About 100,000 years ago, six of our Neanderthal cousins had a terrible end to their compatriots.
In a cave in the southeast of France, two adults, two teenagers between the ages of 12 and 15 and two children aged four were eaten by other Neanderthals.
Archaeologists have long accepted that Neanderthals were occasionally cannibals. The skeletons found at the cave show clear signs of human consumption, such as cut marks and nibbled finger bones.
But the reason for this behavior has not been fully understood.
In a study published in the Journal of Archaeological Science this month, French researchers suggest that Neanderthals are reluctant cannibals forced to eat each other if they had no other readily available sources of food.
Why was there so little to eat? Climate change.
"It took extraordinary conditions for human flesh to become meat," study co-author Alban Defleur told Business Insider.
A cave that has remained undisturbed for tens of thousands of years  The approximately 120 found bones of these six unfortunate cannibalism victims were originally discovered in the 1990s in the small cave of Baume Moula-Guercy in the Rhône Valley in southeastern France. Defleur was the author of a 1999 study in the journal Science, in which the results were documented.
"More than half of these remains had crop marks made with Flint tools," said Defleur.
This indication, along with signs of clubs on the thighs and skulls of Neanderthals, suggests that the brain, the marrow, and the flesh of the dead were consumed.
. Defleur and his co-author Emmanuel Desclaux tried to find out why these individuals were consumed by members of their own species.
For this purpose, the scientists examined a specific layer of the cave, layer XV.
The cave of Baume Moula-Guercy consists of 19 archaeological layers arranged one above the other in chronological order, representing a period of about 100,000 years. This meant that the researchers could compare what types of species lived together in different time periods and what the climate was during those periods. Layer XV – only 16 inches thick – included not only the cannibalized Neanderthal remnants, but also everything they had left behind, including the remains of chimneys, charcoal, flint tools, and animal bones. These objects were "fossilized" without interruption in a layer of "fossilized remnants of that time," said Defleur.
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The contents of Layer XV showed what the area looked like from 128,000 to 114,000 years ago, at a time called the last interglacial period (between glaciations).
The cave of Baume Moula-Guercy is rare; There are very few archaeological sites from this period between the two ice ages, says Defleur. The researchers therefore have little insight into the effects of climate change on the way of life of Neanderthals.
Defleur and Desclaux found that the climate of Neanderthals was up to 4 degrees Fahrenheit warmer than today, and that the climate had changed incredibly quickly from colder to warmer.
This shift was the most significant global warming that our planet has experienced the last 400,000 years, Defleur said.
"We are not [talking] in terms of geological scale, but more of a human scale," said Desclaux Cosmos. "Maybe the landscape has changed completely within a few generations."
In addition, the fossilized animal bones have helped researchers find out how European wildlife was before, during, and after this period of abrupt warming.
Defleur and Desclaux found that climate change led to the development of thick forests across Europe, thus disappearing into the disappearance of the large mammals that typically hunted Neanderthals, such as bison, reindeer and mammoths. Because of this lack of traditional prey, they were left with no food, which may have led them back to cannibalism.
According to the authors of the study, important evidence for their hypothesis that Neanderthals devoured only members of their own species out of despair comes from enamel on the dead Neanderthals. An analysis of her molars indicated severe and persistent deficiencies indicating malnutrition.
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Defleur said similar enamel studies were done in two other places where cannibalized Neanderthals were found and these researchers found the same sign
Of the 220 European sites left by human remains of the Neanderthal lineage, only four sites, including these, have evidence of Neanderthal cannibalism. The other three are in Croatia, Belgium and Spain.
Defleur said, however, that archaeologists have found 17 sites with 34 individual burials, suggesting that Neanderthals ritually buried their dead. This suggests that cannibalism was the exception rather than the rule.
"The low number of confirmed cases of cannibalism among Neanderthals also shows us that they may have the same taboo as we have about eating human flesh, otherwise the cases would be much more numerous," he said. "Only the survival of the group led them to break this possible moral prohibition."