For millions of years, the Turkana Basin in northern Kenya has been a cradle of humanity. The fossils of several of our relatives have been identified in this imposing rift valley, alongside some of the world’s oldest stone tools.

Around 5,000 years ago, the climate there changed dramatically. The weather became hot and harsh. The lake at the basin’s center shrank to half its former size. Hunting opportunities declined, and people had to turn to herding to survive.

With their food sources dwindling and their environment in upheaval, the communities there might have collapsed into chaos. Instead, archaeological evidence suggests, people came together and cooperated.

In a study published Monday in the Proceedings of the National Academy of Sciences, researchers report the discovery of a prehistoric burial ground containing the graves of at least 580 people of all ages and both sexes. There doesn’t seem to be any hierarchy in how they are arranged. Rather, nearly every one was buried with care alongside personalized ornaments: headpieces made of gerbil teeth, chains of brightly colored beads. One infant bore a bracelet made of delicate pieces of ostrich egg shells.

Based on the ages of the skeletons — radiocarbon dating suggest the remains may be as old as 5,300 years and as recent as 3,900 years — the cemetery may have been used for as long as a millennium. Although the people who created the cemetery probably ranged far and wide to graze their herds, they would have returned to this site to honor their dead year after year.

“Given everything these people were dealing with — a new economic life, a shrinking lake — it’s really impressive that their response was to … invest a substantial effort in time and energy to create a lasting monument that will draw people together and create social unity," said Elisabeth Hildebrand, an archaeologist at Stony Brook University and a lead author of the report.

The site of the burial ground, known as “Lothagam North,” is positioned at the western edge of Lake Turkana amid towering ridges of volcanic rock and canyons of red and orange sandstone.

Beneath a raised mound ringed by boulders and pillars of volcanic stone sits several pits dug into the soft bedrock. The entire “mortuary cavity” is more than 1,000 square feet.

“It’s a massive, monumental place,” said University of Florida archaeologist Katherine Grillo, who co-directs the Later Prehistory of West Turkana Project with Hildebrand.

It’s also unexpected. Anthropologists usually associate “monumental” sites with urban societies. Labor-intensive building projects are seen as a sign that people have picked a home, settled down and are asserting their claim on the landscape. Huge funerary monuments are interpreted as evidence of social hierarchies that form in cities — who else but the rich and powerful could devote so much time and money on their tomb?

But the people who inhabited Turkana Basin 5,000 years ago (and some who still live there today) were hunter-gatherers turned pastoralists. Their lives were mobile, their communities egalitarian, their territory subject to change in response to the shifting climate.

Typically, the burial grounds of such groups are haphazard, used only for short periods of time. But building and maintaining this cemetery was undoubtedly the work of generations.

“Amid all these uncertainties, they were choosing to create places of permanence," Hildebrand said. “There must have been great social value to them having places they would be sure to come back to."

It’s likely that the builders of the Lothagam North site performed funerals and other religious ceremonies there. Regular visits to the site would also have enabled regular meetings of the herding groups that inhabited the vast plain. People probably took the chance to compare grazing grounds, exchange news and strategize for the coming year.

In other times and in other parts of the world, global climatic shifts have been associated with violent conflict and social upheaval. Research has found that famines caused by volcanic eruptions were almost always associated with uprisings in ancient Egypt. Severe drought and water shortages have been blamed for the civil war in Syria that rages today. A recent analysis of armed conflicts and natural disasters around the world between 1980 and 2010 found about a quarter of the violence coincided with climate-change-induced catastrophes.

But the archaeologists didn’t find evidence of warfare or inequality at the Lothagam North site.

“This record from 5,000 years ago is a testament that [conflict] is not the only way to respond,” Grillo said. “It’s possible for people to come together and have a more unified social approach to these problems.”

Although Hildebrand, Grillo and their colleagues excavated a small portion of the site, much of their analysis was done with ground-penetrating radar, which allowed them to explore the cemetery without disturbing people’s remains. Researchers from the National Museums of Kenya participated in the research and site conservation.

“We’re trying to respectfully understand the mind-sets and priorities and joys and sorrows of people in ancient times," Grillo said. “Every time a new burial is exposed, that represents the occasion of a family burying their dead, bringing their loved one rest with everybody else."

“Imagining that group of people coming to the site," she added, "it makes you think about archaeology in a different way.”

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