[Paleopsych] SW: New Discoveries of the Dwarf Human Species

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Anthropology: New Discoveries of the Dwarf Human Species

    The following points are made by Daniel E. Lieberman (Nature 2005
    1) The recent announcement[1,2] of a newly discovered species of tiny
    human from the Indonesian island of Flores was astonishing. This
    intriguing scientific story continues with new work[3] which describes
    further fossil evidence from the cave of Liang Bua on Flores. The
    original fossil remains[1] consisted primarily of a single partial
    skeleton (LB1), excavated from deposits in Liang Bua dated to the end
    of the last ice age. Stone tools, evidence of fire-making and the
    bones of a dwarfed elephant species were also found, those bones
    apparently being the result of hunting.
    2) The LB1 skeleton, dated to 18,000 years ago, was probably a female,
    just over a meter tall. It had a brain volume of 380 cm^(3), roughly
    the size of a chimpanzee brain. Although LB1 has a somewhat
    primitively shaped pelvis, it shares many derived characteristics of
    the genus Homo, particularly in the teeth, jaw and cranium. These
    similarities, combined with other distinctive features, led Brown and
    colleagues[1] to propose a new species, Homo floresiensis. They
    further suggested that H. floresiensis was a dwarfed descendant of
    Homo erectus, another hominid species, which is thought to have
    arrived on Flores by 800,000 years ago[4].
    3) Homo floresiensis caused a stir by challenging preconceptions. If
    it is a new species, then we shared this planet with other hominids
    much more recently than anyone thought -- long after the Neanderthals
    became extinct, after modern humans arrived in Australia, and at about
    the time that agriculture was first invented. More unusual is the
    proposal that H. floresiensis evolved from H. erectus through
    dwarfing. This phenomenon, known as endemic or island dwarfing,
    sometimes occurs on islands when species are released from the
    pressures of predation but become constrained by limited resources and
    small population sizes[5]. In such conditions, large animals tend to
    become smaller and small animals tend to become larger. The process
    was clearly occurring on Flores, whose fauna includes giant rats and
    now-extinct miniature elephants. What captures the imagination is that
    dwarfing might have occurred in humans, who often buffer themselves
    from natural selection through cultural means such as tool production
    and fire-making, both evident at Liang Bua[2].
    4) The Liang Bua finds have generated controversy. Two alternative
    hypotheses, yet to be published in the peer-reviewed literature, have
    been proposed. One is that the LB1 skeleton is a pygmy human, not a
    new hominid species. The other is that LB1 is a human who suffered
    from a form of microcephaly, a pathological condition characterized by
    an abnormally small brain and head, and which can also cause dwarfism.
    5) Morwood and colleagues[3] now counter some of these claims with
    evidence recovered during excavations in 2004. The material
    substantially expands the sample attributed to H. floresiensis, and
    provides additional details about the proposed species. The new
    fossils consist of the right humerus, radius and ulna of the LB1
    skeleton, the mandible of a second individual (LB6), and assorted
    other remains including two tibiae, a femur, two radii, an ulna, a
    scapula, a vertebra, and various toe and finger bones. The researchers
    think that the sample includes the remains of at least nine
    References (abridged):
    1. Brown, P. et al. Nature 431, 1055-1061 (2004)
    2. Morwood, M. J. et al. Nature 431, 1087-1091 (2004)
    3. Morwood, M. J. et al. Nature 437, 1012-1017 (2005)
    4. Morwood, M. J., O'Sullivan, P. B., Aziz, F. & Raza, A. Nature 392,
    173-176 (1998)
    5. Foster, J. B. Nature 202, 234-235 (1964)
    Nature http://www.nature.com/nature
    Related Material:
    The following points are made by M.M. Lahr and R. Foley (Nature 2004
    1) The recently discovered Homo floresiensis fossils (1,2) probably
    left no descendants, are not very old, and were found on a remote
    island. Despite this, they are among the most outstanding discoveries
    in palaeoanthropology for half a century. The find is startling. It is
    of a pygmy-sized, small-brained hominin, which lived as recently as
    18,000 years ago, and which was found on the island of Flores together
    with stone tools, dwarf elephants and Komodo dragons.
    2) The Flores fossils add a new and surprising twig to the hominin
    family tree, which diverged from the chimpanzee lineage about 7
    million years ago. The first African hominins existed 7-1.2 million
    years ago, were 1-1.5 meters tall, walked upright on two legs (i.e.,
    were bipedal), and had chimpanzee-size brains. These early forms
    comprised as many as six genera and fourteen species, of which the
    australopithecines are the best known. By 2.5 million years ago, our
    own genus, Homo, had emerged, with its different body shape, slower
    growth, greater reliance on meat in the diet, and "encephalization" --
    larger brains than expected for body size. These were the first
    hominins to make stone tools systematically and to colonize Eurasia.
    They include the familiar names of H. habilis, H. erectus, H.
    neanderthalensis and, finally, H. sapiens, which put in an appearance
    about 160,000 years ago. The new fossil is part of this Homo group.
