Discovery of 1.8-Million-Year Old Skull Suggests Single Lineage for Human Species

A 1.8-million-year-old hominid skull unearthed in the Republic of Georgia eight years ago, has refueled the debate about our ancient human ancestors. Now researchers claim that the skull shows that all homo species were one.

The concept that all members of homo genus that include Homo habilis, Homo rudolfensis, Homo erectus are different, was blown apart  after analysis of the early human fossils unearthed in Africa and Eurasia, which suggests that they were a part of the same species.

The researchers came to this conclusion after spending eight years studying the most complete hominid skull ever found in 2005, which was unearthed in Dmanisi, Georgia. The skull dubbed Skull5 had a small braincase with a long face and large teeth. It was unearthed along with four other human remains, different types of animal fossils and a few stone tools. This find is completely unique because all the objects unearthed belonged to the same location and same time period.

The 1.8 million-year-old skull that was preserved in a siltstone beneath hilltop ruins of a medieval fortress is the earliest known human fossil discovered outside Africa.

The team found enough similarities in the skull of the hominid cranium with  the earliest Homo fossils to conclude that they shares the same species

Traditionally the differences in the homo fossils were used to define different species. But this new finding states that the early diverse homo fossils with their origins in Africa were actually representations from a single evolving lineage, mostly the homo erectus.

There was a lot of variation in the fossil remains that had previously puzzled the researchers. The researchers observed the variability and compared it with the modern humans. They noticed a normal range of variation. Ever since the skull was uncovered, the researchers have compared it to the other homo fossils retrieved from Africa some 2.4 million years ago. They compared the cranium and the jaw and noticed enough similarities to confirm that the earliest homo fossils were similar to species of Dmanisi hominids, BBC Reports.

"Had the braincase and the face of Skull 5 been found as separate fossils at different sites in Africa, they might have been attributed to different species," said Christoph Zollikofer from the Anthropological Institute and Museum in Zurich, Switzerland. "That's because Skull 5 unites some key features, like the tiny braincase and large face, which had not been observed together in an early Homo fossil until now. The Dmanisi finds look quite different from one another, so it's tempting to publish them as different species. Yet we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species."

The hominid fossil retrieved from Dmanisi is an ancient human ancestor that belongs to the Pleistocene epoch, after early Homo diverged from Australopithecus and vanished from Africa.  Looking at the 3.3 cubic inches skull, the researchers claim that it belonged to a male. The skull size also suggests that the early Homo had small brain.

But this finding was discarded by a few people belonging to the scientific community.

"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," Bernard Wood, a paleoanthropologist at George Washington University said.

But Zollikofer confirms his findings and concludes that rather than several ecologically specialized Homo species, a single Homo species emerged from the African continent. 

The findings are published in Science.