News from “Lucy” and Co: The Vormensch Australopithecus afarensis had a brain similar to that of the chimpanzee, is the result of studies of fossil skulls. However, the growth of his thinking organ took a comparatively long time – just like in modern humans. The children of these hominins also needed long parental care. Their delayed brain growth could have formed the basis for the later evolution of the brain and social behavior in our ancestors, say the anthropologists.
Australopithecus afarensis is considered a key figure in modern anthropology: since the first discoveries in the 1970s, this hominin species from East Africa has provided insights into an exciting era of human development. Because the more than three million year old pre-humans had a mixture of still ape-like and human characteristics. One assumes that from A. afarensis all later representatives of the human family tree have emerged – including Homo sapiens. Previous research suggests that these hominins were already upright, had a brain about 20 percent larger than chimpanzees, and may have used sharp stone tools.
On the trail of two open questions
In addition to the famous fossil “Lucy”, the so-called “Dikika child” is the most important find of A. afarensis. “This fossil has been instrumental in exploring how we became humans,” said Zeresenay Alemseged of the University of Chicago. The anthropologist directed the excavations in Ethiopia, where the skeleton of the Australopithecus child was found in 2000. Together with international colleagues, he is now presenting new findings that shed light on two questions that have been controversial until now: Owned the brain of A. afarensis already a human-like organization? And: was the pattern of brain growth similar to that of chimpanzees or ours?
The second question is of great importance, because the comparatively long development time of the human brain is considered to be an important basis of our mental abilities: human children learn longer than the young animals of the chimpanzees due to the delayed brain development. However, this means that they are dependent on parental care for longer. However, the evolutionary roots of delayed brain development and long childhood in humans are still unclear.
Monkey-like structures
About the organization and growth pattern of the brain A. afarensis To investigate, Alemseged and his colleagues examined the skull of the Dikika child and seven other partially preserved skulls from Ethiopia using high-resolution computed tomography and casts. “After seven years of work, we finally had all the pieces of the puzzle to study the evolution of brain growth: the age of death of the Dikika child and his brain volume and that of the best-preserved adult A. afarensis Fossils, as well as comparative data from more than 1,600 modern humans and chimpanzees, ”says the first author of the study, Philipp Gunz from the Max Planck Institute for Evolutionary Anthropology in Leipzig (MPI-EVA). Remains of the brains have not been preserved, but the organs have left imprints on the inside of the skull, which allow conclusions to be drawn about the former structures, the researchers explain.
As they report, contrary to previous assumptions, their results now demonstrate a monkey-like brain organizationi A. afarensis there. A central finding was the position of the so-called sulcus lunatus. It is a furrow that separates the front and back of the brain. Their position differs in humans and chimpanzees: since we have a comparatively large prefrontal cortex, the gap is located further back in the brain than in chimpanzees. When examining the Dikika child’s brain print, the researchers now identified the print of his sulcus lunatus. It was found to be in a position similar to the furrow in the chimpanzee brain. “This ends a discussion that anthropologists have had for years,” said Alemseged. “We can now say that the organization of the brain by A. afarensis was rather ape-like. “
Long brain growth
But a different picture emerges regarding the growth pattern of the Australopithecus brain. The results of this were based on studies of the growth lines of the teeth of the Dikika child using synchrotron microtomography. Similar to the annual rings in trees, these growth lines can indicate the exact date of birth and death of a child. This enabled the experts to precisely determine the age of the Dikika child for the first time: It was 2.4 years old. “This information made clear how much of the brain was already trained at this age,” says Alemseged. It became apparent that the brain volume of the Dikika child was comparatively small for his age. “The results therefore suggest that brain growth in A. afarensis, like in humans, took a long time,” says co-author Simon Neubauer of the MPI-EVA.
This in turn means that these hominins probably lived through a long childhood. This may have made them dependent on parental care for a long time, but it could also have benefits in developing their mental abilities. The long brain growth A. afarensis could thus have formed a basis for the later evolution of the brain and social behavior in hominins, the researchers say. You are now trying to elicit further secrets from the A. afarensis fossils. It will be interesting to see what else they find out about the prehistoric people who ran through East Africa over three million years ago.
Sources: University of Chicago Medical Center, Max Planck Institute for Evolutionary Anthropology, professional article: Science Advances, doi: 10.1126 / sciadv.aaz4729