EVOLUTION OF INTELLIGENCE. 109 



from some primitive adaptable ancestor. Man himself 

 preserves many archaic anatomical characters, and the 

 order Primates, of which he is the highest member, 

 although its history is still imperfectly known, can be 

 traced back to primitive Eocene forms. Extreme 

 specialisation may secure temporary triumph, and in 

 very uniform conditions even lasting success, but adapta- 

 bility is the most precious possession, and it is the crea- 

 tures most ready to meet new and changeable conditions 

 which have the future before them. 



CHAPTEK IX 



PSYCHOLOGY AND THE EVOLUTION OF INTELLIGENCE 



WE have just seen that adaptability is one of the most 

 useful attributes an organism can possess. In plants it 

 may be highly developed, but along comparatively simple 

 lines of direct response. Here adaptability is shown in 

 the power to respond in different ways to a variety of 

 stimuli. The case of alpine and lowland forms has 

 already been mentioned (p. 41), and many others are 

 familiar to botanists. For instance, the plant Ranun- 

 culus acquires a very different shape and internal struc- 

 ture according as it grows on dry land or in water, and 

 the terrestrial or aquatic form can be developed in the 

 same individual, by parts above and below the surface 

 of the water. Also plants which in a normal climate 

 develop ordinary stems and leaves may in dry or desert 

 regions assume a very different form ; the stems become 

 succulent for storing water, and the leaves become re- 

 duced, spines being often developed in their stead, thus 

 diminishing the surface whereby water is lost in tran- 

 spiration. Now these and similar changes are useful 

 responses enabling the plant to accommodate itself to 

 varying conditions. This manifold adaptability is not 