    3) Flores lies to the east of Java, and was probably never connected
    to the mainland. The presence of 800,000-year-old simple stone tools
    first attracted attention in 1998 (3), raising the controversial
    possibility that H. erectus had produced them and had crossed major
    sea barriers to reach Flores. Now we have the announcement of the
    discovery of an 18,000-year-old hominin skeleton from a cave, Liang
    Bua, on Flores. Although this date is more than 140,000 years after
    modern humans evolved in Africa, more than 25,000 years after H.
    sapiens reached Australia, and about 10,000 years after the last known
    Neanderthal, the skeleton is that of a new species -- Homo
    floresiensis. Its most remarkable features are its diminutive body
    (about a meter in height) and brain size (at 380 cm^(3), the smallest
    of any known hominin).
    4) Homo floresiensis is a challenge -- it is the most extreme hominin
    ever discovered. An archaic hominin at that date changes our
    understanding of late human evolutionary geography, biology and
    culture. Likewise, a pygmy and small-brained member of the genus Homo
    raises questions about our understanding of morphological variability
    and allometry -- the relation between the size of an organism and the
    size of any of its parts. Brown et al(1) claim that the skeleton,
    designated LB1, represents a new species within the genus Homo. They
    believe that it may have been a female. They also conclude that it was
    a dwarfed descendant of Javanese H. erectus, and part of an endemic
    island fauna.(4,5)
    References (abridged):
    1. Brown, P. et al. Nature 431, 1055-1061 (2004)
    2. Morwood, M. J. et al. Nature 431, 1087-1091 (2004)
    3. Morwood, M. J., O'Sullivan, P. B., Aziz, F. & Raza, A. Nature 392,
    173-176 (1998)
    4. Conway Morris, S. Life's Solutions: Inevitable Humans in a Lonely
    Universe (Cambridge Univ. Press, 2003)
    5. Wood, B. & Richmond, B. G. J. Anat. 197, 19-60 (2000)
    Nature http://www.nature.com/nature
    Related Material:
    The following points are made by Jeffrey H. Schwartz (Science 2004
    1) The period from 1 million to 500,000 years ago (~1 to 0.5 Ma) is
    well represented in the human fossil records of Europe and Asia. Sites
    containing such fossils include Ceprano, Italy (~0.9 to 0.8 Ma), the
    TD-6 level at Atapuerca's Gran Dolina, Spain (~0.78 Ma), Trinil,
    Indonesia (1 to 0.7 Ma), some parts of the Sangiran Dome, Indonesia
    (1.5 to 1 Ma), Lantian, China (~1 Ma), and probably Zhoukoudian, China
    (0.55 to 0.3 Ma).
    2) By contrast, Africa has been unusually uninformative about this
    part of human evolution. Three partial mandibles unearthed more than
    50 years ago at Tighenif (Ternifine) in Algeria (~0.7 Ma) are similar
    in dental morphology to specimens from Gran Dolina (1), but the former
    are rarely mentioned in the literature. The question thus remained:
    Where are the African fossils?
    3) The recent discovery of the partial Daka skull (~1 Ma) at the Bouri
    site, Middle Awash, Ethiopia (2), provided part of the answer. Potts
    et al (3) recently reported that the archaeologically and faunally
    rich site of Olorgesailie, Kenya, has divulged its first hominid
    fossils: a partial frontal and more fragmentary temporal bone dated
    0.97 to 0.9 Ma. Like the Daka specimen, these fragments (KNM-OL 45500)
    were assigned to the species Homo erectus.
    4) Potts et al. correctly assess the "Homo erectus" debate: "The
    entire sample of fossils from Africa, Asia, and Europe exhibits wide
    morphological variation that some researchers divide into multiple
    lineages and others place in a single, polytypic species." They opt
    for the latter hypothesis and conclude that "comparison of the KNM-OL
    45500 with other crania . . . illustrates that metric and qualitative
    similarities cut across temporal and spatial groups of fossil
    specimens." Assuming that a vast array of specimens of differing
    morphologies constitute the same species, favorable comparisons
    between some of them in one or a few morphologies are expected,
    especially if primitive retentions and shared derived features are not
    sorted out.
    5) But this does not clarify the question, "What is H. erectus?" One
    is left primarily with the traditional approach to the genus Homo: H.
    erectus is not H. habilis, H. heidelbergensis, or H. sapiens, whatever
    they are.
    6) Recognizing that "Homo erectus" may be more a historical accident
    than a biological reality might lead to a better understanding of
    those fossils whose morphology clearly exceeds the bounds of
    individual variation so well documented in the Trinil/Sangiran sample.
    In the meantime, OL 45500 should remind us that hominid systematics
    must be an endeavor of testing long-entrenched hypotheses, especially
    when those who turn to these hypotheses acknowledge them as being
    References (abridged):
    1. J. H. Schwartz, I. Tattersall, The Human Fossil Record, vol. 4,
    Craniodental Morphology of Australopithecus, Paranthropus, and Orrorin
    (Wiley-Liss, New York, in press)
    2. B. Asfaw et al., Nature 416, 317 (2002)
    3. R. Potts, A. K. Behrensmeyer, A. Deino, P. Ditchfield, J. Clark,
    Science 305, 75 (2004)
    4. J. H. Schwartz, I. Tattersall, The Human Fossil Record, vol. 2,
    Craniodental Morphology of Genus Homo (Africa and Asia) (Wiley-Liss,
    New York, 2003)
    5. J. H. Schwartz, I. Tattersall, Acta Anthropol. Sin. 19 (suppl.), 21
    Science http://www.sciencemag.org

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