46 FIFTY YEARS OF DARWINISM 



p. 123, n. 2), while he interpreted the poverty of 

 the Greenland flora and the reappearance of north 

 temperate species in the southern part of South 

 America as results of the same cause. Almost 

 as soon as the facts were before him in Wol- 

 laston's memoirs, Darwin had interpreted the 

 number of wingless beetles in oceanic islands 

 as due to the special dangers of flight. He 

 anticipated H. W. Bates' hypothesis of Mimicry, 

 but drove it from his mind because he did not 

 feel confident about the geographical coincidence 

 of model and mimic (see pp. 123, 124). Long 

 before the Origin appeared, Darwin had thought 

 over and rejected the idea that the same species 

 could have more than a single origin, or could 

 arise independently in two different countries — 

 a hypothesis very popular in later years, but, 

 I believe, now entirely abandoned (see Appendix 

 A, p. 247). 



I should wish to advance one further con- 

 sideration before concluding this section of my 

 address. Certain writers on mutation seem to 

 hold the view that Natural Selection alone pre- 

 vents large variations from often holding the 

 field and leading on to great and rapid changes of 

 species. Such a view is not supported by the 

 history of species which inhabit situations com- 

 paratively sheltered from the struggle, such as 

 fresh water, caves, certain islands, or the depths 

 of the ocean. Organisms in these places tend to 

 preserve their ancestral structure more persis- 



