26 ESSAYS OF A BIOLOGIST 



This has meant, among other things, that for the 

 first time in biological history there has been an 

 aggregation (in the technical biological sense) of minds. 

 Over and over again in evolution does the process of 

 aggregation appear. ^ It is an advantage, for at one 

 jump it lands life on a new level of size, with new 

 possibilities of division of labour and specialization. 

 It appears in the aggregation of Protozoa to form 

 the colonial ancestor of all higher, many-celled forms. 

 It appears again on this new level in the aggregation 

 of hydroid polyps, of polyzoa, of ascidians, and especi- 

 ally in the beautiful floating Siphonophora, in which 

 the polyp-like units (themselves historically aggregates 

 of cells) have become so subordinate in relation to the 

 whole that they can often scarcely be recognized as 

 individuals, and the individuality of the aggregate is 

 much more marked than that of its components. It 

 appears in a new way in the Termites and in the social 

 Hymenoptera — ^ants, bees, and wasps. Here the 

 bonds uniting the members of the aggregate are not 

 physical but mental, their sense-impressions and 

 instincts ; but the principle is identical throughout. 

 Finally in man we have not merely aggregation of 

 physical individuals held together by mental bonds, 

 but aggregation of minds as well as of physical in- 

 dividuals. 



In many mammals and birds, each generation can 

 extend its influence on to the next, and the experience 

 ^ See Huxley, '12. 



