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The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.

Homo erectus was anatomically variable and behaviorally flexible using both Oldowan and Acheulian artifacts., Although stone tools generally co-occur with early members of the genus Homo, they are rarely found in direct association with hominins. We report that both Acheulian and Oldowan artifacts and Homo erectus crania were found in close association at 1.26 million years (Ma) ago at Busidima North (BSN12), and ca. 1.6 to 1.5 Ma ago at Dana Aoule North (DAN5) archaeological sites at Gona, Afar, Ethiopia. The BSN12 partial cranium is robust and large, while the DAN5 cranium is smaller and more gracile, suggesting that H. erectus was probably a sexually dimorphic species. The evidence from Gona shows behavioral diversity and flexibility with a lengthy and concurrent use of both stone technologies by H. erectus, confounding a simple “single species/single technology” view of early Homo.

It has always been difficult to account for the evolution of certain human characters such as language, empathy, and altruism via individual reproductive success. However, the striatum, a subcortical region originally thought to be exclusively motor, is now known to contribute to social behaviors and "personality styles" that may link such complexities with natural selection. We here report that the human striatum exhibits a unique neurochemical profile that differs dramatically from those of other primates. The human signature of elevated striatal dopamine, serotonin, and neuropeptide Y, coupled with lowered acetylcholine, systematically favors externally driven behavior and greatly amplifies sensitivity to social cues that promote social conformity, empathy, and altruism. We propose that selection induced an initial form of this profile in early hominids, which increased their affiliative behavior, and that this shift either preceded or accompanied the adoption of bipedality and elimination of the sectorial canine. We further hypothesize that these changes were critical for increased individual fitness and promoted the adoption of social monogamy, which progressively increased cooperation as well as a dependence on tradition-based cultural transmission. These eventually facilitated the acquisition of language by elevating the reproductive advantage afforded those most sensitive to social cues.

Paleoneurology is an important field of research within human evolution studies. Variations in size and shape of an endocast help to differentiate among fossil hominin species whereas endocranial asymmetries are related to behavior and cognitive function. Here we analyse variations of the surface of the frontal, parieto-temporal and occipital lobes among different species of Homo , including 39 fossil hominins, ten fossil anatomically modern Homo sapiens and 100 endocasts of extant modern humans. We also test for the possible asymmetries of these features in a large sample of modern humans and observe individual particularities in the fossil specimens. This study contributes important new information about the brain evolution in the genus Homo . Our results show that the general pattern of surface asymmetry for the different regional brain surfaces in fossil species of Homo does not seem to be different from the pattern described in a large sample of anatomically modern H. sapiens , i.e., the right hemisphere has a larger surface than the left, as do the right frontal, the right parieto-temporal and the left occipital lobes compared with the contra-lateral side. It also appears that Asian Homo erectus specimens are discriminated from all other samples of Homo , including African and Georgian specimens that are also sometimes included in that taxon. The Asian fossils show a significantly smaller relative size of the parietal and temporal lobes. Neandertals and anatomically modern H. sapiens , who share the largest endocranial volume of all hominins, show differences when considering the relative contribution of the frontal, parieto-temporal and occipital lobes. These results illustrate an original variation in the pattern of brain organization in hominins independent of variations in total size. The globularization of the brain and the enlargement of the parietal lobes could be considered derived features observed uniquely in anatomically modern H. sapiens .

The designation of Homo floresiensis as a new species derived from an ancient population is controversial, because the type specimen, LB1, might represent a pathological microcephalic modern Homo sapiens . Accordingly, two specific craniometric ratios (relative frontal breadth and cerebellar protrusion) were ascertained in 21 microcephalic infants and children by using MRI. Data on 118 age-equivalent control (normocephalic) subjects were collected for comparative purposes. In addition, the same craniometric ratios were determined on the endocasts of 10 microcephalic individuals, 79 normal controls (anatomically modern humans), and 17 Homo erectus specimens. These ratios were then compared with those of two LB1 endocasts. The findings showed that the calculated cerebral/cerebellar ratios of the LB1 endocast [Falk D, et al. (2007) Proc Natl Acad Sci USA 104:2513–2518] fall outside the range of living normocephalic individuals. The ratios derived from two LB1 endocasts also fall largely outside the range of modern normal human and H. erectus endocasts and within the range of microcephalic endocasts. The findings support but do not prove the contention that LB1 represents a pathological microcephalic Homo sapiens rather than a new species, (i.e., H. floresiensis ).

