Updated July 16, 2017 09:45:03

Photo: A forensic anthropologist shows one of the 45 brains saponified of those killed by forces of the dictator Francisco Franco. (Reuters: Juan Medina)

Archaeologists excavating a mass grave in Spain have found the largest collection of naturally preserved human brains in the world, a scientist says.

The brains of 45 people, who were shot and buried on a hillside in the northern province of Burgos eight decades ago, were found in a mass grave from Spain's 1936 to 1939 Civil War.

The findings, which were published in the Science and Justice journal of the Chartered Society of Forensic Sciences, showed almost 50 per cent of individuals from the Spanish 1936 mass grave had their brains preserved.

Forensic scientist Fernando Serrulla says the shrivelled, brown brains — some with the ridges still showing — are a rare find.

"Naturally preserved brains are very rare," Mr Serrulla said

"There are only around 100 documented cases in the world."

How were the brains preserved?

The brains from some of the bodies in the La Pedraja grave were preserved by three main factors: microbiological, chemical and physical.

The soil in the grave and specific weather events in the months after the bodies were buried delayed decomposition.

Photo: The bones of one of the individuals killed by forces of the dictator Francisco Franco which were found in 2010 in a mass grave around the area known as La Pedraja, Spain. (Reuters: Juan Medina)

This "saponification" process turned them into a soap-like substance, causing the bodies to dehydrate and the brains to shrink.

Mr Serrulla, who worked on the dig and has published a study with details of the discovery, said a preserved heart was also unearthed in an "unpreceded finding".

Why has it taken so long to find them?

Spain has hundreds of mass graves from the war and from ensuing decades of dictatorship under General Francisco Franco.

Very few have been dug up due to a lack of funding and Spain's "pact of forgetting" on its return to democracy in the 1970s.

The brains are being kept in a laboratory in Galicia, northwestern Spain, where Mr Serrulla works.

None of the preserved organs and only 16 of the 104 bodies dug up from the grave have been identified.

Rafael Martinez, the president of a socialist association killed by Franco's supporters in 1936, was recently identified as one of the bodies in La Pedraja.

"If only those brains could tell of what happened there," his grandson, Miguel Angel Martinez, said.

ABC/Reuters

Topics: brain-and-nervous-system, science-and-technology, archaeology, community-and-society, human-interest, spain

First posted July 15, 2017 15:41:56