The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Changes in orangutan brain ontogeny indicate parallel evolution


1Department of Biology and Chemistry, Academy for Science and Design, 2Department of Biological Sciences, Texas Tech University, 3Department of Sociology, Anthropology, and Social Work, Texas Tech University, 4Department of Archaeology, Flinders University, 5Department of Anthropology, South Australian Museum

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Different elements of human ontogeny have been described by various heterochronic modes, such as neoteny and sequential hypermorphosis. The evolution of brain ontogeny has received a great deal of attention, owing to the complex and sophisticated nature of our brains. Previous works have determined that a growth phase appears in chimpanzees and humans at around birth and continues on until nine months and one year, respectively. Given the similarities of brain cytoarchitecture in these species, and the dissimilar structures in the more distantly related monkey species, there was an important cytoarchitectural remodeling event sometime during the last 18-20 million years after the divergence of the ape clade from the Old World monkeys. To increase our resolution of ape brain evolution, and by extension, human brain evolution, this study investigates the evolution of orangutan brain ontogeny. Comparing the growth trajectories of humans, chimpanzees, squirrel monkeys, macaques, and orangutans, we discovered that orangutans do not follow the expected growth pattern of humans and chimpanzees. Instead, the orangutan growth trajectory much more closely resembles that of the squirrel monkey and thus indicates parallel evolution of brain growth strategies in these two species.

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