NEW YORK — 

To the primitive hands that deftly shaped it from rose-colored quartz 350,000 years ago, a glittering stone ax may have been as dazzling as any ceremonial saber. 

It was found in the depths of a Spanish cavern among the skeletal remains of 27 primitive men, women and children -- pristine, solitary and placed like a lasting tribute to the deceased whose bones embraced it. 

For the archeologists who unearthed this prehistoric blade, the unique burial site is a compelling but controversial glimpse of arguably the earliest evidence of humanity’s dawning spiritual life. 

The ax may be a token of the first known funeral. 

If so, the find is 250,000 years older than any other evidence that such early human species honored their dead, said experts led by Eudald Carbonell at Universitat Rovira i Virgili in Tarragona, Spain, and the Museum of Natural History in Madrid. 

The researchers believe that the ax -- perhaps the earliest offering to the dead -- testifies to what skulls and bones alone cannot: the origins of spirituality and ritual. In their view, this mute rock embodies compassion, grief and a desire to commemorate the dead among creatures until now considered incapable of modern human behavior. 

“This would mean that human cognitive complexity emerged on the planet much earlier than previously thought,” Carbonell said. 

Exploring the origins of the mind is a risky research endeavor under any circumstances. It can be all but impossible to distinguish hard evidence of something as fleeting as thought, especially from the distance of so many thousands of years. 

But if the research team’s claim is borne out, the ax marks a crucial milestone in the archeology of the mind. 

“This is the first instance in Europe where we have some evidence of burial rites and burial ritual and symbolism,” said paleoanthropologist Marie-Antoinette de Lumley at the Museum of Natural History in Paris. “The hand ax is perhaps tied into this and perhaps shows some sort of symbolic behavior.” 

The researchers found the almond-shaped ax in 1998 mixed with nearly 4,000 fossilized bones belonging to a species called Homo heidelbergensis. The find and their analysis are set to be detailed in the French scientific journal L’Anthropologie this year. The ax has been put on display for the first time, at the American Museum of Natural History in New York. Scholars from London to Los Angeles are puzzling over its meaning. 

The remains were far from any campsite or animal den, at the bottom of a narrow 50-foot-deep shaft that scientists have named Sima de los Huesos -- the Pit of the Bones. The pit can be reached only by crawling a third of a mile through a subterranean passage. 

Carbonell and his colleagues are convinced that the inaccessibility of the pit, which contains the largest assemblage of such hominid fossils in the world, is additional evidence that the cave was the site of a deliberate burial. 

Many experts on the origins of humanity are intrigued and impressed. They are also skeptical and seek more proof. By claiming evidence of a burial ritual, the Spanish researchers may be overreaching, they caution. “The dividing line between reality and paleo-fantasy is very narrow,” one English scholar said. 

Richard Potts, director of the human origins program at the Smithsonian’s National Museum of Natural History, however, said the burial was “so unique and outlandish” that it seems all but certain that the ax is evidence of intentional, symbolic behavior. 

“That does not imply full-blown modern symbolic capability,” Potts said. “I think we need to say it is intentional and purposeful behavior and just leave it at that.” 

Whatever its meaning, the find is unique in the annals of human evolution, said anthropologist Richard Klein at Stanford University. “It is a very strange circumstance,” he said. 

The controversy over Sima de los Huesos goes to the heart of the biggest debate in the field of human evolution, as researchers struggle to reconstruct the origins of the mind. 

How did instinctive urges become thoughts and conscious emotions? When did the urge to mate first become love, or animal howls become language? When did the mind first take flight into itself, to cross a threshold into an inner world of symbols, fantasy and abstraction? 

Throughout the long prehistory of the mind, the brain left few traces of its growth into a self-aware organ of thought. 

Mental development “is pretty much a mystery because we don’t fossilize brains and behavior,” said Marta Mirazon Lahr at the Leverhulme Center for Human Evolutionary Studies in Cambridge, England. 

