This chapter deals with the human record from approximately 7 m.y.a. to 2 m.y.a., from the first humans to the emergence of Homo erectus. The few years elapsed since the third edition of Images of the Past have seen major changes in the fossil record for early humans. This part of the book probably contains the most revisions. The big news of course is the discovery of much older fossil hominins from the late Miocene and early Pliocene in East and especially Central Africa. Many new terms also have appeared from species names to the generic hominin replacing hominid as a more accurate designation of our human ancestors. Although the evidence if fragmentary and rare, it is still possible to put together a picture of the evolutionary history of the hominins during the Miocene, Pliocene, and early Pleistocene. New kinds of evidence (e.g., enamel thickness and sexual dimorphism) are also being used in classification in addition to the usual bipedalism, brain size, and tool use.

Many new varieties of African apes appeared in the late Miocene as the climate of this region became drier and the tropical rain forests shrank. Some of these apes were bipedal by the end of the Miocene. Only a very few examples of these Miocene hominins are known, including Sahelanthropus tchadensis, Orronin tugensis, and Ardipithecus ramidus. They’re known characteristics reveal a mix of ape and more human features.

A variety of hominin forms appeared in the Pliocene, probably in response to the continued climatic trend to drier conditions. These new forms include a variety of Australopithecines and Kenyapithecus. Their bipedal locomotion is well documented, both in the fossil bones themselves and especially in the remarkable footprints from Laetoli, dating to 3.6 m.y.a. They are generally small brained with large teeth.

Sometime between 3 and 2 m.y.a., our ancestors began to make stone tools. In this same period, near the end of the Pliocene, human evolution took two major paths. Paranthropus followed a dead end street and disappeared before 1 m.y.a. Homo habilis started along the pathway to the present, a curious species with a mixture of traits, combining large teeth and small brains, with other more evolved features. Determination of the correct species for habilis — whether Australopithecus or Homo — remains difficult.

These individuals almost certainly lived in small groups, evidenced by the clusters of animal bones and stone tools at Olduvai, Koobi Fora, and elsewhere. Early hominins ate both meat and plants. How they obtained the meat is unclear, but it appears that they may have hunted small animals and scavenged the marrow-rich bones and remaining meat from the large animal kills of other predators.

The sites covered in this chapter are the touchstones of early hominins, Hadar, Laetoli, Swartkrans, and Olduvai. Hadar, as the fossil hunting grounds par excellence in Ethiopia, is the source of many of the best-known early human remains. Laetoli is renowned of course for the footprints preserved in ash, but the area also holds fossils and stone tools. Swartkrans is used as an example of the South African center for early hominins, and certainly the ongoing work there is revealing more and older fossils all the time. Olduvai is world heritage, home of zinj, Homo, Oldowan tools, cutmarks, and Louis Leakey. Olduvai is one of the four of five best-known archaeological sites in the world.

We spend a good bit of time in this chapter on new discoveries and our family tree. The stages of human evolution become more complex and more confusing. We have limited the number of genus and species covered in this chapter to make a more comprehensible story of our early ancestors. We have also included dating methods, and specifically potassium/argon dating as a means for determining the age of early fossil materials. Other dating methods, specifically isotope stages, radiocarbon dating, and dendrochronology are covered in other chapters in Images.

This chapter also is concerned with the non-skeletal evidence of the first tools and faunal remains. Information on the technology of stone tools and on the scavenging vs. hunting debate is provided in the blocks. The Leakey family is also the subject of a section, providing a glimpse of the famous paleoanthropologists and their descendants. The chapter concludes with a summary and a speculative discussion of the biological consequences of becoming human, including the loss of estrus, undeveloped brains at birth, and bipedalism.