236 INTRODUCTION TO EVOLUTION 



cines tell us much about the early stages of human evolution. We have seen 

 that the primates as a whole are characterized by varying degrees of 

 emancipation of the forelimbs from the duties of locomotion (p. 220). The 

 various primates vary in the extent of this emancipation, and the brachia- 

 tors among them have in a sense reversed the trend, although most of them 

 have done so without serious loss of ability to use the hands in grasping 

 objects. The lower monkeys, arboreal but not brachiators, possess hands 

 adapted for grasping and handling objects, as everyone who has visited a 

 zoo knows. They also foreshadow to some extent an upright posture of the 

 trunk as they move through their arboreal habitat. The ancestor of 

 man must have been such an arboreal (and brachiating?) primate who 

 for some reason forsook life in trees for life on the ground. In response to 

 the needs of the new environment, the tendency to upright posture be- 

 queathed him by his tree-dwelling ancestors became perfected. Further- 

 more, the attainment of erect locomotion removed the last necessity for the 

 employment of the hands in locomotion, leaving them free for other duties, 

 notably the handling of objects. The latter led directly to the use of tools, 

 the basis of all man's later achievements. Man without tools would be a 

 most undistinguished member of the animal kingdom. Tools, developed 

 and employed by the human brain, have made possible the development 

 of civilization. To a very considerable extent man's cultural attainments 

 have been, and continue to be, measured by the tools employed, as implied 

 in our designation of cultures as "Old Stone Age" (Paleolithic), "New 

 Stone Age," "Bronze Age," "Iron Age," "Age of Steam," "Age of Elec- 

 tricity," and so on. Accordingly the importance of the changes which 

 paved the way for development of the ability to use tools can not be exag- 

 gerated. The primary change making this possible was attainment of up- 

 right posture, which, as the australopithecines and perhaps even 

 Oreopithecus show us, came at the dawn of human evolution and pre- 

 ceded the great development of brain which was later to characterize man. 

 Hands free to use tools came first; brain development adequate for making 

 effective use of those hands in devising, using, and perfecting tools came 

 later. Probably the brain development never would have occurred had not 

 the hands been available first. In this connection it is interesting to recall 

 that in the evolution of the horse, brain development lagged behind adap- 

 tive changes in the limbs. Hyracotherium with its almost reptilian brain 

 had nevertheless begun the evolutionary changes in the limbs which were 

 to characterize horse evolution (pp. 202-203; Fig. 10.6). 



Were the australopithecines ancestral to later men, including eventually 

 Homo sapiens? We have enumerated above many bodily characteristics of 



