POPULAR SCIENCE 85 



The five existing genera descended from this common 

 ancestor — man and the four apes — have retained many very 

 primitive anatomical features. It is impossible to strike a 

 balance and say that on the whole the gibbon, because more 

 monkey-hke, is more primitive than man. The significance of 

 the primitive features cannot be weighed and measured ; we 

 cannot say that an ounce of brain is equal to a pound of bone. 

 But it appears to be the soundest principle to regard all apparent 

 "reversions as sign of survival unless there is clear evidence to 

 the contrary. 



The common ancestor is usually supposed to have taken 

 to a life on the ground and there acquired a fair approximation 

 to a bipedal gait. In this case his diet would probably have 

 consisted of lizards, gfubs, and scorpions, and the miscellaneous 

 articles collected by baboons. It was evidently of animal 

 origin to a great extent, because the digestive organs continued 

 to be small, and none of his descendants except man have 

 developed the side-to-side movement of the jaw in the act of 

 chewing. This is a fairly constant indication of a vegetable 

 diet in the case of all mammals. 



The plan of the digestive system seems to be an indicator 

 of great importance in tracing out the early history of any 

 species of animal. In man the alimentary canal is nine times 

 the length of the trunk, in which relation he stands intermediate 

 between the carnivora and herbivora. The corresponding ratios 

 are : cat four, dog five, horse twelve, ox twenty, and sheep 

 twenty-six. Many monkeys and the apes (except the orang) 

 have provided for the increased size of their digestive organs 

 by securing thirteen ribs. Even with this support they have 

 protuberant abdomens, no waist, and in the gorilla the caecum 

 and vermiform appendix are pushed deep into the cavity of 

 the true pelvis. There is a species of lagothrix monkey on the 

 Amazon called " barrel-belly " by the Portuguese on account 

 of the immense amount of fruit that it eats. It is not probable 

 that nuts and fruit or even seeds and grasses were so rich in 

 protein in the Pliocene as they are now, because the evolution 

 of nutritious plants has been related to the increasing richness 

 of the surface soil, and this has been the joint work of the animal 

 and plant. In some parts of Australia the vegetation is com- 

 paratively ancient in type and absence of water has restricted 

 the marsupial animals. We therefore find very little difference 

 in regard to the percentage of plant food in the surface soil as 

 compared with the subsoil ; whereas the rule is, in temperate 

 regions, for the surface foot of soil to contain from two to three 

 times as high a percentage of nitrogen and phosphoric acid as 

 is found in the deeper parts. On some of the Australian gold- 

 fields the surface soil and the rock four thousand feet below the 



