At first glance, the study of human evolution is both fascinating and confusing. Gaining a working knowledge of that evolutionary history is complex. Chapter 10 is introduced with an overview of human evolution, covering 6 million years of hominid history, from the point at which the hominin line split from African apes.

The fossil evidence of early hominin history begins with the discovery in 1924 of Australopithecus africanus, a small hominin with human-like teeth and upright posture. This discovery ushered in the beginning of a series of fossil discoveries of 'australopiths' which continues to expand today. Supporting Darwin's idea as the beginning of human evolution, a wide breadth of discoveries of African hominin (as many as 12 species to date) has caused the original branching family 'tree' model to be considered as a 'bush' with many branches. In spite of this diversity of early hominins, shared characteristics are also discussed: bipedalism, ape-sized anatomy, cranial capacities, and stature.

The sheer breadth of the evolution of early hominin species, and fossil evidence supporting it, is chronologically treated in separate sections. The first discussion centers on the first possible hominids, Sahelanthropus , Orrorin , and Ardipithecus, a group of small-brained, very primitive bipeds who all date back 6 million years or more.

The second section covers primitive hominins that lived between 4.2 million and approximately 3 million years ago: Australopithecus anamensis, Australopithecus afarensis, and Kenyanthropus platyops. Also small-brained and bipedal, all retained primitive ape characteristics in their teeth. These characteristics lessened over time.

The third section covers a period in hominin fossil history when a high level of diversity existed, from approximately 3 million to 1.4 million yeas ago. Three robust Australopithecus, Australopithecus aeopithecus, and two later species, Australopithecus robustus and Australopithecus boisei, all represent a collective group of small-brained bipedal hominins possessing very large, robust back teeth, jaws, and faces. Cranial features suggest heavy chewing and suggest a hard diet of seeds, nuts, and hard fruits. Despite their strongly constructed anatomical features, they were our close relatives.

Debate regarding the specific evolutionary relationships of the robust australopiths continues, but there is general agreement that they represent a side branch in human evolution that became extinct. Two species, Australopithecus africanus and Australopithecus ghari may represent an ancestor of the genus Homo . Questions concerning subtle anatomical changes of the latter suggest it is the likely candidate.

The chapter concludes with a discussion of available information that can help reconstruct the general patterns of early hominid evolution, including the construction of family trees which help solve questions concerning the evolutionary relationships of early hominins, the common robust ancestry, and speculation concerning which early hominid or hominids gave rise to the genus Homo. A discussion of the possibilities regarding the origin of bipedalism is also considered.