Europe's prehistoric hunter-gatherers may have practiced human sacrifice, a new study claims.

Investigating a collection of graves from the Upper Paleolithic (about 26,000 to 8,000 BC), archaeologists found several that contained pairs or even groups of people with rich burial offerings and decoration. Many of the remains were young or had deformities, such as dwarfism.

The diversity of the individuals buried together and the special treatment they received could be a sign of ritual killing, said Vincenzo Formicola of the University of Pisa, Italy.

"These findings point to the possibility that human sacrifices were part of the ritual activity of these populations," Formicola wrote in a recent edition of the journal Current Anthropology.