Major Bioanthropology research projects

Identifying the ancestors of Homo floresiensis

Professor Colin Groves and Dr Debbie Argue
ARC Fellowship 2010-2103

The discovery of a tiny, new hominid species living in Indonesia until just 12,000 years ago, at the same time as modern humans in the region, has sparked world-wide public interest and debate. Until now, discussions have focused on whether H. floresiensis represents a modern human with pathology, or whether it represents a distinct, and early, species of Homo as originally proposed (Brown et al., 2004; Morwood et al., 2004. It is now clear, however, that H. floresiensis is indeed a new hominin species (for example, Argue et al., 2006; Tocheri et al., 2007; Argue et al., 2009; Barb et al., 2009; Brown et al., 2009). We can, then, move ahead and consider the question of its ancestry. Identifying the ancestors of human species is fundamental to establishing the role of that species in human evolution. It is the means by which we come to an understanding of how our genus evolved.

We will use the combined techniques of CT scans, and morphological and metric analyses of the skeleton (skulls, teeth, jaws and postcrania) to study H. floresiensis and its potential ancestors. This is the most comprehensive approach that could be envisioned to identify the ancestors of H. floresiensis that will provide a significant break-through in our understanding of this species in human evolution. Our Partner Investigator is Professor William Jungers, of Stonybrook University Medical Center, New York, who brings a wealth of experience in human evolutionary studies.

References

Argue, D., Donlon, D., Groves, C., Wright, R., 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus or Homo? J. Hum. Evol. 51, 360-374.

Argue, D., Morwood, M. J., Sutikna, T., Jatmiko, and Wahyu Saptomo. 2009. Homo floresiensis: a cladistic analysis. J. Hum. Evol.57, 623-629.

Barb, K. L., McNulty, K. P., 2009. Size, shape, and asymmetry in fossil hominins: the status of the LB1cranium based on 3D morphometric analyses. J. Hum. Evol. 57, 208-622.

Brown, P., Maeda, T. 2009. Liang Bua Homo floresiensis mandibles and mandibular teeth: a contribution to the comparative morphology of a new hominin species. J. Hum. Evol. 57, 571-596.

Brown, P., Sutikna, T., Morwood, M.J., Soejono, R.P., Jatmiko, Wayhu Saptomo, E., Awe Due, R., 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431, 1055-1061.

Morwood, M.J., Soejono, R.P., Roberts, R.G., Sutikna, T., Turney, C.S.M., Westaway, K.E., Rink, W.J., Zhao, J.-x., Van den Bergh, G.D., Awe Due, R., Hobbs, D.R., Moore, W.M., Bird, M.I., Fifield, L.K., 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431, 1087-1091.

Morwood, M. J., Brown, P., Jatmiko, Sutikna, T., Wahyu Saptomo, E., Westaway, K. E., Rokus Awe Due, Roberts, R. G., Maeda, T., Wasisto, S., Djubiantono, T., 2005. Further evidence for small-bodied hominins from the late Pleistocene of Flores, Indonesia. Nature 437, 1012 - 1017.

Tocheri, M., Orr, C. M., Larson, S. G., Sutikna, T., Jatmiko, Saptomo, E., Wahyo, Rokus Awe Due, Djubiantano, T., Morwood, M. J., Jungers, W. l. 2007. The primitive wrist bone ofHomo. floresiensis and its implications for hominin evolution. Science 317, 1743 - 1745.

The Flores Hobbit – Homo Floresiensis or Microcephalic Eastern Indonesian?

Dr David Bulbeck and Dr Marc Oxenham
ARC Discovery Grant 2006

The announcement by Brown et al. (2004; Morwood et al. 2005) of a new species of Homo, which survived on the island of Flores in Indonesia till as recently as 13,000 years ago, is rightly hailed as one of the most remarkable discoveries ever in palaeoanthropology. The hominin’s minute stature (1 metre for the type specimen, Liang Bua 1), diminutive cranial capacity (415 cc), and survival till a time well after Homo sapiens had spread across Australasia, have stunned the scientific community. However, almost immediately after the official announcement, an alternative explanation sprang up, claiming that the type specimen was a modern human with microcephaly – a rare genetically based pathology that severely curtails the growth of the brain and stunts the individual’s growth. The specialist debate published so far has focused on craniometrics, and brain growth and development, including studies of endocasts that are claimed to support or refute the microcephaly hypothesis (Falk et al. 2005; Weber et al. 2005). (We are also aware of a wider range of issues being canvassed at the time of writing, but we shall desist from discussing them here as the relevant works are still in press or in preparation.)

