" The Origin of Species " 323 



For the so-called multiple, independently repeated creation of 

 species as an explanation of their very wide and often quite dis- 

 continuous distribution, he substituted colonisation from the nearest 

 and readiest source together with subsequent modification and better 

 adaptation to their new home. 



He was the first seriously to call attention to the many accidental 

 means, "which more properly should be called occasional means of 

 distribution," especially to oceanic islands. His specific, even in- 

 dividual, centres of creation made migrations all the more necessary, 

 but their extent was sadly baulked by the prevailing dogma of the 

 permanency of the oceans. Any number of small changes ("many 

 islands having existed as halting places, of which not a wreck now re- 

 mains 1 ") were conceded freely, but few, if any, great enough to permit 

 migration of truly terrestrial creatures. The only means of getting 

 across the gaps was by the principle of the " flotsam and jetsam," a 

 theory which Darwin took over from Lyell and further elaborated so as 

 to make it applicable to many kinds of plants and animals, but sadly 

 deficient, often grotesque, in the case of most terrestrial creatures. 



Another very fertile source was Darwin's strong insistence upon 

 the great influence which the last glacial epoch must have had upon 

 the distribution of animals and plants. Why was the migration of 

 northern creatures southwards of far-reaching and most significant 

 importance ? More northerners have established themselves in south- 

 ern lands than vice versa, because there is such a great mass of land 

 in the north and greater continents imply greater intensity of selection. 

 " The productions of real islands have everywhere largely yielded to 

 continental forms 2 . "..."The Alpine forms have almost everywhere 

 largely yielded to the more dominant forms generated in the larger 

 areas and more efficient workshops of the North." 



Let us now pass in rapid survey the influence of the publication 

 of The Origin o/Sjjecies upon the study of Geographical Distribution 

 in its wider sense. 



Hitherto the following thought ran through the minds of most 

 writers: Wherever we examine two or more widely separated 

 countries their respective faunas are very different, but where two 

 faunas can come into contact with each other, they intermingle. 

 Consequently these faunas represent centres of creation, whence 

 the component creatures have spread peripherally so far as existing 

 boundaries allowed them to do so. This is of course the funda- 

 mental idea of " regions." There is not one of the numerous writers 

 who considered the possibility that these intermediate belts might 

 represent not a mixture of species but transitional forms, the result of 

 changes undergone by the most peripheral migrants in adaptation to 



1 Tfie Origin of Species (1st edit.), p. 396. 2 Ibid. p. 380. 



21—2 



