v SOCIAL LIFE OF ANIMALS 93 



forms of both sexes. They are children which do not 

 OTOW up. 



8. Evolution of Social Life.- -To Prof. Alfred Espinas 

 both naturalists and sociologists are greatly indebted 

 for his careful discussion of the social life of animals- 

 Des Societes Animates: Etude de Psychologic Compares 

 (Paris, 1877) :- 



Co-operation, which is an essential characteristic of all society, 

 implies, says Espinas, some degree of organic affinity. Of normal 

 societies whose members are mutually dependent, two kinds may 

 be distinguished (a) the organically connected colonies of animals, 

 in which there is a common nutritive life ; (6) those associations 

 which owe their origin and meaning to reproduction. Of the 

 latter, some do not become more than domestic, and these are dis- 

 tinguished as conjugal (in which the parents alone are concerned), 

 maternal (in which the mother is the head of the family), and 

 paternal (in which the male becomes prominent). But higher 

 than the pair and the family is what Espinas calls the ' peuplade,' 

 what we usually call the society, whose bonds are, for the most 

 part, psychical. 



Let us consider this problem of the evolution of soci- 

 ality. Every animal with a " body ' -whether sponge 

 or mammal is a citv of living units or cells. But there 



mi 



are far simpler animals than sponges. The simplest 

 animals, which we call Protozoa, differ from all the rest 

 in being themselves units, having no bodies, in being 

 either " non-cellular ' organisms a mode of expression 

 proposed by Dr. Clifford Dobell, a great authority on 

 Protistology or in being, as some would say, single-cell 

 organisms, " physiologically complete in themselves." 



Here is an apparent gulf. The simplest animals are 

 units single cells ; all other animals are combinations 

 of units cities of cells. How is this gulf to be bridged ? 

 On the transition from a unit to a combination of units 

 the possibility of higher life depends. 



Every higher animal begins its individual life as a 

 single cell, comparable to one of the Protozoa. This 

 single cell, or egg-cell, divides ; so do most of the Pro- 

 tozoa. But when a Protozoon divides, the results usually 

 separate and live independent lives ; when an egg-cell 

 divides, the results of division cohere. Therefore, the 



