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29.7D: Genus Homo

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    The human genus Homo, which includes modern humans as well as extinct human relatives, appeared around 2.3 million years ago.

    Learning Objectives
    • Compare and contrast the evolution and characteristics associated with the various Homo species: Homo habilis, erectus, and sapiens

    Key Points

    • Homo erectus, appearing 1.8 million years ago, was the first hominin species to migrate out of East Africa, use fire, and hunt.
    • Compared to Homo habilis, Homo erectus was more similar to modern humans due to its height and weight, brain size, limited sexual dimorphism, and downward-facing nostrils.
    • Archaic Homo sapiens had a similar brain size to modern humans (Homo sapiens sapiens), but, unlike modern humans, they had a thick skull, prominent brow ridge, and a receding chin.
    • The multiregional hypothesis of modern human origins states that there is an unbroken line of evolution involving regional adaptations and gene flow from H. erectus to H. sapiens sapiens.
    • The recent out of Africa hypothesis of modern human origins states that H. sapiens sapiens arose in Africa between 100,000 – 200,000 years, left Africa around 60,000 years ago, and replaced all archaic humans, with very little inter-breeding.
    • All men today inherited a Y chromosome from a male that lived in Africa about 140,000 years ago.

    Key Terms

    • Homo habilis: (“handy man”) an extinct taxonomic species within the genus Homo that had long arms and may have used stone tools
    • Homo erectus: (“upright man) extinct species of hominin that appeared 1.8 million years ago; the first hominin to use fire, hunt, and have a home base
    • Homo sapiens: evolved from H. erectus starting about 500,000 years ago; humans

    Early Hominins: Genus Homo

    The human genus, Homo, first appeared around 2.3 million years ago. For many years, fossils of a species called Homo habilis were the oldest examples in the genus Homo, but in 2010, a new species called Homo gautengensis was proposed that may be older, although it is not well accepted. In comparison to Australopithecus africanus, H. habilis had a number of features more similar to modern humans. H. habilis had a jaw that was less prognathic (forward projection of the jaw) than the australopiths and a larger brain, at 600–750 cubic centimeters. However, H. habilis retained some features of older hominin species, such as long arms. The name H. habilis means “handy man,” which is a reference to the stone tools that have been found with its remains.

    H. erectus appeared approximately 1.8 million years ago. It is believed to have originated in East Africa and was the first hominin species to migrate out of Africa. Fossils of H. erectus have been found in India, China, Java, and Europe, and were known in the past as “Java Man” or “Peking Man.” H. erectus had a number of features that were more similar to modern humans than those of H. habilis. H. erectus was larger in size than earlier hominins, reaching heights up to 1.85 meters and weighing up to 65 kilograms, sizes similar to those of modern humans. Its degree of sexual dimorphism was less than earlier species, with males being 20 to 30 percent larger than females, which is close to the size difference seen in our species. H. erectus had a larger brain than earlier species at 775–1,100 cubic centimeters, which compares to the 1,130–1,260 cubic centimeters seen in modern human brains. H. erectus also had a nose with downward-facing nostrils similar to modern humans, rather than the forward facing nostrils found in other primates. Longer, downward-facing nostrils allow for the warming of cold air before it enters the lungs and may have been an adaptation to colder climates. Artifacts found with fossils of H. erectus suggest that it was the first hominin to use fire, hunt, and have a home base. H. erectus is generally thought to have lived until about 50,000 years ago.

    image

    Homo erectus

    Homo erectus had a prominent brow and a nose that pointed downward rather than forward.

    Humans: Homo sapiens

    A number of species, sometimes called archaic Homo sapiens, apparently evolved from H. erectus starting about 500,000 years ago. These archaic H. sapiens had a brain size similar to that of modern humans, averaging 1,200–1,400 cubic centimeters. They differed from modern humans by having a thick skull, a prominent brow ridge, and a receding chin. Some of these populations survived until 30,000–10,000 years ago, overlapping with anatomically-modern humans.

    image
    Figure \(\PageIndex{1}\): Homo sapiens neanderthalensis Tools: The Homo sapiens neanderthalensis used tools and may have worn clothing.

    There is considerable debate about the origins of anatomically-modern humans or Homo sapiens sapiens. As discussed earlier, H. erectus migrated out of Africa and into Asia and Europe in the first major wave of migration about 1.5 million years ago. The multiregional hypothesis holds that humans first arose near the beginning of the Pleistocene two million years ago and subsequent human evolution has been within a single, continuous human species. This species encompasses archaic human forms such as Homo erectus and Neanderthals as well as modern forms, which evolved worldwide to the diverse populations of modern Homo sapiens sapiens. The hypothesis contends that humans evolve through a combination of adaptation within various regions of the world and gene flow between those regions. Proponents of multiregional origin point to fossil and genomic data and continuity of archaeological cultures as support for their hypothesis.

    The primary alternative hypothesis is the recent African origin of modern humans, which holds that modern humans arose in Africa around 100,000–200,000 years ago, moving out of Africa around 50,000–60,000 years ago to replace archaic human forms with limited interbreeding: at least once with Neanderthals and once with Denisovans.

    Contributions and Attributions

    This page titled 29.7D: Genus Homo is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Boundless.

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