BBC Focus

OCTOBER 2016

Infant monkeys smile in their

sleep, just like human babies

Who’s a cheeky monkey? Researchers from Japan’s
Kyoto University have discovered that macaques
sometimes break out into smiles while sleeping – a
behaviour previously thought to be unique to higher
order primates such as humans and chimpanzees.
The facial expressions, known as spontaneous
smiles, are considered to be the evolutionary origin of
human smiles and laughter.
“About a decade ago we found that chimp infants
also display spontaneous smiles,” said researcher
Masaki Tomonaga. “Since we see the same behaviour
in more distant relatives, we can infer that the origin
of smiles goes back at least 30 million years, when Old
World monkeys and our direct ancestors diverged.”
The team observed seven infant macaques
during their routine health checks, with all of them
smiling at least once.
“Spontaneous macaque smiles are more like short,
lopsided spasms compared to those of human infants.
There were two significant similarities; they both
happened between irregular REM sleep, and they
show more lopsided smiles compared to symmetrical,
full smiles,” said researcher Fumito Kawakami.
“A major difference, though, is that the smiles were
much shorter.”
It has previously been argued that infants’
spontaneous smiles developed to help parent-child
bonding. However, the Japanese team think they
may simply be used to develop cheek muscles,
enabling macaques, chimpanzees and humans
to form complex facial expressions.

ZOOLOGY

The smiles of

sleeping infant

macaques probably

help develop the

facial muscles

IN NUMBERS

LIGHT

YEARS

The distance of the nearest

known exoplanet from Earth,

Proxima B, discovered by

astronomers at the Carnegie

Institute orbiting the red

dwarf star Proxima Centauri,

the closest star to the

Solar System.

1,

YEARS

The age of a Bosnian pine tree

found growing in northern

Greece by a team from the

University of Stockholm.

It is the oldest living thing

known in Europe, they say.

£

BN

The amount of

money required to save

Australia’s Great Barrier

Reef from dying of coral

bleaching, as estimated by

Queensland’s Water Science

Ta sk f or ce.