38 | New Scientist | 6 March 2021
social interactions. That’s about 3.5 hours
a day talking, eating and sitting with people
in a social context.
This may seem like a lot, but distributed
evenly among your 150 friends and family, it
works out at just 1 minute and 45 seconds per
person per day. Of course, that isn’t what we
do. Around 40 per cent of this social time is
devoted to the five people in our innermost
social circle, the support clique, with another
20 per cent given to the 10 additional people
in the next layer, the sympathy group. That’s
about 17.5 minutes and 4.5 minutes per person,
respectively. The remaining 135 people in
the two outer rings of our social circles get
an average of just 37 seconds a day each.
These interactions are often not face to
face, of course. Throughout most of human
evolution, people lived in the same village as
their friends and family, but today our social
circles are far more geographically dispersed.
In social networks, there is a very strong effect
called the 30-minute rule that dictates how
long you are willing to travel to go to see
someone. It doesn’t matter much whether
this is on foot, by bicycle or by car: it’s the
psychological significance of the time it takes
you that counts. Surprisingly, though, research
reveals that we are also more likely to phone
or text friends if they live nearby. For example,
one study found that the frequency of phone
contact between friends declined gradually
the further apart they lived, with a sharp
drop-off at about 160 kilometres.
Subconsciously, we seem to be aware
that failure to contact someone will weaken
a relationship, so we make up for it. Analysing
mobile phone records, Kunal Bhattacharya and
Asim Ghosh at Aalto University, Finland, found
a correlation between the length of the gap
since the last call and the duration of the next
call – for special friends, but not for weaker
friendships. Indeed, humans aren’t alone in
making such subconscious calculations. I saw
something similar in gelada baboons I was
studying in Ethiopia. As their infants grew,
mothers were forced to spend more time
feeding, leaving less time to groom their
main social partners – their best friendsforever (BFFs). Instead, they relied on
the friends to do all the work to keep the
relationship going. However, once the infant
had started to wean, they paid back the debt,
devoting much more time to grooming the
BFFs than the BFFs groomed them.Oiling your contacts
Such behaviours matter because friendships are
fragile. Unlike family bonds, they depend on
you investing enough time and effort in each
other to keep the relationship well oiled and
functional (see “Six rules for keeping your pals”,
page 40). If you see someone less often, whether
deliberately or by force of circumstance, that
relationship will weaken. Bob Kraut at Carnegie
Mellon University in Pennsylvania calculated
that a friendship of high strength will decline to
no more than a mere acquaintanceship in just
three years. To be fair, there are a few friendships
that stand the test of time and absence: usually
no more than three or four, and they tend to be
people we were particularly close to in early
adult life. However, until the internet, social
media and mobile phones became widely
available a mere decade ago, friendships would
have died naturally if someone moved away.
Is that changing? To take a closer look, Sam
Roberts at the University of Chester, UK, and I
studied a group of 30 students – half of them
female, half male – to find out how moving
away from home affected their social networks.
We picked them up in their final term at school
and monitored them through the following
18 months to the end of their first year at
university. The deal was that we gave them
a free mobile phone subscription in return
for being able to download their monthly bills
so we could see who they phoned and texted.
They also had to fill in a questionnaire at the
beginning, middle and end of the study telling
us who everyone in their network was, how
emotionally close they felt to each person,
when they had last contacted them and how,
and what they had done with them when
they met face to face.
We collected huge quantities of information.
(We were particularly impressed by three of the“ We all spend
about 20 per cent
of our time, on
average, on social
interactions”
Sympathy group 15Support clique 5athy groupup 15ique 5SympathSuppport cliFriends 150
Dunbar’s numberGood friends 50MeThe structure of friendship
We can only manage a maximum of 150 people
in our social circle, and they fall into layers
depending on their emotional closeness
(all figures are cumulative)