Human brain evolution involved both neurological reorganization and an increase in overall brain volume relative to body mass. It is generally difficult to draw functional inferences about the timing and nature of brain reorganization, given that superficial brain morphology recorded on fossil endocasts is functionally ambiguous. However, the cerebellum, housed in the clearly delineated posterior cranial fossa, is functionally and ontologically discrete. The cerebellum is reciprocally connected to each of 14 neocortical regions important to human cognitive evolution. Cerebellar volume varies significantly relative to overall brain volume among mammalian orders, as well as within the primate order. There is also significant diachronic variation among fossil human taxa. In the australopithecines and early members of the genus Homo, the cerebral hemispheres were large in proportion to the cerebellum, compared with other hominoids. This trend continued in Middle and Late Pleistocene humans, including Neandertals and CroMagnon 1, who have the largest cerebral hemispheres relative to cerebellum volume of any primates, including earlier and Holocene humans. In recent humans, however, the pattern is reversed; the cerebellum is larger with respect to the rest of the brain (and, conversely, the cerebral hemispheres are smaller with respect to the cerebellum) than in Late Pleistocene humans. The cerebellum and cerebral hemispheres appear to have evolved reciprocally. Cerebellar development in Holocene humans may have provided greater computational efficiency for coping with an increasingly complex cultural and conceptual environment.human evolution ͉ Plio-Pleistocene hominins ͉ Upper Paleolithic transition P aleoneurologists agree that increased encephalization is an important dynamic of human brain evolution. However, brain evolution involved more than brain expansion. It also involved reorganization to support specific, uniquely human cognitive tasks, including those involved in linguistic processing and a highly developed facility for manufacturing and manipulating tools. Nevertheless, despite more than a century of effort, there is little consensus about how and when such reorganization occurred.One approach to exploring functional reorganization of the brain in humans has been the analysis of impressions of the brain's surface convolutions (sulci and gyri) on the inner table of the endocranium. However, endocranial markings are notoriously difficult to identify reliably (1, 2). Even where the impressions are fairly clear, taphonomic processes may distort the evidence. In addition, the functional correlates of the brain's surface convolutions, especially in fossils, are literally superficial. Cognitive functions occur through internal connections among brain regions, as well as through the distribution of neuroreceptors that cannot be detected by examining the surface of the brain, let alone from endocranial markings. Therefore, functional inferences based on sulcal patterns are problematic.Another approach to endocran...
Neandertal capitate-metacarpal 2 and 3 articulations have been observed to differ in orientation and shape from those of more recent humans. To evaluate this, we tested for differences in capitate-metacarpal 2 (MC2) and MC2-capitate facet orientations and MC2 and MC3 robusticity indices, and for multivariate shape equivalence of the capitate-MC2/MC3 facets and the MC3 diaphysis and styloid process between samples of Neandertals and recent humans. Canonical discriminant functions of log size- and-shape and log shape transformed measurements were run on variables of the capitate-MC2 and MC3 facets, and these plus MC3 diaphysis and styloid process variables. The null hypothesis of shape equivalence is rejected for both variable sets. Modern human capitate-MC morphology results from nonallometric increases in distal capitate breadth and the projection of the MC3 styloid process, and reductions in MC2 facet height and MC3 facet breadth. These shape changes are associated with a significantly less parasagittal orientation of the capitate-MC2 facets in recent humans, but are only trivially correlated with MC 2 and 3 robusticity indices. The recent human capitate-MC 2 and 3 morphology may reflect a shift in habitual joint reaction forces from more axial to more oblique forces while maintaining similar pronation/supination of the MC2. However, the full behavioral implications of these contrasts remain unclear.
Wynn's model for the evolution of spatial cognition is well supported by fossil evidence from brain endocasts, and from neurological studies of the cerebellum and the posterior parietal region of the cerebral cortex. Wynn's intriguing hypothesis that the spatial skill reflected in artifacts is an index of navigational ability, could be further explored by an analysis of lithic transport patterns.
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