Complete and partial skeletons of nearly 30 people unearthed in northern Kenya show signs of the earliest known instances of organized intergroup warfare.

Published in the journal Nature Communications, the new study detailed 12 complete skeletons and 15 partial ones that show evidence of being bound, beaten, and stabbed. The remains represent the first instance of violence between two groups of hunter-gatherers.

"If you take war to mean lethal conflict between groups, the idea is that war in that sense only arose when people had food production, when they had livestock and agriculture - things that could be stolen," study co-author Robert Foley, of the University of Cambridge, told The Washington Post. "This suggests perhaps that intergroup conflict may extend much deeper into our evolutionary past."

The researchers pointed out that remains of at least 10 of the skeletons they found suggested this kind of intergroup violence started earlier still. The skeletons were found near Lake Turkana at a site called Nataruk.

"The Nataruk massacre may have resulted from an attempt to seize resources - territory, women, children, food stored in pots - whose value was similar to those of later food-producing agricultural societies, among whom violent attacks on settlements became part of life," study lead author Mirazón Lahr, of the University of Cambridge, said in a press release. "This would extend the history of the same underlying socio-economic conditions that characterize other instances of early warfare: a more settled, materially richer way of life. However, Nataruk may simply be evidence of a standard antagonistic response to an encounter between two social groups at that time."