Bone daggers from New Guinea, carved from human bone, above, and from the bone of a bird called a cassowary, below. (Nathaniel J. Dominy. © Hood Museum of Art, Dartmouth College)

A hundred years ago, if you lived in the Sepik region of New Guinea and you wanted to impress your neighbors, you'd strap a dagger made of bone to your biceps. Not just any skeletal parts would do. The most common bone weapons came from the legs of giant flightless birds called cassowaries. But the most prized materials were human femurs, removed from a vanquished enemy — or from your father's remains upon his death.

Nathaniel J. Dominy, an anthropologist at Dartmouth College, has been studying these bone daggers for the better part of a decade. He was exploring the Hood Museum of Art in Hanover, N.H., when he found the museum's collection of bone weapons. The ornate designs cut into the daggers captivated him.

The most powerful symbols were carved into the grip, Dominy said, so a wielder could derive strength from holding a dagger. “They’re really striking objects,” he said. “Formidable, fierce-looking and beautiful.”

Human-bone daggers are also rare. Of the 500 or so bone daggers held at the American Museum of Natural History in New York, the Yale Peabody Museum of Natural History in New Haven, Conn., and the Field Museum in Chicago, only 21 are carved from human parts. The last New Guinean people to make such daggers did so at the end of the 19th century and the beginning of the 20th. It was not possible to determine how old this tradition was, Dominy said, because there are few records beyond the contemporary accounts of European colonial observers.

Dominy and his colleagues, in a new study in the journal Royal Society Open Science, quote German anthropologist Leonhard Schultze-Jena, who described the weapons in functional terms in 1914: “The dagger serves not only to stab into the main arteries but at the same time as a lever with which one twists the punctured neck of the enemy in order to tear the throat and, with sufficient power, break the neck.”

Bone daggers were status symbols. “All cultures on Earth will decorate utilitarian objects like pots and pans or their own bodies,” Dominy said. These daggers are no different. Slaying a cassowary was a source of status, and better still was to have a dagger carved from a warrior's bones, Dominy said, to capture that person's symbolic power and strength.

Dominy set the scene: “These are only used for hand-to-hand combat,” he said. “You both are trying to stab each other in the nape in the same time and twist.”

The anthropologist wanted to know how the New Guineans managed this violent action without breaking their prized weapons. Dominy took 10 of the daggers, five cassowary and five human-bone weapons, to Dartmouth-Hitchcock hospital. Dominy and his colleagues sent the items through a CT scanner, which revealed a pattern — the bird-bone daggers were flatter and straighter than the human ones.

The scientists also purchased a modern cassowary bone dagger carved in the 1970s. The scientists drove the tip of the weapon into urethane, to simulate jabbing the dagger into a joint. Then, through mechanical tests, they bent and twisted the bone until it snapped.

This demonstration showed that cassowary bones are “extremely dense,” Dominy said. The giant birds do not have pneumatic bones — that is, they are not filled with air sacs like the bones of most flying birds. In fact, in terms of their mechanical properties, the cassowary bones are “striking similarly to our human femur.”

Given the similarities between bird and human bone, the scientists applied the cassowary data to 3-D computer models of the human weapons. In the simulations, the human daggers proved to be much stronger than the cassowary versions.

These findings suggest the structure of a human dagger, carved to maintain the natural curve of the bone, explains its superior strength. “When men are shaping the dagger from a human femur they retain a lot of the cross-sectional curvature,” Dominy said.

Dominy was not entirely sure why the cassowary bones were engineered to be weaker, but he suspects the flatness of the cassowary dagger might have prioritized comfort over strength. The human daggers, on the other hand, were carved to last, in proportion to their value.

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