Modern human brain structures emerged later than the first dispersal of the genus Homo from Africa, and were probably in place by 1.7 to 1.5 million years ago in African Homo populations, according to new research led by the University of Zurich.
Skulls of early Homo from Georgia with an ape-like brain (left) and from Indonesia with a human-like brain (right). Image credit: M. Ponce de León & C. Zollikofer, University of Zurich.
The human brain is larger than and structurally different from the brains of the great apes, particularly in frontal lobe areas involved with complex cognitive tasks like toolmaking and language.
However, when these key differences arose during human evolution remains poorly understood.
One of the major challenges in tracking brain evolution in early hominid species is that brain tissues rarely fossilize.
As a result, much of what is known is derived from shape and structures on the surface of the brain cases of rare, fossilized skulls.
Representations of these surfaces, or endocasts, can reveal patterned imprints representing the folds and indentations of the brain and its surrounding vasculature.
“The problem is that the brains of our ancestors were not preserved as fossils,” said co-lead author Dr. Christoph Zollikofer, a researcher in the Department of Anthropology and Anthropological Museum at the University of Zurich.
“Their brain structures can only be deduced from impressions left by the folds and furrows on the inner surfaces of fossil skulls.”
“Because these imprints vary considerably from individual to individual, until now it was not possible to clearly determine whether a particular Homo fossil had a more ape-like or a more human-like brain.”
Dr. Zollikofer and his colleagues examined endocasts of early Homo from Africa, Southeast Asia, and the Dmanisi site in Georgia.
They found that the structural innovations in the cerebral regions thought to allow for many of humans’ unique behaviors and abilities emerged later in the evolution of Homo.
“Our findings suggest that modern human-like brain reorganization was neither a requisite trait for genus Homo, nor a prerequisite for early Homo’s dispersals into Europe and Asia,” said Dr. Marcia Ponce de León, a researcher in the Department of Anthropology and Anthropological Museum at the University of Zurich.
“Our analyses suggest that modern human brain structures emerged only 1.5 to 1.7 million years ago in African Homo populations,” Dr. Zollikofer said.
The results appear today in the journal Science.
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Marcia S. Ponce de León et al. 2021. The primitive brain of early Homo. Science 372 (6538): 165-171; doi: 10.1126/science.aaz0032