The trigeminal motor (Vmo), facial (VII), and hypoglossal (XII) nuclei of the brainstem comprise the final common output for neural control of most orofacial muscles. Hence, these cranial motor nuclei are involved in the production of adaptive behaviors such as feeding, facial expression, and vocalization. We measured the volume and Grey Level Index (GLI) of Vmo, VII, and XII in 47 species of primates and examined these nuclei for scaling patterns and phylogenetic specializations. Allometric regression, using medulla volume as an independent variable, did not reveal a significant difference between strepsirrhines and haplorhines in the scaling of Vmo volume. In addition, correlation analysis using independent contrasts did not find a relationship between Vmo size or GLI and the percent of leaves in the diet. The scaling trajectory of VII volume, in contrast, differed significantly between suborders. Great ape and human VII volumes, furthermore, were significantly larger than predicted by the haplorhine regression. Enlargement of VII in these taxa may reflect increased differentiation of the facial muscles of expression and greater utilization of the visual channel in social communication. The independent contrasts of VII volume and GLI, however, were not correlated with social group size. To examine whether the human hypoglossal motor system is specialized to control the tongue for speech, we tested human XII volume and GLI for departures from nonhuman haplorhine prediction lines. Although human XII volumes were observed above the regression line, they did not exceed prediction intervals. Of note, orang-utan XII volumes had greater residuals than humans. Human XII GLI values also did not differ from allometric prediction. In sum, these findings indicate that the cranial orofacial motor nuclei evince a mosaic of phylogenetic specializations for innervation of the facial muscles of expression in the context of a generally conservative scaling relationship with respect to medulla size.

The neocortex of primates contains several distinct neuron subtypes. Among these, Betz cells of primary motor cortex and Meynert cells of primary visual cortex are of particular interest for their potential role in specialized sensorimotor adaptations of primates. Betz cells are involved in setting muscle tone prior to fine motor output and Meynert cells participate in the processing of visual motion. We measured the soma volumes of Betz cells, Meynert cells, and adjacent infragranular pyramidal neurons in 23 species of primate and two species of non-primate mammal (Tupaia glis and Pteropus poliocephalus) using unbiased stereological techniques to examine their allometric scaling relationships and socioecological correlations. Results show that Betz somata become proportionally larger with increases in body weight, brain weight, and encephalization whereas Meynert somata remain a constant proportion larger than other visual pyramidal cells. Phylogenetic variance in the volumetric scaling of these neuronal subtypes might be related to species-specific adaptations. Enlargement of Meynert cells in terrestrial anthropoids living in open habitats, for example, might serve as an anatomical substrate for predator detection. Modification of the connectional and physiological properties of these neurons could constitute an important evolutionary mode for species-specific adaptation.

A key event in human evolution is the expansion of modern humans of African origin across Eurasia between 60 and 40 thousand years (kyr) before present (bp), replacing all other forms of hominins. Owing to the scarcity of human fossils from this period, these ancestors of all present-day non-African modern populations remain largely enigmatic. Here we describe a partial calvaria, recently discovered at Manot Cave (Western Galilee, Israel) and dated to 54.7 ± 5.5 kyr bp (arithmetic mean ± 2 standard deviations) by uranium-thorium dating, that sheds light on this crucial event. The overall shape and discrete morphological features of the Manot 1 calvaria demonstrate that this partial skull is unequivocally modern. It is similar in shape to recent African skulls as well as to European skulls from the Upper Palaeolithic period, but different from most other early anatomically modern humans in the Levant. This suggests that the Manot people could be closely related to the first modern humans who later successfully colonized Europe. Thus, the anatomical features used to support the 'assimilation model' in Europe might not have been inherited from European Neanderthals, but rather from earlier Levantine populations. Moreover, at present, Manot 1 is the only modern human specimen to provide evidence that during the Middle to Upper Palaeolithic interface, both modern humans and Neanderthals contemporaneously inhabited the southern Levant, close in time to the likely interbreeding event with Neanderthals.

A major hall of hominid brain evolution is an expansion of the frontal lobes. To determine if a similar trajectory occurs during modern human development, the MRI scans of 118 living infants, children, and adolescents were reviewed and three specific measurements obtained: frontal width (FW), maximal cerebral width (MW), and maximal cerebral length (ML). The infantile brain is uniformly wide but relatively short, with near equal FW and MW. The juvenile brain exhibits a wider MW than FW, while FW of the adolescent brain expands to nearly equal MW, concurrent with an increase in ML. The preferential frontal lobe expansion during modern human development parallels that observed during the evolution of Homo. In 17 microcephalic individuals, only 6 (35%) exhibited preferential frontal lobe hypoplasia, presumably a reflection of multiple etiologies that adversely affect differing brain regions. Compared to 79 modern human adult endocasts and 12 modern microcephalic endocasts, LB1 (Homo floresiensis) clustered more consistently with the microcephalic sample than with the normocephalic sample.

