Doppelgängers share similar DNA and behaviours

Unrelated people who look alike are likely to share similarities in their DNA, and even some behaviours, researchers report.

Two people who appear almost indistinguishable, without any family ties, are often referred to as doppelgängers. The biological explanation for doppelgängers is the topic of a new study published in Cell Reports, in which researchers address the role of nature versus nurture in determining similarities in facial appearance. By analysing the DNA sequences of unrelated look-alikes, the authors reveal that doppelgängers are likely to share genetic similarities which could influence their facial appearance.

'These people really look alike because they share important parts of the genome', said Dr Manel Estellar, lead author of the study, from the Josep Carreras Leukaemia Research Institute in Barcelona, Spain.

For the study, Dr Estellar and his team recruited 32 look-alike pairs from the photographic work of François Brunelle, a Canadian artist who has been tracking down and photographing doppelgängers since 1999. The doppelgängers then provided a saliva sample and completed a comprehensive lifestyle questionnaire.

Facial similarity between pairs was measured from the photos using facial recognition algorithms. Sixteen of the 32 pairs were calculated as highly similar, with similarity levels matching those of identical twins. These 16 were then compared to the less similar-looking pairs, at the molecular level, to determine what makes them so similar.

The doppelgängers were found to be closer genetically than the less similar-looking pairs. They were not close enough to suggest they were unknowingly related. They also were not closer than two random individuals selected from their ethnic background. The authors suggest their genetic similarity is due to just a fraction of shared DNA that is important for facial appearance. This could mean sharing genes influential in the properties of skin and bone, among others.

Dr Estellar also wanted to understand the influence of environmental factors. Lived experiences can influence gene expression by altering our epigenome. And our microbiome, made up of bacteria, viruses, and fungi, is further affected by the environment we grow up in. However, Dr Estellar discovered that there were no similarities in the epigenomes and microbiomes of the doppelgängers. This tells us that the pairs' similarities have more to do with their DNA than the environment they grew up in, the authors wrote.

But other similarities were evident. Weight, height, and some behavioural traits like smoking and education were correlated within doppelgängers pairs. The authors suggest that their genetic similarity not only influences appearance but could also influence habits and behaviour.

Dr Estellar is hopeful that by understanding the relationship between genetics and appearance this could open new research, with the potential for diagnosing genetic diseases just by analysing the shape of a face.

'The ultimate challenge would be to predict the human face structure based on the individual's multiomics landscape,' said Dr Estellar.