Early Humans in Today’s Israel Used Ash as Their ‘Freezer’

Archaeological analysis of 300,000-year-old stone tools from Qesem Cave shows hominins treated food and animal hides with wood ash from their fires in order to preserve them for a rainy day

Ariel David
Ariel David
Experimental session. Fireplace and roasted tubers (Asphodel, Gundelia)
Experimental session. Fireplace and roasted tubers (Asphodel, Gundelia)Credit: Qesem Cave Research Project Archive
Ariel David
Ariel David

Prehistoric hominins did not have refrigerators, but some 300,000 years ago they figured out a way to preserve their perishables for as long as months – using wood ash, archaeologists have discovered.

A team of Italian and Israeli researchers has found indirect evidence of this sophisticated preservation technique by studying flint tools unearthed in Qesem Cave, a site just east of the modern city of Tel Aviv. The cave, discovered 20 years ago during road works, was inhabited by our very distant ancestors from 420,000 to 200,000 years ago. While these hominins were not the vaunted Homo sapiens, they did display modern characteristics and a surprising array of relatively advanced behaviors, including early use of controlled fire, as evidenced by the remains of a large bonfire dated to 300,000 years ago

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Previous research had already suggested that the people of Qesem stored deer legs to preserve the nutritious bone marrow for times when food was less plentiful. The new study, published last month in the journal PLOS ONE, presents evidence that the locals were not only capable of squirrelling away food for a rainy day, but actively treated perishable goods with ash from their bonfire to stave off decomposition.

Prehistoric chips

The research began when Cristina Lemorini, an archaeology professor at Rome’s La Sapienza University and the lead author on the study, noted there was something unusual about some of the tools found at Qesem. Among the thousands of flints that have been unearthed at the cave, there were 26 tools, found mostly around the hearth, that displayed a band of very bright polish and fine striations along the edges – almost as if they had been buffed by a fine, abrasive powder.

Lemorini and colleagues suspected that these flints, mostly blades and scrapers, had acquired their shiny veneer by being used on materials that had been treated with ash from the hearth.

Cutting roasted Gundelia with a replica of Qesem Cave blade
Cutting roasted Gundelia with a replica of Qesem Cave bladeCredit: Qesem Cave Research Project Archive

To test this hypothesis, they ran a residue analysis on the 300,000-year-old tools, using microscopes and spectroscopy to check for tiny particles that would show what kind of materials the flints had been used on. They also applied an experimental method called use-wear analysis, which involves using replicas of the original tools to process various organic materials and then checking whether the wear-and-tear patterns on the reproductions match those found on the prehistoric flints.

These tests were done on meat, hides and vegetables that were both fresh and previously treated with ash: Sure enough, only the tools used on the ash-covered materials developed the distinctive marking found on the Qesem flints that were part of the study. The chemical analysis of the prehistoric tools also found ash residues and compounds indicating they were used to process animal hides and vegetables, especially roots and tubers.

If cut, cooked or dried before being covered in ash, these tubers would not have looked too different from today’s salted potato chips, Lemorini notes (except of course locally-available roots were used instead of taters, which only reached Eurasia hundreds of thousands of years later, after the discovery of America).

Just like salt, the use of wood ash to preserve perishable goods is documented in modern ethnographic studies, as the material is known to stave off decomposition, keep insects away and prevent bad smells, Lemorini says. The World Health Organization also recommends using ash to cleanse and disinfect hands or utensils if soap is unavailable. 

It is likely that the vegetables gathered by the Qesem people were preserved, cooked or fresh, to be consumed at a later date, while the animal hides were treated with ash when they could not be cleaned and tanned immediately, the archaeologist says.

Lemorini, who heads a lab that specializes in use-wear analysis, uses ash preservation herself to store perishable material that cannot be used right away for her team’s experiments. Her own experience with the technique was what led her to initially suspect it may have been used at Qesem, she says.

Example of Qesem Cave blade showing use-wear from cutting ash-laden hide
Example of Qesem Cave blade showing use-wear from cutting ash-laden hideCredit: Qesem Cave Research Project Archive
Replicas of Qesem Cave blades after processing roasted tubers or fresh tubers
Two replicas of Qesem Cave blades after processing roasted tubers or fresh tubersCredit: Qesem Cave Research Project Archive

“This method is certainly more natural and damages the material less than freezing it, although the preservation time is shorter,” she tells Haaretz.

Once buried under ash, the food and hides could be preserved for weeks or even months, says Prof. Avi Gopher, a Tel Aviv University archaeologist who led the dig at Qesem together with his colleague, Prof. Ran Barkai.

“It was kind of a prehistoric freezer,” Gopher tells Haaretz. “It means that if these prehistoric hunter gatherers returned to the cave after months of absence, they could still find food ready to be eaten if they didn’t have any with them or if they were facing a season in which food was scarce.”

Only one of the 26 tools analyzed exhibited remains of ash-laden fleshy tissues, suggesting that this technique was rarely used to preserve fresh meat, the study notes. This may mean that the inhabitants of Qesem had already developed separate methods, such as smoking or drying, to increase the shelf life of the venison they hunted, Gopher says.

“People think that hunter gathers engage in immediate consumption, they don’t preserve for delayed consumption, which is not true for modern hunter gatherers and now we know is not true also for prehistoric ones,” he says.

Whether the people at Qesem were truly the first to invent this preservation technique and whether they passed it on to later hominin populations is unclear, as this is the first time that unequivocal signs of this method have been documented on prehistoric flints, Lemorini says.

Archaeologists excavating Qesem Cave
Archaeologists excavating Qesem CaveCredit: Ariel David

“Now that we have identified the ‘fingerprint’ of ash preservation on tools we have all the necessary data for other researchers to detect similar behavior at other sites,” she says.

A fistful of teeth

Who exactly the inhabitants of Qesem were remains somewhat of a mystery, because only a handful of human teeth have been uncovered at the cave – not enough to positively identify which group of hominins they belonged to. We do know that these paltry remains do not belong to Homo erectus, the first hominin known to have left Africa and spread across Eurasia some 2 million years ago. The Qesem hominins were likely descendants of erectus, as their teeth have more advanced features and share some characteristics with modern Homo sapiens as well as Neanderthals.

Teeth found in Qesem Cave
Teeth found in Qesem CaveCredit: Prof. Israel Hershkovitz, Tel Aviv University

This has led some experts to suggest the residents of the cave may have belonged to a new lineage somehow related to Homo sapiens and Neanderthals.

Whoever they were, the Qesem people displayed an impressive range of advanced behaviors that show they were anything but primitive brutes. Previous research has shown that they were capable of recycling and reshaping older stone tools as well as using fire to heat flint, making it easier to knap specific utensils.

They also knew how to communicate their advanced flint-knapping techniques to their children, and there was likely an aesthetic, possibly ritualistic aspect to their culture, as shown by their penchant for collecting bird feathers and useless, shiny pebbles.

Now, the study on the use of ash for preservation adds even more evidence on the advanced cognitive abilities of the elusive Qesem hominins.

“This is a sign of a very advanced level of organization, of a complex understanding of the concepts time and seasonality and the ability to take a series of actions to maximize the exploitation of the surrounding area,” Lemorini concludes. “This suggests a cognitive level that until recently we thought belonged only to modern humans.”

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