Researchers re-examined beads excavated from one site in Israel and one in Algeria.

The beads date to around 100,000 years ago —about 25,000 years older than similar beads found in South Africa that were previously considered the record holder.

"Our paper supports the scenario that modern humans in Africa developed behaviours that are considered modern quite early in time," said study co-author Francesco d'Errico of the National Center for Scientific Research in Talence, France.

"These people were probably not just biologically modern but also culturally and cognitively modern, at least to some degree."

Archeologists look for personal ornaments and art as proof of symbolic thinking.

The find includes three shells, two from Skhul in Israel, and one from Oued Djebbana, Algeria, the team reports in Friday's issue of the journal Science.

The researchers concluded people deliberately selected the shells and transported or traded them, given how the beads differ from natural shells, and the 200-kilometre distance between the Algerian site and the seashore.

"We think that the African evidence may point to the beads being used in gift-giving systems which function to strengthen social and economic relationships," said archeologist Marian Vanhaeren of the University of California.

"The European evidence suggests the beads were used as markers of ethnic, social and personal identity," the study's lead author added in a release.

The shells were left by scavenging marine snails now found in the shallow waters of the central-eastern Mediterranean.

The newly analyzed shells and those from Blombos in South Africa come from the same genus of snail, the researchers said. The South African beads were all punctured in the same place and looked as if they were once strung together.

All of the shells are too tiny to be used as a food source, the researchers said.

Before the Blombos paper in 2004, it was generally thought that humans developed symbolic thought about 35,000 to 40,000 years ago.