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Did you know DNA proved the legendary conjoined twins from Angel Mounds were not even related?

DNA test settles the debate of the famous “flesh-joined" twins

Conjoined twins have always fascinated scientists. So when an ancient grave was discovered at Angel Mounds with two babies buried together heads facing away, hands joined and legs intertwined, the archeologist who discovered it speculated that the babies were conjoined twins. More than 70 years later, scientists tested his hypothesis with DNA analyses, and found that not only were the babies not conjoined twins, but they were not even related.

Conjoined twins are a rare congenital abnormality that occurs when a single fertilized egg partially splits into two fetuses (as opposed to completely splitting into two and resulting in identical twins). The most famous conjoined twins in history were Chang and Eng Bunker from Siam (now Thailand) and this is where the expression ‘Siamese twins’ originates. Approximately half of conjoined twins are stillborn, and an additional third die within the first 24 hours. The connection between conjoined twins and how many organs are shared can vary significantly. Sometimes the twins can have fused skulls but separate bodies, or they may be fused at different areas of the body. Sometimes it’s possible to separate conjoined twins by surgery, especially if they don’t share vital organs. Chang and Eng Bunker, for example, were only joined by flesh, cartilage and their livers, which meant that they could have easily be separated if born in the modern times.

Even though there was likely at least a small proportion of conjoined twins born in prehistoric times, there are no archeological records to confirm such cases. Records of twin births are equally rare, with the earliest confirmed case of twin births coming from the Neolithic Era (8000 years ago) of a woman who died with her twins at childbirth. This may be why the discovery of the alleged conjoined twins at Angel Mounds generated so much interest, and a sense of mystery.

Angel Mounds was a palisaded Middle Mississippian agricultural village in Indiana from around A.D. 1050 – 1400. In 1941, the Indiana archeologist Glenn A. Black was leading an excavation that discovered two skeletal infants buried in a single grave. Based on the position of the two skeletons, Black speculated that the two infants were conjoined twins. He suggested that they were “flesh-joined” twins, as there was no evidence to support that they shared any organs or limbs. Black’s conjoined twins were so legendary at Indiana University that 70 years later, a professor at the university (Charla Marshall) decided to test Black’s theory using DNA analyses.

Sketch image of the skeletons that were thought to be of conjoined twins
Sketch image of the skeletons that were thought to be of conjoined twins. (Image from Marshall et al. (2011) Am J Phys Anthropol)

The confirmation of identical twins (and hence conjoined twins too) relies on the analysis of nuclear DNA, as identical (and conjoined) twins are the only individuals that share exactly the same DNA. Even non-identical twins have differences that we can detect using genetic techniques. However, obtaining good quality nuclear DNA from ancient samples can be tricky, as each of our cells only contain two copies of the nuclear DNA genome, hence DNA degradation can reduce the DNA quantity and quality relatively quickly. Unfortunately, the researchers of the Angel Mound twins were unable to obtain enough nuclear DNA for the genetic analyses, so they instead turned to mitochondrial DNA.

Mitochondrial DNA (mtDNA) is very useful for studying ancient samples because we each have hundreds to thousands of copies of the mtDNA genome in most of our cells. Furthermore, the cellular location and small size of the mtDNA genome are thought to slow the rate of degradation. This means that the likelihood of obtaining quality mtDNA is a lot higher then the likelihood of obtaining quality nuclear DNA. MtDNA is maternally inherited (passed from mother to child) and is useful for tracing maternal lineages. Individuals from the same maternal line (such as mother and child, or siblings, or twins) share the same mtDNA profile.

Based on Black’s conjoined twins’ theory, Charla Marshall was expecting the twins to share the same mtDNA profile. However, to the surprise of the scientists, each of the infants had a different mtDNA profile. This meant that the two infants were not even full siblings, let alone conjoined twins.

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If these two infants were not maternally related why were they buried together? It is possible that the infants were half-siblings with a common father, but this could not be confirmed due to the poor quality of the nuclear DNA. Also, approximately 3-5% of all burials at Angel Mounds were co-burials and group burials, and the majority of these do not share common mtDNA profiles, suggesting a maternal relationship does not appear to be a requirement for group burials in ancient Midwestern societies. The reason behind why ancient Mississippians chose to bury unrelated people together, such as these two famous “conjoined” infants, remains a mystery.

The DNA tests conducted in this study have identified two different mtDNA profiles from the Mississippian population of A.D. 1050 – 1400. If you have taken the DNA Maternal Ancestry Test, you can compare your results against these remains to see if you share a similar profile.

Reference:

Marshall C et al. (2011) Brief Communication: Conjoined Twins at Angel Mounds? An Ancient DNA Perspective. Am J Phys Anthropol. 146: 138–142.

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