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A medical illustration from 'Quain's Elements of Anatomy, Eighth Edition, Vol.II' (by William Sharpey MD, LLD, FRS L&E, Allen Thomson, MD, LLD, FRS L&E, and Edward Albert Schafer) depicts the figure of the brain of chimpanzee, 1876. (Photo by VintageMedStock/Getty Images)

A medical illustration from 'Quain's Elements of Anatomy, Eighth Edition, Vol.II' (by William Sharpey MD, LLD, FRS L&E, Allen Thomson, MD, LLD, FRS L&E, and Edward Albert Schafer) depicts the figure of the brain of chimpanzee, 1876. (Photo by VintageMedStock/Getty Images)