Whether fat, thin, fine or fugly, the person you're partnered with on Valentine's Day should be the same level of hotness as you. If not, the relationship may not last. What boffins call 'assortative mating' means we go for people who are similar to us in terms of values, personality, socioeconomic standing, size and shape.

If you want to mate with somebody reeeeeally familiar for Valentine's Day, you could always go with somebody who resembles your mum or your sister. Gross? Yes. Satisfying? Absolutely.

I have a friend who married a woman so similar in looks to him that not only are they both a precise 7.28/10 on the hotness decile scale, the two appear to be twins. Maybe they met through a Jaime and Cersei Lannister fan club, I don't know. They have the same hair and eyes, moles and even jawline.

Will their brotherly love last forever? Will they always be the exact same hotness? So long as they make the same faces in those gross Facebook photos I show all my friends, science says yes: decades from now, they will end up looking more identical than ever.

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Research by social psychologist Robert Zajonc found married couples can begin to resemble one another because subtle shifts in facial wrinkles and muscles will occur in synchrony between lifelong partners. Starting off with 'chance similarities' based on upbringing, diet, lifestyle et cetera, couples will eventually get wrinkles in the same places from cringing at heat pump adverts together, or squinting under a Northland sun while gardening together, or celebrating Beer o'Clock or 4:20 together every day, like lovers do. Zajonc's research even suggested laughing or crying at things at the same time shapes faces similarly. This is because your face is moulded when you mimic your partner's facial expressions in empathy (like the way me and my wife react when we examine our son's lunchbox after it's been forgotten about in his schoolbag all summer.)

What about the opposite of all this, though? If lasting couples are couples that resemble one another, should you be worried if you're a 6 and your partner is a 9? My beautiful wife has been a 10 out of 10 from the get-go, so that's all well and good for her.

The problem is, after I've had a few Valentine's beers, I'm pretty sure I'm a 12.