388 SPREAD OF EVOLUTION. [1862. 



wingless birds had lost their wings by disuse, also that 

 magpies stole spoons, &c., from a remnant of some instinct 

 like that of the Bower-Bird, which ornaments its playing- 

 passage with pretty feathers. Indeed, I am told that he 

 hinted plainly that all birds are descended from one .... 



Your P.S. touches on, as it seems to me, very difficult 

 points. I am glad to see [that] in the ' Origin,' I only say 

 that the naturalists generally consider that low organisms 

 vary more than high ; and this I think certainly is the 

 general opinion. I put the statement this way to show that 

 I considered it only an opinion probably true. I must own 

 that I do not at all trust even Hooker's contrary opinion, as 

 I feel pretty sure that he has not tabulated any result. I 

 have some materials at home, I think I attempted to make 

 this point out, but cannot remember the result. 



Mere variability, though the necessary foundation of all 

 modifications, I believe to be almost always present, enough 

 to allow of any amount of selected change ; so that it does 

 not seem to me at all incompatible that a group which at any 

 one period (or during all successive periods) varies less, should 

 in the long course of time have undergone more modification 

 than a group which is generally more variable. 



Placental animals, e.g. might be at each period less variable 

 than Marsupials, and nevertheless have undergone more 

 differentiation and development than marsupials, owing to 

 some advantage, probably brain development. 



I am surprised, but do not pretend to form an opinion at 

 Hooker's statement that higher species, genera, &c, are best 

 limited. It seems to me a bold statement. 



Looking to the ' Origin,' I see that I state that the pro- 

 ductions of the land seem to change quicker than those of 

 the sea (Chapter X., p. 339, 3rd edition), and I add there is 

 some reason to believe that organisms considered high in the 

 scale change quicker than those that are low. I remember 

 writing these sentences after much deliberation I 



