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Chapter Summary
Bipedal hominoids called hominins evolved in Africa at the end of the Miocene, with the earliest hominin fossils dating between 6 and 7 million years ago. Bipedalism may have been favoured by natural selection in hominoids exploiting food resources on the ground, outside the protection of forests. The earliest direct evidence of hominin bipedalism is a 3.6-million-year-old trail of fossilized footprints found in Laetoli, Tanzania. Hominins were probably omnivorous, and they could carry infants, food, and tools in their newly freed hands. The best-known early hominin fossils from approximately 3–4 mya have been placed in the genus Australopithecus.
Australopiths had distinctive dental features. Their teeth show an evolutionary trend toward smaller front teeth and enormous cheek teeth. This represents an adaptation to diets of coarse vegetable foods that required grinding. Australopith fossils from southern and eastern Africa with this dental pattern are classified into two groups: the gracile australopiths and the robust australopiths. Robust australopiths had more rugged jaws, flatter faces, and larger molars than the gracile australopiths. Apart from these differences, the gracile and robust australopiths had similar postcranial skeletons and chimpanzee-sized cranial capacities. There are many species that have been uncovered to steadily fill in the gaps of the hominin evolutionary record.
The first species of the genus Homo appeared about 2.4 mya. Many paleontologists believe that more than one Homo species may have coexisted in eastern Africa in the early Pleistocene alongside the eastern African robust australopiths. Fossils of early Homo disappear about 1.8 mya, either by evolving into or being replaced by Homo ergaster, or Homo erectus, the first Homo species to spread out of Africa. The cranium of H. erectus averages around 1000 cm3, within the lower range of modern human beings. Homo erectus may have been, to some extent, capable of speech. Wear patterns on teeth suggest that Homo erectus had a diet different from that of previous hominins. The postcranial skeleton of Homo erectus is more robust than that of modern humans and shows a marked reduction in sexual dimorphism compared to earlier hominins. Homo erectus probably did not hunt big-game animals as a major source of food.
Various species of Homo produced stone tools. Oldowan tools date to at least 2.5 mya, and were probably made by early Homo, and Acheulean tools are associated with Homo erectus. In recent years, however, archaeologists have concluded that it is misleading to associate individual stone-tool traditions with only one hominin species, or that stone tools were all used in similar ways. We must also remember that hominins probably produced tools and other forms of material culture made of perishable materials. For instance, some archaeologists have suggested that bamboo was available for toolmaking in those areas in Asia where Acheulean tools are lacking.
Learning Objectives
In this chapter, the student should learn to do the following:
- identify the distinctive morphological features of various hominin species;
- outline how and why bipedalism may have developed and explain why it is an adaptive trait;
- identify the main features of various hominin stone tool industries;
- outline the various theories that have been put forth to explain the appearance and geographical dispersal of Homo sapiens;
- explain various interpretations regarding the fate of Neanderthals;
- outline how and when the peopling of the New World and Australia occurred;
- explain how the concept of culture was an adaptive feature of Homo sapiens.