By Dr David Whitehouse
BBC News Online science editor
Red-stained bones dug up in a cave in Israel are prompting researchers to speculate that symbolic thought emerged much earlier than they had believed.
Ochre-stained rocks have been found in the cave
Symbolic thought - the ability to let one thing represent another - was a giant leap in human evolution.
It was a mental ability that allowed sophisticated language and maths.
New excavations show that a red colour made from ochre was used in burials 100,000 years ago, much earlier than other examples of colour association.
Study in scarlet
Qafzeh Cave in Israel is a remarkable site that contains many skeletons of humans who lived there about 100,000 years ago.
Archaeologists have recently discovered fragments of red ochre - a form of iron oxide that yields a pigment when heated - alongside bones in the cave. The ochre is only found alongside the bones.
"We found 71 pieces of ochre and established a clear link between the red ochre and the burial process, it seems to have been used as part of a ritual," Dr Erella Hovers of the Hebrew University of Jerusalem told BBC News Online.
The association of red ochre with skeletons found in Qafzeh cave in Israel suggests that symbolic burial rituals were being performed almost 100,000 years ago.
This is much older than the 50,000 years that some other scientists believe is the date for the emergence of symbolic reasoning.
The association of ochre with burial indicates that the inhabitants had made the mental leap of associating the coloured pigment with death. Such symbolic thought spurred human progress, allowing the development of sophisticated language and mathematics.
"The red ochre meant something to them, exactly what we do not know, but it is not inconceivable that they painted their dead with red ochre," says Erella Hovers.
"It is an example of symbolic thought, the ochre symbolised death. The humans at this time behaved in a way that was not just functional but symbolic as well," she added.
The researchers believe that the red ochre at Qafzeh was brought to the cave from nearby sources.
In layers in the cave archaeologists have found ochre-stained tools indicating that the red pigment was probably produced in the cave, possibly as part of the burial ritual.
Somehow the ability was then lost. After the initial evidence of symbolic behaviour in Qafzeh about 100,000 years ago it disappears, only to emerge again about 13,000 years ago.
The research is published in the journal Current Anthropology.