The evidence is indirect at best. 

In patterns of scratches on fossilized bones, researchers strain to see the creative spark of art. In patches of heat-seared soil, they seek traces of the first hearths and the beginning of an organized home life. In fields of fractured cobblestones, they search for the origins of invention, science and industry. 

“It is very difficult to see anything other than slender signs of cognitive advances,” Potts said. 

The powers of the mind were long considered the exclusive province of Homo sapiens -- the species to which all modern humanity belongs. 

By this theory, the modern mind was born in a cultural Big Bang -- a creative explosion about 40,000 years ago that left elaborate cave paintings, expert carvings, musical instruments and finely crafted tools throughout Eurasia and Africa. 

More recently, however, researchers have argued that Neanderthals, who lived from 200,000 years ago to 30,000 years ago, also shared the human capacity for art, music and spirituality. 

Most scholars agree that Neanderthals had developed some kind of symbolism related to death as early as 100,000 years ago. 

Throughout the Middle East and Europe, they buried their dead in oval-shaped graves with what may be votive offerings, such as goat horns and, in one possible instance, wildflowers. 

The discovery of the ax and bones in the Sima de los Huesos pushes that debate back even earlier, to the species who were the forebears of Neanderthals. 

The ax belongs to an era when early Europeans -- the Homo heidelbergensis -- were settling the rolling limestone hills of Atapuerca in northern Spain, not far from the modern city of Burgos. 

Most scholars believed that these hominids were relatively primitive scavengers with a knack for making stone tools, not so much smarter than chimpanzees that can fish for termites with twigs or New Caledonian crows, which scientists recently discovered can bend wire to suit their purpose. 

Although their brains were about as large as those of modern humans, these hominids were only beginning to master fire. They were cannibals, evidence from Atapuerca suggests. They left no evidence of art, language, religion or, until now, complex cognitive behavior. 

“We don’t have anything that screams out that these people had a more elaborate, sophisticated intelligence,” said Lesley Aiello, who, as an anthropologist at University College London, studies the evolution of cognition. 

The ax, however, “seems to be shouting that something is going on,” Aiello said. 

That something could have been the stirrings of mental and emotional capacities. 

Other hints have survived. 

In 1995, researchers in Germany discovered several well-preserved wooden spears dating from about 380,000 years ago, suggesting that the creatures who used them could plan, cooperate and pursue game with considerable skill. 

In Zambia, researchers found what some scientists say are 350,000-year-old paint pigments that may represent a small stepping stone in the evolution of art. Ochre crayons of about the same age found in southern Africa may have been used to decorate the body. 

In the same way, the presence of a single pristine ax among so many human bones at Sima de los Huesos also could be a sign of the development of the mind’s inner life. 

So far, the ax is the only artifact found in the pit itself. 

Microscopic examination of its sharp edges revealed no signs of wear, suggesting that the hand ax was never used to butcher prey. Ground water could have eroded evidence of use, the researchers acknowledged. 

Of the hundreds of stone tools found outside the cavern at nearby sites, the ax is the only one made of quartzite. Other tools were made of flint, limestone and sandstone. The only source of the reddish quartzite is an outcrop about 12 miles away. 

“It is the only tool at all in Sima de los Huesos, which is completely strange,” said Marina Mosquera, a Universitat Rovira i Virgili expert on prehistoric tools. “There has to be a meaning.” 

The bones are also strange. 

By and large complete, the skeletons show no evidence that they were carried down by carnivores or washed into place, the researchers said. 

The dead included surprisingly few children and no elderly, suggesting that they may have been victims of famine, disease or catastrophe. 

The placement of such an unusual tool with the bodies suggests that these human ancestors may have been prompted by stirrings of emotional intelligence and an effort to memorialize the burial of so many of their own. 

“The ax would speak to some feeling of compassion,” Aiello said. “The stone indicates some feeling of loss, of wanting to leave something of themselves with the dead members of their group.”