SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS 253 i 



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to serve as reproductive individuals solely. Every \ 

 member of the colony must obey the first precept of \ 

 nature, otherwise it would be unable to play its part in i 

 the life of the whole community. But the discharge of ! i 

 the second natural obligation, namely to preserve the ; | 

 race, is here assigned to some, and to some only, of the | V 

 whole group of cell individuals. It follows therefore i ! 

 that the division of the tasks necessary for the mainte- ' ^ 

 nance of a complete biological individual, and the differ- 

 entiation of the members of the group into two kinds, 

 leads to the establishment of an individuality of a 

 higher order than the cell. Neither the purely nutritive 

 nor the reproducing member is complete in itself; 

 the two kinds must be combined to make a perfect 

 organism. The life of any member can be selfish no 

 longer, for if it is to exist itself, it must help others for 

 the mutual advantage of all. A clear social relation is 

 thus established ; and the reflex conduct of the units 

 of a Volvox colony can be justly denofeH ^altruistic, 

 eT^""tliough in this case, as before, there can be no con- 

 scious recognition of the reasons why mutual interests 

 are best served by what is actually done. 



One of the most interesting and significant aspects 

 of the life-history of Volvox is the appearance for the 

 first time of biological death. More elementary or- 

 ganisms are immortal potentially even if not actually, 

 for every portion of the body is capable of passing over 

 into an animal of a succeeding generation. But in 

 Volvox a division of labor has been effected of such a 

 nature that most of the components discharge the tasks 

 of individual value, and with the performance of these 

 they die. Only the reproductive members are immortal 



