13-1 Introduction

Hominids are the branch of apes that walk upright (Section 13-2). The first bipedal hominid in the fossil record was Sahelanthropus (7 Ma). Ardipithecus and Orrorin appeared 6 Ma. Orrorin, which appeared earlier, had teeth that were more human like than Ardipithecus. Australopithecus appeared 4 Ma and was the first homonin with feet that were designed for walking on the ground rather than grasping trees. They still had small brains. Tools and a larger brain size appeared 2.5 Ma with Homo habilis and Paranthropus boisei. Homo habilis was the first Homo species, albeit controversial.

Paranthropus boisei (2.6–1.2 Ma) was discovered in 1959 by Mary Leakey in the Olduvai Gorge in Tanzania. Paranthropus was a contemporary of australopithecines, and like the australopithecines, they were approximately 4 ft tall; however, they had a much larger brain (500–550 cc) and were heavier (68 kg). The males were much larger than the females. Although they appear to be transitional early Homo species, they were not ancestral to the Homo genus.

In the current classification scheme, there are four adaptations that define the Homo genus: a brain larger than 600 cc, proportions of limbs similar to humans (long legs and short arms), the use of language, and use and manufacture of stone tools. Although Homo habilis does not definitively fulfill these classifications, scientists have continued to classify Homo habilis as part of the Homo genus (Section 13-3).

Early species of Homo erectus, Homo erectus ergaster or Homo ergaster and Homo erectus georgicus appeared 2 million years ago. The earliest species appeared in China. They were much more similar to Homo sapiens than previous marginal Homo species. They had a much larger brain, complex tools, long legs and short arms, and small teeth. With the advent of cooking and a change in diet, they did not need large teeth. They were the dominant Homo species on earth for 1.5 million years (Section 13-4).

About 500,000 years ago, two new Homo species appeared, Homo heidelbergenesis, and Homo neanderthalensis (Section 13-5), which had brain sizes in the range of human (Homo sapiens) brains (Section 13-6). Humans that looked like humans appeared 200,000 years ago, and modern thinking humans appeared in South Africa approximately 70,000 years ago when humans began to spread around the world (Section 13-7) .