You may have a twin and you don’t know it: the science of look-alikes

Perhaps someone has already told you that you look like someone else, but is it actually true? It is! Science suggests that there is someone in the world that looks like you and that even shares your facial genetic variants!

Artwork by Alexandra Banbanaste

It’s fascinating that in the world there are people that have exactly the same face, isn’t it? Scientists have been discussing what distinguishes twins for a long time. Most of us may remember when NASA in 2019 selected two identical twins, Scott and Mark Kelly, to test the impact of space on the human body: while they sent Scott to space, Mark  was kept on earth and, over 25 months, data was collected from them both. Once Scott came back, they observed that the genomes of the twins differed in their DNA methylation levels (1). DNA methylation is a type of epigenetic marker which contributes to the regulation of gene expression. DNA is not the only factor responsible for your uniqueness. The way DNA is modified and how much your genes are expressed matters too! Many other studies showed that monozygotic twins share the same DNA but not the epigenome. We could say that despite the fact that they share the same language, they have a different accent (2).

Twins can look alike and share DNA but their environment impacts their epigenome. So, is it possible that people that are not twins (not even relatives!) share the same face? If so, will they share the same DNA or epigenome? How will the environment impact them?

It has already happened to all of us that someone told us we look alike to someone else – for example, a famous actor or singer. When we think about our identity it is normal to think about our face traits, but is our face unique? In 2015 Australian researcher Teghan Lucas  found out that, when considering only four facial measurements, the likelihood of finding a duplicate is about 1 in 10 million (3). That’s probably why it’s that complicated to find stunt doubles for movie scenes, but it also means that there is someone in the world that looks like you. 

A canadian photographer Fancois Brunelle in 1999, fascinated by this phenomenon, created a project called “I’m not a look-alike” in which he collected photos of look-alikes from all-over the world. From this artistic project, a group of scientists in Spain decided to understand if there are any common genetic, epigenetic and microbial features between the doubles, like in the twins’ studies. This innovative  approach, proposed in 2022, used a facial recognition algorithm to measure the “look-alike-ness” of the doubles in Brunelle’s pictures (4). Once confirmed with the algorithm that the doubles have correspondent facial traits, they extracted the genome, epigenome, and microbiome from their saliva. Surprisingly, they found that 56.2% of the doubles share common genotypes for face variants. So, it’s not only an impression: intrapair look-alikes share some genes. However, epigenome and microbiome seem to be different between them, exactly like for the twins. The mentioned article is limited by the small sample size and it’s only a starting point for the study of the look-alikes. Yet, it’s very interesting to think about the nature vs nurture dilemma from another perspective and unravel the mystery of look-alikes with science!

The study also examined key lifestyle factors in look-alike pairs, such as smoking habits and education levels, revealing a strong correlation. This raises an intriguing question: does sharing genetic variants lead to both similar faces and behaviors, or do shared lifestyle choices influence physical traits and genes over time?

Remember, the identical twins and astronauts Scott and Mark Kelly developed distinct epigenomes due to their different environments—one in space, the other on Earth—showing how external factors shape biology. Likewise, unrelated look-alikes may adopt similar lifestyles that subtly mold their appearance, highlighting the complex interaction between genetics and environment.

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References

1. Garrett-Bakelman et al. (2019). The NASA Twins Study: a multidimensional analysis of a year-long human spaceflight. Science https://doi.org/10.1126/science.aau8650. 

2. Fraga et al. (2005). Epigenetic differences arise during the lifetime of monozygotic twins. Proc Natl Acad Sci U S A https://doi.org/10.1073/pnas.0500398102.

3. Lucas et al. (2015) Are human faces unique? A metric approach to finding single individuals without duplicates in large samples. Forensic Sci Int. DOI: 10.1016/j.forsciint.2015.09.003 

4. Joshi et al. (2022) Look-alike humans identified by facial recognition algorithms show genetic similarities. Cell Reports https://doi.org/10.1016/j.celrep.2022.111257 

This article was copy edited by Marielle Piber and Claire Lavergne.

Meet the author: Silvia Comunian