I have known my wife, Clare, since our first year at medical school, which was more than 40 years ago. Since then we have we have grown an almost telepathic understanding of each other’s moods and thoughts. That might sound rather dull but it is actually a very bonding experience.


This got me wondering about the extent to which we were also growing more alike in other ways. Take looks. There is a wealth of research which shows that long-term couples tend to look alike. But is this because they start off looking like each other, or is it that couples become more similar-looking over time? Perhaps because of shared diets, or lifestyles, or mannerisms, or some other factor?

To find out, a team of researchers from Stanford University in the US put together a database of pictures of 517 couples, taken soon after getting married and then decades later. Using advanced facial recognition software and human judges, they showed that although long-term couples do tend to look alike, they don’t become more alike over time. In other words, this study supports the claim that we tend to choose partners who look like us.

“This brings facial appearance in line with other traits – such as interests, personality, intelligence, attitudes, values and wellbeing – which show initial similarity but do not converge over time,” they wrote.

But though we may not grow more alike in appearance, over the years our skin microbiome certainly does. In a study carried out a few years ago, which was published in the journal mSystems, scientists decided to analyse the skin microbiomes of cohabiting couples and they found that living together significantly influences the microbial communities on each other’s skin.

To carry out the study, the researchers collected samples from numerous sites on the volunteers’ bodies, including their upper eyelids, outer nostrils, inner nostrils, armpits, torso, back, navel, and palms of hands.

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The impact of living together on their microbial community was so strong that computer algorithms could identify cohabiting couples with 86 per cent accuracy based on their skin microbiomes alone. The area of the body where cohabiting couples were the most alike, microbe-wise, was the feet. This is not altogether surprising as many of us will pad around our homes barefooted.

Although the couples did show striking skin microbiome similarities, there were some areas of the body where the gender of the volunteer mattered more than whether they were cohabiting. For example, they discovered that the microbial communities growing on the inner thigh were more similar among people of the same biological sex than between cohabiting partners.

And again, it turned out that their computer algorithms could differentiate between men and women with 100 per cent accuracy by analysing inner thigh samples alone. Who knew?

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Dr Michael Mosley is former medical doctor, health writer and BBC presenter. He’s best known as presenter of Trust Me I’m a Doctor on BBC Two but has also written a number of bestsellers about personal health and medicine, including The Fast Diet, Fast Asleep and Fast Exercise.