178 EVOLUTION OF THE EARTH 



gory from the dog and the pig. Aside from agriculture 

 nothing did more than their domestication to give man that 

 sense of ownership and feeling of responsibility which are 

 among the most essential prerequisites of high civilization. As 

 soon as herds were in his care, man was compelled to watch 

 them day by day. Carelessness was fatal. He must defend 

 them from wild animals, drive them to new supplies of grass 

 and water, and plan to sustain them through the winter. Not 

 only did man thus become a property owner by reason of his 

 beasts, but he himself was able to increase in numbers to a 

 degree utterly impossible while he still depended on the chase. 

 Therefore the contact of family with family greatly increased. 

 That necessitated either war and destruction, or some kind of 

 mutual agreement whereby was laid the basis of a rudimentary 

 social and political organization. As to the climate under 

 which domestication of the grass-eating animals took place, it is 

 almost certain that the horse, ox, and sheep all were first tamed 

 in the subtropical grasslands of central Asia thirty or forty 

 degrees from the equator. Since this occurred during the 

 change from the last glacial epoch to the present, it presumably 

 took place in a climate closely resembling that which we have 

 found to be ideal. Two other animals, the llama and the 

 camel, have been domesticated under less favorable circum- 

 stances, but neither is truly tropical. The llama of Peru lives 

 where it is decidedly cool. The camel may frequent the hot 

 desert, but the only known wild camels are in the deserts of 

 central Asia where the winter temperature may be 20° below 

 zero. Neither of these animals can vie with the horse, ox, 

 and sheep as contributors to civilization. In the case of the 

 llama this may be due to small size, but probably in both cases 

 a more important factor is the fact that neither animal flour- 

 ishes in the kind of climate in which man is at his best. 



Rise of agriculture. During the whole course of human 

 history probably no one thing has had a greater influence upon 



