384 EVOLUTION [Chap.V 



Letter 295 in the upraised shells of Coquimbo, in Chili, as mentioned in 

 my Geological Observations on South America. 



Of all the wonders in the world, the progress of Japan, in 

 which you have been aiding, seems to me about the most 

 wonderful. 



Letter 296 To A. R. Wallace. 



Down, Jan. 5th, 1880. 



As this note requires no sort of answer, you must allow 

 me to express my lively admiration of your paper in the 

 Nineteenth Century} You certainly arc a master in the 

 difficult art of clear exposition. It is impossible to urge too 

 often that the selection from a single varying individual or 

 of a single varying organ will not suffice. You have worked 

 in capitally Allen's - admirable researches. As usual, you 

 delight to honour me more than I deserve. When I have 

 written about the extreme slowness of Natural Selection 3 (in 

 which I hope I may be wrong), I have chiefly had in my 

 mind the effects of intercrossing. I subscribe to almost 

 everything you say excepting the last short sentence. 4 



1 Nineteenth Century, Jan. 1SS0, p. 93, "On the Origin of Species 

 and Genera." 



2 J. A. Allen, " On the Mammals and Winter Birds of East Florida, 

 etc." {Bull. Mus. Coiup. Zoolog. Harvard, Vol. II.) 



3 Mr. Wallace makes a calculation based on Allen's results as to the 

 very short period in which the formation of a race of birds differing 

 10 to 20 per cent, from the average in length of wing and strength of 

 beak might conceivably be effected. He thinks that the slowness of the 

 action of Natural Selection really depends on the slowness of the changes 

 naturally occurring in the physical conditions, etc. 



4 The passage in question is as follows : " I have also attempted to 

 show that the causes which have produced the separate species of one 

 genus, of one family, or perhaps of one order, from a common ancestor, 

 are not necessarily the same as those which have produced the separate 

 orders, classes, and sub-kingdoms from more remote common ancestors. 

 That all have been alike produced by ' descent with modification ' from 

 a few primitive types, the whole body of evidence clearly indicates ; 

 but while individual variation with Natuial Selection is proved to be 

 adequate for the production of the former, we have no proof and hardly 

 any evidence that it is adequate to initiate those important divergences 

 of type which characterise the latter." In this passage stress should be 

 laid (as Mr. Wallace points out to us) on the word proof. He by no 

 means asserts that the causes which have produced the species of a 

 genus are inadequate to produce greater differences. His object is 

 rather to urge the difference between proof and probability. 



