Biological Point of View 



built up out of their prolonged rivalries the 

 complex series of the animal kingdom. In 

 response to the demands of the struggle came 

 swifter fins and feet, more powerful jaws, and 

 more capacious stomachs. Each weapon of 

 attack was met by a new defense, giving rise 

 to a formidable series of scales, shells, and 

 other armor plate, until the possibilities seem 

 to have been exhausted, and the future passed 

 into the control of more enterprising types that 

 challenged the risks of active life in the open. 



J. Life on the Land 



Just how animal life emerged from its origi- 

 nal watery habitat to the free air of the land 

 we do not know, but we may imagine on the 

 basis of remaining transition forms that, like 

 migrants thrown by social forces from an old 

 world to a new, the teeming sea threw out its 

 adventurers until they established themselves 

 in the new environment. The evolution of 

 land life once well begun, there developed with 

 increasing speed two tendencies previously 

 started. One of these was the development of 

 the brain as an instrument of survival, and the 

 other was the pooling of interests in the form- 

 ing of groups for mutual protection and attack. 



