CHAPTER XIX 

 ANIMAL AGGREGATIONS AND SOCIAL LIFE 



We have seen something of the kinds and the extent of the aggre- 

 gation phenomena in nature and in the laboratory, among members 

 of the animal kingdom and among specialized cells such as bacteria 

 and spermatozoa, as well as cells under the artificial conditions that 

 obtain in tissue cultures. We have reviewed the action of the direct 

 and indirect environmental forces which control the formation of 

 such aggregations. We have found that methods and different de- 

 grees of integration exist, which may serve to organize a group close- 

 ly, although it lies well below the division-of-labor level of social life. 



The well-known harmful effects of crowding have been summa- 

 rized, as has the newer evidence that, despite the menace of over- 

 crowding, many aggregations have survival values for their members 

 and may even produce morphological changes as well as the more 

 easily induced physiological effects. A further discussion of the ex- 

 tent and implication of the co-operation involved in these loosely 

 integrated groupings is reserved for the final chapter. It is sufficient 

 to state here that aggregations formed without sexual stimuli and 

 at the lowest level of group integration may have survival value for 

 their members and, under certain conditions, are essential for the 

 survival of the race. 



Although the matter has not been discussed, it has been the open 

 as weU as the impHed suggestion throughout that these aggregations 

 are important in social evolution. This question must now be faced 

 directly. One avenue of approach to such a consideration might lie 

 through an extensive review of the evidence concerning the origin 

 of the social habit, but we shall limit this aspect of the discussion by 

 citing summaries of generally accepted points of view and testing 

 these against some of the known facts. 



We have already suggested that sex may have evolved from the 

 mutual stimulation which has been demonstrated to occur under 



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