>“play vocalisations” in 65 species. Most are
mammals, but a handful of bird species are
also known to signal their harmless intentions
in this way. Kea parrots, for example, warble
gently as they tussle on the ground or chase
each other through the air.
In many animals, including chimpanzees,
gorillas, rhesus macaques and dogs, play
vocalisations take the form of fast, rhythmic
panting. Cotton-top tamarins whistle. Rats
emit an ultrasonic squeak beyond human
hearing. And elephants make a kind of soft
trumpeting noise. Winkler and Bryant
speculate that such sounds represent a
rudimentary form of proto-laughter that could
have formed the evolutionary basis of our own
humour. As Bryant puts it: “A phenomenon
once thought to be particularly human turns
out to be closely tied to behaviour shared with
species separated from humans by tens of
millions of years.” Given its prevalence among
primates, he estimates that proto-laughter
evolved in one of our direct mammalian
ancestors at least 100 million years ago.
Human relationships are much more
complicated than those of the average
mammal – and we have much more control
over our voice. As a result, human laughter has
evolved to be a potent and flexible social tool.
According to Adrienne Wood at the University
of Virginia, it serves three main purposes.
The first is reward: when we laugh together, it
shows appreciation of a particular behaviour
and reinforces the interaction, so that we are
more likely to act in the same way in the future.
Spontaneous laughter triggers the release of
opioids, which is probably what creates these
rewarding feelings. Laughter’s second function
is to signal connection. These affiliation laughs
tend to be voluntary (or “fake”) and help to
smooth over tension and embarrassment
rather than reinforcing a particular behaviour.
If you have said something potentially hurtful,
for example, a polite chuckle might help to
reassure someone that it was just playful
teasing. The third purpose of laughter is to
signal dominance – like when your boss laughs
dismissively at your outlandish idea. Whereas
a direct challenge, such as a cutting put-down,
might trigger aggression, laughter indicates
disapproval in a more subtle way. “It maintains
a facade of social harmony,” says Wood.
To provide evidence for this hypothesis,
Wood and her colleagues asked 762 people to
rate various samples of laughter on whetherthey sounded rewarding, reassuring (a sign of
affiliation) or mocking (a sign of dominance).
Each type was found to have different acoustic
properties. The reward laughs were louder
and longer. The affiliation laughs were quieter,
shorter and mellower. The dominance laughs,
meanwhile, lacked the pleasing melodic
features of the others. “They were basically
uglier and noisier and had all these acoustic
markers of chaos,” says Wood.
The conclusion that laughter is a powerful
social signal chimes with findings by Bryant
and his colleagues that participants could
predict the closeness of people’s relationships
based solely on the sound of their guffaws,
giggles and snide little titters. The laughers
were all from the US, yet people from Europe,
Asia and Africa were just as able to identify the
nature of the laughs as fellow Americans were.
People’s capacity to tell whether a laugh isspontaneous or fake is also equally good across
cultures. Other research has identified subtle
differences in the ways that people laugh
between cultures, but Bryant’s results suggest
that the core signals remain recognisable
across the world.
Further evidence for laughter’s universality
comes from its early emergence in a child’s
emotional vocabulary. A baby’s first laugh
typically arrives by the age of 4 months –
long before their first words. “It’s the least
complicated type of laughter because it’s
purely emotional, bubbling up from the limbic
system, and it doesn’t require control of the
vocal track,” says Mireault, who was inspired to
study this developmental process by her own
baby’s helpless giggles at her brother sneezing.
As any caregiver knows, people will go to
ridiculous lengths to tickle a baby’s funny
bone. In Wood’s framework, these are rewardGina Mireault at Northern Vermont University.
This has been science’s loss because recent
results reveal that there is far more to laughter
than you might think. Beyond the obvious
connection with humour, it offers some
truly profound insights into the nature of
our relationships and the state of our health.
The study of infant giggles may even help us
understand how we develop our sense of self
and the ability to read the minds of others.
What’s more, laughter turns out to be
surprisingly common in other species.
Non-human animals aren’t known for their
sharp wits, but many do engage in play, often
producing characteristic sounds to signal
that their behaviour is friendly rather than
aggressive. According to a review by Sasha
Winkler and Gregory Bryant at the University
of California, Los Angeles, published this
year, scientists have documented these
“ Laughter has
evolved as a
potent and
flexible social
tool with three
key purposes”
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TY
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