Robin Dunbar is an Oxford evolutionary psychologist who has written extensively about friendship, amongst other things, not least in relation to “Dunbar’s Number”.

We talked about what friendship is, and how it differs from other loves. We explored the varieties of friendship that people experience, and why metaphors such as “circles of friends” are so significant.

Numbers are illuminating when it comes to understanding the dynamics of friendship, not only Dunbar’s Number, but also other threshold numbers – 5, 15, 50, 150, 500. Get those group sizes right, and much will be gained.

We also asked about why social media seems to corrosive to friendship, how notions of friendship do and don’t vary across cultures, why gender differences in attitudes to friendship seem so robust, and whether we need rituals of friendship to guide this most important of relationships.

Robin referenced the seven pillars of friendship. These are language or dialect, geography, educational experiences, hobbies and interests, moral or spiritual viewpoints, political views, sense of humour and taste in music.