K )( ; The Outline of Science 



became the supporting and branch-gripping member, and the 

 hand was set free to reach upward, to hang on by, to seize the 

 fruit, to lift it and hold it to the mouth, and to hug the young one 

 close to the breast. The hand thus set free has remained plastic 



a generalised, not a specialised member. Much has followed 



from man's "handiness." 



The arboreal life had many other consequences. It led to 

 an increased freedom of movement of the thigh on the hip joint, 

 to muscular arrangements for balancing the body on the leg, to 

 making the backbone a supple yet stable curved pillar, to a 

 strongly developed collar-bone which is only found well-formed 

 when the fore-limb is used for more than support, and to a power 

 of "opposing" the thumb and the big toe to the other digits of the 

 hand and foot an obvious advantage for branch-gripping. But 

 the evolution of a free hand made it possible to dispense with 

 protrusive lips and gripping teeth. Thus began the recession of 

 the snout region, the associated enlargement of the brain-box, and 

 the bringing of the eyes to the front. The overcrowding of the 

 teeth that followed the shortening of the snout was one of the 

 taxes on progress of which modern man is often reminded in his 

 dental troubles. 



Another acquisition associated with arboreal life was a 

 greatly increased power of turning the head from side to side a 

 mobility very important in locating sounds and in exploring with 

 the eyes. Furthermore, there came about a flattening of the 

 chest and of the back, and the movements of the midriff (or 

 diaphragm) came to count for more in respiration than the move- 

 ments of the ribs. The sense of touch came to be of more impor- 

 tance and the sense of smell of less ; the part of the brain receiving 

 tidings from hand and eye and ear came to predominate over the 

 part for receiving olfactory messages. Finally, the need for 

 carrying the infant about among the branches must surely have 

 implied an intensification of family relations, and favoured the 

 evolution of gentleness. 



