Patterns of hominid evolution and dispersal in the Middle Pleistocene

Abstract

At the onset of the Quaternary, hominids identified as Homo erectus spread widely across the Old World. These populations persisted in the Far East until late in the Middle Pleistocene, while in the West, the species disappeared at a relatively early date. Humans that are different from Homo erectus evolved first in Africa or western Eurasia. One of the most important fossils now thought to document a distinct species was discovered at Broken Hill (Kabwe) in Zambia in 1921. This well-preserved cranium reveals many aspects of the morphology of the face, braincase, and skull base. Broken Hill is similar to other less complete fossils from Elandsfontein and Bodo in Africa and also to hominids including Arago and Petralona from Europe. These crania exhibit some archaic (erectus-like) characters, but there is an increase in brain size. Also, the morphology of the nose and palate, the temporal bone and the occipital region is advanced relative to the condition in Homo erectus. This evidence is in keeping with an episode of speciation occurring in the mid-Quaternary and giving rise to populations that are more modern anatomically. Although there is disagreement about taxonomy, it can be argued that the new species is appropriately called Homo heidelbergensis. Key questions awaiting resolution concern the geographic region where this taxon originated, its subsequent dispersal, and the role played by these populations in the spread of Acheulean stone technologies. Other issues are phylogenetic, and it is important to clarify the relationship of Homo heidelbergensis to Neanderthals and recent humans.