traits that are very different. Two legged walking, or bipedalism seems to be one of the earliest of the major hominine characteristics to have evolved. To Snell 2accommodate this strange position, we have developed a specialized pelvis, hip and leg muscles, and an S-shaped vertebral column. Because these changes can be documented in fossil bone, bipedalism is seen as the defining trait of the sub family Homininae. Much of the human ability to make and use tools and other objects stem from the large size and complexity of the human brain. Most modern humans have a braincase volume of between 79.3 and 91.5 cubic inches. In the course of human evolution the size of the brain has more than tripled. The increase in brain size may be related to changes in hominine behavior. Over time stone tools, and other artifacts became increasingly numerous and sophisticated. It is likely that the increase in human brain size took place as part of a complex interrelationship that included the elaboration of tool use and tool making, as well as other learned skills, which permitted our ancestors to be increasingly able to live in a variety of environments. The earliest hominine fossils show evidence of marked differences in body size, which may reflect a pattern of the different sexes in our early ancestors. The bones suggest that females may have been 3 to 4 ft in height and about 60 to 70 lb. in weight, while males may have been somewhat more than about 5 ft tall, weighing about 150 lb. The reasons for this body size difference are disputed, but may be related to specialized patterns of behavior in early hominine social groups. This extreme difference between sexes appears to disappear gradually sometime after a million years ago. The third major trend in hominine development is the gradual decrease in the size of the face and teeth. All the great apes are equipped with large, tusk-like canine teeth that project well beyond the level of the other teeth...
