18 EVOLUTION 



island contained more than one race or 

 species." The same is true of the tortoises 

 and the birds, and no scientific interpretation 

 has been suggested except that which Dar- 

 win gave of divergent evolution from a 

 common stock. 



We cannot here enter into a discussion of 

 the geological history of the Galapagos Isl- 

 ands, in regard to which there is some differ- 

 ence of opinion; it must suffice to state one 

 of the theories that advanced by Baur in 

 the Woods Holl Biological Lectures for 1894. 

 "At a former period these islands were con- 

 nected with each other, forming a single 

 large island, which itself at a still earlier 

 time was united with the continent, probably 

 with Central America and the West Indies. 

 When this large island was not yet broken up 

 into a series of smaller islands, the number of 

 species must have been very much smaller; 

 probably there was only one species of Neso- 

 mimus, of Certhidia, of Tropidurus, of the 

 Land Tortoise, and so on. Through isola- 

 tion into single islands the peculiar differen- 

 tiation of the species began; an originally 

 single species was differentiated in many 

 different forms; every, or nearly every, 

 island developed its peculiar races. We still 

 see to-day that islands which are close to- 

 gether and not separated by deep water show 



