Human Evolutionary History
We briefly review the relationships of modern humans and the great apes before considering the evidence for and against Ardipithecus ramidus, Ardipithecus kadabba, Orrorin tugenensis, and Sahelanthropus tchadensis being the earliest members of the hominin clade. We then describe each of the well-established hominin taxa recognized in a speciose interpretation of the hominin fossil record into five morphological grades, “archaic hominins,” “megadont and hypermegadont archaic hominins,” “transitional hominins,” “premodern Homo,” and “anatomically modern Homo” (the grade that includes modern humans). Within each grade we summarize the species and site samples in historical order. We also consider evidence for anagenesis and cladogenesis within the hominin clade. Finally, we summarize currently available estimates for endocranial volume and body mass, two variables particularly relevant for understanding the evolution of the hominin nervous system.
