Scientists in Spain have uncovered new evidence that they claim ties Neanderthals closer to humans in evolution than previously thought. (© Javier Trueba/Madrid Scientific Films)

Scientists in Spain have uncovered new evidence that they claim ties Neanderthals closer to humans in evolution than previously thought. (© Javier Trueba/Madrid Scientific Films)

In a cave in northern Spain, a team of scientists has retrieved the remains of 28 prehistoric humans, members of an enigmatic species that could be described as a little bit Neanderthal.

They had Neanderthal faces, with heavy brows and protruding noses. They had powerful mandibles and mouths that could open extremely wide, indicating that they used their teeth as gripping tools. But they didn’t have the large skulls or other robust skeletal features seen in the prototypical Neanderthals who, hundreds of millennia later, roamed Ice Age Europe.

These were apparently ancestors of Neanderthals, inhabitants of a line that many thousands of years earlier had split from the ancestors of modern humans. An international team of scientists published the description of the Spanish fossils Thursday in the journal Science but has not yet given this population a new species name. That will come later, the scientists said, after consultations with colleagues.

The discovery does not dramatically change the general picture of human evolution, but it complicates it a bit, providing new evidence that there were many distinct, and largely isolated, human species existing simultaneously and sometimes competing with one another in a harsh environment marked by advancing and retreating ice sheets.

The lead author of the new paper, paleoanthropologist Juan Luis Arsuaga of the Universidad Complutense de Madrid, refers to this as “a ‘Game of Thrones’ scenario.”

Scientists reconstruct skull 17 at the field laboratory. (Photo by Javier Trueba/Madrid Scientific Films)

As he put it, there was no Middle Pleistocene kingdom ruling over everything, but rather many competing houses vying for the same land.

“Hominin evolution was not a peaceful, boring process of very slow change over time,” Arsuaga said during a teleconference with reporters.

The fossil site, in a cave called Sima de los Huesos (Pit of Bones), is in a chamber at the bottom of a vertical shaft. Arsuaga thinks it was a mortuary — a repository for the dead. There are also many fossilized bones of bears and claw marks on the wall. The bears may have fallen into the pit and become trapped.

Archeologists have bones but not much else to work with — there are no cultural artifacts in the pit other than a single hand ax.

The first bones were found at the Sima site many years ago, and Arsuaga and his colleagues originally lumped them together with another early human species called Homo heidelbergensis. But the new analysis, which includes the description of 17 skulls, concludes that these early humans were physically distinct from their heidelbergensis contemporaries.

“This is a big advance. I’m sorry that it’s still sort of swinging out there in taxonomic limbo instead of having been given its own designation,” said Ian Tattersall, a paleoanthropologist at the American Museum of Natural History who was not involved in the new research.

Arsuaga and his colleagues think the fossils show that the Neanderthal lineage did not get all its distinctive anatomical features as a complete set, but rather, these appeared individually in “a mosaic pattern of evolution, with different anatomical and functional modules evolving at different rates,” in the words of the Science paper.

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The scientists suggest that the evolution of the Neanderthal lineage is tied to an adaptive trait associated with chewing. Although the paper in Science does not speculate about what, exactly, drove the evolution of specialized features for chewing, Arsuaga said in the teleconference he thinks these Neanderthal ancestors could have used their teeth to grip meat or other objects.

“We could speculate that Neanderthals had three grasping organs instead of two,” he said.

A key finding is the date of the fossils: Six distinct techniques converge on an estimated age of roughly 430,000 years old. One technique dated crystals of calcium carbonate that had built up on skulls at the bottom of shallow pools. Another dated the light-colored mud that sits atop the red mud in which the fossils are embedded.

This precise dating makes the Sima fossils the oldest in the Neanderthal lineage and confirms that the ancestors of modern humans and the Neanderthal line diverged more than 430,000 years ago.

Arsuaga and his colleagues think these proto-Neanderthals possessed the power of speech and lived in social groups. The fossils in the Sima pit come from people who lived close to one another in time and were possibly members of a clan, the scientists said.

There are few human ancestors more intriguing than the Neanderthals, who could be described as the best example in the history of the planet of an intelligent species that has gone extinct. They had large craniums and larger brains than modern humans (although that doesn’t mean they were smarter). They existed as recently as about 30,000 years ago, when their kind disappears from the fossil record.

How they died out, and why, and to what extent they may have interbred with anatomically modern humans is an ongoing source of debate and contentiousness among highly credentialed scientists. Recent research shows some admixture of genes, with modern humans outside of Africa having roughly 1 to 3 percent Neanderthal DNA.

But as a species, the Neanderthal vanished. In their place came anatomically modern humans, who evolved in Africa and are the ancestors of everyone alive today.

The Neanderthals, Tattersall said, “obviously were very intuitively smart. They were great toolmakers. They were ingenious. They were resourceful. They were living through difficult times.”

But they did not create symbolic objects, such as artwork, and presumably their speech did not include symbolic language, he said. They may not have imagined the future or created narrations of the past the way we do. Tattersall said the first known symbolic objects are geometrical engravings on smooth ochre plaques in southern Africa, dated to about 80,000 years ago.

The new discoveries in Spain add to the mounting evidence that human prehistory was a complicated period with a diverse cast of human species.

“We tend to think it’s normal for there to be only one kind of Homo in the world,” Tattersall said. “But if you look back on the fossil record, you realize it’s totally routine to have several different types of species of Homo in the world, trying to exist at the same time. What is unusual is for us to be on our own. I think that says something very specific about how different we are.”