The parietal bones approximately cover the extension of the underlying parietal lobes. Although the boundaries of these two anatomical elements do not coincide, during morphogenesis the growth of the parietal bones is largely induced by the pressure exerted by the parietal lobes. Modern humans display larger parietal chords and arcs compared with non-modern human species. However, the variation of these variables have not been analyzed before according to the covariation with the general endocranial diameters. When the curvature of the parietal bones is regressed onto the main neurocranial distances, modern humans show larger relative values, suggesting not only an absolute enlargement but a definite allometric change. Taking into account the morphogenetic relationships with the parietal lobes, these results further support previous hypotheses suggesting a relative enlargement of these cortical areas in Homo sapiens, by using simple and reliable homologous neurocranial arcs. Anat Rec, 2011. © 2011 Wiley-Liss, Inc.

Within the genus Homo, the most encephalized taxa (Neandertals and modern humans) show relatively wider frontal lobes than either Homo erectus or australopithecines. The present analysis considers whether these changes are associated with a single size-based or allometric pattern (positive allometry of the width of the anterior endocranial fossa) or with a more specific and non-allometric pattern. The relationship between hemispheric length, maximum endocranial width, and frontal width at Broca's area was investigated in extant and extinct humans. Our results do not support positive allometry for the frontal lobe's width in relation to the main endocranial diameters within modern humans (Homo sapiens). Also, the correlation between frontal width and hemispheric length is lower than the correlation between frontal width and parieto-temporal width. When compared with the australopithecines, the genus Homo could have experienced a non-allometric widening of the brain at the temporo-parietal areas, which is most evident in Neandertals. Modern humans and Neandertals also display a non-allometric widening of the anterior endocranial fossa at the Broca's cap when compared with early hominids, again more prominent in the latter group. Taking into account the contrast between the intra-specific patterns and the between-species differences, the relative widening of the anterior fossa can be interpreted as a definite evolutionary character instead of a passive consequence of brain size increase. This expansion is most likely associated with correspondent increments of the underlying neural mass, or at least with a geometrical reallocation of the frontal cortical volumes. Although different structural changes of the cranial architecture can be related to such variations, the widening of the frontal areas is nonetheless particularly interesting when some neural functions (like language or working memory, decision processing, etc.) and related fronto-parietal cortico-cortical connections are taken into account.

The anatomic pattern and left hemisphere size predominance of the planum temporale, a language area of the human brain, are also present in chimpanzees ( Pan troglodytes ). The left planum temporale was significantly larger in 94 percent (17 of 18) of chimpanzee brains examined. It is widely accepted that the planum temporale is a key component of Wernicke's receptive language area, which is also implicated in human communication-related disorders such as schizophrenia and in normal variations such as musical talent. However, anatomic hemispheric asymmetry of this cerebrocortical site is clearly not unique to humans, as is currently thought. The evolutionary origin of human language may have been founded on this basal anatomic substrate, which was already lateralized to the left hemisphere in the common ancestor of chimpanzees and humans 8 million years ago.

A crucial component of research on brain evolution has been the comparison of fossil endocranial surfaces with modern human and primate endocrania. The latter have generally been obtained by creating endo- casts out of rubber latex shells filled with plaster. The extent to which the method of production introduces errors in endocast replicas is unknown. We demonstrate a powerful method of comparing complex shapes in 3- dimensions (3D) that is broadly applicable to a wide range of paleoanthropological questions. Pairs of virtual endocasts (VEs) created from high-resolution CT scans of corresponding latex/plaster endocasts and their associated crania were rigidly registered (aligned) in 3D space for two Homo sapiens and two Pan troglodytes specimens. Distances between each cranial VE and its corresponding latex/plaster VE were then mapped on a voxel-by-voxel basis. The results show that between 79.7% and 91.0% of the voxels in the four latex/plaster VEs are within 2 mm of their corresponding cranial VEs surfaces. The average error is relatively small, and variation in the pattern of error across the surfaces appears to be generally random overall. However, inferior areas around the cranial base and the temporal poles were somewhat overestimated in both human and chimpanzee specimens, and the area over- laying Broca's area in humans was somewhat underesti- mated. This study gives an idea of the size of possible error inherent in latex/plaster endocasts, indicating the level of confidence we can have with studies relying on compari- sons between them and, e.g., hominid fossil endocasts. Am J Phys Anthropol 132:183-192, 2007. V C 2006 Wiley-Liss, Inc.

