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Study of the Brain of LB1, Homo Floresiensis (Hobbit)

Charles Hildebolt, Kirk Smith, Barry Brunsden, and Fred Prior

Description

In September of 2003 on the Indonesian Island of Flores, a team of Australian and Indonesian archaeologists made an unexpected find, that of a new humanlike species—classified as Homo floresiensis.  The fossilized remains included bones from many individuals; however, one nearly complete skeleton included a complete skull.  The skeletal bones indicated a female about one meter (about 3 feet) tall and a cranial capacity about one-third the size of modern humans, however, study of the cranial sutures and tooth wear indicated that she was a full-grown adult at the time of death.  Radiocarbon testing has shown that this dwarflike creature lived around 18,000 years ago, alongside Komodo dragons and pygmy elephants (or stegodons), whose skeletons have been discovered in the same cave (Liang Bua) where LB1 was found. The specimen LB1 came to be known as the Hobbit because of her small size.

Two articles on the discovery, published in the journal Nature, appeared in October 2004 and sparked widespread comment in the anthropological community, where there is considerable dispute over what Hobbit is and what it represents. Never before has such a small brain size been associated with a cognitive level capable of making such advanced tools.  Some skeptics claimed that this must be a microcephalic modern human—a position undermined by the discovery at the same site of partial skeletons of other individuals from this same species. Others, including the archaeologists who unearthed it, believe LB1 to be the heretofore-unknown descendant of a Homo erectus population that somehow traveled to this island and, with long-term isolation, adapted to its harsh new life by becoming smaller and more dwarflike.

Goals

Using CT data that were obtained in Indonesia and advanced computer software, we produced a digital representation, or ‘virtual endocast’ of the Hobbit's brain case. Nothing remains of the Hobbit's brain in her fossilized skull, but the living brain makes lasting impressions on the interior of the skull that can be used to infer some aspects of brain structure.

Homo floresiensis
Figure 1.  Three-dimensional (3D)  rendering of computed tomographic (CT) data of Homo floresiensis (LB1). The virtual endocast (brain) of LB1 is red.


For comparison, we scanned skulls on loan from the Cleveland Museum of Natural History and the American Museum of Natural History. Included among the human skulls were those of a microcephalic and a pygmy. Three-dimensional images of various fossil endocasts, including Hobbit’s, were generated and placed on the CT computer screen side-by-side for comparison. The images were also normalized to the volume of the Hobbit endocast to facilitate direct shape comparisons.  Physical models of the Hobbit, pygmy, and microcephalic endocasts were created from the virtual models with the assistance of two local companies (Realadi and QTE, both in St. Charles, MO).

Our detailed analysis revealed little similarity to microcephalics and pygmies and support the theory that the fossil is a member of a unique ancestral species. Little similarity was found between the Hobbit virtual endocast and either the pygmy or microcepahlic endocast. In addition to studying brain shapes, we conducted detailed comparisons of dimensions in the virtual endocasts. These analyses identified several similarities between the Hobbit's brain and that of Homo erectus. There were, however, significant differences between the Hobbit and Homo erectus.


hobbit
Figure 2.  Superior and right lateral views of the brains of a normal contemporary human (HS), a human microcephalic (mcHs), a Homo erectus (He), and a chimp (Pt). Homo floresiensis (LB1) is in the middle. The brains are all scaled to the same size. 

hobbit
Figure 3.  Right lateral and frontal views of Homo floresiensis (LB1).

Affiliations

Dean Falk, Florida State University
Lead author Dean Falk, Ph.D., the Hale G. Smith Professor and chair of anthropology at Florida State University, is an expert in paleoneurology, the study of brain evolution. Falk normally studies skull structure with measuring calipers and dental floss. When the National Geographic Society supplied her with a cast of the Hobbit's skull for analysis, Falk approached Washington University's Mallinckrodt Institute of Radiology for help.

Thomas Sutikna, Jatmiko, Radien P. Soejono, and E. Wayhu Saptomo, Indonesian Centre for Archaeology, Indonesian

Michael. J. Morwood and Peter Brown, University of New England, Australia

Realadi, St. Charles, MO http://www.realadi.com/

QTE, St. Charles, MO http://www.qtecad.com/

Support

Funding from the National Geographic Society (Link) and Mallinckrodt Institute of Radiology at Washington University School of Medicine (link) supported this research.

References

28 October 2004 article in which the discovery of
Homo floresiensis
was first described.

Brown P, Sutikna T, Morwood MJ, Soejono RP, Jatmiko, Saptomo EW, and Due RA (2004) A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia.[see comment]. Nature 431:1055-61.

http://www.nature.com/nature/journal/v431/n7012/pdf/nature02999.pdf

Supplementary on line material:
http://www.nature.com/nature/journal/v431/n7012/suppinfo/nature02999.html

Abstract:Currently, it is widely accepted that only one hominin genus, Homo, was present in Pleistocene Asia, represented by two species, Homo erectus and Homo sapiens. Both species are characterized by greater brain size, increased body height and smaller teeth relative to Pliocene Australopithecus in Africa. Here we report the discovery, from the Late Pleistocene of Flores, Indonesia, of an adult hominin with stature and endocranial volume approximating 1 m and 380 cm3, respectively--equal to the smallest-known australopithecines. The combination of primitive and derived features assigns this hominin to a new species, Homo floresiensis. The most likely explanation for its existence on Flores is long-term isolation, with subsequent endemic dwarfing, of an ancestral H. erectus population. Importantly, H. floresiensis shows that the genus Homo is morphologically more varied and flexible in its adaptive responses than previously thought.

