774 Causes and Course of Organic Evolution 



of them. But, while most of the highly carnivorous species 

 live an isolated or feebly social life, others of semi-carnivorous 

 habit of life like the herring, the salmon, and the sardine 

 live, feed, mate and often spawn in large shoals. The exten- 

 sive and often exact migrations carried out from one locality 

 to another by large shoals indicates that some common sense 

 relation guides them in their movements. The greatly larger 

 proportion of individuals that are social and semi-carnivorous 

 as compared with others like the sharks, codfish, and catfish 

 that are strongly carnivorous suggest an advantage that tends 

 to become dominant, though we would not press the view 

 too strongly here. 



The Amphibia and Reptilia are on the whole solitary and 

 non-cooperative. In spite of varied and at times elaborate 

 means for defense, they are in no sense dominant or directive 

 classes. The group Aves on the other hand deserves some 

 study. We have already pointed out (p. 556) that the modi- 

 fication of the forelimbs into wings and the strictly limited 

 use of these as the collectors of sense impressions have seri- 

 ously militated against high nervous evolution in this class. 

 The great majority of the species then are solitary, and are 

 relatively poor in individuals. On the other hand the most 

 widely distributed genera or species at the present day all 

 show social and even markedly cooperative qualities in that 

 they attack and repel a common foe, select breeding places 

 in common, advance in groups to new feeding grounds, and 

 often carry out extensive migrations in large flocks. While 

 the solitary species are often carnivorous, the social ones are 

 nearly always vegetarian in diet. 



The penguins, solan-geese, flamingoes, and ducks represent 

 abundant and widely distributed groups of low social organi- 

 zation; the pigeons, the fowls, and the swallows form a still 

 higher series; while the sparrows, the parrots, the jackdaws, 

 and the crows seem to be the highest and dominant ones. In 

 the last of these the beak and one of the hind feet are often 

 efficiently used for a wide range of activities, and such use 



seems to have stimulated to increasing development of the 



brain (p. 55Q). 



