BIOLOGY. THE DARWINIAN THEORY. 5 



they clearly state the theory of natural selection, at 

 which they had simultaneously and independently 

 arrived. AVe cannot wonder that Darwin's views 

 should have at first excited great opposition. Never- 

 theless from the first they met with powerful support, 

 especially, in this country, from Hooker, Huxley, and 

 Herbert Spencer. The theory is based on four 

 axioms : 



' 1. That no two animals or plants in nature are 

 identical in all respects. 



' 2. That the offspring tend to inherit the peculiar- 

 ities of their parents. 



' 3. That of those which come into existence, only a 

 small number reach maturity. 



' 4. That those, which are, on the whole, best 

 adapted to the circumstances in which they are placed, 

 are most likely to leave descendants.' 



Darwin commenced his work by discussing the 

 causes and extent of variability in animals, and the 

 origin of domestic varieties ; he showed the impossibility 

 of distinguishing between varieties and species, and 

 pointed out the wide differences which man has pro- 

 duced in some cases as, for instance, in our domestic 

 pigeons, all unquestionably descended from a com- 

 mon stock. He dwelt on the struggle for existence 

 (since become a household wor/d), which, inevitably 

 resulting in the survival of the fittest, tends gradually 

 to adapt any race of animals to the conditions in which 

 it occurs. 



While thus, however, showing the great importance 

 of natural selection, he attributed to it no exclusive in- 

 fluence, but fully admitted that other causes the use 



