160 THE EVOLUTION OF MAN 



generally true in complex phenomena it is best defined in terms 



of causes rather than of results. 



Everywhere in the living world, progress is brought about 

 by increasing specialization and cooperation, or, in the lan- 

 guage of biology, by increasing differentiation and integration. 

 Whether it be the development of an egg into an adult, the 

 evolution of primitive animals and plants into their more com- 

 plex descendants, or the development and evolution of the 

 body, mind, and society of man, progress everywhere is caused 

 by increasing specialization and cooperation. In the develop- 

 ment of an egg, which is the symbol and epitome of all prog- 

 ress, there is segregation of different structures and functions 

 in different cells and parts of the body, that is, there is mor- 

 phological division of substance and physiological division of 

 labor, and at the same time there is increasing perfection of 

 functions and adaptations. In the evolution of limbs or eyes 

 or brains there is a similar increase in the complexity of differ- 

 entiation and integration. In both the ontogenetic and the 

 phylogenetic development of intellect and of society, there is 

 increasing complexity and perfection of function and adapta- 

 tion. All kinds of progress, whether of body, mind, society, 

 art, industry, or science, are marked by increasing specializa- 

 tion and cooperation. As thus defined, progress may lead in 

 different directions to very different ends, as is shown in the 

 various types of locomotion, offense and defense, sense organs, 

 nervous systems, etc., found in the animal kingdom. In man it 

 has led to increased cranial and intellectual capacity, increased 

 control over environment and greater freedom, increased size 

 and complexity of social units, etc. But progress in each of 

 these many paths is caused by increasing complexity and per- 

 fection of specialization and cooperation. 



Limits of Progress. Biological progress, however, always 

 has its limits; sooner or later differentiation reaches a stage 

 beyond which it cannot go without destroying the internal 



