Just over 10 years ago an evolutionary psychologist designed a study investigating people’s
Christmas Card lists.
The tradition of sending a Christmas card is, in itself, an interesting behaviour.
Yet it gives us clues about one of the things that defines us as human throughout evolution--
the social brain.
The social brain hypothesis suggests that human intelligence evolved to negotiate our
complicated social groups.
We have these complex behaviours and the more information that we need to store and manipulate
about our environment, the bigger the computer needs to be.
What’s really interesting is that one part of our brain, the neocortex, is correlated
with the size of our social groups.
The neocortex is the outer layer of our brain and it’s responsible for our higher functions,
like conscious thought, language or spatial reasoning.
Researchers looked at the neocortex of other primates, compared it as a ratio to the size
of the rest of their brain, and they found a pattern.
Lemurs, with a smaller neocortex, live in social groups of 9; long-nosed monkeys with
a larger neocortex and live in groups of 14.
The western red colobus monkey, slightly larger neocortex again, lives in groups of 35.
And the chimpanzee, with the largest neocortex of all primates - except for humans - lives
in a social group of 53.
So, hypothetically, we could apply this pattern to humans.
But, because we don’t all live in local groups, and because we don’t groom each
other, it’s kind of tricky to work out our social network sizes.
So this is where the Christmas Cards come in.
In the Christmas Card study, participants were asked how many people they were sending
cards to, how far away they were, the last time they’d been in touch and how emotionally
close they were.
Researchers found the average number of cards sent was 68, and because you can send a card
to more than one person, the average social network size was 153 people.
But the study’s kind of problematic.
You can send cards for political as well as social reasons, and people put a different
amount of thought into their Christmas Card list, if you celebrate Christmas or send cards
at all.
The psychologist who designed the Christmas Card study was Robin Dunbar, one of not very
many people who has a number named after them.
The Dunbar number is the limit of meaningful relationships that one person can maintain.
But the number doesn’t have a precise value.
In the early 90s, using that primate neocortex ratio and applying it to humans, Dunbar estimated
his number to be 150 meaningful relationships per person.
It’s consistent with the groups size in neolithic farming villages and armies in Roman
antiquity.
And because our neocortex can only be so big, it’s actually hard for our brain to accommodate
more relationships.
But thinking about the size of a neolithic farming village is literally comparing the
present to the stone age.
What does the Dunbar number mean now?
And is it changing with ever-expanding social networks?
Even though you may have 300 Facebook friends or 1000 followers on Instagram, you only have
so much time.
Friendships are maintained by investing time in them.
Sure a status update or posting a photo is efficient, you don’t spend as much time,
but it’s not as personal as a form of communication.
Dunbar suggests we face-to-face interaction to maintain quality relationships.
Physical proximity to our friends and loved ones means we release more endorphins and
have a higher level of oxytocin, which we need for social bonding.
Sure, our neocortices are only so big, but our brains have this amazing plasticity to
grow and develop to suit our environments.
It’s possible that kids of today will have a different neural organisation to handle
the changes in our social interactions.
Studying today’s children is some ways away, by which time tradition such as this one could
be a relic from the stone age.