Our project takes a different approach by studying features which, if associated with microcephaly, would be associated as secondary features, and which may well be entirely independent of brain size development. Brown and Morwood (2004), in their vigorous response to the microcephaly hypothesis, claim that Liang Bua 1 (along with other remains assigned to the species) expresses a suite of features that are absent from Homo sapiens, pathological or otherwise. The main examples of these features are: Tomes’ root on second lower premolar, molariform lower first premolar, rotated upper second premolars, anterior narrowing of the lower tooth row, posterior slope of the mandibular symphysis with complete absence of any chin, superior and inferior tori crossing the posterior surface of the mandibular symphysis, very large mandibular ramus relative to the corpus, a large fissure between the mastoid process and the petrous crest, a recess between the tympanic plate and the entoglenoid pyramid, a smooth tabular surface to the petrous pyramid, and a constricted foramen lacerum. To this impressive list of claimed, non-sapient characters can be added further traits that occur only infrequently in H. sapiens, such as a Tomes’ root on the first lower premolar, and multiple mental foramina. Postcranial peculiarities of the Liang Bua 1 type specimen further include relatively elongated arms and lack of humeral torsion.

However, can we be certain that these characters are entirely absent from microcephalic individuals and from eastern Indonesian Homo sapiens? Osteological studies of microcephaly are few and far between, and certainly have not extended to recording details of the morphology of the dentition, mandibular symphysis, cranial base, or postcranial anatomy. Similarly, the osteological documentation of recent eastern Indonesians is essentially restricted to craniometric comparisons (Pietrusewsky 1984) and some limited dental observations. If we could find a microcephalic eastern Indonesian, it would be possible to compare its features with those claimed for Homo floresiensis, to directly test the microcephalic hypothesis. No such specimen is known, however, so the only means to simulate such a test is to integrate (1) a “cross-racial” anatomical description of the secondary effects of microcephaly with (2) a description of the occurrence of the claimed H. floresiensis characters on eastern Indonesians. If the characters listed by Brown and Morwood (2004) are associated neither with microcephaly nor with eastern Indonesian anatomy, the microcephalic hypothesis would be falsified, perhaps fatally so; if on the other hand there is a tendency for these features to occur with microcephaly and amongst eastern Indonesians, the microcephalic hypothesis would have survived a falsification test.

Most of the known microcephalic specimens are of Europeans, and so our project has focused on European comparisons; in particular, the large collection at the Musée de l’Homme in Paris. However, we are also studying microcephalic skulls of a South African (Bradford University), a Mauritian of suspected African ancestry (Peabody Museum), two prehispanic Peruvians (Peabody and Smithsonian Institute), a New Caledonian (Musée de l’Homme), a South Indian (Royal College of Surgeons, London), an Egyptian and a Sri Lankan (British Museum of Natural History, London). During 2006 we shall also make comparable observations on non-microcephalic skulls from all of the populations represented by microcephalic specimens, as well as samples of eastern Indonesians (including prehistoric Flores burials represented by postcranial as well as cranial elements – Sukadana 1984; van der Plas 2002), to evaluate the microcephaly hypothesis.

Our observations will by no means be limited to the list of H. floresiensis characters identified by Brown and Morwood (2005), for two main reasons. First, our study may reveal further characters specifically relevant to microcephaly or to the morphology of eastern Indonesians, of benefit to these research areas as well as the specific hypothesis tested by the project. Secondly, a wide menu of measurements and morphological observations will provide a statistical context of observations for evaluating the discriminatory weight that should be assigned to the features specifically linked to microcephaly (or the morphology of Liang Bua 1). This latter point is in anticipation of the statistical analyses to be carried out on our results, including cladistic analysis, logistic discrimination, and multivariate analysis including principle coordinates analysis and linear discrimination analysis.

Acknowledgments

We gratefully thank the following curators who have facilitated our access to relevant museum collections: Philippe Mennecier (Musée de l’Homme), Jo Buckberry (Bradford University), John de Vos (Natural History Museum, Leiden), Olivia Herschensohn (Peabody Museum of Archaeology and Ethnology), David Hunt (American Museum of Natural History), Robert Kruszynski (British Museum of Natural History), and Simon Chaplin and Martyn Cooke (Royal College of Surgeons, London).

References

Brown, P., T. Sutikna, M.J. Morwood, R.P. Soejono, Jatmiko, E. Wahyu Saptomo and Rokus Awe Due, (2004), A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia, Nature 431:1055-61.

Brown, P. and M. Morwood, (2004), Comments, Before Farming 2004/4 article 1.

Falk, D., C. Hildebrot, K. Smith, M.J. Morwood, T. Sutikna, P. Brown, Jatmiko, E.W. Saptomo, B. Brunsden and F. Prior, (2005), The brain of LB1, Homo floresiensis, Science308:242-45.

Morwood, M.J., P. Brown, Jatmiko, T. Sutikna, E.W. Saptomo, K.E. Westaway, Rokus Awe Due, R.G. Roberts, T. Maeda, S. Wasisto, and T. Djubianto, (2005), Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia, Nature 437:1012-17.

Plas, M. van der, (2002), A New Model for the Evolution of Homo sapiens from the Wallacean Islands, Leiden University Biology Department undergraduate program paper, to be published online in PalArch.

Sukadana, A., (1981), Peninggalan manusia di Liang Bua dan hubungannya dengan penemuan di Lewoleba dan Melolo, Berkala Bioantropologi Indonesia 1, S. 53-72.

Weber, J., A. Czarnetzi and C.M. Pusch, (2005), Comment on “The brain of LB1, Homo floresiensis”, Science 310:236b.

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