378 EVOLUTION [Chap. V 



Letter 288 descent. Now it seems to mc improbable in the highest 

 degree that a species should ever have been exposed in two 

 places to infinitely complex relations of exactly the same 

 nature during a long series of modifications. An illustration 

 will perhaps make what I have said clearer, though it applies 

 only to the less important factors of inheritance and varia- 

 bility, and not to adaptation — viz., the improbability of two 

 men being born in two countries identical in body and mind. 

 If, however, it be assumed that a species at each successive 

 stage of its modification was surrounded in two distinct 

 countries or times, by exactly the same assemblage of plants 

 and animals, and by the same physical conditions, then I can 

 see no theoretical difficulty [in] such a species giving birth to 

 the new form in the two countries. If you will look to the 

 sixth edition of my Origin, at p. 100, you will find a some- 

 what analogous discussion, perhaps more intelligible than this 

 letter. 



Letter 289 W. T. Thiselton-Dyer to the Editor of Nature. 



The following letter {Nature, Vol. XLIII., p. 535) criticises the inter- 

 pretation given by the Duke to Mr. Darwin's letter. 



Royal Gardens, Kew, March 27th [1891]. 



In Nature of March 5th (p. 415), the Duke of Argyll has 

 printed a very interesting letter of Mr. Darwin's, from which 

 he drew the inference that the writer "assumed mankind to 

 have arisen ... in a single pair." I do not think myself 

 that the letter bears this interpretation. But the point in its 

 most general aspect is a very important one, and is often 

 found to present some difficulty to students of Mr. Darwin's 

 writings. 



Quite recently I have found by accident, amongst the 

 papers of the late Mr. Bentham at Kew, a letter of friendly 

 criticism from Mr. Darwin upon the presidential address 

 which Mr. Bentham delivered to the Linnean Society on 

 May 24th, 1869. This letter, I think, has been overlooked 

 and not published previously. In it Mr. Darwin expresses 

 himself with regard to the multiple origin of races and 

 some other points in very explicit language. Prof. Mcldola, 

 to whom I mentioned in conversation the existence of the 

 letter, urged mc stnmgly to print it. This, therefore, I now 

 do, with the addition of a few explanatory notes. 



