GENERAL OBSERVATIONS. 1033 



life," the clb-ect effects of struggle or labor on the individual, that is, the 

 beneficial and other effects of struggle itself, are not intended, though not 

 excluded; only the effects of struggle or strife on disappearings and sur- 

 vivals, under the changing conditions, are referred to. 



Augmentation of variations by interbreeding fundamental in evolution. — 

 Man, by selective breeding carried on for successive generations, has obtained 

 cattle with long horns, short horns, and no horns ; fowls with large combs 

 on the head, with no combs, or with a rosette of feathers in place of the 

 crested comb, with bare legs and with feathered legs, with long spurs and long 

 legs for fighting, and with no spurs and short legs, and with great diversity 

 of color; Pigeons with long bills and with short bills, giving them characters 

 belonging to different tribes of Birds, with long or short legs, with the fan- 

 like tail of a Peacock and an attendant increase in the number of feathers. 

 And, similarly, diversity has been obtained in the case of many other species. 

 The varieties obtained range through a vastly wider diversity of characters 

 than occurs under any species in nature. 



It is perceived that the law of nature here exemplified is not "like 

 produces like," but like ivith an increment or some addition to the variation. 

 Consequently, the law of nature, as regards the kingdoms of life, is not 

 permanence, but change, evolution. 



Great plasticity in organic structures under variant agencies. — This is 

 another principle taught by the above-mentioned facts. This plasticity 

 under any type is usually most prominent in one or two of the kinds of 

 organs, and consequently it leads to the evolution of species in lines, deter- 

 mining genera or natural groups. 



" A tendency upward," determined, in the Animal Kingdom, by the existence 

 of a cephalic nervous mass or brain. — This principle is explained on page 

 439. 



Articidates and Vertebrates first appear as midtiplicate species : as exem- 

 plified in Worms, the earliest Crustaceans, and Fishes, and in the Myriapods, 

 successors to the Worms. Through subsequent changes, types having a 

 definite or normal number of parts are introduced, as Insects after Myria- 

 pods (page 721), Amphibians after Fishes (page 725), and so on. 



In degeneration, Reptiles and Mammals, in some cases, have become mid- 

 tiplicate: as exhibited in the vertebrae and teeth, and sometimes in the 

 phalanges and number of the digits. (Pages 797, 931.) 



Natural selection not essential to evolution, variations being effectual with- 

 out it. — The theory of natural selection is based on the assumption that 

 variations come singly or nearly so, and that the selected are therefore few 

 compared with the multitudes that disappear. The idea is derived from 

 facts afforded by domesticated or cultivated races. But such races are in a 

 large degree artificial products, selective methods carrying the individuals 

 rapidly in the direction of the variation, and producing, in a few scores of 

 generations, divergencies that in wild nature would require thousands of 

 years. The structures are therefore in a strained or artificial state, and 



