Skull find points to single, evolving human species

After eight years spent studying a 1.8-million-year-old skull uncovered in the Republic of Georgia, scientists have made a discovery that may rewrite the evolutionary history of the human genus known as Homo.

The research suggests that early man was a single, evolving species with a wide range of appearances, and not a wide range of different species as currently thought.

Diverse fossils currently recognised as coming from distinct species like Homo habilis, Homo erectus and others may represent variation among members of a single lineage. In other words: just as people look different from one another today, so did early hominids look different from one another, and the dissimilarity of the bones they left behind may have fooled scientists into thinking that they came from different species.

This was the conclusion reached by an international team of scientists led by David Lordkipanidze, a palaeoanthropologist at the Georgian National Museum in Tbilisi, as reported on Thursday in the journal Science.

The key to this revelation was a cranium excavated in 2005 and known as Skull 5, which scientists described as "the world's first completely preserved adult hominid skull" of such antiquity. Unlike other Homo fossils, it had a number of primitive features: a long, ape-like face, large teeth and a tiny braincase, about one-third the size of that of a modern human being. This confirmed that, contrary to some conjecture, early hominids did not need big brains to make their way out of Africa.

The discovery of Skull 5 alongside the remains of four other hominids at Dmanisi, a site in Georgia rich in material of the earliest hominid travels into Eurasia, gave the scientists an opportunity to compare the physical traits of ancestors that apparently lived at the same location and around the same time.

Lordkipanidze and his colleagues said the differences between these fossils were no more pronounced than those between any given five modern humans or five chimpanzees. The hominids who left the fossils, they noted, were quite different from one another but still members of one species.