Parents clasped the hands of their children in a 4600 year-old grave which researchers believe to be the oldest evidence discovered so far of the nuclear family in early human development, according to a new study.

The remains of 13 people believed to have been killed during a violent raid were laid out in an unusual pattern for the Neolithic period in a gravesite discovered in Germany in 2005.

Several pairs were buried face-to-face with their hands and arms interlinked in four nearby graves which researchers believed were once covered in burial mounds.

Two of the gravesites were sufficiently well-preserved to allow for DNA analysis.

In one, researchers from Britain and Australia were able to determine that the man and woman clasping the hands of two boys were indeed their parents.

"Their unity in death suggests a unity in life," writes lead author Dr Wolfgang Haak of the University of Adelaide in the journal Proceedings of the National Academy of Science.