Hominine Evolution

What adaptations enabled later hominine species to walk upright?

Between 6 and 7 million years ago, the lineage that led to humans split from the lineage that led to chimpanzees. The hominoids in the lineage that led to humans are called hominines. Hominines include modern humans and all other species more closely related to us than to chimpanzees. Hominines evolved the ability to walk upright, grasping thumbs, and large brains. Figure 26–16 shows some ways in which the skeletons of modern humans differ from those of hominoids such as gorillas. The skull, neck, spinal column, hip bones, and leg bones of early hominine species changed shape in ways that enabled later species to walk upright. The evolution of this bipedal, or two-footed, locomotion was very important, because it freed both hands to use tools. Meanwhile, the hominine hand evolved an opposable thumb that could touch the tips of the fingers, enabling the grasping of objects and the use of tools.

Hominines also evolved much larger brains. The brains of chimpanzees, our closest living relatives, typically range in volume from 280 to 450 cubic centimeters. The brains of Homo sapiens, on the other hand, range in size from 1200 to 1600 cubic centimeters! Most of the difference in brain size results from a radically expanded cerebrum.

FIGURE 26–16 Comparison of Hominoids Modern hominines walk upright on two legs; gorillas use all four limbs. The diagrams show many of the skeletal characteristics that allow hominines to walk upright. Compare and Contrast According to the chart and illustrations, what are the other skeletal differences between humans and gorillas?

ddd