CHET C. SHERWOOD,a,b,c RALPH L. HOLLOWAY,a,c PATRICK J. GANNON,c,d KATERINA SEMENDEFERI,e JOSEPH M. ERWIN,f KARL ZILLES,g AND PATRICK R. HOFb,c,f aDepartment of Anthropology, Columbia University, New York, New York 10027, USA bKastor Neurobiology of Aging Laboratory and Fishberg Research Center for Neurobiology, and dDepartment of Otolaryngology, Mount Sinai School of Medicine, New York, New York 10029, USA cNew York Consortium in Evolutionary Primatology, New York, New York eDepartment of Anthropology, University of California, San Diego, La Jolla, California 92093-0532, USA fFoundation for Comparative and Conservation Biology, Needmore, Pennsylvania 17238, USA gInstitut fur Medizin, Forschungszentrum Julich und C.& O. Vogt-Institut fur Hirnforschung, Heinrich-Heine-Universitat, Dusseldorf, Germany

Social life in anthropoid primates is mediated by interindividual communication, involving movements of the orofacial muscles for the production of vocalization and gestural expression. Although phylogenetic diversity has been reported in the auditory and visual communication systems of primates, little is known about the comparative neuroanatomy that subserves orofacial movement. The current study reports results from quantitative image analysis of the region corresponding to orofacial representation of primary motor cortex (Brodmann's area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens) using the Grey Level Index method. This cortical region has been implicated in the execution of skilled motor activities such as voluntary facial expression and human speech. Density profiles of the laminar distribution of Nissl-stained neuronal somata were acquired from high-resolution images to quantify cytoarchitectural patterns. Despite general similarity in these profiles across catarrhines, multivariate analysis showed that cytoarchitectural patterns of individuals were more similar within-species versus between-species. Compared to Old World monkeys, the orofacial representation of area 4 in great apes and humans was characterized by an increased relative thickness of layer III and overall lower cell volume densities, providing more neuropil space for interconnections. These phylogenetic differences in microstructure might provide an anatomical substrate for the evolution of greater volitional fine motor control of facial expressions in great apes and humans.

This study presents a comparative stereologic investigation of neurofilament protein- and calcium-binding protein-immunoreactive neurons within the region of orofacial representation of primary motor cortex (Brodmann's area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens). Results showed that the density of interneurons involved in vertical interlaminar processing (i.e., calbindin- and calretinin-immunoreactive neurons) as well pyramidal neurons that supply heavily-myelinated projections (i.e., neurofilament protein-immunoreactive neurons) are correlated with overall neuronal density, whereas interneurons making transcolumnar connections (i.e., parvalbumin-immunoreactive neurons) do not exhibit such a relationship. These results suggest that differential scaling rules apply to different neuronal subtypes depending on their functional role in cortical circuitry. For example, cortical columns across catarrhine species appear to involve a similar conserved network of intracolumnar inhibitory interconnections, as represented by the distribution of calbindin- and calretinin-immunoreactive neurons. The subpopulation of horizontally-oriented wide-arbor interneurons, on the other hand, increases in density relative to other interneuron subpopulations in large brains. Due to these scaling trends, the region of orofacial representation of primary motor cortex in great apes and humans is characterized by a greater proportion of neurons enriched in neurofilament protein and parvalbumin compared to the Old World monkeys examined. These modifications might contribute to the voluntary dexterous control of orofacial muscles in great ape and human communication.

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.

Ever since Anders Retzius' invention of the cephalic index late in the nineteenth century, legions of anthropologists armed with spreading calipers have bravely endured the apprehension of their subjects and have accumulated thousands of measurements of head lengths and breadths and divided the latter by the former to achieve that purportedly objective characterization, the cranial index, mellifluously categorized as “dolichocephalic, mesocephalic, or brachycephalic.” From this index, one could (if properly trained) hazard a guess about whether someone was from the Northwestern, the Mediterranean, or the Alpine region of Europe. There was even hope that all groups throughout the world could be characterized and classified similarly. The uses to which this index were put ranged from the beneficent to the grotesque, from simple curiosity to preventing people from being accepted as immigrants, and to the characterization of “ideal” racial types as ingredients in racial classifications. On the humorous side, Hooten (1) noted that only hat makers paid no attention to the differences in head shape. I confess that over my years of teaching human skeletal biology, I have enjoyed almost each and every head measurement that I've taken. I ordinarily managed to demonstrate that the index meant nothing in terms of defining whence came a person. I doubt that any of us practicing these arts have failed to mention the findings of Franz Boas' 1910–1913 publications (2) that the offspring of immigrants born in the United States showed a “significant” difference from their immigrant parents in this index. (I say significant because that was what we were taught.) This finding was perhaps one of the most …

