NATURE'S INSURGENT SON 23 



small bulk of brain-substance. Fish, lizards, and croco- 

 diles with their small brains carry on a complex and 

 effective life of relation with their surroundings. It 

 appears that the increased bulk of cerebral substance 

 means increased * educability ' an increased power of 

 storing up individual experience which tends to take 

 the place of the inherited mechanism with which it is 

 often in antagonism. The power of profiting by indi- 

 vidual experience, in fact educability, must in conditions 

 of close competition be, when other conditions are equal, 

 an immense advantage to its possessor. It seems that 

 we have to imagine that the adaptation of mammalian 

 form to the various conditions of life had in Miocene 



FIG. 5. 



Four casts of the brain-cavities of a series of large Ungulate Mammals 

 in order to shew the relatively small size of the cerebral hemispheres of 

 the extinct creature from which A is taken. 



A is that of Dinoceras, a huge extinct Eocene mammal which was as 

 large as a Rhinoceros ; B is that of Hippopotamus ; C of Horse ; and D of 

 Rhinoceros. 



times reached a point when further alteration and 

 elaboration of the various types, which we know then 

 existed, could lead to no advantage. The variations 

 presented for selection in the struggle for existence 

 presented no advantage the ' fittest ' had practically 

 been reached, and was destined to survive with little 



