Chap. Y.] ANALOGOUS VARIATIONS. 205 



a common parent — are more variable 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 charac- 

 ters differ much in the species of the same group. 

 Variability in the same parts of the organisation 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 species of the 

 same genus. Any part or organ developed to an 

 extraordinary size or in an extraordinary manner, 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 

 selection will in such cases not as yet have had time to 

 overcome the tendency to further variability and to 

 reversion 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 



