324 Geographical Distribution of Animals 



tlieir new surroundings. The usual standpoint was also that of 

 Pucheran^ in 1855. But what a change within the next ten years ! 

 Pucheran explains the agreement in coloration between the desert 

 and its fauna as "une harmonic post-^tablie " ; the Sahara, formerly a 

 marine basin, was peopled by immigrants from the neighbouring 

 countries, and these new animals adapted themselves to the new 

 environment. He also discusses, among other similar questions, 

 the Isthmus of Panama with regard to its having once been a strait. 

 From the same author may be quoted the following passage as a 

 strong proof of the new influence : " By the radiation of the con- 

 temporaneous faunas, each from one centre, whence as the various 

 parts of the world successively were formed and became habitable, 

 they spread and became modified according to the local physical 

 conditions." 



The " multiple " origin of each species as advocated by Sclater 

 and Murray, although giving the species a broader basis, suftered 

 from the same difficulties. There was only one alternative to the 

 old orthodox view of independent creation, namely the bold accept- 

 ance of land-connections to an extent for wliich geological and 

 palaeontological science was not yet ripe. Those who shrank from 

 either view, gave up the problem as mysterious and beyond the 

 human intellect. This was the expressed opinion of men like 

 Swainson, Lyell and Humboldt. Only Darwin had the courage to 

 say that the problem was not insoluble. If we admit "that in the 

 long course of time the individuals of the same species, and likewise 

 of allied species, have proceeded from some one source ; then I think 

 all the grand leading facts of geographical distribution are explicable 

 on the theory of migration. . .together with subsequent modifica- 

 tion and the multiplication of new forms." We can thus under- 

 stand how it is that in some countries the inhabitants "are linked 

 to the extinct beings which formerly inhabited the same continent." 

 We can see why two areas, having nearly the same physical 

 conditions, should often be inhabited by very different forms of 

 life,... and "we can see why in two areas, however distant from 

 each other, there should be a correlation, in the presence of iden- 

 tical species... and of distinct but representative species^." 



Darwin's reluctance to assume great geological changes, such as 

 a land-connection of Europe with North America, is easily explained 

 by the fact that he restricted himself to the distribution of the 

 present and comparatively recent species. " I do not believe that it 

 will ever be proved that within the recent period continents which 



1 " Note sur I'dquateur zoologique," Rev. et Mag. de Zoologie, ItfoS ; also several 

 other papers, ibid. 1865, 1866, and 1867. 



2 The Origin of Species (1st edit.), pp. 408, 409. 



