Prehistoric man may have executed rivals from neighbouring tribes to steal their women, research has found.
A study of 7,000-year-old skeletons, led by Durham University scientists, found that one of the burial groups consisted only of men and children.
This indicated that the women were spared and their capture could have been the motive for the attack.
The findings, from a burial pit in Talheim, Germany, are published in the journal Antiquity.
The 34 skeletons were discovered in the 1980s, but new studies of different types (isotopes) of atoms in their teeth show that they came from three groups - locals, cattle-herders and a "family" of a man, woman and two children.
All the skeletons bore marks to the left side of the skull showing that they were hit in the head with an axe, indicating they were executed while bound.
The scientists concluded the absence of local females meant they were captured instead.
Dr Alex Bentley, from Durham University's Anthropology Department, said: "It seems this community was specifically targeted, as could happen in a cycle of revenge between rival groups.
"Although resources and population were undoubtedly factors in central Europe around that time, women appear to be the immediate reason for the attack.
"Our analysis points to the local women being regarded as somehow special and were therefore kept alive."
Dr Bentley added: "It looks like tribal warfare on a small scale."It's crucial for a group which has a very small population to have access to mates."