According to a new report, even after ancient humans first stepped out of Africa, they may have had brains that were more like those of great apes than modern humans.
In the mid-1990s, University of Zurich paleoanthropologists Marcia Ponce de León and Christoph Zollikofer started developing techniques to study the inner surface of skulls and infer the brain structures of fossilised hominins. Nowadays, they use computed tomography and MRI to determine the imprint, which they call an endocast, that a brain leaves on the internal cranial vault.
For decades, scientists believed that modern humanlike brain structure organisation emerged shortly after the – lineage Homo appeared about 2.8 million years ago (SN: 3/4/15). However, an examination of fossilized human skulls that still bear the imprints of the brains they once possessed indicates that brain formation took place much later. Researchers say in the April 9 issue of Science that modern-like brains may have evolved during an evolutionary sprint that began about 1.7 million years ago.
Our brain is most certainly what distinguishes us from our nearest living relatives, the great apes. The researchers studied replicas of the brain’s convoluted outer surface, which were re-created from the oldest known fossils to preserve the inner surfaces of early human skulls, to learn more about how the modern human brain developed. The 1.77- to 1.85-million-year-old fossils came from the Dmanisi archaeological site in modern-day Georgia, and they were compared to bones from Africa and Southeast Asia that ranged in age from 2 million to 70,000 years.
The researchers concentrated on the frontal lobes of the brain, which are associated with complex mental tasks like toolmaking and language. Paleoanthropologist Philipp Gunz of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the research, says that early Homo from Dmanisi and Africa already had a great ape–like organisation of the frontal lobe 1.8 million years ago, “a million or so years later than previously thought.”
Early humans may have had relatively primitive brains even after they dispersed from Africa 2.1 million years ago, according to these results (SN: 7/11/18). About 210,000 years ago, modern humans began migrating from the continent (SN: 7/10/19). Nonetheless, Marcia Ponce de León, a paleoanthropologist at the University of Zurich, emphasises the importance of not underestimating early humans’ mental abilities. “As we know from the Dmanisi site, these people ventured out of Africa, created a range of tools, abused animal resources, and cared for elderly people,” she says.
Between 1.5 million and 1.7 million years ago, she and her colleagues discovered that modern human–like brain organisation began to appear in Africa. “I don’t know about anyone else, but I’ve recently established a strong desire to learn everything I can about what hominins were doing during [those] 200,000 years,” says paleoanthropologist Dean Falk of Florida State University in Tallahassee, who was not involved in the research.
The researchers have discovered that modern human–like brains emerged in Southeast Asia about 1.5 million years ago, implying that there was another dispersal from Africa after the first migration around 2.1 million years ago, according to Ponce de León. The researchers point out that it’s unclear if this second wave combined with or replaced the earlier classes.
Paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., who was not involved in the research, cautions that much remains controversial regarding reconstructing the organisation of ancient brains from skulls. Deducing how the insides of fossil braincases represented bumps and grooves on the brain’s surface, or the effects of such brain organisation on brain function, for example, can be difficult (SN: 4/1/20; SN: 4/25/17). “I believe that this is just the beginning of debates on what this means,” Wood says.
Future studies should look at the evolutionary forces that led to the development of modern human–like brain organization. According to study author Christoph Zollikofer, a paleoanthropologist at the University of Zurich, such studies may eventually show how brain reorganisation is linked to the evolution of language and symbolic thinking.
However, there may have been no such pressures, and “this reorganisation was a by-product of improvements in other areas,” according to paleoanth .The only way to address this question “would be to study more fossils from the time span ranging from the earliest human members 2.8 million years ago to Homo after 1.8 million years ago and reconstruct the contexts in which they lived and evolved,” according to the researchers. ropologist Amélie Beaudet of the University of Cambridge, who published an analysis of the study for Science on April 9.
According to Zollikofer, “the prevalent hypothesis up to now was that human-like brains developed at the very beginning of our own genus Homo, so perhaps two million years ago or even earlier.” However, the researchers discovered that some of the earliest members of the genus Homo—both from Africa and from Dmanisi fossils dating back more than 1.7 million years—had brains that were far more comparable in size and organisation to those of the australopithecines, the largely bipedal early hominins like Lucy, or to modern great apes. “There isn’t much in common with modern human brains,” says Zollikofer.
The researchers were able to narrow down the time range within which modern brain structures evolved to between 1.7 million and 1.5 million years ago by comparing the position of the coronal suture—a part of the skull where the bones knit together—and impressions in the skulls from a groove on the surface of the brain called the precentral sulcus. “Just because you have an ancestral brain doesn’t mean you can’t do interesting things like venture out of Africa, care for the elderly, leverage meat capital, and so on,” Zollikofer explains.
“In their new paper, Marcia Ponce de León and her colleagues reinforce this concept of late brain reorganisation by arguing that even early human genus members have an apelike prefrontal cortex organisation,” writes Philipp Gunz. in an email to The Scientist, a biological anthropologist at the Max Planck Institute for Evolutionary Anthropology in Germany and leader of the A. afarensis thesis with Falk last year. “These findings suggest that important aspects of brain reorganisation developed much later in the evolution of hominins than previously thought,” says the author.