A good conversation should proceed like a tennis match: players each take turns responding, knowing instinctively when to speak and when to listen. This kind of lively banter is often considered uniquely human, a trait that separates us from the rest of the animal kingdom. But in fact, sophisticated, back-and-forth conversations are happening all around us.
They might occur in a low, barely audible rumble felt through the pads of giant elephants’ feet, or the singsong chatter of skylarks. They might involve the delicate hand gestures of chimpanzees, or whale songs that travel thousands of miles through lonely oceans. In some cases they exist only in the brief bioluminescent flashes between frisky fireflies in the dark.
And according to a recent scientific review, a common theme runs through many of these verbal or non-verbal dialogues: animals, too, seem to know when to speak and when to listen.The review, published last week in the Philosophical Transactions of the Royal Society B: Biological Sciences, looked at over 300 studies of animals including birds, mammals, insects, frogs and toads who practice turn-taking behavior.
It turns out that a great number of animals alternate their call and response in a similar way that humans communicate. Marmosets, for example, often exchange calls to locate each other in the wild and figure out whether they know one another while dolphins chatter back and forth while coordinating attacks on prey. Many male birds call out propositions to prospective mates, and only proceed if females respond with interest.
While many of these forms of communication are sound-based—from frog croaks to the crackling noises made by some insects—some species have more creative methods of communication. Bonobo infants let their parents know they want to be carried with arm gestures, while birds, insects and frogs can get their messages across through colorful displays. Elephants can literally feel the vibrations that move through the earth when they emit low rumbles to find each other in the wild.
Many of these less traditional modes of communication also resemble the turn-taking common in human conversation, with elephants waiting their turn before responding to rumbles.
Since conversations don’t fossilize, any evolutionary interpretation is difficult. Yet Kobin Kendrick, a linguistics lecturer at the University of York and co-author on the study, says that making comparisons among animals that take turns when communicating can give us a better understanding of how this trait evolved in humans and our ancestors. “The biggest goal when we’re doing the comparisons is to reconstruct the evolution of these turn-taking behaviors,” he says.
He adds that, “our understanding of the evolution and the origin of language is not very well fleshed out. We know very little about the origin of the human language—so any possibility of gaining insight into it is worth pursuing.”
Thom Scott-Phillips, a senior researcher in cognitive science at the Central European University in Budapest who was not involved in the review, says that Kendrick and his coauthors’ paper “seems authoritative.” But he adds that while he accepts that many different species use coordinated exchanges to communicate, “we need to be careful what conclusions we draw from that.”
Just because similar behavior can be observed in different species, he points out, doesn’t mean that these traits involve similar psychology or biology. “Shared behavior between species is not evidence of shared mechanisms,” he says.
One of the main questions is whether this turn-taking trait could have evolved independently in different species, rather than evolved once long ago in an ancestor shared by all the disparate species. Scott-Phillips believes that turn-taking as it’s used by humans has evolved independently from other species, though he adds that more research and data will bring greater clarity to the issue.
Kendrick singles out another element worth comparing: the silence between exchanges. In a typical human conversation, we generally pause for 200 milliseconds or so before answering. According to Kendrick, a longer or shorter pause tends to signal something is amiss, such as a delayed response from a politician when confronted with an allegation of corruption, or a lightning quick “it wasn’t me” from a kid with a baseball bat beside a broken window.
“If you ask someone to dinner, then there is a 600 millisecond pause, one of the inferences you might draw is the answer might not be ‘yes,’” he says.
Additionally, while the idea of turn-taking might bring to mind a picture of orderly, well-mannered animals, Kendrick stresses that this isn’t always the case. Like politicians interrupting each other or reporters jockeying to get their question answered, barn owl chicks may try to outdo each other by chirping louder or more quickly in an effort to attract favor from their mothers during feeding.
Some skilled operators even know how to hijack the conversation to their advantage. Antbird males, for instance, call out flirtatious entreaties to single females in their vicinity. But just when a young female gets interested enough to respond, another male will often jam up the process by answering her before the first male can continue his conversation, either calling more loudly or at the same time in an effort to steal the female’s affection.
These cases of overlapping signals can be seen as the exception to the rule, highlighting the importance of turn-taking in general, says Kendrick.
One of the problems with studying this kind of turn-taking is that researchers themselves do not know how to communicate with others outside their particular species of interest. Kendrick says another goal of the review is to create a framework that brings together all the disparate research on turn-taking, allowing scientists to conduct more cross-species comparisons. “We’ve been trying to unify this research and bring it all under one umbrella,” he says.
What’s certain is that humans can glean much about the mechanics of communication from our fellow earth-dwellers. In a press release, Sonja Vernes, a coauthor on the recent review and a researcher at the Max Planck Institute for Psycholinguistics, expressed a desire for more comparisons across species: “We all believe strongly that these fields can benefit from each other, and we hope that this paper drives more cross talk between human and animal turn-taking research in the future.”