CHAPTER VII. 



THE EVOLUTION OF ANIMALS. 

 (Etiology.) 



I. The Doctrine of Descent. 



When we ask, as we are bound to ask, how the living plants 

 and animals that we know came to be what they are — very 

 numerous, very diverse, very beautiful, marvellous in their 

 adaptations, harmonious in their parts and qualities, and 

 approximately stable from generation to generation, — we may 

 possibly receive three answers. According to one, the plants 

 and animals that we know have always been as they are ; but 

 this is obviously contradicted by the record in the rocks, 

 which contain the remains of successive sets of plants and 

 animals very different from those which now live upon the 

 earth. By another, it is supposed that each successive fauna 

 and flora was destroyed by mundane cataclysms, to be 

 replaced in due season by new creations, by new forms of 

 life which arose after a fashion of which the human mind 

 can form no conception. The third answer is, that the 

 present is the child of the past in all things, that the plants 

 and animals now existing arose by a natural evolution from 

 simpler pre-existing forms of life, these from still simpler, and 

 so on back to a simplicity of life such as that now represented 

 by the very lowest organisms. 



This third theory is really an old one ; it is merely man's 

 application of his idea of human history to the world around 

 him. It was maintained with much concreteness and 

 power by Buffon (1749), by Erasmus Darwin (1794), and 

 by Lamarck (1801). But in spite of the labours of these 

 thoughtful naturalists and of many others, the general idea of 

 the natural descent of organisms from simpler ancestors, 



