Globalization has a new face – and it is a rather long one.
Researchers working in the foothills of the Caucasus mountains in the Republic of Georgia have unveiled a fossil they say could shift thinking on the earliest chapters of the human story.
The 1.8-million-year-old adult skull is the best preserved example yet of a hominid species that once roamed the forests and plains of western Asia – the first members of the genus Homo, which includes modern humans, to wander out of Africa.
But with its small brain case, long face, large teeth and massive jaw, the creature also presents scientists with a puzzle.
"This is a strange combination of features that we didn't know before in early Homo," said Marcia Ponce de León, a researcher at the Anthropological Institute and Museum in Zurich, Switzerland, and co-author of the research published on Friday in the journal Science.
Dr. Ponce de León and her colleagues took nearly eight years to prepare and study the skull, which was unearthed in 2005 at the Dmanisi excavation site, about 60 kilometres southwest of the capital, Tbilisi. Scientists were ecstatic when it matched a lower jawbone found a short distance away five years earlier, a case of "extreme fortune," Dr. Ponce de León said.
The skull's bulky features mean that it was likely male. It has a healed fracture on one cheek, perhaps the result of an injury sustained in conflict with another individual, researchers say, or battling with predators over an animal carcass, a key food source for hominids that lived in the region.
Because it shares traits with at least two early species, Homo habilis and Homo erectus, the find puts a new spin on the debate over whether the species distinctions are as real as previously thought. The authors argue that both species, along with a third, Homo rudolfensis, discovered in Kenya in 1972, are part of a continuous population that once stretched from Africa to Southeast Asia.
"We have, now, one global human species," Christoph Zollikofer, also with the Zurich museum, said of present-day humans. "What we can infer from our studies at Dmanisi is that, 1.8 million years ago, there was another single, global species" that included all the early varieties of Homo.
The authors base their case not just on the newly described skull but on the way it relates to four less-complete ones from Dmanisi. Because the site was abruptly buried in ash from a volcanic eruption, all the skulls are thought to be from the same general time and location. That implies the differences in their features are the result of individual variation rather than species differences. The authors argue that the differences that distinguish what are now considered separate species of early Homo found in other locations fall within the range of variation seen among the individuals at Dmanisi.
Other scientists have called the new find spectacular even if they do not agree with the authors' interpretation, noting that similar-looking species of hominids could have exhibited significantly different behaviour.
"Seen across a parking lot, a Mercedes and a Chrysler might look pretty similar, but there's a hell of a lot going on inside that suggest these are very different motor cars," said Bernard Wood, a paleoanthropologist at George Washington University, who is skeptical of the one-species theory.
Yet the new find adds to an increasingly nuanced picture of early Homo that may have included "back-migration" from Asia as well as outward migration from Africa. How this story connects to modern humans remains unclear. Gaps in the fossil record mean that researchers are not sure whether Homo erectus, including the Dmanisi hominids, was an ancestral species to Homo sapiens or an offshoot that was later supplanted by a separate African line.
What the Dmanisi finds do show is that early Homo "did not need a large brain or sophisticated stone tools to disperse out of Africa," said lead author David Lordkipanidze of the Georgian National Museum in Tbilisi.
Susan Antón, a professor of anthropology at New York University, who was not involved with the find, agrees that the need to adapt to new environments and challenges required by such a large-scale migration means that the hominids of that period were not just evolving biologically, but exhibiting a behavioural flexibility that would later become the precursor to culture.
"They've pushed that part of being human back much, much earlier," Prof. Antón said.