Did you know DNA is useful for identifying victims buried in mass graves?
World War II and the tragic aftermath that followed it
More than 60 million people were killed during World War II, and many of them were buried in mass graves scattered all across Europe. As these graves are later discovered, the bones are often all mixed together, rendering typical identification procedures impossible. In many cases, DNA analyses has proven useful in identifying the skeletal remains. Below are stories from three such mass grave discoveries in Croatia, Italy and Slovenia.
World War II is deemed the deadliest conflict in all human history, lasting six years from 1939 to 1945. It divided countries around the world into two opposing military alliances: the Allies (UK, France, US, Russia, China) and the Axis (Germany, Italy, Japan). There were millions of casualties of war, but the total number is unknown, as many deaths went unrecorded. Most records suggest over 60 million people died in the war, 40 million of whom were civilians that were killed by genocide, massacres, mass-bombings, disease and starvation.
Many of the victims of WWII were buried in mass graves, scattered all across Europe. Since the war, thousands of these graves have been discovered, but often the bones are all mixed together making it difficult to determine how many skeletons are in each grave, let alone identify the remains. Most of the typical identification procedures (fingerprints, dental analyses, clothing, morphological data etc.) are also not feasible, and the identification of the remains must rely on DNA analyses.
The science behind DNA analyses
Everyone’s DNA is different, and we each inherit some DNA from our mother and some from our father. From generation to generation, this DNA is recombined (mixed) to make us all unique. However, there is some DNA that doesn’t recombine and remains unchanged from generation to generation. This is the paternally inherited Y-DNA and the maternally inherited mitochondrial DNA. Both of these types of DNA are invaluable for genetic analyses, especially going back multiple generations.
Y-DNA is the DNA located on the Y chromosome – the sex chromosome present in males. Males have one copy of the Y chromosome and one copy of the X chromosome per cell, while females carry two copies of the X chromosome per cell. Only males have Y-DNA and it is passed essentially unchanged from father to son along the direct paternal lineage. There are two common types of variation in the Y-DNA: fast changing Y-DNA STRs (short tandem repeats) to trace recent ancestry, and slow changing Y-DNA SNPs (single nucleotide polymorphisms) to trace ancient ancestry. Males that are paternally related within the last few generations have identical or very similar Y-DNA STR profiles, providing an accurate way to trace paternal lineages and identify unknown remains by matching to paternal reference samples (e.g. a son or grandson of a missing man).
Mitochondrial DNA (mtDNA) is the small DNA molecule found in our mitochondrial organelles within most of our cells. Each of us (male and female) inherit mtDNA only from our mothers, and there is no mtDNA input from our fathers. There can be hundreds to thousands of copies of the mtDNA genome in a single cell, meaning there is a higher chance of obtaining adequate DNA for analyses of degraded or ancient samples, compared to just two copies of most of our nuclear DNA, or just a single copy of Y-DNA in males. Maternally related individuals, even from multiple generations apart, have identical or very similar mtDNA profiles, providing a way to accurately trace maternal lineages.
Mass grave in Croatia
In 2005, the skeletal remains of 18 male victims were discovered in a mass grave near Zagvozd, Croatia. It was speculated that the bodies belonged to a group of 19 civilians (including at least eight friars), who were allegedly tortured and killed in the village of Zagvozd in the Dalmatian mountains. Evidence suggests that the civilians had been initially buried near the execution site, before they were moved to a field just outside the village.
Morphological analyses of the remains identified gunshot wounds in eleven of the skeletons, and the arms of six skeletons were tied with wire. To identify the remains, partial Y-DNA STR profiles (up to 17 STR markers) were generated from teeth and bone samples from each skeleton. These Y-DNA profiles were compared to available reference samples – individuals that had lost family members during the war. The researchers were able to confirm that three of the skeletons did belong to the three of the friars who had been captured and killed during the war. However, they were unable to identify the remaining skeletons, as they did not match to any of the available reference samples.
Mass grave in Italy
A mass grave was recently discovered in northern Italy with several skeletons all mixed together. The identity of these remains was unknown, and could be from several different groups who all lost their lives in the area – including Germans, Allied forces, RSI troops, members of the Italian resistance movement and civilians.
The researchers analyzing the remains analyzed the mtDNA from 14 bone samples (six femurs and eight humeri) from the mass grave to first determine how many individuals were buried together, and then to attempt to identify each individual. They identified seven distinct mtDNA profiles across the 14 bone samples, suggesting that at least seven individuals were buried in this grave. However, it is possible that there were more than seven people buried in the grave, because people who are maternally related (e.g. brothers) will share the same mtDNA profile, and can’t be distinguished using mtDNA analysis.
They also compared these mtDNA profiles to living relatives of individuals who disappeared in that area during World War II. Unfortunately, none of these mtDNA profiles matched the available reference samples. It is hoped that as reference numbers increase, more of these remains can be positively identified.
Mass graves in Slovenia
It is estimated that there could be up to tens of thousands of missing persons in Slovenia that were killed during World War II, and so far around 600 mass graves have been discovered. A 2009 study, illustrated the benefits of typing Y-DNA STRs from the remains found in mass graves in the Škofja Loka and Ljubljana areas of Slovenia. This study obtained partial Y-DNA profiles from over 40 skeletons, with six of these matching to available reference samples. Many more skeletons are likely to be identified as reference numbers increase.
More reference samples are needed
These studies illustrate the value of DNA analyses for the identification of skeletal remains, even from mass graves that are over 70 years of age. However, the identification of skeletons in mass graves from war periods is often hindered by the lack of available reference samples to positively identify the remains. Although direct reference samples (i.e. sons of missing male victims, or children of missing female victims), may no longer be available, it is still possible to identify remains using other reference samples. For example, the grandson and great-grandson of a missing male soldier will still share the same Y-DNA as their missing relative. Likewise, any individuals related through the maternal line to a war victim will share the same mtDNA profile.
Marjanović D et al. (2009) Identification of skeletal remains of Communist Armed Forces victims during and after World War II: combined Y-chromosome (STR) and MiniSTR approach. Croat Med J. 50(3): 296-304.