The animal paintings and engravings in caves such as Lascaux and Chauvet in France, and Altamira in Spain, represent the epitome of prehistoric art in Europe. But ever since they were discovered, starting 150 years ago, investigators have struggled to understand exactly what the images meant to the people who made them. In addition to the vivid depictions of animals, enigmatic abstract markings and geometric signs often appear alongside them. Few researchers have examined them in any detail, and most have concluded that their meaning will never be known. 

Now, a new study published in Cambridge Archaeological Journal presents evidence that these signs recorded specific information about the timing of the reproductive cycles of the animals depicted on the cave walls. This information would have been essential to the survival of the Ice Age hunter-gatherers who created the art, according to the authors of the study. They also suggest that the signs represent a kind of “proto-writing,” predating the emergence of token-based records in the Middle East by some 10,000 years.

“We’re able to show that these people—who left a legacy of spectacular art in the caves of Lascaux and Altamira—also left a record of early timekeeping that would eventually become commonplace among our species,” study coauthor and archaeologist Paul Pettitt said in a statement.

One of the biggest and best-known cave painting is an 18-foot-wide image of an extinct wild ox, or aurochs, that seems to gallop across the Great Hall at Lascaux—and dates to around 18,000 years ago. In 2016, London-based amateur researcher Ben Bacon looked at a photo of the painting and noticed four small dots painted across the animal’s back. Wondering what the dots could signify, he quickly came across other examples of depictions of aurochs with four dots. And when he looked at other species, he found that each seemed to be associated with specific numbers, recorded by rows of dots or lines: for example, horses with three, bison with four, salmon with three and six, and so on. Moreover, a “Y” symbol (formed by a line with two branches) frequently appeared second in a row of markings. 

Pursuing these clues, Bacon spent years collecting data from drawings and photos of Ice Age art in scientific publications. He widened his search to include not only cave paintings but also engravings on thousands of small, decorated objects and portable stones found in Ice Age archaeological sites. 

Eventually, he amassed a database of more than 700 images, many of which consistently displayed the associations he had spotted between species and specific numbers of marks. The same numbers kept cropping up across a vast range of sites, spanning much of western Europe from at least 25,000 to 14,000 years ago. The regularity of the numbers suggested to Bacon that the artists might have been keeping track of major cyclical events in the lives of each animal, such as mating, migration, or giving birth, with some sort of calendar system. 

Bacon was not the first to have that idea. In the 1960s, another amateur researcher, science journalist Alexander Marshack, used a microscope to examine dozens of Ice Age carved portable objects and stones. He theorized that the rows of abstract marks on these objects represented daily “notations” for keeping track of the Moon’s monthly cycle, each day marked with a single line or notch. Since many of the animal images depict their seasonal appearance during mating or migration, Marshack proposed that the lunar counts were used to track and predict their behavior. Subsequent investigators refined Marshack’s methods and confirmed his basic idea that the intricate arrays of lines and notches carved on certain Ice Age objects were likely to be recording some type of information over time. But Marshack’s lunar calendar theory failed to get much traction as it was hard to test, and the meaning of the painted signs and notched records remained elusive.

To develop a fresh approach, Bacon contacted Tony Freeth at University College, London, a mathematician known for decoding the ancient Greek astronomical device known as the Antikythera mechanism. Freeth and Bacon came up with another lunar calendar theory, but with a crucial difference from Marshack’s: Rather than a daily record, Freeth and Bacon suggested that each marking stood for a lunar month. Building on this idea, the team hypothesized that the hunters would reset their lunar counts each year by starting them at a recurring natural event, such as the thawing of rivers or other signs of spring. Then they would count off each month after that event, enabling them to record and predict when the animals they depended on mated or gave birth. These were times when the herds would congregate in large numbers and be most vulnerable to the hunters. 

But were all these assumptions correct? One way to test the theory was to compare the numbers Bacon found for the Ice Age animals against the life cycles of their present-day descendants, such as horses, bison, reindeer, and salmon. Study coauthor Robert Kentridge, a Durham University psychologist with extensive knowledge of statistics, analyzed the team’s data and found strong correlations between the numbers of marks, the position of the “Y” sign, and the months in which modern animals mate and give birth.  

The lunar calendar theory mirrors numerous accounts of Indigenous hunter-gatherers who have historically relied on counting lunar months to predict the arrival and behavior of the species that sustain them. For example, each year, the Yurok of northern California used an intricate lunar count to decide when to construct a fish weir to capture migrating steelhead trout along the Klamath River. Although weir trapping is no longer permitted on rivers in California and Oregon, many Indigenous peoples in the Northwest still use and have awareness of lunar cycles in their hunting today, according to Bernie Taylor, an independent researcher who has compiled accounts and interviews with members of these communities.

Similarly, the Yami people of Taiwan continue to follow a lunar calendar to determine when to head out to sea to harvest migratory flying fish, which congregate near the surface during the darker nights around New Moon. 

“The authors deserve a lot of respect for taking such an innovative approach,” says archaeologist Genevieve von Petzinger, whose extensive survey of the designs was the subject of her book “The First Signs.” “I’ve always thought that at least some of the dots and lines are probably some type of notation and involve counting, so the idea of trying to anchor them against natural cycles—whether lunar or the biology of the animals—is a great one,” von Petzinger says. But she advises caution. “We’re talking about 30,000 years of history, multiple cultures and different peoples. I don’t think there’s one reason why they were making the art or the signs. There would always have been multiple motivations.”

As to the question of whether the signs represent a precursor of writing, von Petzinger notes that “writing—even proto-writing—is generally related to representing spoken language and a series of connected symbols. I think it would be more accurate to describe it as a form of graphic communication.” 

As the archaeological community begins to debate the theory, Ben Bacon’s team says it is preparing several additional papers that would demonstrate further associations and meanings among the signs. If their findings hold up, these studies could open up glimpses into Ice Age minds that never seemed possible before. “What we are discovering is that these ancient ancestors are a lot more like us than we had previously thought,” Bacon said in a statement, “these people, separated from us by many millennia, are suddenly a lot closer.”