CHAPTER VI. 



THE DOCTRINE OF DESCENT. 



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

 and animals that we know have come 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 at once 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. According to another, 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. Of such cataclysms there is no 

 evidence, and if it be enough to postulate one creation, we 

 need not assume a dozen. 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). Yet 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, 



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