88 SCIENCE PROGRESS 



Oligocene eoliths found in Belgium prove to be manufactured 

 articles. A small animal seeking its food amongst the rocks 

 between the tide-lines would be compelled to try to stand on 

 its hind legs in order to use a pebble at first with both its hands. 

 As it grew larger and firmer on its feet, one hand became strong 

 enough to do the work. As the upright position gradually- 

 asserted itself, it was an advantage in searching the sides of 

 the rocks to have the axis of the eyes at right angles to the 

 perpendicular trunk. Hence the occipital foramen gradually 

 reached the centre of the base of the skull, and its plane became 

 nearly horizontal. The most successful of these dwellers on 

 the beach were those that learnt to walk upright. Provided 

 the little animals were not hunted by enemies, they had no need 

 to scamper away on all-fours, and the type of body gradually 

 changed until they became bipeds. Balancing the body and 

 the new uses of the hand and foot were muscular functions 

 that advanced the type of brain. The smaller the animal that 

 began this series of changes the easier it is to account for the 

 results, and it is clear that such a life was more varied and 

 complicated than the old one in the trees. 



At whatever point therefore in such a history the ancestors 

 of the apes left the seaside and went back to the forest, they 

 were at once exposed more fully to the stress of the ordinary 

 struggle for existence. The earlier they went back the less they 

 resembled the human type in the matter of the foot and head 

 AsPropliopithecus and other apes of the Egyptian Late Oligocene 

 appear to be early gibbons, and as tree-living gibbons are found 

 in the Miocene, this genus seems to have been the first to 

 return to the trees. The large canines, long fingers and arms, 

 long toes, and great toe at right angles to the foot are modifi- 

 cations that have been elaborated since the Oligocene, for the 

 Egyptian fossils have comparatively small teeth. The next 

 emigrant was the orang. Some of the families that left at 

 that time may have been slim creatures that have died out, 

 but one of them was prepotent in regard to immense strength 

 combined with a short spinal column, and these two features 

 have survived. Last of the surviving apes was the common 

 ancestor of the gorilla and chimpanzee. As we have already 

 pointed out, he carried away the human spine, and the need 

 of protection has modified his ribs in two ways : they are 

 broader and stronger than those of man, and the thirteenth 

 has become a permanent addition to the chest. 



Concerning the Teeth 



The orang and gorilla make great use of their canine teeth 

 in obtaining their food. These teeth are not so specialised as 



