EVIDENCES OF ORGANIC EVOLUTION 33 
that, for instance, in the hand of a man, the paw of a 
dog, the wing of a bat, and the paddle of a whale, 
almost identically the same series of bones can be 
traced. An obvious explanation is to be found in the 
supposition that these parts have arisen by the 
divergent modification of parts which were originally 
identical. 
4. GEOGRAPHICAL DISTRIBUTION. — Observation 
shows that groups of closely allied creatures are often 
found living in neighbouring districts, and that when 
such a barrier as an ocean or a range of lofty moun- 
tains is passed an entirely new fauna and flora are 
usually to be met with. These facts may be explained 
by the hypothesis that allied groups of species origi- 
nated by a process of descent in the same countries 
which they now inhabit, and they can be explained 
by no other known hypothesis. The alternative sup- 
position that each species was specially created and 
placed in the locality in which it was best adapted 
to dwell is singularly in disagreement with the well- 
known facts that animals and plants transported into 
entirely new regions often thrive better than in their 
original homes. The examples of rabbits in Australia 
and of cardoons and thistles on the Pampas of La 
Plata are familiar to all from the writings of Darwin. 
5. THE GEOLOGICAL SUCCESSION OF ORGANISMS.— 
The general facts regarding the distribution of allied 
species of animals and plants in time point in pre- 
cisely the same direction as those relating to their 
distribution in space. In a few cases, notably in that 
of the extinct horse of North America, a long chain of 
3 
