fahrbot-bot shares a report from Smithsonian Magazine: The brain is one of the first organs to begin decomposing after death. Yet archaeologists have discovered more than 4,400 preserved human brains around the world, some of which have remained intact for the last 12,000 years. In hundreds of cases, the brain was the only soft tissue left among otherwise skeletal remains. But how and why do brains sometimes persist for millennia while all other types of soft tissue disappear? This preservation paradox has stumped scientists for years. Now, however, a team of researchers say they may have solved the mystery. If a brain ends up in a wet, oxygen-starved environment, the processes that usually cause decay can have the opposite effect, researchers report in a study published in the August 7 issue of the Journal of Proteome Research. "Under the right conditions, preservation actually arises from decay itself: The same reactions that degrade tissue can also weld the breakdown products together into something far tougher," study co-author Alexandra Seviour, a paleobiologist at the University of Oxford in England, tells Live Science's Victoria Atkinson. Following experiments on 72 mouse carcasses (described in the article) the scientists think they know why. When oxygen is abundant, it triggers a cascading, chemical chain reaction that causes brain proteins to break down rapidly. This sequence hinges on free radicals, highly reactive, unstable molecules that "steal" electrons from nearby atoms and molecules. The process happens in the brains of living people too, and if left unchecked, can cause health problems. In low-oxygen environments, however, this chemical sequence appears to play out differently. The researchers' analyses hint that free radicals instead react and bond with nearby proteins, making the overall tissue tougher and more resistant to decomposition, Seviour tells Chemical and Engineering News' Anirban Mukhopadhyay. The findings show that "decay is not the opposite of preservation but, under specific chemical constraints, one of its mechanisms," the researchers write in the paper.Read more of this story at Slashdot.