title: Brain shape in human microcephalics and Homo floresiensis.
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.
authors.affiliation: Department of Anthropology, Florida State University, Tallahassee, FL 32306, USA. dfalk@fsu.edu
authors.forename: Dean
authors.initials: D
authors.lastname: Falk
authors.forename: Charles
authors.initials: C
authors.lastname: Hildebolt
authors.forename: Kirk
authors.initials: K
authors.lastname: Smith
authors.forename: M J
authors.initials: MJ
authors.lastname: Morwood
authors.forename: Thomas
authors.initials: T
authors.lastname: Sutikna
authors.lastname: Jatmiko
authors.forename: E Wayhu
authors.initials: EW
authors.lastname: Saptomo
authors.forename: Herwig
authors.initials: H
authors.lastname: Imhof
authors.forename: Horst
authors.initials: H
authors.lastname: Seidler
authors.forename: Fred
authors.initials: F
authors.lastname: Prior
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology* / Q000473:pathology; D002508:Cephalometry; D002531:Cerebellum / Q000473:pathology; D005260:Female; D005580:Fossils; D015186:Hominidae / Q000145:classification*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008831:Microcephaly / Q000175:diagnosis* / Q000473:pathology; D012886:Skull / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed