Paolo Rossi Castelli 22 September 2022 18 min read

Doppelgangers don’t just look alike

A study by the University of Barcelona reveals the unexpected features of people who, although not related, have identical faces. Shared genetic variants also influence other biological parameters and behaviour.

Many people worldwide have a Doppelgänger (to use a specific German term), i.e. a quasi-twin or look-alike, to whom they are in no way related, but with whom they share an outward appearance: a phenomenon that has been known for a long time. Now, however, a recently-published study in the scientific journal Cell Reports by researchers at the University of Barcelona explores this reality (which, with the growth in the world's population, and with the spread of images through social media, is increasingly being encountered) in depth and sheds a whole new light on this 'world', showing that the similarities between unrelated ‘twins’ goes far beyond appearance.

It has always been thought that people who look alike might share certain features of the genetic code (at the very least, those that determine the shape of the face, or eye colour), but no one had ever explored these issues in depth, due to the difficulty of finding these pairs and because it was thought that these were entirely random occurrences.

A new research method
However, the Barcelona researchers took a different approach and contacted 32 pairs of doppelgangers photographed by Canadian artist François Brunelle - who has been travelling the world since 1999 in search of people who look like each other. They initially submitted them to three of the longest-established facial recognition programmes to see whether artificial intelligence also noticed the same similarities. 75% of the pairs were categorised as compatible (the same classification as monozygotic twins) by at least two of the three programmes, and 16 by all three. These results demonstrated, among other things, that the facial recognition ability of these software programmes is similar to that of humans.

Also similar in some features of the genetic code
Researchers took saliva samples from these 16 pairs to extract their DNA and sequence it in its entirety. This enabled them to identify common genetic variations and also epigenetic profiles (i.e. mechanisms that regulate how individual genes are expressed). Researchers also examined microbiota ('good' gut bacteria). The genetic analysis revealed that 9 of the 16 pairs studied shared several major polymorphisms (DNA variants), while also exhibiting personal characteristics.

The 16 pairs also showed strong similarities in weight and other biometric parameters (like height and body type), as well as in various habits - e.g. smoking - or level of education, suggesting that shared genetic variation not only regards physical appearance, but may also influence common habits and behaviour. In contrast, the composition of the microbiota was different in most cases.

Applications in other fields, too
Doppelgangers are therefore much more than people who resemble each other in appearance, and this could have important spin-offs in a range of fields. "Our results,” confirms Manel Esteller, professor of genetics at the University of Barcelona and coordinator of the study, “provide a basis for future applications in fields like biomedicine and forensic medicine. In the latter, for example, it may be possible to reconstruct the physical features of an unknown person through their DNA by comparing it with that of known people on large databases, who have the same genetic features and variants”.

In a similar vein, Esteller suggests - researchers could also study whether certain physical traits are linked to any disorders in any way (for example, helping to improve early diagnosis of certain diseases). However, it is clear, that these are very sensitive issues from an ethical point of view and they will need clear and precise controls as studies progress. It is not sure that the members of doppelganger pairs will want to be recognised and categorised in the legal sphere, or for their risk of developing a particular disease.

 

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Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by corriere.it on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.