Last Common Ancestor of Humans, Neanderthals Still Remains a Mystery

It is widely believed that humans and Neanderthals share a common ancestor who lived in Europe. However, a new study suggests that archaeologists may have failed in constructing an accurate human family tree as the common ancestor still remains a mystery.

Researchers at the Indiana University and colleagues analyzed fossilized dental samples to see whether any of them belonged to hominins, a group that preceded Neanderthals and humans. The term hominin is used to refer to any extinct member of the human lineage. Homo neanderthalensis (the Neanderthals), Homo erectus, Homo habilis, and various species of Australopithecus are all thought to be related by a common ancestor. The only member of hominins alive today is the Homo sapiens.

Recently, a team of researchers, who analyzed a fossilized skull, suggested that experts have wrongly constructed the human family tree and that all humans originated from a single ancestor- Homo erectus.

The scientists found that none of the samples matched the expected profile of the ancient hominid. Their study also supported the idea that humans and Neanderthals diverged at least a million years ago, much earlier than previous estimates.

The strength of their research was in their study approach and the number of dental samples analyzed. About 15 percent of the samples came from Atapuerca sites, which are well-known for archaeological evidence supporting human evolution. Researchers looked at over 1,200 molars and premolars from 13 species or types of hominins.

"Our results call attention to the strong discrepancies between molecular and paleontological estimates of the divergence time between Neanderthals and modern humans. These discrepancies cannot be simply ignored, but they have to be somehow reconciled," said Aida Gómez-Robles, lead author of the paper and a postdoctoral scientist at the The George Washington University, according to a news release.

Morphometric analysis and phylogenetic statistics were used to scrutinize every detail of the dental morphology of the last "possible" ancestor of humans and Neanderthal. However, none of the samples showed that they could belong to the line of homonins that gave rise to humans. In fact, their study showed that the dental samples from Europe actually belonged to the ancestor of Neanderthals.

"None of the species that have been previously suggested as the last common ancestor of Neanderthals and modern humans has a dental morphology that is fully compatible with the expected morphology of this ancestor," Gómez-Robles said.

Other studies had shown that Neanderthals diverged from a primate line that gave rise to modern humans about 400,000 years. This group then moved to Eurasia and completely disappeared from the world about 30,000 years back. Other studies have shown that Neanderthals might have lived near the Arctic Circle around 31,000 to 34,000 years ago. The latest study argues that the line that gave rise to Neanderthals lived about 1 million years ago and that humans diverged from Neanderthals much earlier than previous estimates.

According to the researchers, the latest finding proves that quantitative and statistical analysis can help trace human evolution. The study team will be analyzing fossil records from Africa to find the common ancestor of humans and Neanderthals.

"Our primary aim," they write, "is to put questions about human evolution into a testable, quantitative framework and to offer an objective means to sort out apparently unsolvable debates about hominin phylogeny."

The study was published in the journal Proceedings of the National Academy of Sciences.