![]() Because there is little evidence that the simple addition or subtraction of genes is sufficient to explain the observed differences ( Hill and Walsh, 2005), changes in the regulation (levels and patterns of expression) of genes shared between humans and chimpanzees have been proposed to play an important role ( King and Wilson, 1975 Enard et al., 2002). Similarly, the maturation of pyramidal neurons appears to be protracted in hominids compared to macaques ( Cupp and Uemura, 1980 Petanjek et al., 2011 Sedmak et al., 2018) and in humans compared to chimpanzees ( Bianchi et al., 2013a Teffer et al., 2013), possibly accounting for longer and more branched dendrites with higher numbers of dendritic spines in humans ( Bianchi et al., 2013b Petanjek et al., 2008). Humans and apes share a pattern of prolonged postnatal growth in brain size that sets them apart from Old World monkeys ( Leigh, 2004). In the case of human brain evolution, sequential hypermorphosis, a type of heterochrony characterized by prolongation of all stages of brain development compared to the ancestral state ( McNamara, 2002 Vrba, 1998 McKinney, 2002), has been proposed as an evolutionary mechanism underlying cerebral expansion in humans. Developmental differences between species represent an important component in evolutionary studies, as small changes in the timing of development translate into morphological differences in adulthood, often with important functional implications. Since cortical pyramidal neurons represent the most common type of neuron in the cortex and form basic units of cortical microcircuitry ( DeFelipe and Fariñas, 1992), comparative analyses directed specifically at pyramidal neurons can yield insights into the organization of the microcircuitry that is typical of each species.ĭifferences observed in the adult phenotype between humans and chimpanzees likely reflect differences in timing and/or rate of cortical development. ![]() One of these is the dendritic morphology of cortical pyramidal neurons, which differs between humans and the common chimpanzee ( Pan troglodytes) ( Bianchi et al., 2013a). ![]() While these changes cannot be inferred directly from the fossil specimens, comparative analyses of cortical organization between extant primate species suggest that the human brain indeed differs from the brain of other hominid species in several important microstructural aspects ( Semendeferi et al., 2001 Barger et al., 2007 Semendeferi et al., 2011). Equally important were the subtle changes in brain organization at the microscopic level. ![]() The increase in the cranial capacity in fossil hominins has been tied to behavioral changes, including the appearance of the first stone tools and their subsequent elaboration, increases in population size, and the spread of hominins into ecologically challenging habitats ( Ambrose, 2001 Stout, 2011). Since the split from the last common ancestor of hominins ( Homo) and African apes ( Gorilla and Pan spp), human brain evolution has been characterized by several waves of increases in cranial capacity ( Carlson et al., 2011 Falk et al., 2000) and selective expansion of regions implicated in complex cognition ( Semendeferi et al., 2010 Semendeferi and Damasio, 2000).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |