Today’s humans differ from other primates in particular by their large brain with a particularly pronounced frontal lobe. But contrary to what was previously assumed, the modern brain structure was not at the beginning of the development of the homo genus. As a new study shows, our ancestors had smaller, more ape-like brains until around 1.7 million years ago. Even so, they were already using tools and were even able to leave Africa and survive in colder regions. This is proven by fossil finds from Dmanisi in what is now Georgia. The results shed new light on the evolution of the human brain.
The earliest fossil traces of the genus Homo are 2.8 million years old. Did our early human ancestors already have a brain comparable in size and structure to ours at this point in time? For a long time, scientists assumed that a modern brain structure was already at the transition from the pre-human Australopithecus to the genus Homo and laid the foundation for the further development of humans. Evidence was difficult, however. Since the brain itself does not petrify, researchers can only examine the imprints inside fossilized skulls and draw conclusions about how big the brain was and which structures took up a particularly large amount of space.
Out of Africa with a primitive brain
A team led by Marcia Ponce de León from the University of Zurich has now found that the modern human brain emerged later than previously assumed. For their study, the researchers examined around 40 fossil skulls of early humans who lived in Africa and Eurasia one to two million years ago. To reconstruct the brains, they used computed tomography to analyze the furrows and grooves on the inside of the skull. They compared their results with data from modern humans and great apes.
“According to our analyzes, modern human brain structures only emerged 1.5 to 1.7 million years ago – in African homo populations,” says Ponce de León’s colleague Christoph Zollikofer. Well-preserved skulls from the Dmanisi site in what is now Georgia were particularly revealing for the researchers. They come from the first known homosexual population outside of Africa and are almost 1.8 million years old. According to the analyzes, the brains of these early humans were still as small and original as those of their earlier African relatives. “Our data show that the modern brain did not develop during the transition from Australopithecus to Homo, but only much later, after the first early humans had left Africa,” the researchers write.
Brain regions for more complex thinking
Modern brains are not only characterized by a larger volume, but also by a new structure of certain brain regions. “Typically human are primarily those regions in the forehead area that are responsible for the planning and execution of complex thought and action patterns and ultimately also for the language,” says Ponce de León. Since these are significantly enlarged in humans, all neighboring brain regions are shifted further back.
The researchers found the earliest evidence of such a modern brain in skulls from Africa between 1.7 and 1.5 million years old. “It was during this period that the earliest forms of human language developed,” says Ponce de León. The variety of tools also increased. According to the researchers, biological and cultural evolution went hand in hand and were mutually dependent. Fossil finds from Java show that the new populations were extremely successful. Shortly after their appearance in Africa, they had spread to Southeast Asia.
New questions about the evolution of the brain
But even the early humans from Dmanisi, despite their more primitive brain structure, were apparently already in a position to manufacture numerous tools, adapt to the new environmental conditions of Eurasia, tap animal food sources and take care of needy group members. This is proven by archaeological finds. To what extent early humans from the first wave of emigration mixed with later populations with larger brains or whether they were displaced by them is unclear. “To assess this, additional fossil and archaeological evidence is needed,” the researchers say.
Apparently the modern brain was not a prerequisite for leaving Africa and surviving in unknown regions. This raises new questions about the evolution of the human brain: “What kind of selection pressure could have been responsible for the reorganization of the frontal lobes?” Asks paleoanthropologist Amélie Beaudet of the University of Cambridge in an article accompanying the study, which is also published in the journal “ Science ”was published. From their point of view, it is conceivable that the new structures in the area of the frontal lobe may not have been created by a certain selection pressure, but were only a by-product of other changes. “The emergence of language would then have been the result of an evolutionary misappropriation,” says Beaudet. “Future discoveries of new specimens from this period will be critical to understanding the evolutionary context of these brain changes.”
Source: Marcia Ponce de León (University of Zurich) et al., Science, doi: 10.1126 / science.aaz0032