200 GEOEGE JOHN EOMANES I88I- 



principle you have sought to test it. Pray read the 

 passages referred to, which present the shortest 

 summary of what I regard as the very backbone of 

 my evidence. 



If your large knowledge of geographical distribu- 

 tion should enable you to supply me with specific 

 cases of the general principle mentioned by Darwin in 

 the quotation given on page 392 (' Origin of Species,' 

 6th ed., pp. 134-5), I should much like to try experi- 

 ments on the sterihty which I should expect to find 

 between these interlocking species. 



It seems comical to ask a scientific opponent for 

 assistance, but the fact of being able to do so 

 proves the superiority of science to poHtics. 



December 25, 1888. 



It is very good of you to write such a long and 

 suggestive letter. 



As a result of attentively reading your letter, it 

 appears to me that you think I suppose sterihty in a 

 high degree to be much more usual among alhed 

 species than I do suppose it. I well know the large 

 amount of natural as well as artificial hybridisation 

 that goes on. But, on the other hand, there are so 

 many species which either will not cross at aU, or 

 produce sterile hybrids, that, taking a general view 

 of all species together, mutual sterility does become 

 by far the most generally distributed single pecuharity 

 — i.e. is the one peculiarity which, more than any 

 other that can be named, is common to numberless 

 species. 



Thus much for mutual sterihty that is absolute, 



