The explanation seemed straightforward: After a few million years of evolution in Africa, hominids developed a new technology — an advanced stone toolkit called Acheulean — about 1.6 million years ago. Better tools led to more efficient hunting and scavenging, which allowed early humans to march out of Africa and begin colonizing the world.

Then came Dmanisi. Now both the timing and the explanation for that first critical step out of Africa must be rewritten — for here were hominids on the edge of Europe 1.75 million years ago, well before Acheulean tools were developed in Africa.

The Dmanisi site, in the Republic of Georgia in the Caucasus Mountains, sits on an isolated, triangular spur of basalt. A medieval settlement called Dmanisi prospered for a time as a trading center, though it was eventually abandoned. Archaeologists explored the medieval ruins for decades. Then, in 1983, while excavating a deep storage pit originally dug by the medieval inhabitants, investigators happened upon curious stone artifacts.

The artifacts had unequivocally been produced by humans and were associated with the bones of mammals, such as elephant and rhinoceros, that were long extinct in this region. Paleontologist Abesalom Vekua, after analyzing the faunal remains, estimated the age of the archaeological horizon as more than one million years.

That began years of meticulous excavations, the analyses of the archaeological finds, and — above all —
the collaboration of an international team.

This 1.6 million-year-old skull represents the the earliest evidence of human ancestors in Europe. Photos courtesy of Antje Justus.

These years of endeavor were rewarded in 1999, when two almost-complete human skulls were discovered. These finds throw new light not only on human evolution, but also on the first settlement of Eurasia.

The Georgian-German Research Project Dmanisi officially began in 1991. Prior to this, David Lordkipanidze of the Georgia State Museum had spent several months at the Palaeolithic Research Institute of the Römisch-Germanisches Zentralmuseum Mainz in Neuwied, Germany.

But the ball was really set rolling by Gerhard Bosinski of the Römisch-Germanisches Zentralmuseum, who visited Georgia to take a closer look at several sites. After studying all the Lower Paleolithic artifacts from Dmanisi, he was convinced this was an important site from the earliest period of human history. He proposed a joint effort between the research institute and the Archaeological Centre of the Georgian Academy of Sciences — a difficult undertaking for both sides, as this coincided with the collapse of the Soviet Union.

Toward the end of that first excavation season, a mandible with full dentition from a 20- to 25-year-old human was found. Its anatomy, such as the robust, narrow jawbone and absence of a chin, showed that it belonged to an early human. The mandible rekindled discussion of the hominid migration out of Africa, but it was not conclusive.

We spent the next five years excavating and interpreting the upper levels of the site, where the bulk of the stone artifacts were found. In 1997, we finally returned to the lower find level where the mandible was discovered, this time moving some 25 meters (82 feet) from the trench that had yielded the mandible. Our excavations in this area revealed a concentration of animal remains and, under these, a human metatarsus (a foot bone).

The large-scale excavation clearly showed the lower levels were far more complex geologically, with tunnel-like formations formed by water. The level was capped and the erosion ceased when a calcite crust formed and sealed the site.

The age of our find horizon has, however, been quite accurately assessed. Our colleagues Paul v. d. Bogaard and Carl C. Swisher III agree that the basalt underlying the horizon dates to about 1.85 million years ago. This is based on the argon-40/argon-39 dating method, which utilizes the decay of radioactive potassium-40 to argon-40 as a time-scale. Additional paleomagnetic analyses were undertaken by Swisher, who concluded that the intruding sediments must have been deposited around 1.75 million years ago.

The antiquity of the find was further confirmed for the more than 2,000 animal remains identified as species belonging to the “Villafranchium” faunal complex, which includes ancestral mammoths, Etruscan rhinoceros, giraffes, stenonid horses, gazelles, and large and small forms of saber-toothed cats. It is typical of the period from 2 million to 1.6 million years ago.

Armed with this information, we finally began to investigate the areas close to where the mandible had been found. Once again, we were incredibly lucky. Even as the site was being prepared for the 1999 excavation, Gotcha Kiladze found the first human skull. Almost the whole cranium, from the brow ridges to the foramen magnum (where the spinal cord enters), had been preserved.

Only two meters (6.5 feet) from this fossil, Georgi Nioradze found a second, better-preserved skull. Parts of the maxilla (the upper jaw) were recovered with the second skull, which was surrounded by animal bones, as was the mandible discovered in 1991.

As Abesalom Vekua was preparing the finds in the laboratory in Tiflis, he found four teeth in the maxilla bones. The teeth were not comparable, either in size or wear, to those in the mandible; the mandible and the second skull do not belong to the same individual. Whether the mandible belongs to the first skull or represents a third individual will be determined by further analysis of all the human remains by anthropologist Leo Gabunia.

Although the study of these fossils has only just begun, most parallels can be found in African Homo erectus forms, especially the early form described as Homo ergaster. The age of these early Homo forms is estimated at about 1.8 to 1.5 million years, which compares well with the age of the find-level at Dmanisi. The fact that so far only a handful of fossils described as Homo ergaster have been found in the whole of Africa and facial bones are preserved on only two of these finds underscores the great importance of our discovery.

The results of the excavations at Dmanisi have shown that the first wave of human expansion took place at an earlier date than previously thought, with simple tools similar to “Oldowan” technology used in Africa for 750,000 years before these humans reached Dmanisi. If it was not new technology that let humans leave Africa, perhaps it was new biology. Time will tell.

Antje Justus is a scientist in the Paleolithic Department of the Römisch-Germanisch Zentralmuseum Mainz in Neuwied, Germany. Medea Nioradze is head of the Department of Prehistory in the Archeological Centre of the Georgian Academie of Science.