It has long been thought that the prefrontal cerebral cortex has been greatly expanded in the human brain. Semendeferi et al. ([2001] Am. J. Phys. Anthropol. 114:224-241) showed that Brodmann's area 10 is relatively larger in the human compared to pongid brains. The question is: how much larger relatively is it? Using their data, it can be shown that the relative increase for human prefrontal area 10 is only 6% larger. Looking at the data base of neural structures provided by Stephan et al. ([1981] Folia Primatol. (Basel) 35:1-29), it is apparent that 6% is a relatively low residual value from a predicted value based on allometric considerations between total brain weight and any given neural structure. When this small increase is combined with their earlier findings on area 13 of prefrontal cortex (Semendeferi et al. [1997] J. Hum. Evol. 32:375-388), it appears that the prefrontal cortex in humans is not some 200% larger as claimed by some researchers (Deacon [1997] Symbolic Species, New York: W.W. Norton; cf. Holloway [1998] Am Sci 86:184-186), and that the findings of Semendeferi et al. ([2001] Am. J. Phys. Anthropol. 114:224-241) are in agreement with the earlier work (Semendeferi and Damasio [2000] J. Hum. Evol. 38:317-332; Semendeferi et al. [1997] J. Hum. Evol. 32:375-388), showing that the human frontal lobe volume is what would be expected for a primate of its brain size. While the prefrontal cortex may have increased relatively in Homo sapiens, the increase is likely to have been far less than currently believed.

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.

This paper describes the morphology and phylogenetic significance of a well-preserved fossil human cranium found near Reilingen, Germany in 1978. The specimen consists of two complete parietals, most of the right temporal, and 70% of the occipital. The specimen displays several features characteristic of early "archaic" Homo sapiens: maximum breadth at the supramastoid crests, roughly pentagonal occipital view, an angular torus, superoinferiorly elongate/ anteroposterior shortened squamous temporal, strong mastoid, and separation of the tympanic and mastoid temporal portions. Other features align the Reilingen cranium with the "classic" Neandertals: developed suprainiac fossa, bilaterally protuberant occipital torus, strong juxtamastoid eminence, a highly convex occipital plane, and lambdoid flattening. This morphology and our cephalometric analysis support the assignment of this specimen to a Stage 2 "pre-Neandertal" group (e.g., Steinheim, Swanscombe, and Atapuerca [SH site]). Following an "Accretion Model" of European hominid evolution, Stage 2 succeeds Stage 1 European "early-pre-Neandertals" (e.g., Mauer and Petralona), and precedes both the Saale-Eem Stage 3 "early Neandertals" (e.g., Biache 1), which present greater platycephaly, a reduced mastoid process, an enlarged juxtamastoid eminence, and true "en-bombe" (parieto-occipital form), and Weichsel Stage 4 "Neandertals" (sensu stricto, i.e., "classic" Neandertals).

Endocasts provide evidence on size and shape characteristics, blood supply trajectories, and neurological features of the brain, allowing comparative analyses of fossil hominins crucial to our understanding of human brain evolution. Here, we assess the morphological features of the virtual endocast of the Cioclovina Upper Paleolithic calvarium, one of the earliest reliably dated European modern human fossils. Our study was conducted on a computed tomography (CT) scan of the original specimen. The endocranial profile was approximated via a semiautomatic segmentation of the CT data. Virtual reconstructions of the endocast were used for assessing the morphological features of the endocranium and for the estimation of the endocranial volume. Cioclovina exhibits a clockwise torque with a small anterior extension of the left frontal lobe over the right one and a protrusion of the right occipital lobe over the left, most likely due to the superior sagittal sinus coursing over the occipital pole. There is an obvious right predominance of the posterior drainage system. Interestingly, the area of the frontal sinus is occupied by dense bony tissue with small air cells corresponding probably to a natural bony loss in the diploe ¨ and to vascular spaces. An estimated endocranial volume of 1498.53 cc was calculated. The convolutional details of the third inferior frontal gyrus (Broca’s caps) are indistinguishable from those found in modern Homo sapiens, and the left occipital lobe appears wider than the right, a possible correlate of right-handedness. Our metric analysis of endocranial measurements also aligns Cioclovina with modern humans. Anat Rec, 294:1083–1092, 2011. V

