Anthropologists found an intact hominid skull fossil in Dmanisi, Georgia that is turning evolutionary theory on its head.

The theory of multiple human species has been dealt a blow by the 1.8 million-year old skull fossil. Unearthed in 2005, the skull fossil (one of five skull fossils at Dmanisi) indicates that early human fossils found elsewhere—Homo habilis, Homo rudolfensis and Homo erectus—were linked to the same Homo lineage and not different species, according to the study published in Science.

Or, more plainly:

“The Dmanisi sample, which now comprises five crania, provides direct evidence for wide morphological variation within and among early Homo paleodemes. This implies the existence of a single evolving lineage of early Homo, with phylogeographic continuity across continents.”

Got that? The Dmanisi skull fossil is believed to be an early form of Homo erectus, the first species with body proportions like a modern human.

“Since we see a similar pattern and range of variation in the African fossil record, it is sensible to assume that there was a single Homo species at that time in Africa,” said Professor Christoph Zollikofer, co-author of the study.

“Since the Dmanisi hominids are so similar to the African ones, we further assume that they both represent the same species.”

Not everyone agrees on the impact of the skull fossil.

“They do a very general shape analysis of the cranium which describes the shape of the face and braincase in broad sweeping terms,” Prof. Fred Spoor told the BBC.

“The problem is that those Homo species are not defined using such a broad overview of what their general cranial shape is.”

The team does not dismiss the multiple human species theory outright, however.

“We are not against the idea that there might have been multiple species 2 million years ago,” Zollikofer said. “But we don’t have sufficient fossil evidence to make the distinctions between species.”

What do you think of the skull fossil discovery? Does the skull fossil disprove the multiple human species theory? What is the importance of the skull fossil?