Neanderthals may have never co-existed with ancestors of modern humans, according to a new study that suggests they became extinct in their last refuge in Spain much earlier than previously thought.

Neanderthals may have died out earlier than believed, said researchers, adding much of the earlier evidence is based on a series of radiocarbon dates, which cluster at around 35,000 years ago.

The theory that the last neanderthals – Homo neanderthalensis – persisted in southern Iberia at the same time that modern humans – Homo sapiens - advanced in the northern part of the peninsula, has been widely accepted by the scientific community during the last twenty years.

Now, an international study has questioned the hypothesis.

“It is improbable that the last Neanderthals of central and southern Iberia would have persisted until such a late date, approximately 30,000 years ago, as we thought before the new dates appeared,” said Jesus F Jorda, from Department of Prehistory and Archaeology of the Spanish National Distance Education University.

The scientific team, with researchers also from Oxford University and Australia National University applied a new technique in order to repeat analyses at the sites of Jarama VI (Guadalajara) and Zafarraya (Malaga), considered up to now two of the last refuges of the Iberian Neanderthals.

To the usual radiocarbon dating method, the ultrafiltration protocol was added, which aims to purify the collagen of the bone samples from contaminants. The AMS dating technique was applied that requires minimum sample quantities. The scientists, by applying this new method, assure that the neanderthal occupation of the sites did not last until as late as previously thought, instead it should be placed approximately 45,000 years ago.

“The problem with radiocarbon dating alone is that it does not provide reliable dates older than 50,000 years,” said Jorda.

Researchers said the older the samples are the more residues are accumulated. If contaminants are not removed the obtained dates are incorrect.

New analyses were applied to bone remains found in the archaeological deposits in association with Middle Paleolithic stone artifacts.

Bones bearing clear signs of human manipulation (cut marks, marks of percussion or intentional breakage) were selected in order to rule out possible intrusions by carnivores.

Despite the fact that samples were collected from numerous sites in southern Iberia, it was only possible to date those of Jarama VI and Zafarraya, as the remaining samples did not contain enough collagen to be dated.

In view of the new data according to Jorda “prehistory books would need revision”, especially as new results become available.