Three independent autopsy samples of brains without apparent neuropathology were studied to ascertain whether there was sexual dimorphism in the human corpus callosum (CC). Using planimetric measurements on midsagittal brain sections, several morphometric features of the CC were studied: total callosal area, maximum dorsoventral splenial width, the posterior one fifth of the total area of the CC (mostly splenium), and brain weight. Ratio data correcting for brain size were also studied. In all samples, absolute brain size was larger in males, and significantly so. Measurements of splenial dorsoventral width were higher in females than males, but not significantly, except in the Australian sample. Total callosal area was absolutely higher in the Australian female sample than in males, and almost equal in the two American samples, without statistically significant differences. The posterior one-fifth area (splenium) was larger for females in each of the samples. The variables which were corrected for brain size were usually significantly larger in females, although this pattern varied in each sample. The statistical pattern of sexual dimorphism for the human CC differs from that found in most other neural structures, such as the amygdaloid nucleus, cerebellum, hippocampus, and thalamus. The absolute sizes of these structures are always significantly larger in males. When corrected for brain size, the relative sizes are not significantly larger. The CC is the only structure to show a larger set of relative measures in females.

Based on 244 measurements of the relationship of the squamosal suture to the landmark asterion in 49 chimpanzee skulls, it is shown that in the normal lateral view the squamosal suture is very rarely inferior to asterion. In hominid crania, the squamosal suture is always well superior to asterion. Even in Pan, that part of the squamosal suture most homologous with the remnant found on the Hadar AL 162-28 Australopithecus afarensis hominid cranial fragment is very rarely inferior to asterion. Such variability suggests that Falk's (Nature 313:45-47, 1985) orientation of the Hadar specimen is incorrect; she places asterion superior to the position of the squamosal suture if projected endocranially. The implication for the brain endocast is that, however the fragment is oriented, the posterior aspect of the intraparietal (IP) sulcus is in a very posterior position relative to any chimpanzee brain. The distance from the posterior aspect of IP to occipital pole is twice as great in chimpanzee brain casts than on the Hadar AL 162-28 endocast, even though the chimpanzee brain casts are smaller in overall size. This suggests that brain reorganization, at least as exemplified as a reduction in primary visual striate cortex (area 17 of Brodmann), occurred early in hominid evolution, prior to any major brain expansion.

One of the more vexing problems with hominoid endocasts has been to secure reliable information that goes beyond their volumes. One method is explored here, where a large number ( N = 171) of radial distances from a homologous internal central point to the dorsal endocast surface are measured in a polar coordinate system. From two pilot studies, one with a hominoid sample of N = 64, and the other with an enlarged sample of N = 92, the following results can be mentioned tentatively: (1) there are residual data that differ taxonomically in different cortical regions once overall endocast size is corrected in allometric fashion; (2) the major cortical regions where these differences appear most strongly are in the lower parietal lobule, anterior occipital zone, and the dorsoanterior region of the frontal lobe; (3) the method shows excellent promise in objectively and quantitatively depicting taxa-specific shape differences in functionally understood cortical regions through multivariate statistical analyses.

A restudy of the Danish brain weight data published by Pakkenberg and Voigt ('64), using partial correlation techniques, confirms and extends their earlier conclusions regarding a much stronger allometric relationship between height and brain weight than between body weight and brain weight. The relationship is particularly strong in males, and not in females, which is hypothesized to be related to higher fat components in the latter. Comparative data for smaller samples of Pan, Gorilla, Pongo, Macaca, Papio, and Saimiri using body weights, suggest that such relationships also hold more strongly in males than females, although more reliable data are greatly needed. In addition to providing within-species ranges of variability for variously derived neural statistics (e.g., encephalization quotients, "extra neurons," etc.), for "normal" primates, it is suggested that while allometric trends do exist within species, and particularly males, evolutionary pressures leading to larger brain size were probably very diverse, and that any one homogenistic theory is unlikely.

A quantitative neuropathological necropsy study of 22 control and 22 chronic alcoholic subjects showed a statistically significant loss of brain tissue in the chronic alcoholic group. The loss of tissue appeared to be from the white matter of the cerebral hemispheres rather than the cerebral cortex. This may reflect a primary alteration in the composition or structure of the white matter or it may be secondary to loss of nerve cells from the cortex with subsequent degeneration of the axons in the white matter. Further morphometric analyses including cortical neuronal counts will be necessary to clarify this issue.

