Scientists say their study of a 1.8 million year old skull has led them to believe several early human species previously identified are, in fact, part of the same lineage.
Writing in the US journal Science, the team said the skull shared the features of Homo habilis, Homo rudolfensis and Homo erectus, which meant they were all part of a single evolving lineage that led to modern humans.
The skull was uncovered in Dmanisi, Georgia, eight years ago and since then the team has compared it to other homonid fossils as much as 2.4 million years old found in Africa.
It had a small braincase, large teeth and a long face, characteristics it shares with H. habilis. But many features from the braincase were also "unique" to H. erectus.
The comparative analysis of the cranium revealed enough similarities for the team to consider the earliest homonid fossils as the same species as the Dmanisi hominids.
The fossil remains showed a lot of variation that had previously puzzled researchers, but lead author Professor David Lordkipanidze, of the Georgian National Museum, said it was clear these features were all from one population.
"When we looked at this variability and compared it with modern humans, you can see this is a normal range of variation," Prof Lordkipanidze told the BBC.
Other palaeoanthropologists, however, believe that at least three distinct species of humans co-existed in Africa.
They include Fred Spoor from University College London. He told the BBC that the methods of analysis that the team used were not sufficient to infer that these fossils were the same species.
The Dmanisi site has given up the biggest collection of well-preserved early-human remains known anywhere in the world.
