28 THE LESSON OF EVOLUTION 



the development of the hand. Again, man could not 

 have attained civilisation if he had not been able 

 to domesticate animals and to cultivate food-plants. 

 Euminant mammalia were therefore required ; and 

 these can only exist in large flocks, through the peculiar 

 growth of the leaves of grasses on which they feed. 

 Most leaves grow very rapidly after the bursting of 

 the bud, and then cease to grow altogether. The con- 

 sequence is that if the leaves of one of these plants 

 are continuously cut or pulled off, they are not repro- 

 duced, and the plant dies. But in the grasses and 

 their allies the leaves continue to grow at their bases 

 all through life, so long as the temperature and moisture 

 of the soil are favourable ; and cutting and biting off 

 their ends does the plant good instead of harm, for it 

 exposes the newly grown parts of the leaves to the 

 sun. Thus large herds of animals are enabled to live 

 together without destroying the vegetation ; and it was 

 this that tempted primeval man to leave the forest 

 and live on the open land. 



Now hoofed mammals required a long time for their 

 development ; and, if they had not been a very early 

 branch of the eutherian stock, they would not have 

 been ready for man to domesticate at the close of the 

 pleistocene period. We have thus no less than five 

 different groups of plants and animals, which must 

 precede man in a certain order, to allow the possibility 

 of human civilisation. Phanerogamous trees and birds 

 must precede the earliest Primates. Grasses and 

 ruminants must follow ; yet they also must precede 

 man. Now we find that this is just the order in 

 which they did appear. Phanerogamous trees are 

 known first in the carboniferous period. Mammals in 



