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1.
Proc Natl Acad Sci U S A ; 111(36): 13022-7, 2014 Sep 09.
Article in English | MEDLINE | ID: mdl-25157138

ABSTRACT

Falk and colleagues [Falk D, Zollikofer CP, Morimoto N, Ponce de León MS (2012) Proc Natl Acad Sci U S A 109(22):8467-8470] hypothesized that selective pressures favored late persistence of a metopic suture and open anterior fontanelle early in hominin evolution, and they put an emphasis on the Taung Child (Australopithecus africanus) as evidence for the antiquity of these adaptive features. They suggested three mutually nonexclusive pressures: an "obstetric dilemma," high early postnatal brain growth rates, and neural reorganization in the frontal cortex. To test this hypothesis, we obtained the first high-resolution computed tomography (CT) data from the Taung hominin. These high-resolution image data and an examination of the hominin fossil record do not support the metopic and fontanelle features proposed by Falk and colleagues. Although a possible remnant of the metopic suture is observed in the nasion-glabella region of the Taung partial cranium (but not along the frontal crest), this character state is incongruent with the zipper model of metopic closure described by Falk and colleagues. Nor do chimpanzee and bonobo endocast data support the assertion that delayed metopic closure in Taung is necessary because of widening (reorganization) of the prefrontal or frontal cortex. These results call into question the adaptive value of delaying metopic closure, and particularly its antiquity in hominin evolution. Further data from hominoids and hominins are required to support the proposed adaptive arguments, particularly an obstetric dilemma placing constraints on neural and cranial development in Australopithecus.


Subject(s)
Biological Evolution , Brain/diagnostic imaging , Cranial Sutures/diagnostic imaging , Fossils , Hominidae/anatomy & histology , Skull/diagnostic imaging , Tomography, X-Ray Computed , Animals , Brain/anatomy & histology , Skull/anatomy & histology
2.
Am J Phys Anthropol ; 146(2): 319-22, 2011 Oct.
Article in English | MEDLINE | ID: mdl-21826639

ABSTRACT

The Taung endocast is one of the best-preserved and most important known in paleoanthropology. Although the endocast is undistorted and preserves distinctive landmarks, Taung has proved a difficult endocast, because it is only about 60% complete. To reconstruct Taung it is necessary to first use the available anatomical landmarks to define the midline of the endocast. It is only with a proper description of the midline that it is possible to reconstruct the endocast and obtain an accurate measurement of Taung's endocranial volume. Holloway (Science 168 (1970) 966-968) determined a conservative estimate for Taung of 404 ml. More recently this estimate has been revised downward by Falk and Clarke (Am J Phys Anthropol 134 (2007) 529-534) to 382 ml, giving Taung the smallest endocast for A. africanus. Certain challenges exist with the reconstruction of any endocast, particularly a hemi-endocast such as Taung. A virtual reconstruction of Taung must assume perfect symmetry, a feature called into question here in Taung's most recent reconstruction by Falk and Clarke (2007). Holloway's (1970) reconstruction of Taung provides a guidepost for a conservative approach to endocast reconstructions, and the most reliable measurement of Taung's true endocranial volume.


Subject(s)
Brain/anatomy & histology , Fossils , Hominidae/anatomy & histology , Skull/anatomy & histology , Animals , Paleontology
3.
Am J Phys Anthropol ; 143(3): 426-36, 2010 Nov.
Article in English | MEDLINE | ID: mdl-20949613

ABSTRACT

Despite centuries of investigation, the function of the maxillary sinus (MS) and underlying patterns governing its form remain elusive. In this study, we articulate a methodology for collecting volumetric data for the MS and nasal cavity (NC) from computed tomography (CT) scans and report details for a small sample of 39 dried human crania of known ecogeographic provenience useful for assessing variation in MS size and shape. We use scaling analyses to preliminarily test the hypothesis that volumes of the nasal cavity (NCV) and maxillary sinus (MSV) are inversely correlated such that the NC covaries with size of the face, whereas the MS "fills in" the leftover space [proposed by Shea: Am J Phys Anthropol 47 (1977):289-300]. Against expectation, MSV is not significantly correlated with NCV or any cranial size variable. NCV, on the other hand, scales isometrically with facial size. The results of this pilot study suggest that NCV covaries with facial size, but that the MS does not simply fill in the leftover space in the face. The role, if any, of the MSs in midfacial function and architecture remains unclear. Larger sample sizes, additional environmental variables, and assessment of MS and NC shape are necessary to resolve this issue.


