A zigzag engraving on a mussel's shell may transform scientific understanding of what has long been considered a defining human capacity: artistic creativity.

Until now, the earliest evidence of geometric art was dated from 70,000 to 100,000 years ago. Scratched into rocks found in South African caves, those engravings signified behavioral modernity: Homo sapiens' unique cognitive journey into a sophisticated world of abstraction and symbol.

But new analysis of an engraving excavated from a riverbank in Indonesia suggests that it's at least 430,000 years old—and that it wasn't made by humans, scientists announced Wednesday. At least it wasn't made by humans as most people think of them, meaning Homo sapiens.

Rather, the earliest artist appears to have been one of our ancestors, Homo erectus. Hairy and beetle-browed, H. erectus was never before thought to have such talents.

"The origin of such cognition, such abilities," said archaeologist Josephine Joordens, "is much further back in time than we thought."

Secrets of the Shells

The engraving belongs to a trove of fossils unearthed in 1891 by Dutch paleoanthropologist Eugène Dubois. Among them were the first specimens of what Dubois called Pithecanthropus erectus, later known as Homo erectus: They were the first in their lineage to leave Africa and founding members of the family that eventually included us.

Dubois didn't describe the engraving, though. It was first noticed seven years ago by Joordens and Steven Munro, a collaborator and anthropologist at the National Museum of Australia.

Joordens's group, which now numbers 21 researchers, spent the intervening time painstakingly dating the shell to between 430,000 and 540,000 years ago. They also ruled out alternative explanations for the engraving and for holes in other shells that suggest they were opened by tool—using H. erectus.

In a field where researchers endlessly second-guess how best to interpret stories told by stone fragments, "the methodology is very well developed," said paleoanthropologist Alison Brooks of the Smithsonian Institution. "It reads like a good detective story."

'Profound Implications' for Human Evolution

It's a story with profound implications, said Brooks, for understanding both H. erectus and ourselves. It's generally thought that humans became anatomically and behaviorally modern between 100,00 and 200,000 years ago, in a relatively quick stroke of evolutionary inspiration.

In subsequent millennia would come cave paintings and sculpted figures, the full flowering of an ostensible cognitive uniqueness reflected in our very name: H. sapiens, or "wise man." Neanderthals may also have possessed a rich symbolic culture, but theirs was relatively recent, and they are arguably not so evolutionarily distinct from modern humans as H. erectus.

A geometric artmaking H. erectus challenges the narrative of dramatic human exceptionality. "What we think of as typically modern human behavior didn't suddenly arise, in sparklike fashion," Joordens said. "Something like that seems to have been in place much earlier." (Learn more about H. erectus smarts in "Homo Erectus Invented "Modern" Living?")

In their Nature paper, Joordens's group avoids terms like art, symbolism, and modernity. It's hard to know, she said, the intentions of the engraver. But if the shell was 100,000 years old and found among Homo sapiens fossils, "it would easily be called symbolic or early art."

"This raises the big, hairy question of what is 'modern human behavior' all over again," said paleoanthropologist Pat Shipman of Pennsylvania State University.

Indeed, the very notion of modern humans as being cognitively unique is now "up for reconsideration," said Joordens.

That will likely be argued for years to come. In the meantime, the researchers plan to further study the collection and revisit the excavation site.

"We're certain we haven't found everything yet," Joordens said.