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Human brain, braincase evolved independently, researchers say

New research suggests an understanding of the evolutionary relationship between the brain and its housing, which led to brains three times bigger than those of great apes.

By
Brooks Hays
Scientists used CT and MRI data to retrace the evolution of the brain and braincase in modern humans and chimpanzees. Photo by J.L. Alatorre Warren/UZH
Scientists used CT and MRI data to retrace the evolution of the brain and braincase in modern humans and chimpanzees. Photo by J.L. Alatorre Warren/UZH

Oct. 15 (UPI) -- The evolution of the brain allowed humans to acquire a knack for language and tool production. The braincase, the portion of the skull that houses the brain, also changed shape, but new research suggests the two components evolved independently.

Scientists have long sought to unravel the evolutionary relationship between the human brain and braincase, and to determine which of the two led the evolutionary dance that produced a brain three times the size of the brains of great apes.

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Anthropological and biochemical evidence suggests the brain evolved to meet the needs of humans as communication, cooperation and technological innovation became increasingly important. Because the brain almost entirely fills out the braincase, it follows that the braincase evolved in response to the brain's structural changes.

But while the latest study showed the two components evolved side by side, the evidence -- presented this week in the journal PNAS -- suggests they took mostly independent evolutionary paths.

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"We use combined computed tomography and MRI head data of humans and chimpanzees and quantify the spatial correlations between brain sulci and cranial sutures," scientists explained in their paper.

In the brain, structural changes are delineated by gyri, or convolutions, and sulci, or furrows, while cranial adaptations are marked by bony sutures.

The brain's evolutionary restructuring is most visible in the frontal lobe of the brain, where neuroanatomical boundaries shifted to empower complex cognitive tasks related to language, social cognition and manual dexterity. The latest analysis showed these neuroanatomical changes did not trigger corresponding adaptations in the bony structures of the braincase.

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Instead, researchers at the University of Zurich in Switzerland determined changes in the braincase helped to accommodate locomotive changes associated with bipedalism. To improve balance, the opening at the base of the skull for the spinal cord shifted forward. Researchers determined the changes in braincase size and shape failed to influence the evolution of the brain.

"The brain followed its own evolutionary path of neural innovation while freely floating in the braincase," said lead study author Alatorre Warren. "The position and size of braincase bones thus don't enable us to draw conclusions about evolutionary changes in the size or rearrangement of adjacent brain regions."

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