Even after ancient humans took their first steps outside of Africa, they still unexpectedly possessed brains more like those of great apes than modern humans, a new study suggests.
For decades, scientists have thought that the modern human organization of brain structures evolved shortly after the Homo human lineage emerged about 2.8 million years ago (SN: 3/4/15). But an analysis of fossilized human skulls that preserve the footprints of the brains they once had now suggests that this brain development occurred much later. Modern brains can emerge in an evolutionary sprint that began about 1.7 million years ago, researchers report in the April 9 issue of Science.
What most differentiates modern humans from our closest living relatives, the great apes, is most likely our brain. To learn more about how the modern human brain evolved, the researchers analyzed replicas of the brain’s convoluted outer surface, recreated from the oldest fossils known to preserve the inner surfaces of the first human skulls. Fossils from 1.77 million to 1.85 million years old come from the Dmanisi archeological site in the modern nation of Georgia and have been compared to bones from Africa and Southeast Asia ranging from 2 to 70,000 years ago.
Scientists have focused on the frontal lobes of the brain, which are linked to complex mental tasks such as making tools and language. The primitive Homo of Dmanisi and Africa still retained a large monkey-like organization of the frontal lobe 1.8 million years ago, "about a million years later than previously thought," says paleoanthropologist Philipp Gunz of the Max Planck Institute in Evolutionary Anthropology of Leipzig, Germany, who did not participate in this study.
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These findings reveal that the first humans possessed relatively primitive brains even after they began to disperse from Africa about 2.1 million years ago (SN: 7/11/18). Modern humans began migrating from the continent about 210,000 years ago (SN: 10/10/19). Still, it is essential not to underestimate the mental abilities of early humans, says Marcia Ponce de León, a paleoanthropologist at the University of Zurich. “These people have ventured out of Africa, produced a variety of tools, exploited animal resources and cared for the elderly, as we know at the Dmanisi site,” he says.
She and her colleagues found that modern brain organization such as humans began to appear in Africa between 1.5 and 1.7 million years ago. “I don’t know of anyone else, but I just developed a great interest in learning as much as possible about what hominins were doing for (those) 200,000 years” that drove this apparent brain change, says paleoanthropologist Dean Falk of Florida State University in Tallahassee, who did not participate in the study.
Scientists also found that hominids with modern brains like humans appeared in Southeast Asia shortly after 1.5 million years ago, hinting at another scattering of Africa separate from the first migration about 2.1 million years ago, says Ponce de Leon. Researchers point out that it remains unknown whether this second wave merged or replaced the previous groups.
There remains controversy over the reconstruction of the organization of ancient brains from skulls, warns paleoanthropologist Bernard Wood of George Washington University in Washington D.C., who did not participate in this study. For example, it may be challenging to deduce how the interiors of tiny fossils reflected bumps and grooves on the surface of the brain or what the consequences of that brain organization might have on brain function (SN: 1/4/20; SN: 4/25/17) . “I think this is just the beginning of discussions about what this means, rather than the end,” Wood says.
Future research may investigate what evolutionary pressures may have driven the emergence of modern human-like brain organization. Ultimately, such research could reveal how brain reorganization is related to the evolution of language and symbolic thinking, says study author Christoph Zollikofer, a paleoanthropologist at the University of Zurich.
But perhaps there were no such pressures, “and this reorganization was a byproduct of changes in other areas,” says paleoanthropologist Amélie Beaudet of Cambridge University, who wrote a review of this study for the April 9 Science. The only way to answer this question "would be to study more fossils from the time period that oscillated between the first human representatives 2.8 million years ago and Homo after 1.8 million years ago and reconstruct the contexts in which they lived and they were evolving. "