What happens when we make friends across borders? Two writers talk about their British-Italian friendship – and the fascinating cognitive science on such cross-cultural bonds.

David Robson, London: Aristotle famously described friendship as having "one soul dwelling in two bodies", but what are the challenges of stretching that bond across countries?

Having explored the psychology of social connection in my most recent book, I find that my conversations with my own acquaintances can become rather meta – in the sense that I now often talk to my friends about friendship. I was particularly interested to hear the thoughts of my Italian "sister" Alessia Franco, who lives in Palermo in Sicily, on the joys of befriending someone from another country.

Although certain psychological barriers can make it harder to establish a rapport with someone from a different background, the research suggests that these cross-cultural and cross-linguistic connections also bring some unique benefits – a fact that we have experienced in our own friendship.

As friends and frequent co-writers, it seemed natural to put our (metaphorical) pens to paper and explore the topic in depth. I'll leave it to Alessia to start.

Alessia Franco, Palermo: Across one's professional life, a journalist encounters hundreds of people. The number clearly depends on the type of work one does, whether we feel the need to be present for every story, all the time, or whether we wish to alternate between moments of observation and moments of introspection. But we rarely expect to form a lasting connection with the people we encounter.

I first met David in one of Sardinia's remotest villages to record a series of short films exploring the forces behind its residents' extraordinary longevity. David was the host, and I was the producer. We had every reason to believe that, after our job was done, we would each return to our individual lives in London and Sicily without any further contact.

One of the first things I appreciated was David's willingness to "take one for the team". I am teetotal, and yet the Sardinians that we met had the habit of offering us their homemade wine as if it were coffee. To refuse would have been bad manners, but David was always ready to help me finish my glass without our hosts noticing.

This secret complicity was the first step on the path to our friendship. It was only a few months after the work was finished that we got back in touch, however. I can't remember which of us was the first to make the call, but after very little time we started to brainstorm ideas for future projects. We soon recognised how well our interests complemented each other. I am a cultural journalist and storyteller, who writes magical realism novels. David is a science communicator, who tries to find sense in the world through data and analysis.

Together, we have covered such diverse subjects as the mysterious disappearance of the Island Ferdinandea; the shipwrecks rewriting world history; the secret of the Montessori method and the challenge of how to help children raised in Mafia families. Throughout these projects, we have come to feel more like siblings than colleagues.

From our appearance, it's hard to imagine two more improbable "siblings": unlike me, David is long-limbed, blond and blue-eyed. But our sense of kinship can be found in the novels we read: our shared love of Virginia Woolf, Anna Maria Ortese and Zadie Smith. We each feel that literature is a part of who we are and it is also central to our friendship.

David: I couldn't have said it better myself (though few English people would consider my hair to be blond). Despite the physical distance – we have spent fewer than two weeks in the same location together – Alessia lies at the very centre of my social circle with just a handful of other people.

This may be surprising given that we don't share all of the seven pillars of friendship – seven factors that can deeply shape the closeness of social bonds, according to research by Robin Dunbar at the University of Oxford. Having the same language or dialect, and growing up in the same location, are two of these crucial factors. Alessia and I don't share a mother tongue, and grew up in very different places, the UK and Italy.

We do however tick the five remaining boxes on Dunbar's list: having similar educational history or profession; the same hobbies and interests; the same world view (an amalgam of moral, religious and political views); the same sense of humour; and the same musical taste.

As Dunbar explains in his book

© BBC