“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’”) 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 versd, 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?.”...“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 of Species 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 The Origin of Species (1st edit.), p. 896. 2 Ibid. p. 380. 
21—2 
