SCIENCE AND TRAVEL 211 



variation of plants and animals, wild or domesticated, 

 light might be thrown on the whole subject. " I 

 worked on true Baconian principles, and, without 

 any theory, collected facts on a wholesale scale." He 

 saw that pigeon-fanciers and stock-breeders develop 

 certain types by preserving those variations that have 

 the desired characteristics. This is a process of arti- 

 ficial selection. How is selection made by Nature ? 



In 1838 he read Malthus' Essay on the Prin- 

 ciple of Population, which showed how great and 

 rapid, without checks like war and disease, the in- 

 crease in number of the human race would be. He 

 had seen something in his travels of rivalry for 

 the means of subsistence. He now perceived " that 

 under these circumstances favorable variations would 

 tend to be preserved, and unfavorable ones to be de- 

 stroyed. The results of this would be the formation 

 of a new species." As special breeds are developed by 

 artificial selection, so new species evolve by a process 

 of natural selection. Those genera survive which give 

 rise to species adapted to new conditions of exist- 

 ence. 



In 1858, before Darwin had published his theory, 

 lie received from another great traveler, Alfred 

 Russel Wallace, then at Ternate in the Moluccas, a 

 manuscript essay, setting forth an almost identical 

 view of the development of new species through the 

 survival of the fittest in the struggle for existence. 



