Human Evolution, the biological and cultural development of the species Homo sapiens, or human beings. A large number of fossil bones and teeth have been found at various places throughout Africa, Europe, and Asia. Tools of stone, bone, and wood, as well as fire hearths, campsites, and burials, also have been discovered and excavated. As a result of these discoveries, a picture of human evolution during the past 4 to 5 million years has emerged.
Human Physical Traits Humans are classified in the mammalian order Primates; within this order, humans, along with our extinct close ancestors, and our nearest living relatives, the African apes, are sometimes placed together in the family Hominidae because of genetic similarities, although classification systems more commonly still place great apes in a separate family, Pongidae. If the single grouping, Hominidae, is used, the separate human line in the hominid family is distinguished by being placed in a subfamily, Homininae, whose members are then called homininesthe practice that is followed in this article. An examination of the fossil record of the hominines reveals several biological and behavioral trends characteristic of the hominine subfamily.
Bipedalism Two-legged walking, or bipedalism, seems to be one of the earliest of the major hominine characteristics to have evolved. This form of locomotion led to a number of skeletal modifications in the lower spinal column, pelvis, and legs. Because these changes can be documented in fossil bone, bipedalism usually is seen as the defining trait of the subfamily Homininae.
Brain Size and Body Size Much of the human ability to make and use tools and other objects stems from the large size and complexity of the human brain. Most modern humans have a braincase volume of between 1300 and 1500 cc (between 79.3 and 91.5 cu in). 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. Archaeological sites, too, show more intense occupation in later phases of human biological history. In addition, the geographic areas occupied by our ancestors expanded during the course of human evolution. Earliest known from eastern and southern Africa, they began to move into the tropical and subtropical areas of Eurasia sometime after a million years ago, and into the temperate parts of these continents about 500,000 years ago. Much later (perhaps 50,000 years ago) hominines were able to cross the water barrier into Australia. Only after the appearance of modern humans did people move into the New World, some 30,000 years ago. 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 toolmaking, 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 sexual dimorphism in our early ancestors. The bones suggest that females may have been 0.9 to 1.2 m (3 to 4 ft) in height and about 27 to 32 kg (about 60 to 70 lb) in weight, while males may have been somewhat more than 1.5 m (about 5 ft) tall, weighing about 68 kg (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 dimorphism appears to disappear gradually sometime after a million years ago.
Face and Teeth 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, tusklike canine teeth that project well beyond the level of the other teeth. The earliest hominine remains possess canines that project slightly, but those of...