An injury to the head, not an arrow wound, may have killed Ötzi the Iceman, the 5,300-year-old mummy found in the Italian Alps, says a new paleoproteomic study into the brain of Europe's oldest natural human mummy.
The protein investigation appears to support a 2007 research into the mummy's brain. The study pointed to a cerebral trauma as the cause of death.
At that time, the research relied on a CAT scan of the mummy's brain, which showed two dark-colored areas at the back of the cerebrum. The injury added to the already known arrowhead wound on the shoulder and wounds on the hand.
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Found in Ötzi's left shoulder in 2001, the stone arrowhead has long been thought to have caused the prehistoric man's death, fatally severing his left subclavian artery.
The 2007 study suggested that blood loss from the arrow wound would have first made Ötzi lose consciousness, with death coming later, from a violent blow to the head.
Either the man's killer gave Ötzi the final whack, possibly by hitting him with a stone, or he could have fallen over backwards and hit his head on a rock, the researchers concluded.
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The hypothesis had been left unexplored until 2010, when a research team from the European Academy of Bolzano/Bozen (EURAC), Saarland University, Kiel University and other partners decided to investigate the proteome of two pinhead-sized samples of brain tissue from the world-famous glacier corpse.
"The use of new protein-analysis methods has enabled us to pioneer this type of protein investigation on the soft tissue of a mummified human, extracting from the tiniest sample a vast quantity of data which in the future may well answer many further questions," the researchers said.
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Indeed, the scientists were able to identify a total of 502 different proteins.
"Of these, 41 proteins are known to be highly abundant in brain tissue and nine are even specifically expressed in the brain," microbiologists Frank Maixner of EURAC, Andreas Tholey of Kiel University, and colleagues wrote in the journal Cellular and Molecular Life Sciences.
"Furthermore, we found 10 proteins related to blood and coagulation. An enrichment analysis revealed a significant accumulation of proteins related to stress response and wound healing," they wrote.
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Found in a corpse almost devoid of blood, the astonishingly well-preserved clotted blood cells provide further evidence that Ötzi's brain had possibly suffered bruising shortly before his death.
Whether this was due to a blow to the forehead or a fall after being injured by the arrow remains unclear.
"Our data reopens former discussions about a possible injury of the Iceman's head near the site where the tissue samples have been extracted," the researchers said.
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Since his discovery in 1991 in a melting glacier in the Ötztal Alps - hence his name - the mummy has been extensively investigated.
Scientists discovered that Ötzi had brown eyes, was lactose intolerant, had a genetic predisposition for an increased risk for coronary heart disease, and probably had Lyme disease.
The new protein-based research method could now provide insights that previously had not been possible, the researchers said.
Image: Red blood cells from the iceman's brain. Credit: Marek Janko, TU Darmstadt.