Chap, v.] ANALOGOUS VARIATIONS. 205 



ble than generic characters, or those which have long 

 been inherited, and have not differed within this same 

 period. In these remarks we have referred to special 

 parts or organs being still variable, because they have 

 recently varied and thus come to differ; but we have 

 also seen in the second chapter that the same principle 

 applies to the whole individual; for in a district where 

 many species of a genus are found — that is, where there 

 has been much former variation and differentiation, 

 or where the manufactory of new specific forms has 

 been actively at work — in that district and amongst 

 these species, we now find, on an average, most varieties. 

 Secondary sexual characters are highly variable, and 

 such characters differ much in the species of the same 

 group. Variability in the same parts of the organisa- 

 tion has generally been taken advantage of in giving 

 secondary sexual differences to the two sexes of the 

 same species, and specific differences to the several spe- 

 cies of the same genus. Any part or organ developed 

 to an extraordinary size or in an extraordinary man- 

 ner, in comparison with the same part or organ in the 

 allied species, must have gone through an extraordinary 

 amount of modification since the genus arose; and thus 

 we can understand why it should often still be variable 

 in a much higher degree than other parts; for variation 

 is a long-continued and slow process, and natural selec- 

 tion will in such cases not as yet have had time to over- 

 come the. tendency to further variability and to rever- 

 sion to a less modified state. But when a species with 

 any extraordinarily-developed organ has become the 

 parent of many modified descendants — which on our 

 view must be a very slow process, requiring a long lapse 

 of time — ^in this case, natural selection has succeeded 



