CHAPTER XXX 



SOCIAL AND COMMUNAL LIFE, COMMEN- 

 SALISM AND PARASITISM 



Social life and gregariousness. TECHNICAL NOTE. 



Students should refer to examples of gregariousness from their own 

 observations of animals. The roosting together of crows and of black- 

 birds ; the gathering of swallows preparatory to migration ; the 

 flocking of geese and ducks, with leaders, in their migratory flights, 

 all can be readily observed. From observation or general reading 

 students will be more or less familiar with prairie-dog villages, 

 beaver-dams and marshes, the one-time great herds of bison, etc. 



The struggle for existence is always operative ; but in 

 some cases one or more phases of it may be ameliorated. 

 For example, the amelioration of the struggle among 

 individuals of one species obtains in a lesser or greater 

 degree in the case of those animals which exhibit a social 

 life, of which mutual aid and mutual dependence are the 

 basis. The honey-bee and the ants are familiar examples 

 of animals which show a high degree of social life. They 

 live, indeed, a truly communal life, where the fate of the 

 individual is bound up in the fate of the community. 

 But there are many animals which show a much lower 

 degree of mutual aid and a far less coherent society. 

 The simplest form of social life exists among those animals 

 in which many individuals of one species keep together, 

 forming a great band or herd. In this case there is not 

 nearly so much mutual aid or mutual dependence as in 

 that of the honey-bee, and the safety of the individual is 

 \ot wholly bound up in the fate of the herd. Such 



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