370 EVOLUTION OF PHYSICAL CHAEACTEES 



the emergence of man and during what we have called the first 

 and second periods of his history. 



2. During the intermediate period, which was of relatively- 

 immense length, the greater part of human bodily evolution 

 was accomplished. Only two or three worn and fragmentary 

 remains have as yet been discovered from this period. It is at 

 least apparent from them that the amount of physical evolution 

 which has been accomplished since the end of that period is slight 

 compared with what was accomplished within that period. We 

 may assume that lethal selection was strongly at work. Changes 

 in mode of life — the assumption, for instance, of a terrestrial 

 for an arboreal existence and the adoption of an upright posture — 

 must have involved lethal selection. These changes of habit 

 must also have brought ancestral man into contact with new 

 enemies. The spreading of man into new climatic zones was 

 doubtless followed by selection, and must again have involved 

 contact with new enemies. So, too, selection followed upon the 

 first great steps in the acquirement of skill — the making of clothes, 

 the use of fire, and so on. In addition to lethal selection, differen- 

 tial fertility acting through polygamy must have been at work. 

 In part no doubt differential fertility merely reinforced lethal 

 selection ; but in part also it may have taken the form of sexual 

 selection and have favoured other types. 



But when we come to details we find that we are ignorant 

 regarding the causes of even the largest changes. Some guesses 

 have been hazarded. The increase in the capacity of the skull 

 is connected with the evolution of the intellect and may be left 

 for consideration in the next chapter. The decrease in the size 

 of the jaw and the corresponding decrease in the size of the teeth 

 were perhaps connected with a change in diet. The loss of the 

 hairy covering may have been connected with sexual selection 

 or it may have been favoured because it removed a lodging-place 

 for parasites. 



3. As we pass from the intermediate to the first period of 

 human history we reach a region of less uncertainty. We are 

 ignorant as to the physical characters of man at the close of the 

 intermediate period, but we know that in the earlier part of the 

 Upper Palaeolithic there was existing one variety — the Grimaldi 

 race — which bears certain resemblances to the negroid type, and 

 that in the latter part of the same period there were existing 



