Friday, August 04, 2006

Strontium analyses reveals ancient Wari took noncombatant trophy heads

"The Wari were notably violent. Unearthed stone iconography, for example, depicts Wari warriors carrying or wearing decapitated heads. They were known to eat the bodies of vanquished enemy warriors.

In 2001, researchers from the University of North Carolina at Chapel Hill found direct evidence of the Wari's grisly ways: 21 trophy heads buried at a site called Conchopata near the city of Ayacucho in southern Peru. The heads had been severed, the brains scooped out and holes drilled through the crania and jawbones.

But the skulls were not solely those of enemy warriors killed in battle. Many, in fact, belonged to women, children and old people. Scientists didn't know what to make of the discovery. Was this evidence of a more benevolent side to the Wari? Did they, like other early cultures, practice some kind of ancestor veneration? Were these skulls the cherished remains of Wari mothers and daughters, sons and grandparents?

"It's been a huge debate," said Tiffiny Tung, a member of the North Carolina research team and now at Vanderbilt University. "Where did the Wari get their heads?"

Recently, a different group of scientists came up with a possible answer by measuring levels of a trace element in the skulls and in guinea pigs living in the region. Strontium is a radioactive alkaline earth metal found in rocks and soils, and by extension in plants and animals living in the region.

Kelly Knudson, director of the Center for Bioarchaeological Research at Arizona State University, looked at the ratio of two isotopes or forms of strontium found in the trophy skulls and in nontrophy skulls recovered in the same area. Because geologists did not have strontium isotope measurements for Conchopata bedrock, they used measurements taken from native guinea pigs.

In the skulls, Knudson and colleagues measured strontium isotope ratios in tooth enamel and in bone. The isotope ratio in tooth enamel remains constant throughout life, a reflection of where the person originates. The ratio in bone changes constantly, reflecting a person's recent history (for example, diet).
All the strontium isotope ratios detected in the nontrophy heads were similar, suggesting that their owners had all eaten food from the same geographic region throughout their lives. The trophy heads, however, displayed much more variability in their strontium isotope ratios. Those ratios also differed markedly from measurements in the Conchopata guinea pigs.

Such diversity, says Knudson, suggests the original owners of the trophy heads were not locals or cherished ancestors, but rather luckless victims of Wari raids upon enemy communities. The Wari took the heads of enemy warriors, but apparently considered skulls of all ages and genders to be trophy material."