The 65,000-year-old cave paintings were little more than stencil-like drawings, an abstract combination of lines and geometric shapes and handprints, as well as rudimentary attempts at animal representations.

And yet those drawings, recently discovered in three caves in Spain by a team of archaeologists, might have just changed what it means to be human.

The cave art was made by Neanderthals, representing the first certain Neanderthal paintings ever discovered and suggesting that the modern human species didn’t invent creative expression, as previously thought, according to an article published Thursday in Science and Science Advances.

The discovery brings researchers one step closer to understanding how it is that humans developed art and language and religion — the types of symbolic and cultural expressions that have always been thought to elevate humans from other species, said archaeologist Alistair Pike, a professor at Britain’s University of Southampton who was part of the research team.

“It’s almost the definition of being human,” Pike told The Washington Post. “It’s how we define ourselves as different from other animals and primates, having language and cultural expression. There’s been a lot of work trying to understand where in Homo sapiens’ lineage did we first become symbolic individuals?”

Perhaps, Pike said, it started with Neanderthals.

The archaeologists were able to determine that the paintings were made by Neanderthals through a type of carbon-dating involving uranium-thorium. Understanding the rate at which uranium-thorium decays, scientists can at least determine the minimum age of the top layer of the rock, the surface marked with the drawings.

The earliest known modern humans had migrated to Spain roughly 40,000 to 45,000 years ago, according to the article. But these paintings predate the time of modern humans by at least 20,000 years, providing what Pike described as the first form of “incontrovertible proof” that Neanderthals made them. They are the oldest-known paintings in the world, the article says.

Professor Chris Stringer, a researcher at London’s National History Museum who was not involved in the discovery, told the BBC that the latest findings “seem to remove any doubt” about whether Neanderthals were capable of symbolic expression. “They further narrow any perceived behavioral gap between the Neanderthals and us,” he said.

Still, Stringer stressed that there is still not definite proof of Neanderthals’ ability to make figurative art — of animals and people — because the animals the researchers found on the paintings in Spain have uncertain origins. Pike said it was not entirely clear whether humans may have stumbled upon the Neanderthal paintings and simply added to them with the vague animal drawings, or if they were a part of the original Neanderthal designs; the researchers have not yet dated them, he said.

Neanderthals had been tentatively credited in the past with the cave drawings. The problem, according to the article, was that the drawings weren’t old enough to rule out the possibility that modern humans made them during the time that Homo sapiens briefly coexisted with Neanderthals. Some archaeologists theorized that the Neanderthals may have even copied modern humans’ paintings, yet still did not possess the creativity to do it themselves.

The discovery that they did not, in fact, need the help of modern humans puts Neanderthals and humans on a more level playing field, Pike said, given that tens of thousands of years ago, modern humans weren’t all that sophisticated either. The end goal with this research, he said, is to understand how the brain became wired for symbolic expression — but that’s going to require a lot more cave discoveries.

“If we’re going to try to find out when we started thinking like humans, we’re going to have to go back further in time,” Pike said. “What we’re interested in is when the brain became modern, and that’s a really difficult thing to get at. You can see how big it was by looking at the size of the skull, but it’s really hard to know how it was wired inside. If the use of symbols and symbolic behavior can be used as a proxy for how the brain was wired, then we can understand how the brain evolved.”

The Neanderthals went extinct about 5,000 years after humans arrived in Europe. The suspected causes have ranged from climate change that affected available food to competition with modern humans. As research moves forward, Pike said, it may be useful to keep in mind that perhaps humans and Neanderthals were not as different as we thought.

“There’s always been a sense that all this expression, this art, arrived with modern humans, and Neanderthals might have been copying them in the very late period of their existence,” Pike said. “But wouldn’t it be interesting if it was in fact the other way around? Modern humans may have landed on the moon — but they started out in the same place as Neanderthals.”

A night at the museum: Neanderthal skeleton (Gillian Brockell/The Washington Post)