THEORIES OF EVOLUTION 153 



development (1852) and by other writers. The times 

 were more favorable for launching the great idea of 

 evolution. But the wide currency which the idea 

 immediately attained was chiefly owing to Darwin's 

 exposition of the idea of natural selection. He 

 designated explicitly a natural cause for the changes 

 in animals that had heretofore been so perplexing. 

 Even the masses could understand his argument. 

 The character of his first publication (Origin of 

 Species, 1859) was also such as to attract attention 

 and secure respect. He had been at work on his 

 theory, experimenting and observing, for more than 

 twenty years, and his publication showed that 

 quality of thoroughness, fairness and ripeness that 

 commanded consideration. 



Among those who assisted in the spread of the 

 Darwinian theory amongst English-speaking people, 

 Thomas Henry Huxley (Fig. 31) stood preeminent. 

 Darwin was of pacific disposition while Huxley was 

 aggressive and both ready and forceful in public 

 debate. He became the recognized champion of the 

 theory of descent, and vigorously and effectively de- 

 fended it against attack. 



It is an interesting circumstance that Alfred Rus- 

 sell Wallace (1823-1913), by a flash of insight, had 



