Durban - A three-million-year-old fossil skull has revealed that the infant brain development of this human ancestor was not the same as that of modern babies.
This was announced on Tuesday by Wits researcher Kristian Carlson and colleagues in a paper published online in the Proceedings of the National Academy of Sciences.
Carlson based his findings on a hi-tech analysis of the Taung child skull, found 90 years ago by quarry workers in Taung in North West. The skull was first described by Wits professor Raymond Dart in 1925, and has been studied extensively. It is regarded as the best example of early brain evolution of hominins, the name given to the group of modern humans and all extinct human species on our evolutionary path.
Theories put forward are that the skull of this young Australopithecus africanus shows key adaptations which are found in modern human babies. But Carlson says this is not the case.
He said colleagues had proposed that the Taung skull had a persistent metopic suture and an open anterior fontanelle, two features that help brain growth in human babies after birth. They close by the time a baby is about one year old. They also allow easier birthing by enabling the skull bones to slide over one another, giving some flexibility in the birth canal.
Using a new CT-scan technique developed in 2012, Carlson found neither of these features in the fossil child’s skull.
“We were able to take a better look inside the bones using this more powerful CT-scanner. Colleagues have proposed that these two features of modern babies were present in the Taung skull, and so had their origins in Australopithecus africanus. But we’ve found that the ancientness of these features can’t be traced back to Australopithecus africanus,” Carlson said.
He goes further to say that by showing that these two feature are not present in the Taung child, he therefore disputes whether these skull structures were selectively advantageous in hominin evolution. Carlson said the skull of the Taung child was smaller than that of a human baby, more the size of a chimpanzee, and the pelvic dimensions of Australopithecus africanus adults were different from those of modern women.
“So they would not have needed this feature during birth. We’re not suggesting that the advantages of having these two features are incorrect, we’re just saying that these advantages did not apply as early as as our colleagues have suggested,” Carlson said.