A handout photo provided by Nature on January 19, 2016, shows the skull of a skeleton unearthed at Nataruk, the site of the earliest known evidence of inter-group conflict. Researchers in Japan scoured the country for similar sites and found none, leading them to conclude that violence is not an inescapable aspect of human nature. (Marta Mirazon Lahr/AFP/Getty Images)

The skeletons told an alarming tale: One belonged to a woman who died with her hands and feet bound. The hands, chest and knees of another were fragmented and fractured — likely evidence of having been beaten to death. Stone projectiles protruded ominously from skulls; razor-sharp obsidian blades glittered in the dirt.

The grotesque tableau, discovered in Nataruk, Kenya, is the oldest known evidence of prehistoric warfare, scientists said in the journal Nature earlier this year. The scattered, scrambled remains of 27 men, women and children seemed to illustrate that conflict is not simply a symptom of our modern sedentary societies and expansionist ambitions. Even when we existed in isolated bands roaming across vast, unsettled continents, we showed capacity for hostility, violence and barbarism. One of the members of the “Nataruk Group” was a pregnant woman; inside her skeleton, scientists found her fetus’s fragile bones.

“The deaths at Nataruk are testimony to the antiquity of inter-group violence and war,” lead author Marta Mirazon Lahr, a paleoanthropologist at the University of Cambridge, said in a statement. She told Smithsonian, “What we see at the prehistoric site of Nataruk is no different from the fights, wars and conquests that shaped so much of our history, and indeed sadly continue to shape our lives.”

And yet, for all the evidence that warfare is a deep and ancient aspect of human behavior, there are also signs that it may not be an inevitable one. Another group of ancient skeletons from the other side of the world tells a different story: One about humans who had the capacity for violence, but refrained.

In a study published Wednesday in the journal Biology Letters, researchers say they found little evidence on the ancient skeletons of the Jomon people in Japan — hunter gatherers not unlike those at Nataruk. Surveying bones from a more than 10,000-year-long stretch of prehistory, from 13,000 BC to 800 BC, they found that the average mortality rate due to violence for the Jomon was just under 2 percent. (By way of comparison, other studies of the prehistoric era have put that figure somewhere around 12 to 14 percent.)

What’s more, when the researchers sought out “hot spots” of violence — places where lots of injured individuals were clustered together — they couldn’t find any. Presumably, if the Jomon had engaged in warfare, archaeologists would have bunches of skeletons all in a heap, like the bones in the Nataruk group. That no such bunches seemed to exist suggests that wars weren’t being fought.

The implication of both those finds, the authors argue, is that humans are not as innately drawn to violence as the Nataruk group and Thomas Hobbes might lead us to believe.

“It is possibly misleading to treat a few cases of massacre as representative of our hunter-gatherer past without an exhaustive survey,” they wrote in their study. “We think warfare depends on specific conditions, and the Japanese data indicate that we should examine these more closely.”

This innocuous-sounding assertion hits at the heart of an ongoing debate in the field of anthropology: Where does our violence come from, and is it getting better or worse?

One school of thought holds that coordinated conflict, and eventually all-out warfare, arose with the establishment of permanent settlements and the development of agriculture. Though it smacks of 18th century sentimentalism, not to mention racism (the idea of a “noble savage” whose innate goodness has not been corrupted by civilization was used to justify all manner of abuses against non-European people) there is a logic to this way of thinking. Farming is associated with the accumulation of wealth, the concentration of power and the evolution of hierarchies — not to mention the rise of good-old-fashioned notion “this is mine” — all phenomena that make it more likely that one group of people will band together to attack another.

But other anthropologists ascribe to the Thomas Hobbesian notion that people have an innate capacity for brutality — though perhaps modern civilization gives us more outlets for expressing it. Luke Glowacki, a Harvard University anthropologist who studies the evolutionary roots of violence, believes that the Nataruk discovery illustrated this second view.

“This new study shows that warfare can and did occur in the absence of agriculture and complex social organization,” he told Scientific American in January. “It fills in important gaps in our understanding of the human propensity for violence and suggests a continuum between chimpanzee raiding and full-blown human warfare.”

Some studies have even suggested that violence is essential to our evolution. In a 2009 study in the journal Science, the economist Samuel Bowles modeled how prehistoric warfare may have given rise to complex communities that took care of one another — forming the genetic basis of altruism — because evolution favored groups that were able to get along during their violent pursuit of victory over others.

If that’s the case, the authors of the Japanese study say, inter-group violence must have been pretty pervasive during the prehistoric period — that’s the only way it could have so dramatically shaped human evolution in a relatively short span of time.

But their study, and others like it, have found hunter-gatherer societies where lethal conflict was relatively rare.

“We are not asserting warfare was uncommon among hunter-gatherers in all areas and times,” they write. “However … it is possibly misleading to treat a few cases of massacre as representative of our hunter-gatherer past without an exhaustive survey.”

Instead, they argue, warfare is probably the product of other forces — scarce resources, changing climates, growing populations.

This actually isn’t so different from an argument made by Mirazon Lahr, the lead author on the Nataruk study. Even though the human capacity for violence is deep-rooted, it doesn’t get expressed in all-out war until it is triggered by the right array of circumstances: a sense of membership in a group, the existence of an authority to command it and a good reason — land, food, wealth — to risk your life.

“Being able to carry out violence is a prerequisite for warfare,” she told Discover. But, “one does not necessarily lead to the other.”