216 THE WHENCE AND THE WHITHETi OF MAN 



should begin a century or two before its birth ; man 

 really began his mental education at least as early as 

 the appearance of vertebrate life. 



But man is a mammal. This means that every or- 

 gan is at its best. The digestive system, while making 

 but a small part of the weight of the body, and built 

 mainly on the old plan, is wonderfully perfect in its 

 microscopic details. The muscles are heavy and pow- 

 erful, arranged with the weight near the axis of the 

 body, and replaced near the ends of the appendages by 

 light, tough sinew r s. The higher mammal is this com- 

 pact, light, and agile. The skeleton is strong, and the 

 levers of the appendages are fitted to give rapidity of 

 motion even at the expense of strength. And this 

 again is possible only because of the high develop- 

 ment and strength of the muscles. Moreover, the high- 

 est mammals are largely arboreal, and in connection 

 with this habit have changed the foreleg into an arm 

 and hand. The latter became the servant of the brain 

 and gave the possibility of using tools. 



But increase in size and activity, and the expense of 

 producing each new individual, led to the adoption of 

 placental development. And the mammal is so com- 

 plex, the road from the egg to the fully developed 

 young is so long, that a long period of gestation is nec- 

 essary. And even at birth the brain, especially of man, 

 is anything but complete. Hence the necessity of the 

 mammalian habit of suckling and caring for the young. 

 And this feebleness and dependence of the young had 

 begun far below man to draw out maternal tenderness 

 and affection. And the mammalian mode of repro- 

 duction and care of young led to a more marked differ- 

 ence and interdependence between the sexes, 



