36 | New Scientist | 6 March 2021
two quite distinct sets of people: friends and
family. What’s more, we tend to give preference
to the latter. With our social networks limited
to around 150 relationships, we first slot in
family members and then set about filling
any spare places with unrelated friends.
As a result, people who come from large
families tend to have fewer friends.
Some years ago, I examined evidence
from various cultures and economies to try
to find out how much time we actually spend
on social interactions with our friends and
family. I found around half a dozen studies
where researchers had recorded the amount of
time in the day that people devoted to different
activities, including things like sleeping,
cooking, relaxing and interacting socially.
This gave me a diverse selection of societies:
Maasai pastoralists in East Africa, Nepalese
hill farmers, New Guinea horticulturalists,
agricultural tribes in sub-Saharan Africa,
!Kung San hunter–gatherers from southern
Africa and housewives in Dundee, UK. My
analysis revealed that people spent around
20 per cent of their time, on average, onFriendship-ology
Why do some friendships last and others fade? Evolutionary
psychologist Robin Dunbar reveals the hidden rules of our
relationships and what your social style says about you
F
ACEBOOK users used to have a lot more
friends. The social networking site
pursues a commercial strategy of trying
to persuade people to “friend” as many others
as possible. However, sometime around 2007,
users began to question who all these people
they had befriended were. Then, someone
pointed out that we can only manage around
150 relationships at any time. A flurry of
“friend” culling followed and, since then,
the number 150 has been known as
“Dunbar’s number”. Thank you Facebook!
Modern technology may have brought me
notoriety, but Dunbar’s number is rooted in
evolutionary biology. Although humans are
a highly social species, juggling relationships
isn’t easy and, like other primates, the size of
our social network is constrained by brain size.
Two decades ago, my research revealed that
this means we cannot meaningfully engage
with more than about 150 others. No matter
how gregarious you are, that is your limit.
In this, we are all alike. However, more recent
research on friendship has uncovered some
fascinating individual differences.My colleagues and I have made eye-opening
discoveries about how much time people
spend cultivating various members of their
social networks, how friendships form and
dissolve and what we are looking for in our
friends. What has really surprised us is that
each person has a unique “social fingerprint” –
an idiosyncratic way in which they allocate
their social effort. This pattern is quite
impervious to who is in your friendship
circle at any given time. It does, however,
reveal quite a lot about your own identity –
and could even be influencing how well you
are coping with social restrictions during
the covid-19 pandemic.Layers of intimacy
The typical social circle of 150 people is made
up of a series of layers, each containing a well-
defined number of people and associated
with specific frequencies of contact, levels
of emotional closeness and willingness to
provide help (see “The structure of friendship”,
page 38). In fact, our social world consists of >Features Cover story