Subject(s)
Anthropology, Physical/methods , Imaging, Three-Dimensional/methods , Maxillary Sinus/anatomy & histology , Nasal Cavity/anatomy & histology , Tomography, X-Ray Computed/methods , Adult , Climate , Female , Geography , Humans , Male , Middle Aged , Racial Groups , Regression Analysis , Skull
4.
Anat Rec A Discov Mol Cell Evol Biol ; 273(1): 594-602, 2003 Jul.
Article in English | MEDLINE | ID: mdl-12808644

ABSTRACT

Human brain evolution is characterized by an overall increase in brain size, cerebral reorganization, and cerebral lateralization. It is generally understood when brain enlargement occurred during human evolution. However, issues concerning cerebral reorganization and hemispheric lateralization are more difficult to determine from brain endocasts, and they are topics of considerable debate. One region of the cerebral cortex that may represent the earliest evidence for brain reorganization is the primary visual cortex (PVC), or area 17 of Brodmann. In nonhuman primates, this region is larger in volume (demarcated anteriorly by the lunate sulcus), and extends further rostrally than it does in modern humans. In early hominid fossil (Australopithecus) endocasts, this region appears to occupy a smaller area compared to that in nonhuman primates. Some have argued that the brain first underwent size expansion prior to reorganization, while others maintain that reorganization predated brain expansion. To help resolve this question, we provide a description of two male, common chimpanzee (Pan troglodytes) brains, YN77-111 and YN92-115, which clearly display a more posterior lunate sulcal morphology than seen in other chimpanzees. These data show that neurogenetic variability exists in chimpanzees, and that significant differences in organization (e.g., a reduced PVC) can predate brain enlargement. While the human brain has experienced numerous expansion and reorganization events throughout evolution, the data from these two chimpanzees offer significant support for the hypothesis that the neurogenetic basis for brain reorganization was present in our early fossil ancestors (i.e., the australopithecines) prior to brain enlargement.


Subject(s)
Biological Evolution , Hominidae/anatomy & histology , Pan troglodytes/anatomy & histology , Visual Cortex/anatomy & histology , Animals , Brain/anatomy & histology , Functional Laterality , Humans , Male , Species Specificity
5.
Anat Rec A Discov Mol Cell Evol Biol ; 271(2): 276-85, 2003 Apr.
Article in English | MEDLINE | ID: mdl-12629670

ABSTRACT

The cortical circuits subserving neural processing of human language are localized to the inferior frontal operculum and the posterior perisylvian region. Functional language dominance has been related to anatomical asymmetry of Broca's area and the planum temporale. The evolutionary history of these asymmetric patterns, however, remains obscure. Although testing of hypotheses about the evolution of language areas requires comparison to homologous regions in the brains of our closest living relatives, the great apes, to date little is known about normal interindividual variation of these regions in this group. Here we focus on Brodmann's area 44 in African great apes (Pan troglodytes and Gorilla gorilla). This area corresponds to the pars opercularis of the inferior frontal gyrus (IFG), and has been shown to exhibit both gross and cytoarchitectural asymmetries in humans. We calculated frequencies of sulcal variations and mapped the distribution of cytoarchitectural area 44 to determine whether its boundaries occurred at consistent macrostructural landmarks. A considerable amount of variation was found in the distribution of the inferior frontal sulci among great ape brains. The inferior precentral sulcus in particular was often bifurcated, which made it impossible to determine the posterior boundary of the pars opercularis. In addition, the distribution of Brodmann's area 44 showed very little correspondence to surface anatomy. We conclude that gross morphologic patterns do not offer substantive landmarks for the measurement of Brodmann's area 44 in great apes. Whether or not Broca's area homologue of great apes exhibits humanlike asymmetry can only be resolved through further analyses of microstructural components.


Subject(s)
Frontal Lobe/anatomy & histology , Gorilla gorilla/anatomy & histology , Language , Pan troglodytes/anatomy & histology , Africa , Animals , Biological Evolution , Frontal Lobe/physiology , Gorilla gorilla/physiology , Humans , Magnetic Resonance Imaging , Pan troglodytes/physiology , Species Specificity
6.
Anat Rec ; 266(4): 249-57, 2002 04 01.
Article in English | MEDLINE | ID: mdl-11920388

ABSTRACT

The Omo L338y-6 occipital region has been recently studied by White and Falk (1999), who claim that it shows a readily identifiable enlarged left occipital-marginal sinus (O/M). These observations are contrary to the direct observations of previous investigators (Rak and Howell, 1978; Kimbel, 1984; Holloway, 1981; Holloway, 1988). White and Falk (1999) further argue that the presence of this enlarged O/M strongly suggests that the Omo L338y-6 hominid was indeed a "robust" Australopithecus. We used direct sectioning and CT scanning to analyze magnified sections of a high-quality first-generation cast of the newly cleaned original fossil. These methods fail to show any evidence of a morphological landmark that can be interpreted as an enlarged O/M, either as an eminence or a sulcus. In contrast, the same techniques used with both SK 1585 and OH5 ("robust" Australopithecus with an enlarged O/M) show extremely visible and palpable enlarged O/M's. Examination of the original Omo fossil confirms that it lacks an O/M. This evidence clearly shows that an enlarged O/M cannot be identified on either the original fossil or a first-generation cast, although this does not rule out the possibility that the Omo L338y-6 hominid was a "robust" Australopithecus. We believe that the differences between observers regarding this feature are most probably due to displacement caused by a crack and the different source materials employed, i.e., the difference between a first-generation cast of the original fossil and a third- or fourth-generation cast of the endocast made two decades ago.


Subject(s)
Brain/anatomy & histology , Cranial Sinuses/anatomy & histology , Fossils , Hominidae/anatomy & histology , Occipital Bone/anatomy & histology , Animals , Anthropology, Physical , Anthropometry , Biological Evolution , Classification , Humans , Tomography Scanners, X-Ray Computed
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