 

8 April 2005 article in which the analysis of
the endocast of LB1 was presented.

Falk D, Hildebolt C, Smith K, Morwood MJ, Sutikna T, Brown P, Jatmiko, Saptomo EW, Brunsden B, and Prior F (2005) The brain of LB1, Homo floresiensis. Science 308:242-5.

http://www.sciencemag.org/cgi/reprint/308/5719/242.pdf

Supporting on line material:
http://www.sciencemag.org/cgi/data/1109727/DC1/1

Abstract:The brain of Homo floresiensis was assessed by comparing a virtual endocast from the type specimen (LB1) with endocasts from great apes, Homo erectus, Homo sapiens, a human pygmy, a human microcephalic, specimen number Sts 5 (Australopithecus africanus), and specimen number WT 17000 (Paranthropus aethiopicus). Morphometric, allometric, and shape data indicate that LB1 is not a microcephalic or pygmy. LB1's brain/body size ratio scales like that of an australopithecine, but its endocast shape resembles that of Homo erectus. LB1 has derived frontal and temporal lobes and a lunate sulcus in a derived position, which are consistent with capabilities for higher cognitive processing.

14 October 2005 Comment on
“The Brain of LB1, Homo floresiensis.”

J. Weber, A. Czarnetzki, C. M. Pusch, Comment on “The Brain of LB1, Homo floresiensis.” Science 310, 236 (2005);

www.sciencemag.org/cgi/content/full/310/5746/236b.
http://www.sciencemag.org/cgi/reprint/310/5746/236b.pdf

Abstract:Falk et al. (Reportts, 8 April 2005, p 242) presented new data on the brain of the type specimen of Homo floresiensis, LB1. We argue that the size, proportions, and shape of the LBq endocast fall withinthe range of variation observed for microcephalics.  This specimen mirght therefore represent a pathological human being rather than a new hominid species.

Response to 14 October 2005 Comment on
“The Brain of LB1, Homo floresiensis.”

Falk D. Hildebolt CF, Smith K, Morwood MJ, Sutikna T, Jatmiko, Saptomo WE, Brunsden B, Prior F. Response to Comment on “The Brain of LB1, Homo floresiensis.”  Science 310:235, 2005.

http://www.sciencemag.org/cgi/reprint/310/5746/236c.pdf

Abstract:Weber et al. claim to have one microcephalic individual whose endocast shape is essentially identical to that of LB1, but they fail to provide its absolute measurements or illustrate it properly.  We show that images of their microcephalic endocasts resemble those of the microceplic we compared to LB1. 

19 May 2006 Comment on
“The Brain of LB1, Homo floresiensis.”

Martin, RD, MacLarnon, AM, Phillips, JL, Dussubieux, L P,  Williams, R, Dobyns WB. Comment on "The brain of LB1, Homo floresiensis" Science 312, 999 (2006)

www.sciencemag.org/cgi/content/full/312/5776/999b

Abstract:Endocast analysis of the brain Homo floresiensis by Falk et al. (Reports, 8 April 2005, p. 242) implies that the hominid is an insular dwarf derived from H. erectus, but its tiny cranial capacity cannot result from normal dwarfing.  Consideration of more appropriate micrephlic syndromes and specimens supports the hypothesis of modern human microcephally. 

Response to 19 May 2006 Comment on
“The Brain of LB1, Homo floresiensis.

Falk, D.; Hildebolt, C.; Smith, K.; Morwood, M.J.; Sutikna, T.; Jatmiko; Saptomo W.E.; Brunsden, & Prior, F. Response to comment on "The brain of LB1, Homo floresiensis" by Martin et al. Science Online, Science 312:999, 2006.

http://www.sciencemag.org/cgi/content/full/312/5776/999c

Martin et al. claim that they have two endocasts from microcephalics that appear similar to that of LB1, Homo floresiensis. However, the line drawings they present as evidence lack details about the transverse sinuses, cerebellum, and cerebral poles. Comparative measurements, actual photographs, and sketches that identify key features are needed to draw meaningful conclusions about Martin et al.'s assertions.

13 Feb 2007 article illustrating
microcephalic and LB1 brain differences

Falk D, Hildebolt C, Smith K, Morwood MJ, Sutikna T, Jatmiko, Saptomo EW, Imhof H, Seidler H, Prior F. Brain shape in human microcephalics and Homo floresiensis Proc Natl Acad Sci USA 104(7):2513-8, 2007

http://www.pnas.org/cgi/reprint/104/7/2513.pdf

Abstract: Because the cranial capacity of LB1 (Homo floresiensis) is only 417 cm(3), 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 approximately 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.