Humans and chimpanzees split from their last common ancestor several hundred thousand years earlier than believed – and this occurred in Europe, not Africa – according to an international team of scientists.
University of Toronto’s David Begun, a paleoanthropologist in the Faculty of Arts & Science, is a co-author of one of two controversial studies reported today on the pre-human remains in PLOS ONE.
“Our discovery outlines a new scenario for the beginning of human history – the findings allow us to move the human-chimpanzee split into the Mediterranean area,” Begun said. “These research findings call into question one of the most dogmatic assertions in paleoanthropology since Charles Darwin, which is that the human lineage originated in Africa.
“It is not a matter of continental bragging rights. It is critical to know where the human lineage arose so that we can reconstruct the circumstances leading to our divergence from the common ancestor we share with chimpanzees. Not having this information is like having a crime without the crime scene.”
Researchers analyzed two known fossil specimens of Graecopithecus freybergi using state-of-the-art methods – a lower jaw from Greece and an upper premolar from Bulgaria – and came to the conclusion that they belong to pre-humans. Furthermore, Graecopithecus is several hundred thousand years older than the oldest potential pre-human from Africa, the six to seven-million-year-old Sahelanthropus from Chad.
Using computer tomography, they visualized the internal structures of the Graecopithecus fossils and demonstrated that the roots of premolars are widely fused. The lower jaw, nicknamed El Graeco by the scientists, has additional dental root features, suggesting that the species Graecopithecus freybergi might belong to the pre-human lineage.
“While great apes typically have two or three separate and diverging roots, the roots of Graecopithecus converge and are partially fused – a feature that is characteristic of modern humans, early humans and several pre-humans including Ardipithecus and Australopithecus,” said Madelaine Böhme from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen, who co-led the investigations with Nikolai Spassov from the Bulgarian Academy of Sciences.
A 7.24-million-year-old upper premolar of Graecopithecus from Azmaka, Bulgaria (photo courtesy of Wolfgang Gerber, University of Tübingen)
The research team, which also included scientists from Greece, France and Australia, dated the sedimentary sequence of the Graecopithecus fossil sites in Greece and Bulgaria with physical methods and got a nearly synchronous age for both fossils – 7.24 and 7.175 million years before present.
“It is at the beginning of the Messinian, an age that ends with the complete desiccation of the Mediterranean Sea,” Böhme said.
Present-day chimpanzees are the nearest living relatives for humans. Where the last chimp-human common ancestor lived, however, is a central and highly debated issue in palaeoanthropology.
Researchers have assumed up until now that the lineages diverged five to seven million years ago and that the first pre-humans developed in Eastern Africa. According to the 1994 theory of French palaeoanthropologist Yves Coppens, climate change in the region could have played a crucial role.
As with many animals, the evolution of pre-humans was driven by dramatic environmental changes.
The team led by Böhme demonstrated that the North African Sahara desert originated more than seven million years ago. They concluded this based on geological analyses of the sediments in which the two fossils of Graecopithecus were found.
Although geographically distant from the Sahara, the red-coloured silts are very fine-grained and could be classified as desert dust. An analysis of uranium, thorium, and lead isotopes in individual dust particles yields an age between 0.6 and 3 billion years and infers an origin in Northern Africa.
Lower jaw of the 7.175 million year old Graecopithecus freybergi (El Graeco) from Pyrgos Vassilissis, Greece (photo courtesy of Wolfgang Gerber, University of Tübingen)
The dusty sediment also has a high content of different salts. The data document for the first time a spreading Sahara 7.2 million years ago, whose desert storms transported red, salty dusts to the north coast of what was then the Mediterranean Sea.
This process is also observable today. However, the researchers’ modelling shows that the dust in the past was more than 10 times the amount of recent dust loadings in Southern Europe – comparable to the present-day Sahel zone in Africa that marks the transition between the Sahara and the Sudan region.
The researchers further showed that while the Sahara was developing in North Africa, a savannah biome was formed in Europe. Using a combination of new methodologies, they studied microscopic fragments of charcoal and plant silicate particles, called phytoliths.
Many of these phytoliths derive from grasses and particularly from those that use the metabolic pathway of C4-photosynthesis, which is common in today’s tropical grasslands and savannahs. The global spread of C4-grasses began eight million years ago on the Indian subcontinent – their presence in Europe was previously unknown.
Electron microscope image of a dust particle rounded by eolian transport. It originated in the Sahara desert and was found in 7.2 million year old sediments in Greece (photo courtesy of Ulf Linnemann, Senckenberg Center for Human Evolution and Palaeoenvironment, University of Tübingen)
The record provided by the phytoliths gives evidence of severe droughts, and the charcoal analysis indicates recurring vegetation fires.
“In summary, we reconstruct a savannah, which fits with the giraffes, gazelles, antelopes, and rhinoceroses that were found together with Graecopithecus,” said Spassov.
Böhme calls this hypothesis the North Side Story, in contrast to Yves Coppens' theory known as the East Side Story.
“The incipient formation of a desert in North Africa more than seven million years ago and the spread of savannahs in Southern Europe may have played a central role in the splitting of the human and chimpanzee lineages,” said Böhme.
Begun said researchers need to be more open minded in the quest to uncover the origins of the human lineage.
“This fossil shows that Europe is just as likely to hold the key to the answer to this eternal question as Africa,” he said.
The findings are described in two studies published in PLOS ONE titled “Potential hominin affinities of Graecopithecus from the late Miocene of Europe” and “Messinian age and savannah environment of the possible hominin Graecopithecus from Europe.”