The modern human brain developed around 1.7 million years ago in Africa, according to a study published in Science (1). This involved not only an increase in brain size but also crucial changes in structure that give us a frontal lobe capable of complex patterns of thought and action.
The genus Homo – to which we belong – emerged in Africa about 2.5 million years ago. They knew how to walk on two legs, but their brains were still very much like primitive ape brains. So, the big question is, when did the modern human brain evolve?
A team of researchers from the Department of Anthropology at the University of Zurich (UZH) has now answered this question. The team analysed a series of five skulls found in Dmanisi in Georgia (USA) – believed to be around 1.8 million years old – and then compared this data to other fossils from Africa and Asia and modern great apes and humans.
More complex and diverse
It turns out the first Homo populations outside Africa, probably as early as 2.1 million years ago, were able to make tools, use different types of food and care for members of the group but still had brains just as primitive as great apes.
According to these results, the modern human brain must have developed sometime between 1.7 and 1.5 million years ago in Africa. Fossils found in Asia, dated around 1.5 million years old and relating to the second migration out of Africa, already show a large and complex brain, capable of new complex skills.
Not surprisingly, a more complex and diverse brain was accompanied by a more complex and diverse culture, with many different types of tools appearing at this stage. In fact, the researchers believe that cultural and physiological evolution are intimately interconnected and happened simultaneously. It is also likely that the earliest forms of human language developed during this period.
Changes in brain structure
Physical changes in brain structure during human evolution have been a bone of contention among researchers for a long time. “The problem is that the brains of our ancestors were not preserved as fossils. Their brain structures can only be deduced from impressions left by the folds and furrows on the inner surfaces of fossil skulls,” says study leader Christoph Zollikofer.
As these imprints can vary between different skulls, it’s been virtually impossible to establish which Homo skulls had a more ape-like or a more human-like brain. Finally, with the help of computer tomography, the team could start answering these questions for the first time.
Interestingly, this analysis revealed that the earliest members of the genus Homo had a very primitive frontal lobe located at the front of the brain. As evolution occurred, the frontal lobe developed and grew more prominent, with other regions eventually pushed to the back of the brain. In a way, this frontal area is what makes us humans. It’s the control panel of our personality, including the ability to solve problems and communicate with others. “The features typical to humans are primarily those regions in the frontal lobe that are responsible for planning and executing complex patterns of thought and action, and ultimately also for language,” said first author Marcia Ponce de León.
There are still many questions to solve, however, including whether to attribute variation in brain structure to simple population diversity within a single hominin species or whether the taxonomy of early Homo species needs some re-thinking. For the team, deciphering the evolutionary process in early Homo remains a challenge that will only be solved with further analysis of fossil samples from a controlled chronological era.
(1) León M, Bienvenu T, Marom A, Engel S, Tafforeau P, Warren J, Lordkipanidze D, Kurniawan I, Murti D, Suriyanto R, Koesbardiati T, Zollikofer C (2021) The primitive brain of early Homo. Science 372: 165-171. DOI: 10.1126/science.aaz0032