158 DISTINCT SPECIES PRESENT Chap. V. 



species, ihan of generic characters, or those which the species 

 possess in roinmon ; that the frequent extreme variability of 

 any part which is developed in a species in an extraordinary 

 manner in comparison with the same part in its congeners ; 

 and the slight degree of variability in a part, however extraor- 

 dinarily it may be developed, if it be common to a whole group 

 of species ; that the great variability of secondarj' sexual char- 

 acters, and the great amount of difference in these same char- 

 acters between closely-allied species ; that secondary sexual 

 and ordinary specific differences are generally displayed in the 

 same parts of the organization — are all principles closely con- 

 nected together. All being mainly due to the species of the 

 same group having descended from a common progenitor, from 

 whom they have inherited much in common — to parts whicli 

 have recently and largely varied being more likely still to go 

 on varying than parts which have long been inherited and 

 have not varied — to natural selection having more or less com- 

 pletely, according to the lapse of time, overmastered the ten- 

 dency to reversion and to further variability — to sexual selec- 

 tion being less rigid than orchnary selection — and to variations 

 in the same parts having been accumulated by natural and 

 sexual selection, and having been thus adapted for secondary 

 sexual, and for ordinary purposes. 



Distinct Species present analogous Variations ; and a Variety 

 of one Species often assumes some of the Characters of an 

 allied Species, or reverts to soyne of the Characters of an 

 early Progenitor. 



These propositions will be most readily understood by look- 

 ing to our domestic races. The most distinct breeds of pigeons, 

 in countries most widely apart, present sub-varieties with re- 

 versed feathers on the head and feathers on the feet — charac- 

 ters not possessed by the aboriginal rock-pigeon ; these, then, 

 are analogous variations in two or more distinct races. The 

 frequent presence of fourteen or even sixteen tail-feathers in the 

 pouter may be considered as a variation representing the nor- 

 mal structure of another race, the fantail. I presume that no 

 one will doubt that all such analogous variations are due to the 

 several races of the pigeon having inherited from a common 

 ]>arent the same constitution and tendency to variation, when 

 acted on bv similar unknown influences. In the vegetable 

 kingdom we have a case of analogous variation in the enlarged 



