I 
ON THE LAW WHICH HAS REGULATED THE INTRODUCTION 
OF NEW SPECIES 1 
Geographical Distribution dependent on Geologic Changes 
Every naturalist who has directed his attention to the subject 
of the geographical distribution of animals and plants must 
have been interested in the singular facts which it presents. 
Many of these facts are quite different from what would have 
been anticipated, and have hitherto been considered as highly 
curious, but quite inexplicable. None of the explanations 
attempted from the time of Linnseus are now considered at 
all satisfactory ; none of them have given a cause sufficient 
to account for the facts known at the time, or comprehensive 
enough to include all the new facts which have since been, 
and are daily being, added. Of late years, however, a great 
light has been thrown upon the subject by geological investi- 
gations, which have shown that the present state of the earth 
and of the organisms now inhabiting it is but the last stage 
of a long and uninterrupted series of changes which it has 
undergone, and consequently, that to endeavour to explain 
and account for its present condition without any reference 
to those changes (as has frequently been done) must lead to 
very imperfect and erroneous conclusions. 
The facts proved by geology are briefly these : That 
1 This article, written at Sarawak in February 1855 and published in the 
Annals and Magazine of Natural History , September 1855, was intended to 
show that some form of evolution of one species from another was needed in 
order to explain the various classes of facts here indicated ; but at that time 
no means had been suggested by which the actual change of species could 
have been brought about. 
