MAMMALS 315 



wonderful organ of prehension in the world, the hand, which is 

 man's one point of high structural adaptation. 



It is difficult to say whether the brain taught the hand, or the 

 hand helped develop the brain, but it is certain that these three 

 factors, erect position, hand, and brain, have been the essential 

 ones in man's development. 



There is more structural difference between the lowest primates 

 (lemur) and the chimpanzee or gorilla, than there is between these 

 higher apes and man. Also there is a greater difference between 

 the lowest type of savage man and the highest type of civilized 

 man, than there is between the savage and the ape. 



Results of Erect Posture. As a consequence of his erect posture, 

 man's hands are left free for use in grasping things. However, 

 nature does not give something for nothing, and man has to pay 

 for his upright position by certain disadvantages. In the first 

 place, since only one pair of limbs are used in locomotion, he must 

 balance upon two feet instead of four, and has the center of weight 

 high above the point of support. This necessitates the long and 

 difficult process of " learning to walk " which other animals do 

 not experience. 



Placing the weight vertically on the hips instead of at right angles 

 to them, renders man more liable to hip, spinal, and foot, diseases 

 and deformities. The internal organs rest one upon another in a 

 vertical pile instead of lying side by side, producing a tendency 

 to pressure or displacement. When sick or tired we instinctively 

 lie down to relieve this strain. 



The arteries of the arm-pit, neck, and groin are now exposed 

 toward the front, whereas in quadrupeds they face downward 

 and are protected. In man, the trachea and appendix open up- 

 ward, instead of forward, giving opportunity for the entrance of 

 irritating substances. 



All these difficulties, which are the price of our erect posture, 

 are more than repaid by the advantage of the human hand and 

 the mental and social development which it has made possible. 



It rests with the intelligence of man to overcome the natural 

 difficulties of his structure by especial attention to correct posture, 



