Alfred Russel Wallace 



forms of the germs of life. But there is no such difference, 

 the primitive germ -cells of man, fish or oyster being almost 

 indistinguishable, formed of identical matter and going 

 through identical primitive changes. 



As to the humming-bird and hippopotamus, there is no 

 doubt whatever of a common origin — if evolution is accepted 

 at all; since both are vertebrates — a very high type of 

 organism whose ancestral forms can be traced back to a 

 simple type much earlier than the common origin of mam- 

 mals, birds and reptiles. — Yours very truly, 



Alfred R. Wallace. 

 To Sir Francis Darwin 



Parkstone, Dorset. July 3, 1901. 



Dear Mr. Darwin, — Thanks for the letter returned. I do 

 hold the opinion expressed in the last sentence of the article 

 you refer to, and have reprinted it in my volume of Studies, 

 etc. But the stress must be laid on the w^ord proof. I in- 

 tended it to enforce the somewhat similar opinion of your 

 father, in the " Origin " (p. 424, 6th Edit.), where he says, 

 " Analogy may be a deceitful guide.'* But I really do not 

 go so far as he did. For he maintained that there was not 

 any proof that the several great classes or kingdoms were 

 descended from common ancestors. 



I maintain, on the contrary, that all without exception 

 are now proved to have originated by '' descent with modi- 

 fication," but that there is no proof, and no necessity, that 

 the very same causes which have been suflftcient to produce 

 all the species of a genus or Order were those which initiated 

 and developed the greater differences. At the same time I 

 do not say they were not sufficient. I merely urge that 

 there is a difference between proof and probability. — Yours 

 very truly, Alfred R. Wallace. 



TO 



