A new analysis of that ancient person's skull suggests Homo sapiens left their birthplace in Africa about 16,000 years earlier than previously thought, according to a report published Wednesday in the journal Nature.
The human skull was one of two cranial fossils found in Apidima Cave, one of a series of cave sites along the southwestern coast of the Peloponnese in Greece.
Both skulls were found in a block of breccia, or broken fragments of rock and fossil cemented together, wedged high between the walls of the Apidima Cave in southern Greece.
But, to the shock of scientists, the skull named Apidima 1 pre-dated Apidima 2 by as much as 40,000 years, and was determined to be that of a Homo sapiens.
Assigning an age for the specimens also proved challenging, according to Katerina Harvati, the lead author of the new study.
"Now our scenario was that there was an early modern group in Greece by 210,000 years ago, perhaps related to comparable populations in the Levant, but it was subsequently replaced by a Neanderthal population (represented by Apidima 2) by about 170,000 years ago", said co-author Prof Chris Stringer, from London's Natural History Museum. Their presence is documented by finely-worked stone tools and other finds.
After decades of work, the team was able to use CT scans of the bones to virtually reconstruct the damaged and missing parts of the skulls.
A team of researchers from Greece, Germany, Australia and the United Kingdom has used modern dating and imaging techniques to figure out how they belonged to and how long they've been sitting there.
Apidima 1 also lacked any features that were typical of Neanderthals or other archaic human species, she said.
The best explanation, said study co-author Rainer Grun, a geochemist at Griffith University in Australia, is that "Apidima 1 must come from quite a different environment originally, before it was deposited at the site". This confirmed it was an early Neanderthal dating from around 150,000 years ago.
Havarti thinks this part of Eurasia might have served as a refuge for animals and human populations during that period, since the mild coastal climate was a preferable alternative to other parts of Europe.
Eric Delson, an anthropologist with Lehman College who was unaffiliated with the study, said in an accompanying Nature article that these groups "reached the Middle East and southeastern Europe, but did not persist in these regions". That's because it was rounded in a way that's unique to modern humans, Harvati said.
The incomplete nature of the Apidima 1 skull may leave some experts uncertain about its true origin, wrote Eric Delson, a paleoanthropologist from City University of NY, in a commentary that accompanied the study.
The sensational discovery adds to evidence of an earlier migration of people from Africa that left no trace in the DNA of people alive today.
The oldest known African fossil attributed to a member of the Homo family is a 2.8 million-year-old jawbone from Ethiopia. Then the species that eventually gave rise to Neanderthals moved into Europe between 600,000 and 800,000 years ago.
In the last few years, palaeontologists have discovered modern human fossils from Daoxian and Zhirendong in China dating to between 80,000 and 120,000 years ago. Over time, these ancestors replaced Neanderthal populations in those areas. But those early migrants don't appear to have been successful.
The fossilised and Neanderthal skulls were discovered in Apidima Cave, southern Greece, in the late 1970s.