The human brain and braincase differ significantly from those of great apes in size and structure. Brain structures of fossil hominins are typically inferred from braincase structures, but the extent to which brain and braincase structure coevolved remains unclear.
Researchers analyzed MRI and CT/MRI skull and brain imaging data for 41 humans, ages 4–74 years; 24 chimpanzees; and 2 gorillas. The authors quantified structural variation in brain surface and braincase morphology, both within and between species, based on the relative positions of cortical sulci and the sutures between cranial bones.
The authors found moderate levels of covariation between brain and braincase features in both humans and chimpanzees. Compared with chimpanzees and gorillas, human brains exhibited distinct positions of brain sulci relative to cranial sutures and less overall covariation between brain and braincase features. The results suggest that brain and braincase structures evolved independently from each other.
According to the authors, changes in braincase morphology observed in the fossil record might reflect constraints related to increased encephalization and evolution of obligate bipedalism, rather than changes in brain structure.
Brain reorganization during human evolution
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