324 Geographical Distribution of Animals 
their 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 harmonie post-établie”; the Sahara, formerly a 
_mImarine 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, suffered 
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 which 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. “Ido not believe that it 
will ever be proved that within the recent period continents which 
1 “Note sur Péquateur zoologique,” Rev. et Mag. de Zoologie, 1855; also several 
other papers, ibid. 1865, 1866, and 1867, 
2 The Origin of Species (1st edit.), pp. 408, 409. 