If there is any hallmark that might be said to be unique to the human animal, it is surely the ability to speculate about the origin of language. I have too much respect and regard for the intellective capacities of chimpanzees to imagine them prone to such exercises in egoistic futility. Thus I approach the topic with a mild case of schizophrenic serenity, in which I simultaneously share a n agreement with the very rational Frenchmen of the Nineteenth Century who banned such discussions from their learned society, and yet share a delight that the topic is available for organized discussion from so many viewpoints, disciplines, and scientific experimentation as represented by the interactants of these conferences. For me, a t least, the very fact that this Conference has been organized, and that human animals are ready to engage in a great “garrulity” over the merits and demerits of essentially unprovable hypotheses, is an exciting testimony to the gap between human and other animals, whether continuous or not in nature. My assigned task is to assess the paleoneurological evidence for language resulting from our rather meager fossil hominid record. This is, at least on one level, an exceedingly simple task, since there is no good paleoneurological evidence as yet from the fossil hominid record that either proves or disproves when this or that hominid acquired the capacity for language. At the level of precise unambiguity, the endocasts leave much to be desired, as I have repeatedly emphasized. 1-8 Still, these are the most proximal evidencial links we have, and when combined with the other indirect lines of evidence from the fossil record, such as stone tools made to standardized patterns of arbitrary shape, or the rest of the musculoskeletal evidence, or the remaining archaeological record of different functioning sites, the combination raises significantly, I believe, the probability that this uniquely human activity came relatively early in hominid evolution, perhaps two to three million years ago.7-9 I have tried in most of my publications to suggest that “reorganization of the brain,” i.e., the study of the quantitative changes in the various neural systems of the brain and their integrated interactions, coupled with our ever-increasing knowledge of neurofunctioning, is a profitable way of approaching the problem of human (indeed any taxa) brain evolution. Most of those earlier publications were a reaction to the views most popular during the 40s to the early 60s, in which brain mass, taken alone, by and of itself, was regarded as the level a t which human behavioral specificities would be eventually understood. Consequently, I purposely played down the role of brain size alone in the case of human evolution. Perhaps I went too far, judging by the reactions of some of my critics.“J-13 Still, I never claimed that brain size was totally meaningless; only that it was insufficient as a lone datum level from which human behavioral evolution, or even a truly comparative neurobiology, could be understood.~4-~6 In the last few years this position is being met with serious rebuke by other scientists,lO-IJ who have raised a number of issues with greater clarity than existed before. In this paper, I will address myself to certain of these criticisms as they

M an is not the largest of the pri­ mates (the gorilla is larger), but he has the largest brain. How did this come about? The question is hardly a new one, but a considerable amount of new evidence is now available to those in search of the answer. In brief the evidence suggests that, contrary to what is widely believed, the human brain was not among the last human organs to evolve but among the first. Neurologically speaking, brains whose organization was essentially human were already in existence some three million years ago.

Latex rubber brain endocasts of solo I, V, VI, X, and XI crania were prepared in order to determine accurate volumes by H2O-displacement and morphological description. The new volumes are not markedly different from previous estimates that had been done by mensuration formulae. The mean volume is 1,151 ml. The endocast surfaces, while devoid of gyral and sulcal relief patterns, do show a preponderance of left-occipital-right-frontal petalia patterns, suggesting right-handedness. Metrical observations support the viewpoint that the solo crania are more closely related to earlier Indonesia homo erectus than to Neandertals.

To summarize the pertinent findings of this review, it may be said that reorganization of the primate cortex is indicated at a number of levels. Intrinsic thalamic afferents to the cortex increase with increasing association cortex. A series of various indices were given to illustrate this, such as the A/S ratio, and various surface areal and volume measures. At a more molecular level, comparative, ontogenetic and experimental evidence showed that increasing brain size is associated with decreased density, or increased gray cell coefficient, and that this is paralleled by increase in dentritic branching parameters. With the increase in dendritic branching, and thus more synapses through more connectivity, the complexity of behavior was seen to increase. The experimental evidence tried to show this point. Finally, it was suggested that this interpretation based on a conceptual distinction between complexity processes in behavior and that of emergence with respect to the code or arbitrary representative factors, could be integrated with the quantitative-emergence views of Hebb and Herrick, as well as ablation data. While little space was devoted to the neurophysiological aspects, enough had been presented concerning Clare and Bishop's view to find a means of integration of this aspect with the purely anatomical. The following sections will attempt to relate these discussions of reorganization at all the levels discussed to some aspects of the emergent, specifically human kind of behavior. Three hypotheses will suggest relevant neurological mechanisms that might relate to behaviors of kind rather than degree. This will then be followed by a discussion of hominid evolution and the fossil record, and an attempt will be made to relate aspects of this dichotomy to the evolution of man. While the interpretations of this section may be open to question, one fact clearly emerges from all this discussion: a comparison of cerebral units (volumes) is not a comparison of equal units. Endocasts cannot show this. Discussions of the brain in terms of total mass must be replaced by more molecular appreciation of the range of structural and behavior changes for different extant primate species. Quantification is but one necessary early step toward systems synthesis of the naturalistic and anatomical data.

