ZOOLOGY AND HUMAN WELFARE 



for specialization. The group as a whole is largely responsi- 

 ble for defense against enemies, and so individuals — 

 sometimes whole classes of individuals — are left free to 

 devote themselves to getting food, building shelters, caring 

 for the young, etc. This social division of labor tends to 

 make the group efficient; and all the individuals benefit 

 by the safe, stable, and complex mode of life which can 

 often be attained in this way. 



While the ants and the human species have been most 

 successful in forming such a social organization, there 

 are many other animals which have developed it in a 

 lesser but still useful degree; and a study of the latter helps 

 us in understanding and appreciating more complex social 

 states as well as in inferring the probable course of their 

 evolutionary history. Among the fishes, for example, group 

 life takes the form of a loose aggregation or swarm, in 

 which the chief advantage seems to be no more than the 

 mere weight of numbers and the certainty that enemies 

 cannot accomplish complete extermination. Its maintenance 

 involves enormous reproductive activity, which exhausts 

 most of the energy of the species; and there is little or no 

 opportunity afforded for specialization among the members 

 of the swarm. In the flocks or herds of various birds and 

 mammals, certain individuals act as leaders, scouts, or 

 lookouts, and so division of labor begins to appear. In 

 certain insects, such as the ants, life follows complex and 

 rigidly organized social patterns, the individual being 

 almost completely subordinated in the interest of the 

 group as a whole. Various castes may exist, devoted to 

 certain duties and adapted to them not only in activity and 

 skill but even in fixed, hereditary structure and instincts. 

 Some species of ants have a military caste made up of 

 members unable to do ordinary work; and some have a 

 sexual or reproductive caste so specialized that its members 

 cannot even feed themselves. 



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