habitat range. 



9. Darwin's finches 



A remarkable example of evolution and adaptive radiation is pro- 

 vided by the birds of the Galapagos Islands. It was these birds and 



90°W 



85 W 



80 W 



90 W 



85 W 



80 U W 



Fig. 311. Position of the Galapagos Islands. (From Lack, Darwin's Finches, 

 Cambridge University Press.) 



the giant tortoises (after which the islands are named) that started 

 Darwin on his study of evolution. 'In July opened first note-book on 

 "Transmutation of Species". Had been greatly struck from about 

 month of previous March on character of S. American fossils — and 

 species on Galapagos Archipelago — These facts origin (especially 

 latter) of all my views' (Darwin's Diary 1837). 



These islands are volcanic and probably of Tertiary ( ? Miocene) 

 date. They lie on the equator, 600 miles west of Ecuador, the only 

 other nearby land being the island of Cocos, 600 miles north-west 

 (Fig. 311). Though it has been suggested that the islands were con- 



