The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

The positioning of the lunate sulcus in Pan troglodytes: a statistical analysis


Department of Anthropology, Florida Atlantic University

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Previous research indicates variability in the positioning of the lunate sulcus, the boundary of the primary visual cortex, in Pan troglodytes (Holloway et al., 2003). However, the statistical significance of this variation has not yet been established. The purpose of this research is to test whether or not the position of the lunate sulcus can be predicted in chimpanzees as suggested by Holloway (1985; 1997). Variability in the location of this landmark has been used as evidence to support the hypothesis that differences in brain organization precede brain enlargement. If the position of the lunate sulcus is variable, yet predictable, this data can be expanded and used as the basis for future hypotheses. Endocasts of fossil hominins can be examined to see if the position of the lunate sulcus varies significantly from the position in chimpanzees, and therefore if it varies from the presumed position in the last common ancestor.

The variations in the position of the lunate sulcus between individuals, the hemispheres of the brain, and the sexes were taken through three cord measurements. These measurements were standardized using hemispheric weight and overall brain weight. The standard deviations for these values are low and the three measurements are strongly correlated (p < 0.0005). There is no significant variation between hemispheres (p > 0.1) or between the sexes (p > 0.1) with regard to the position of the lunate sulcus. This data indicates that the position of the lunate sulcus can be accurately estimated.

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