160 'DESCENT OF MAN 'EXPRESSION. [1872. 



on my father's views on the action of isolation as regards the 

 origin of new species :] 



C. Darwin to K. Semper. 



Down, November 26, 1878. 



MY DEAR PROFESSOR SEMPER, When I published the 

 sixth edition of the ' Origin/ I thought a good deal on the 

 subject to which you refer, and the opinion therein expressed 

 was my deliberate conviction. I went as far as I could, 

 perhaps too far, in agreement with Wagner ; since that time I 

 have seen no reason to change my mind, but then I must add 

 that my attention has been absorbed on other subjects. 

 There are two different classes of cases, as it appears to me, 

 viz. those in which a species becomes slowly modified in the 

 same country (of which I cannot doubt there are innumerable 

 instances) and those cases in which a species splits into two 

 or three or more new species ; and in the latter case, I should 

 think nearly perfect separation would greatly aid in their 

 " specification," to coin a new word. 



I am very glad that you are taking up this subject, for you 

 will be sure to throw much light on it. I remember well, 

 long ago, oscillating much ; when I thought of the Fauna and 

 Flora of the Galapagos Islands I was all for isolation, when I 

 thought of S. America I doubted much. Pray believe me, 



Yours very sincerely, 



CH. DARWIN. 



P.S. I hope that this letter will not be quite illegible, 

 but I have no amanuensis at present. 



C. Darwin to K. Semper. 



Down, November 30, 1878. 



DEAR PROFESSOR SEMPER, Since writing I have recalled 

 some of the thoughts and conclusions which have passed 



