4 HUMAN BIOLOGY 



development. The erect position has given greater freedom to the 

 chest. Man uses fewer organs of locomotion than any other animal. 

 The opossum has two hands, but they are on the hind limbs. The 

 ape has four hands, but must use them all in locomotion. (What is a 

 hand ?) The erect position, however, makes spinal deformity easier to 

 acquire, and the whole weight being upon one hip at each step man is 

 liable to hip-joint diseases. In the horizontal trunk the organs lie one 

 behind another ; in man they lie one upon another, and are more liable 

 to crowding and displacement. The prone position in sickness helps 

 to restore them. Large blood vessels at neck, armpits, and groins, 

 which occupy protected positions in quadrupeds, are held to the front 

 and exposed to danger. The open end of the vermiform appendix and 

 of the windpipe are upward in the erect trunk of 'man. Valves are 

 lacking in some vertical veins and present where little needed in hori- 

 zontal veins. But the freedom of the hands more than makes up for 

 all the disadvantages of erectness. 



The Survival of the Fittest. Those who do not work degenerate. 

 Those who overwork, or work with only a few organs, as the brain and 

 nerves, degenerate. The workers survive and increase in numbers, the 

 idle perish and lea-i>e few descendants. 



What rate of adjustment to new environment is possi- 

 ble for man? This has not been ascertained; it is prob- 

 ably much slower than has been generally imagined. The 

 natives of Tasmania, New Zealand, and many of the 

 Pacific Islands became extinct in less than a century after 

 adopting clothing and copying other habits from Euro- 

 peans. Life in the country in civilized lands differs less 

 from the environment of primitive man than does life in 

 cities. Cities have been likened to the lion's cave in the 

 fable, to which many tracks led, but from which none led. 

 The care of health in cities is now making rapid strides 

 along the biological basis of purer air, more open space, less 

 noise, simple food, and pure water. Biology, by supplying 

 as a standard the conditions which molded man's body 

 for ages, furnishes a simple and sure basis for hygiene. 

 To mention one instance among many, man blundered for 

 centuries in attempting the cure of consumption, and well- 



