Archaeologists and palaeontologists have worked tirelessly over the last decades to attempt to piece together a complete fossil record of our human ancestry. However, time and again, study results leave many scientists still scratching their heads. One of the focal points of research has been the search for a common ancestor linking modern humans with Neanderthals. But one new study , which will be published this week by the Proceedings of the National Academy of Sciences, has shown that this search is far from complete.

An international team of scientists investigated the topic by examining the shape of a diverse range of dental fossils. Around 1,200 molars and premolars from 13 species or types of hominins (humans and human relatives and ancestors) were examined and results showed that none of the hominin species fit the expected profile of an ancestor of Neanderthals and modern humans. The researchers also presented evidence that the lines that led to Neanderthals and modern humans diverged nearly 1 million years ago, and not 350,000 years ago as previous studies based on molecular evidence suggested.

"Our results call attention to the strong discrepancies between molecular and paleontological estimates of the divergence time between Neanderthals and modern humans," said Aida Gómez-Robles, lead author of the paper. "These discrepancies cannot be simply ignored, but they have to be somehow reconciled."

It was found that none of the species that had been previously suggested as the last common ancestors of Neanderthals and Homo sapiens were a match. These include Homo heidelbergensis, Homo erectus and Homo antecessor.

"Our primary aim," the researchers wrote, "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."

While progress is being made on a daily basis, scientists have a long way to go in resolving discrepancies in the fossil record, as well as uncovering the true ‘missing link’ between apes and humans. That is, of course, if there is any connection at all.

By John Black