Discovery of 12,000-year-old preserved human brains could change what we know about the organ
Experts have long believed that the human brain is one of the first organs to rot and decompose after we die, but new research suggests this is not the case.
And it actually turns out that brains are quite well preserved, according to a team of scientists from the University of Oxford – although they don’t know how almost a third of brains survived as long as they have.
Until now, every time archaeologists found an ancient, well-preserved brain, it was considered something strange – or at least the product of deliberate conservation efforts by ancient people.
But the team behind a new study scoured an archaeological archive of more than 4,000 human brains, many dating back 12,000 years or older, to uncover the truth about brain decay.
This thousand-year-old brain belonged to an individual whose remains were excavated from the 10th-century cemetery of St. Martin’s Church in Ypres, Belgium. The folds of the fabric are still soft and wet. They are colored orange with iron oxides
They concluded that the tissues that make up the brain are much more resistant to breakdown than scientists previously thought.
Organizing the brains based on where they were found also revealed that local environmental conditions can lead to even better preservation.
In general, archaeologists find soft tissues like muscles and internal organs much less frequently than things like bones and skin.
They thought this was because skin can be preserved the way leather and bones are, well, hard.
Typically, decomposition is only slowed or stopped by processes such as mummification, embalming, or freezing.
Very occasionally, these things can happen naturally, as with the remains of people buried in dry, mineral-rich soil – or preserved in peat bogs.
But for a long time it was believed that the brain was one of the first things to break down after death.
To refute this, the team behind the new research searched the scientific literature for reports of preserved tissues of the human nervous system.
With data in hand, they analyzed the chemical and physical characteristics of the remains in question and considered where they had been found.
This included not only where on a map they were found, but also what the climate conditions were like when the person died and the chemical evidence surrounding the preservation of their brain.
The study included a total of 4,405 brain samples, found around the world – mainly in Europe, none in Antarctica.
Among the samples, they identified five different types of preservation: saponification, freezing, tanning, dehydration, and a mystery category simply called “unknown.”
Brains preserved by unknown processes make up almost a third of the recorded brains.
Specimens in this category have been found in sunken ships, in graves, and in wooden and lead coffins.
In these ancient human remains, the brain is often the only soft tissue archaeologists find.
Alexandra Morton-Hayward, a forensic anthropologist and PhD candidate at the University of Oxford, holds the two halves of a 200-year-old brain, preserved in formalin.
This graph shows the five main types of brain preservation: saponification, freezing, browning, dehydration and ‘unknown’. The bars in the middle show that the further we go back in time, the less of each type of preservation is found.
Saponification is the same process that turns fat and lye into soap, and it can leave the brain in much the same consistency: from hard and crumbly to soft and pasty.
This type of preservation occurred when the chemical bonds of fats in the brain were broken and their components combined with metals such as calcium, sodium or magnesium to form a substance known as adipocere or ‘grave wax’.
Most saponified brains date from less than 200 years ago.
Frostbite is self-explanatory, and it usually happened when someone died in cold climates.
Because cells can break down after repeated thawing and refreezing—think frozen spinach after it’s been thawed—freeze-preserved brains are often difficult to study.
Tanning produces a ‘slightly supple, dark-colored mass’, comparable to another well-known tanning product: leather.
This brain belonged to a person buried in the First Baptist Church of Philadelphia, which was founded in 1698. More than 40 brains were excavated from this cemetery, and many of the brains’ owners had died from a devastating yellow fever epidemic in 1698. the late 18th century.
Brain fragments from a person buried in a Victorian workhouse cemetery in Bristol, UK, about 200 years ago. No other soft tissue survived among the bones dredged from the heavily waterlogged grave.
The tanning was usually done with the brains of bodies preserved in peat, because environmental conditions prevented bacteria from breaking down the tissues.
Dehydration, the most common form of preservation, made up 1,667 of the samples – 38 percent.
Due to water loss, these brains became quite fragile.
These brains either came from natural processes such as hot, dry climates or exposure to air currents, or from actual intentional mummification.
Strikingly, the ‘unknown’ brains were similar in consistency and chemical composition.
This group included 1,308 brains, almost a third.
In these samples, these were the only soft tissue remains with skeletons – and they were the very oldest, some as old as 12,000 years.
But scientists still don’t know how this preservation method, which appears to be unique to the brain and no other body tissue, works.
These brains were not found in a specific environment, but were often found in people buried in mass graves.
The study was published in the journal Proceedings of the Royal Society B.