178 FROM FISH TO PHILOSOPHER 



—but boasted instead, where they sat down, callosities 

 that were frequently surrounded by red, blue or purple 

 skin and that became enlarged in the female just before 

 ovulation, an event which was followed, for the first time 

 among mammals, by external menstrual bleeding. The 

 absence of a prehensile tail in the progenitors of the Old 

 World monkeys may or may not be related to the fact 

 that among them there developed the tailless apes that 

 lived for the most part on the ground, notably the genus 

 Dryopithecus (tree ape) which roamed over Europe, 

 Africa and Asia in the Miocene and, as far as teeth go, 

 could have given rise to the gibbon, orang, chimpanzee, 

 and gorilla, or to man. 



The circumstances surrounding ape-to-man evolution 

 are still obscure, but all authorities are agreed that the 

 step is importantly concerned with the assumption of 

 the erect attitude and the liberation of the forelimbs for 

 use as hands, a transition to which both the human brain 

 and skeleton bear ample witness. The great apes in vary- 

 ing degree use their forelimbs to swing from branches, 

 and on the ground they more or less support the body 

 on the knuckles. The transition from the brachiating to 

 the bipedal habitus might be expected to occur under 

 circumstances where forms that had hitherto been 

 arboreal were forced by recession of the forests to seek 

 their food in the open plains. In assuming the upright 

 posture, the foot had to be remodeled in order to bal- 

 ance the body; then the pelvis, backbone, and head had 

 to be realigned until the arms hung free at the sides. 

 Once the hands were relieved of all responsibility in loco- 

 motion, natural selection could foster the further evolu- 

 tion of the brain around the sense of touch and the motor 

 activities involved in manual dexterity. 



Recognized human remains do not go back of the 

 Middle or Early Pleistocene, at most not more than one 

 million years ago. The preceding PHocene saw the be- 

 ginning of the most recent of mountain-building epi- 

 sodes, the Cascadian disturbance which, continuing 