Full brain endocast reconstructions of the Neanderthals, Spy I and II, Djebel Ihroud I, and the Homo erectus specimen from Sale, Morocco have yielded accurate volumes. Spy I = 1,305 ml; Spy II = 1,553 ml; Djebel ihroud I = 1,305 ml; Sale = 880 ml. While there are no remarkable gyral and sulcal patterns one can delineate, the brain endocasts do show evidence of left-occipital, right-frontal petalias, suggesting right-handedness, and possibly human cognitive specialization, involving symbol processing and visuospatial integration. Some speculations regarding Neanderthal brain size are also offered, in which it is suggested that their possibly larger brain sizes were related to greater muscularity than in modern Homo sapiens.

It is rare for cerebral convolutional details to be imprinted on the internal table of cranial bone of fossil hominids. To date, the South African examples have shown the best detail, although surrounded by considerable controversy1–3. Given that the Hadar specimens are the oldest hominids known (3–4 Myr BP)4,5, and have been the subject of considerable debate and interpretation, it is fortunate that such details are found on the cranial bones of at least one specimen, AL 162-28, a small adult6. I report here a preliminary description of that endocast and it appears that despite its smallish pongid-sized brain, some degree of cerebral organization had occurred almost 3–4 Myr ago towards a more human pattern. If correct, this would mean that brain size increase may well have followed locomotion, but that brain organization may have occurred early in hominid evolution. Such a finding would call for a re-examination of our understanding about human evolution, and would require much more caution in assuming either ‘gradualist’ or ‘punctuated equilibria’ models in hominid evolution7,8.

The O.H.7 brain endocast was reexamined using a stereoplotting apparatus to quantify the amount of distortion. Some 127 measurements for each of the left and right sides were taken and treated statistically by student t-tests, both in paired and grouped fashion. Grouped data indicated no significant left-right differences. Paired data suggested three small regions of distortion, which produced three pairs of left-right differences that were significantly different. Given the very local nature of these minor distortions, it is concluded that the original reconstruction by Tobias was essentially correct. In addition, multiple regression analyses of selected chord-arc dimensions suggest that a volume in excess of 700 ml is most probable.

Some recent studies correlating cranial capacity with behavioral development and more molecular parameters such as neuron number are critically examined. These studies are found lacking in terms of basic assumptions and empirical support from other studies. In general, it is shown that these studies have overlooked an important aspect of brain evolution in the Primate Order, i.e., reorganization, or the shifting quantitative relationships of subsystems and components of the nervous system. A distinction is made between two approaches to the problem of the evolution of brain and behavior: (1) the “quantitative-specific” and (2) the “quantitative-general.” Attempts to derive specificity in terms of estimates of the number of cortical neurons in different pongid and hominid brains are premature unless basic data regarding organizational shifts are known. A supporting argument for the priority of the “quantitative-general” approach for all levels of the primate nervous system is made. Such a descriptive level is more amenable to synthesis with current neurophysiological knowledge and primate field and laboratory studies than the “quantitative-specific” approach.

THIS is a preliminary report on research carried out during 1971 and 1972 on the endocranial values of some East African hominids from Olduvai Gorge, Tanzania, and East Lake Rudolf, Kenya. The cranial remains suitable for the reconstruction of volumetrically accurate endocranial casts are as follows: from Olduvai Gorge, hominids OH 7, 9, 12, 13 and 24; from East Lake Rudolf, KNM-ER 732 and 406. Each set of hominid remains required its own reconstructive procedures; a full description of each is unnecessary here but will be published elsewhere. In this communication I report only the results and make some preliminary observations as to their significance. Table 1 shows the cranial capacities found for each hominid. Not all of these results should be equally regarded; some results are only approximations but others are stated with more confidence.

Preliminary observations suggest a sex difference in the shape and surface area of the human corpus callosum. The sexual dimorphism is striking in the splenium, the caudal or posterior portion of the corpus callosum. The female splenium is both more bulbous and larger than the male counterpart. Since peristriate, parietal, and superior temporal fibers course through the splenium, this finding could be related to possible gender differences in the degree of lateralization for visuospatial functions.

PROF. P. V. TOBIAS1 has produced a range of values for the cranial capacity of the ‘pre-Zinjanthropus’ juvenile from Bed I, at the F.L.K.N.N. I site at Olduvai Gorge, Tanganyika. This communication presents evidence which confirms Tobias's calculations.