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Ancient Taung Child's Brain Not Human-Like

Aug 26, 2014 11:21 AM EDT

The Taung Child, a hominin discovered in South Africa 90 years ago, may not be as human-like as scientists previously thought after CT scans of its brain cast doubt on its similarity to modern humans, according to a new study.

According to the Smithsonian Institution, Australopithecus africanus displayed a combination of human-like and ape-like features. Compared to A. afarensis - a hominin believed to be more closely related to humans, or the genus Homo - A. africanus had a rounder cranium, larger brain and smaller teeth, but it also had some ape-like features including relatively long arms and a strongly sloping face with a pronounced jaw.

Wits University Professor Raymond Dart first discovered A. africanus 90 years ago, and was the first and best example of early hominin brain evolution. Since then, the ancient child's skull has shed light on human origins and theories have been put forward that it exhibits key cranial adaptations found in modern human infants and toddlers.

However, now researchers from the University of the Witwatersrand have finally tested the theory, and are in effect disproving the previous belief that the Taung Child shows infant brain development in the prefrontal region similar to that of modern humans.

They performed an in silico dissection of the Taung Child with high-resolution computed tomography (CT). Then, they compared it with the existing hominin fossil record and chimpanzee variation.

"A recent study has described the roughly 3 million-year-old fossil, thought to have belonged to a 3 to 4-year-old, as having a persistent metopic suture and open anterior fontanelle, two features that facilitate post-natal brain growth in human infants when their disappearance is delayed," Dr. Kristian J. Carlson, Senior Researcher from the Evolutionary Studies Institute at the University of the Witwatersrand, said in a press release.

Carlson explains that physical evidence does not irrefutably link features of the Taung skull to early prefrontal lobe expansion. Given these results, scientists now wonder whether these structures were selectively advantageous in hominin evolution, particularly in australopiths.

The findings reveal a bit more about this ancient specimen and, consequently, more about human evolution overall. They are described in the journal Proceedings of the National Academy of Sciences (PNAS).

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