Rachel Green and Monica Geller. Blair Waldorf and Serena van der Woodsen. Thelma and Louise. Clueless’s Cher and Dionne. The pop culture pantheon is replete with best friend duos: pairs who would do anything for their platonic soulmate, operating on the same elusive frequency and speaking the same secret language of in-jokes and shared memories.

You may well have felt some of that magic in real life too. A 2020 study by researchers at Oxford University found that 98% of women have a best pal, compared to 85% of men; even if you’d struggle to single out one of your nearest and dearest as your top choice right now, you might have experienced that all-consuming closeness with one person when you were younger. But how do we form that much-mythologised BFF bond, and what’s behind our desire to elevate one close pal above the rest? 

Dr Anna Machin, author of Why We Love: The New Science Behind Our Closest Relationships, is an evolutionary anthropologist who specialises in the study of close human relationships, and worked on the aforementioned Oxford University study. A best friend, she explains, occupies the very core of our social network, known as the central support clique. In this ‘clique’, you would also expect to find our nearest family members, partner or children - but unlike those relationships, Machin says, our attachment to our best friend is not rooted in ‘duty’. Instead, much like a romantic partner, our bestie is one of the close connections we actually get to choose.