These caves were famous as being sites for preserving the remains of a gruesome massacre supposed to have been dating back to the Spanish Civil War when the Republican soldiers used the cave to hide.

Most evidence peg the appearance of Neanderthals on earth to years as early as 600,000 - 350,000 years ago.

The first clues were bone fragments discovered by the Spanish police in 1994 who gave them over to scientists to decipher. The bones have now yielded valuable DNA that showed the bones didn't belong to modern humans but were from nearly 50,000 years ago.

In a paper, published last week, the Proceedings o f the national academy of science, says that the bones have a gruesome story to tell. They are remains of extended families possibly killed by cannibals.

Clues to social structures

Careful examination has showed proof that these are remains of victims of cannibalism. A hint of cannibalism has been found among Neanderthals in various other sites but the scale of El Sidron remains unparalleled.

There were no animal remains found in the cave. The bones, all human, have marks that indicate that muscles have been sliced from the bone. This is important data pointing at cannibalism.

From some of the teeth that fit into jaws and the bone fragments matched, the scientists have been have able to put together 12 individuals which include women and teenager. Matching instances of mitochondrial DNA, that show that they were of the same family, have been found among the male skeletons.

This discovery is exciting because, scientists hope that they will yield new evidence to draw more detailed genealogical references in the coming years and prove better clues as to how they died.

Image © Steve Young