SAN MIGUEL DE AZAPA, Chile - Living in the harsh desert of northern Chile's Pacific coast more than 7,000 years ago, the Chinchorro fishing tribe mysteriously began mummifying dead babies — removing internal organs, cleaning bones, stuffing and sewing up the skin, putting wigs and clay masks on them.

The Chinchorro mummies are the oldest-known artificially preserved dead, dating thousands of years before Egyptian mummies, and the life quest of the archaeologists who study them is to discover why this early society developed such a complex death ritual.

Archaeologist Bernardo Arriaza, who studies the Chinchorro at the University of Tarapaca in Chile's northernmost city, Arica, launched a daring new theory this year.

"I was reading a Chilean newspaper that talked about pollution and it had a map of arsenic and lead pollution, and it said arsenic caused abortions. I jumped in my seat and said, 'That's it,'" Arriaza said.

Arriaza says high levels of arsenic in the water in the region, which persist to this day, meant more premature births, stillbirths, spontaneous abortions and higher infant mortality among the Chinchorro.

"We've always known that the Camarones (the area where the mummies are found) had a lot of arsenic, and the first mummies were children," he said.

He posits the Chinchorro began preserving dead babies to express personal and community grief and later began mummifying adults as well, and the practice became more elaborate.

Since the 1960s, archaeologists have excavated more than 100 delicate, diminutive bodies, many preserved intentionally. They were stuffed with plants and sea grasses and decorated with clay. They have also found fishing hooks, baskets and sea shells used as pallets, still stained with the red and black paint used to decorate the mummies.

The Chinchorro were hunter-gatherers who lived at river mouths, fishing with spears, hooks and nets and building their movable shelters from sea-lion pelts and bones.

Their primitive life without domesticated animals, pottery, agriculture or metallurgy contrasts with the elaborate mummification they developed, thousands of years before the Inca civilization dominated this same area and also practiced mummification.

"These complex funerary practices are usually associated with more advanced societies with a state system, but here you are talking about hunter-gatherers who lived with a simple social and political organization," said Arriaza's colleague at the University of Tarapaca, archaeologist Vivien Standen.

The practice lasted more than 3,000 years and went through different stages before the Chinchorro society disappeared about 2000 B.C.

The earliest mummies were like statues covered with unbaked black clay.

Thousands of years later the treatment of the skin and bones became more elaborate and the Chinchorro began finishing their mummies with red ochre paint on open-mouthed masks.

Story continues: msnbc.msn.com.

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