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A new project led by researchers at the University of Oxford, which has collated evidence from around the world, has shown that the human brain can remain preserved in diverse environments for at least 12,000 years.
When human brains are found in the archaeological record – such as the discovery of the Iron Age brain at Heslington, Yorkshire, in 2008 (see CA 227) – they often make headlines due to their perceived rarity. A new project, however, has demonstrated that the human brain may actually be one of the best-preserved soft tissue organs found archaeologically. Collating records from across the world, the team found that since the mid-17th century more than 4,400 human brains have been uncovered from over 200 sites, and that they are reported from every region of the world apart from Antarctica. Additionally, they found that in more than 1,300 cases the brain was the only soft tissue found in otherwise completely skeletonised remains.
A brain from an individual buried in a Victorian workhouse cemetery in Bristol some 200 years ago. Image: Alexandra L Morton-Hayward
In total, the team identified five ways in which the brain remains preserved, including through dehydration, freezing, a chemical process called saponification, and tanning. The fifth category was ‘unknown’, and represented the second-largest proportion of recovered brains (30.1%), after dehydrated ones. While dehydrated brains were most-commonly found in hot and dry climates, frozen brains were associated with cold and dry climates. The vast majority of saponified remains came from one medieval site in Paris, while tanned brains were mainly reported from oceanic climates. Brains in the ‘unknown’ category, however, were found in more diverse environments, including milder climates, and, when compared with the other categories, were associated with the highest daily precipitation, and appear to have remained preserved irrespective of any protective action of the skull. Intriguingly, they were also the oldest brains found in the record, with the earliest-known example dating back more than 12,000 years.
The team suggest that these unusual characteristics could indicate there is some intrinsic quality in the central nervous system that allows the brain to remain preserved in this way. While noting that much more research needs to be done to confirm this, they suggest two possible means by which the brain may remain exceptionally preserved: molecular crosslinking, whereby the proteins, lipids, and sugars present in the brain are chemically stabilised through lipidation and glycation; and metal complexation, whereby metals in the brain, particularly iron, are able to replicate or chemically stabilise the nervous tissue. Whatever the means, it appears that the brain, at least compared to other soft tissue, may not be such an unusual archaeological survivor after all.
Text: Kathryn Krakowka
