Scientists at the University of California, Los Angeles took a closer look at vocal play signals — or what might be thought of as laughter — across the animal kingdom.
Play is common in a few lineages of the animal kingdom, being especially prevalent among some birds and many mammals.
Many theories of the function and types of play have been proposed, although difficulties exist, including but not limited to the basic problems of defining, identifying, and quantifying supposed play behavior.
In a new review of scientific literature, University of California, Los Angeles Professor Greg Bryant and graduate student Sasha Winkler focused on social play, the most frequently described type of play in mammals.
They looked for information on whether the animal vocalizations were recorded as noisy or tonal, loud or quiet, high-pitched or low-pitched, short or long, a single call or a rhythmic pattern — seeking known features of play sounds.
“This work lays out nicely how a phenomenon once thought to be particularly human turns out to be closely tied to behavior shared with species separated from humans by tens of millions of years,” Professor Bryant said.
“When we laugh, we are often providing information to others that we are having fun and also inviting others to join,” Winkler added.
“Some scholars have suggested that this kind of vocal behavior is shared across many animals who play, and as such, laughter is our human version of an evolutionarily old vocal play signal.”
The researchers found vocal play behavior documented in at least 65 species, including a variety of primates, domestic cows and dogs, foxes, seals, and mongooses, as well as three bird species, including parakeets and Australian magpies.
“Our comprehensive literature review reveals that vocal signals during social play are quite common across mammal species, and some birds, further challenging the once ‘conventional wisdom’ that animal play is silent,” they said.
“There’s much existing documentation of play-based body language among animals, such as what is known as ‘play face’ in primates or ‘play bows’ in canines,” they added.
“Since what constitutes ‘play’ in much of the animal kingdom is rough-and-tumble and can also resemble fighting, play sounds can help emphasize non-aggression during such physical moments.”
“While further observation and research into vocalizations would be fruitful, such observations can be hard to come by in the wild, especially for animals whose play sounds might be quieter,” they noted.
“Paying attention to other species in this way sheds light on the form and function of human laughter and helps us to better understand the evolution of human social behavior.”
The findings were published in the journal Bioacoustics.
Sasha L. Winkler & Gregory A. Bryant. Play vocalisations and human laughter: a comparative review. Bioacoustics, published online April 19, 2021; doi: 10.1080/09524622.2021.1905065