They expropriated bones from two very different sources -- one was the thigh bones of fierce and flightless birds called cassowaries, and the other, the bones of their ancestors.
A recent study
published in Royal Society Open Science gives an insight into the reverence with which they held the daggers made from human bones -- showing how they engineered them to better protect these weapons in combat.
Warriors typically sourced human thigh bones from the skeletons of their fathers who had proven themselves in battle, or other men of status in the community, explained cultural anthropologist Paul Roscoe, one of the authors of the report.
"It was almost like a spiritual aura, like your father was watching over you, and you were carrying him into battle with you," said Roscoe.
In the Sepik region of New Guinea, up until as recently as the 1970s, men would arm themselves with bone daggers in large raids or small-scale ambushes of neighboring groups, he explained.
The attack would start at a distance with spears and arrows, and bone daggers would be used to stab opponents in the neck in hand-to-hand fighting.
While bone daggers primarily functioned as weapons, they were also prized ceremonial ornaments conspicuously worn on the bicep.
Human bone daggers often had elaborate designs and patterns incised on the daggers to project a feeling of "power and menace" and instill fear, added Roscoe.
Dissecting a drawer full of daggers
Biological anthropologist and lead author of the study, Nathaniel Dominy, first discovered a drawer full of bone daggers from New Guinea when "poking around in the underbelly" of the Hood Museum of Art in Dartmouth College, USA, where he is a professor of anthropology.
While initially struck by the ornamentation on the daggers, Dominy was puzzled by the fact that the daggers were made from two completely different bones.
"You'd think that men would be incentivized to use the best dagger possible once their life is on the line," said Dominy. "It provoked the question: did they differ in terms of their mechanical efficiency?"
While scant research had been conducted on these objects, it had previously been speculated
that human bone daggers were more prestigious.
"By default you inherited all those powers and the magic and the rights of that person who had surrendered the bone," added Dominy.
Although cassowaries were believed to possess a mystical and powerful strength, which could be co-opted and added to one's own prowess when holding the dagger, explained Dominy.
To investigate the mechanical strength of the bone daggers, Dominy and his colleagues took CT scans of 11 daggers -- five made from human bone and six from cassowary bone -- from the late 19th and early 20th century, and simulated the effect of applying stress to the daggers.
They found that while the mechanical properties were similar in both the human and cassowary bones, dagger-makers deliberately retained a lot of the round curvature of the human leg bone to make a stronger weapon. Whereas, with the cassowary daggers, they removed a lot of the sides of the bone, resulting in a flatter, weaker design.
The study speculates that this flatter dagger may have been a strategy to increase comfort when worn on the upper arm, or to reduce friction when inserted into a victim.
Dominy added that the reason human bone daggers were made stronger was that, while cassowary bone daggers are easy to replace, if a human bone dagger was to break, both its utilitarian use and symbolic value would be lost.
"The way we see it, you would probably invest more to protect the family heirloom," explained Dominy.
"A human bone dagger is practically irreplaceable, so you're going to shape it in such a way as to maximize the longevity of the dagger to prevent it from being broken."