CHAPTER XXII 



THE DEVELOPMENT OF THE BRAIN 



It seems at first sight impossible to derive any advances 

 in brain development from the mere habit of tree-climb- 

 ing, and yet it is precisely these important and dominating 

 advances which can most surely be linked up with the 

 changing fortunes of the arboreal stock. Since any 

 story of brain evolution is of necessity extremely com- 

 plex, and since the different chapters in this story are 

 interwoven in a very complicated manner, it is necessary 

 to be quite certain of a tolerable degree of agreement 

 about two things; the first, What sort of brain was that 

 inherited by the earliest mammal ? And the second. 

 In what way will environmental possibilities of education 

 affect such a brain ? Fortunately, within rather wide 

 limits, we may expect agreement upon these two points, 

 and as the working basis of this review I shall take 

 unreservedly the researches of Professor Elliot Smith. 

 In that writer's paper on the " Origin of Mammals " the 

 following statement occurs: "In spite of the certainty 

 that the mammalian brain passed through a reptilian 

 stage in its phylogeny, the brain of no living reptile 

 fulfils the conditions required in the actual ancestor of 

 the Protomammalia." Here we have evidentlv the same 

 story, some of the pages of which we have turned pre- 

 viously. Somewhere, the Protomammal and the Primitive 

 Reptile meet, somewhere in the geological past these 

 two stocks branch off from a common ancestor. There 

 is every reason to imagine that among the Cynodontia 

 of the Triassic there was this blend of primitive Reptile 



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