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Published online on February 2, 2007, 10.1073/pnas.0609185104
PNAS | February 13, 2007 | vol. 104 | no. 7 | 2513-2518


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BIOLOGICAL SCIENCES / NEUROSCIENCE
Brain shape in human microcephalics and Homo floresiensis

Dean Falk*,{dagger}, Charles Hildebolt{ddagger}, Kirk Smith{ddagger}, M. J. Morwood§, Thomas Sutikna, Jatmiko, E. Wayhu Saptomo, Herwig Imhof||, Horst Seidler**, and Fred Prior{ddagger}

*Department of Anthropology, Florida State University, Tallahassee, FL 32306; {ddagger}Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110; §Archaeology and Palaeoanthropology, University of New England, Armidale, New South Wales 2351, Australia; Indonesian Centre for Archaeology, JI. Raya Condet Pejaten No. 4, Jakarta 12001, Indonesia; ||Clinic for Radiodiagnostics, Medical University of Vienna, A-1090 Vienna, Austria; and **Department of Anthropology, University of Vienna, A-1090 Vienna, Austria

Edited by Marcus E. Raichle, Washington University School of Medicine, St. Louis, MO, and approved December 7, 2006 (received for review October 18, 2006)

Because the cranial capacity of LB1 (Homo floresiensis) is only 417 cm3, some workers propose that it represents a microcephalic Homo sapiens rather than a new species. This hypothesis is difficult to assess, however, without a clear understanding of how brain shape of microcephalics compares with that of normal humans. We compare three-dimensional computed tomographic reconstructions of the internal braincases (virtual endocasts that reproduce details of external brain morphology, including cranial capacities and shape) from a sample of 9 microcephalic humans and 10 normal humans. Discriminant and canonical analyses are used to identify two variables that classify normal and microcephalic humans with 100% success. The classification functions classify the virtual endocast from LB1 with normal humans rather than microcephalics. On the other hand, our classification functions classify a pathological H. sapiens specimen that, like LB1, represents an {approx}3-foot-tall adult female and an adult Basuto microcephalic woman that is alleged to have an endocast similar to LB1's with the microcephalic humans. Although microcephaly is genetically and clinically variable, virtual endocasts from our highly heterogeneous sample share similarities in protruding and proportionately large cerebella and relatively narrow, flattened orbital surfaces compared with normal humans. These findings have relevance for hypotheses regarding the genetic substrates of hominin brain evolution and may have medical diagnostic value. Despite LB1's having brain shape features that sort it with normal humans rather than microcephalics, other shape features and its small brain size are consistent with its assignment to a separate species.

virtual endocast

Author contributions: D.F., C.H., and K.S. designed research; D.F., C.H., K.S., M.J.M., T.S., J., E.W.S., H.I., H.S., and F.P. performed research; D.F., C.H., and K.S. analyzed data; and D.F., C.H., K.S., M.J.M., and F.P. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS direct submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0609185104/DC1.

{dagger}To whom correspondence should be addressed. E-mail: dfalk{at}fsu.edu

© 2007 by The National Academy of Sciences of the USA


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