Institute of Human Morphology in Moscow.
In 2014, Burghardt and his colleagues
even described an instance of fish playing:
three male white-spotted cichlids started
headbutting a thermometer in their tank,
causing it to tip over and then right itself.
Still, vertebrates are only a small part of the
animal kingdom. What about all the creatures
that don’t have backbones? We often think
of inverterbrates as being simpler or more
primitive than vertebrates, but this is a
gross oversimplification – and evidence
for invertebrate play has been accumulating
for two decades.
In 1999, Jennifer Mather at the University
of Lethbridge in Canada reported that giant
Pacific octopuses seemed to play. In the lab,
the octopuses fired water jets to make a
floating bottle whizz around. In later studies,
Mather found that common octopuses will
also play with Lego bricks. She has recently
used her play studies as part of a broader
argument for advanced cognition in octopuses
and other cephalopods.
Octopuses are one thing – we know they
have complex brains, albeit quite unlike ours.
What about insects? In 2006, researchers led
by Elisabetta Palagi at the University of Pisa in
Italy described play-like behaviours in paper
wasps. When immature, the wasps performed
exaggerated versions of adult dominance
behaviours, which weren’t combined with
genuinely aggressive moves. They seemed to
be play-fighting. “If we follow the definition
[Burghardt’s five criteria],” says Palagi, “we
need to speak about play for paper wasps.”
Similarly, in 2011, Burghardt and his
colleagues described what they say is spider
play. Juvenile male Anelosimus studiosus
spiders performed mock courtship displays to
juvenile females, and the pairs even engaged in
mock copulations. “The females who have had
that playful experience lay more eggs,” says
Burghardt, and the males that played are less
likely to be killed or injured during courtship
when the animals are sexually mature.
So although the behaviour did appear to payoff in the long run, it didn’t achieve anything
at the time it was performed, so Burghardt
argues that it fits his five criteria. Behncke,
however, isn’t so sure about this spider
behaviour. “I don’t think they play. Of course,
I’m happy to be proved wrong,” she says.
According to Palagi, many researchers
remain cautious about some claims of
invertebrate play, but other examples have
been broadly accepted. “Nobody has a problem
to think an octopus can play,” she says.
What is clear is that play is scattered like
confetti over the animal family tree. But just
because one species does this, it doesn’t mean
its closest relatives do. Behncke says this is
because play doesn’t evolve for one reason,
but for many. “Some forms of play train more
cognitive aspects,” she says, whereas other
types of play are more physical or social.
That’s why there is no simple pattern to
which animals do it and which don’t.
“Play enriches diversity of experience and,
I think, enriches adaptation to complexity,”
says Behncke. The prediction is that you will
see it in species that live in more complex
niches, she says, meaning environments that
are highly variable or unpredictable. This can
include the social environment, for animals
that live in complex groups.
For example, in a study published in
October, Palagi and her colleagues showed
that spotted hyenas spend a lot of time play-
fighting. At first glance, this seems odd,
because in hyena clans the dominant females
are “extremely despotic”, as Palagi puts it.
However, these females also sometimes form
alliances, and she thinks play-fighting may
help cement these bonds.
The findings so far suggest that play didn’t
evolve just once, early in the history of animals.
“If you look at the animal kingdom, very, very
few species show the behaviour,” says Palagi.
Instead, it seems play arose independently in
different lineages. But because so few species
have been studied to see if they play, there
is currently no way to tell how many times
play evolved.
It may well be ancient. If Komodo dragons
and birds can both play, it seems possible that
some of their dinosaur relatives did, too. Sixty-
six million years ago, maybe Tyrannosaurus
rex enjoyed tug of war – pulling with its jaws
rather than those silly little arms. ❚“ If Komodo
dragons and
birds can play,
maybe some
dinosaurs
did too”
Michael Marshall
isn’t playing games78 | New Scientist | 18/25 December 2021