chap. v. Analogous Variations. _____ J^7 



sively due to analogous variation would probably be of an unim- 

 portant nature, for the preservation of all functionally important 

 characters will have been determined through natural selection, m 

 accordance with the different habits of the species. It might 

 further be expected that the species of the same genus would occa- 

 sionally exhibit reversions to long lost characters. As, however, 

 we do not know the common ancestor of any natural group, we 

 cannot distinguish between reversionary and analogous characters. 

 If, for instance, we did not know that the parent rock-pigeon was 

 not feather-footed or turn-crowned, we could not have told, whether 

 such characters in our domestic breeds were reversions or only 

 analogous variations ; but we might have inferred that the blue 

 colour was a case of reversion from the number of the markings, 

 which are correlated with this tint, and which would not probably 

 have all appeared together from simple variation. More especially 

 we might have inferred this, from the blue colour and the several 

 marks so often appearing when differently coloured breeds are 

 crossed. Hence, although under nature it must generally be left 

 doubtful, what cases are reversions to formerly existing characters, 

 and what are new but analogous variations, yet we ought, on our 

 theory, sometimes to find the varying offspring of a species assuming 

 characters which are already present in other members of the same 

 group. And this undoubtedly is the case. 



The difficulty in distinguishing variable species is largely due to 

 the varieties mocking, as it were, other species of the same genus. 

 A considerable catalogue, also, could be given of forms intermediate 

 between two other forms, which themselves can only doubtfully be 

 ranked as species ; and this shows, unless all these closely allied 

 forms be considered as independently created species, that they 

 have m varying assumed some of the characters of the others. But 

 the best evidence of analogous variations is afforded by parts or 

 oigans which are generally constant in character, but which occa- 

 sionally vary so as to resemble, in some degree, the same part or 

 «S? w 8 ? aUied Spedes - l have collected a long list of such 

 W i!i ^ re • aS 1 T fore ' * He Under the § reat disadvantage of not 



tZlal g T them ' J Can ° nl ? re P eat that s ™ h cases cer- 

 tainly occur, and seem to me very remarkable. 



affectin ' *Z*™' ^ ° ne CUri ° US and com P lex ca ^ not indeed as 

 ^&T imP ° rtant CharaCter ' but from occ ™ in S in *™ml 

 under nature T" genils ' P ar % ™^ domestication and partly 

 sometimes h<is vt£ I ^^ almost certai ^y of reversion. The ass 



on the liSX^v^T 1 ™ 8 ^ ° n ^ ^ ^ th0SG 

 zebra . it has been asserted that these are plainest 



