Every human is biologically unique thanks to DNA composition, the environment, and our life experiences. However, it’s still possible to stumble across somebody whose face resembles ours – a doppelgänger. Cases of biologically unrelated lookalikes are quite common, and they’re now even easier to spot thanks to social media.

Canadian artist François Brunelle has been obtaining worldwide pictures of look-alikes since 1999 as part of a project called “I’m not a look-alike”. Scientists led by Manel Esteller from the Josep Carreras Leukaemia Research Institute in Spain have now used Brunelle’s work to compare humans that share facial features at a molecular level.

“Our study provides a rare insight into human likeness by showing that people with extreme look-alike faces share common genotypes, whereas they are discordant at the epigenome and microbiome levels,” said Esteler, senior author of the study, in a statement. “Genomics clusters them together, and the rest sets them apart.”

Photos and DNA

The researchers obtained headshot pictures of 32 look-alike pairs from Brunelle’s work, including 22 males and 42 females, between 23 and 78 years of age. They applied different facial recognition algorithms to quantify objective likeness. In addition, participants had to complete a biometric and lifestyle questionnaire, as well as provide DNA samples.

The questionnaire assessed blood type, socio-economic background, height, weight, diet, lifestyle, and relationship factors. Meanwhile, the DNA samples were obtained to conduct multiomics analysis, meaning a study of many “omes,” such as the genome, microbiome, metabolome, lipidome, and epigenome.

From the 32 look-alike pairs, 16 were clustered by the three facial recognition algorithms – unable to distinguish the faces from one another. A genome-wide association study (GWAS) of the DNA obtained from these 16 participants’ saliva showed that nine of these pairs clustered on a genetic level, the researchers said.

Lookalikes tended to share genes associated with the shape and form of lips, mouth and eyes, genes involved in bone formation that can relate to skull shape, genes involved in skin textures and liquid retention, as well as genes of yet unknown precise function related to facial properties.

Moreover, the researchers found that physical traits like weight and height, as well as behavioral traits like education and smoking, were also correlated in the look-alike pairs. That’s remarkable considering the lookalikes weren’t genetically related to one another.

Taken together, the results likely mean that shared genetic variation related to physical appearance can also influence common habits and behavior, the authors of the new study explained.

“These results will have future implications in forensic medicine—reconstructing the criminal’s face from DNA—and in genetic diagnosis—the photo of the patient’s face will already give you clues as to which genome he or she has,” Esteller said. “The ultimate challenge would be to predict the human face structure based on the individual’s multiomics landscape.”

The researchers acknowledge that the study carries a set of limitations, including the use of black and white 2D imagery and the reduced sample size, mainly European. However, they argue that their findings offer insights into human likenesses, showing that people with very similar faces have common genotypes but different epigenetic and microbiome profiles.

The study was published in the journal Cell.