Alfred Russel Wallace 



Hurstpierpomt. [?] April 8, 1868. 



Dear Darwin, — I am sorry you should have given your- 

 self the trouble to answer my ideas on Sterility. If you 

 are not convinced, I have little doubt but that I am 

 wrong; and in fact I was only Jialf convinced by my own 

 arguments, and I now think there is about an even chance 

 that Natural Selection may or not be able to accumulate 

 sterility. If my first proposition is modified to the exist- 

 ence of a species and a variety in the same area, it will 

 do just as well for my argument. Such certainly do 

 exist. They are fertile together, and yet each maintains 

 itself tolerably distinct. How can this be, if there is no 

 disinclination to crossing ? My belief certainly is that 

 number of offspring is not so important an element in 

 keeping up population of a species as supply of food and 

 other favourable conditions, because the numbers of a 

 species constantly vary greatly in different parts of its 

 area, whereas the average number of offspring is not a 

 very variable element. 



However, I will say no more but leave the problem aa 

 insoluble, only fearing that it will become a formidable 

 weapon in the hands of the enemies of Natural Selection. 



While writing a few pages on the northern alpine 

 forms of plants on the Java mountains I wanted a few 

 cases to refer to like Teneriffe, where there are no northern 

 forms, and scarcely any alpine. I expected the volcanoes 

 of Hawaii would be a good case, and asked Dr. Seeman 

 about them. It seems a man has lately published a list of 

 Hawaiian plants, and the mountains swarm with European 

 alpine genera and some species!* Is not this most extra- 

 ordinary and a puzzler ? They are, I believe, truly oceanic 



^ " This turns out to be inaccurate, or greatly exaggerated. There are no 

 true alpines, and the European genera are comparatively few. See my ' Island 

 Life/ p. 323."— A. R. W. 



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