250 APPENDIX A 



was not unwilling to contemplate multiple 

 centres with a vengeance ; for he put forward 

 as a difficulty the fact that mammals had not 

 arisen independently on oceanic islands. Refer- 

 ring to this point, Darwin wrote to him (Sept- 

 ember 1, 1860) as follows : 



' With respect to a mammal not being developed on any 

 island, besides want of time for so prodigious a development, 

 there must have arrived on the island the necessary and 

 peculiar progenitor, having a character like the embryo of 

 a mammal ; and not an already developed reptile, bird or 

 fish. We might give to a bird the habits of a mammal, but 

 inheritance would retain almost for eternity some of the 

 bird-like structure, and prevent a new creature ranking 

 as a true mammal.' 1 



Lyell does not appear to have been convinced 

 by the argument, and Darwin wrote again on 

 September 23, 1860 : 



' I have a very decided opinion that all mammals must 

 have decended from a single parent [species]. Reflect on the 

 multitude of details, veiy many of them of extremely little 

 importance to their habits (as the number of bones of the 

 head, &c., covering of hair, identical embryological develop- 

 ment, &c. &c.). Now this large amount of similarity I must 

 look at as certainly due to inheritance from a common stock. 

 I am aware that some cases occur in which a similar or 

 nearly similar organ has been acquired by independent acts 

 of natural selection. But in most of such .cases of these 

 apparently so closely similar organs, some important homo- 

 logical difference may be detected. '* 



Lyell had argued that, just as man would now 

 keep down any new man that might be developed, 

 so the bats and rodents of oceanic islands may 



1 Life and Letters, ii. 335. 2 1. c., ii. 341. 



