SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS 253 



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 

 the hfe of the whole community. But the discharge of 

 the second natural obligation, namely to preserve the 

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

 whole group of cell individuals. It follows therefore 

 that the division of the tasks necessary for the mainte- 

 nance of a complete biological individual, and the difTcr- 

 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 denoted altruistic, 

 even though 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 



