Archaeologists Have Found Thousands of Intact Ancient Human Brains. Scientists Say They've Figured Out Why the Organs Don't Always Rot

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 human 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. Many of the intact brains were found in watery, low-oxygen areas, such as shipwrecks, riverbeds, lakeshores and flooded caves. But since water is a key driver of decay, this pattern is puzzling.

Seviour and her colleagues wanted to figure out why the brain specifically seemed to be immune to water’s destructive powers. Ancient preserved brains look very similar to fresh brains, except they’re usually discolored and shrunken. The researchers gathered 72 mouse carcasses and placed each in its own glass jar partially filled with quartz sand.

The animals’ bodies were evenly divided among four burial conditions: wet and oxygen-rich, wet and oxygen-poor, dry and oxygen-rich, and dry and oxygen-poor. The team created wet or dry conditions by adding different amounts of water, and the oxygen-rich or oxygen-poor conditions by leaving the jars open or sealing them with airtight silicon gaskets. Then, the researchers waited.

They removed and analyzed three different mice from each burial condition at six time points: 24 hours, 72 hours, one week, six weeks, three months and six months. They dissected the animals’ brains, then looked at the molecular makeup of the tissue to track which proteins remained intact and which had broken down; they also looked at the chemical marks on the surviving proteins. At first, the brains showed similar patterns of decay across all four conditions.