Morphology and Histology of Chimpanzee Primary Visual Striate Cortex Indicate that Brain Reorganization Predated Brain Expansion in Early Hominid Evolution

Ralph L. Holloway, Douglas C. Broadfield, Michael S. Yuan

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)594-602
Number of pages9
JournalAnatomical Record - Part A Discoveries in Molecular, Cellular, and Evolutionary Biology
Volume273
Issue number1
DOIs
StatePublished - Jul 2003
Externally publishedYes

Keywords

  • Brain evolution
  • Chimpanzee
  • Human evolution
  • Lunate sulcus
  • Primary visual cortex

ASJC Scopus subject areas

  • Anatomy
  • Agricultural and Biological Sciences (miscellaneous)

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