We’re all familiar with the rules of polite conversation, allowing the other person to take a turn to speak. Surprisingly, marmoset monkeys can do this too, says a study from Princeton-based researchers Dr Asif Ghazanfar and Dr Daniel Takahashi.
We have an extremely intricate way of talking to each other, but the foundation for our communication manifests itself most simply in the fact that we take turns to speak. “If we didn’t take turns to speak we wouldn’t be able to do all the other sophisticated things we can with our language,” Dr. Ghazanfar told Decoded Science.
“This turn-taking has two universal features no matter what language you look at – we don’t overlap with one another when we’re speaking – or we try not to – and there is a silent gap between our exchanges.” The million dollar question now is, how did the ability to wait for our turn evolve?
Dr Ghazanfar and his team placed 27 pairs of marmoset monkeys in opposite corners of a room, with a curtain between them so they could hear, but they couldn’t see each other. The conversation immediately sparked between the two animals and could last up to 30 minutes, sharing the same turn-taking rules that humans have.
Marmosets politely waited about 5 seconds to respond after the other finished ‘talking’. In humans, the interval between interventions is about 200 ms – roughly just about long enough to pronounce a syllable – but, as Dr Ghazanfar explains, “the minimal unit for marmoset vocalisation may be the entire call, which is about 5 seconds.”
Understanding the Development of Human Conversation
Our closest relatives – chimpanzees – prefer to use their hands to gesture, and don’t really exchange vocalisations in any cooperative way. Based on this lack of vocalisations, many researchers have speculated in the past that human communication started with manual gestures and eventually moved to a vocal system, but Dr Ghazanfar finds this idea flawed, saying, “The switch from a manual to a vocal system remains mysterious and no one has really bothered to try to explain.”
In contrast, the fact that marmosets exhibit this turn taking ability provides an “alternative evolutionary route” for our own conversation skills. Like us, these monkeys are co-operative breeders, which means they help each other to look after their offspring. “Our ancestors evolved a cooperative breeding strategy, which may have led to a more friendly outlook towards other group members, causing friendly vocal interaction,” explains Dr Ghazanfar. The scientist believes cooperative breeding may be the foundation for the evolution of vocal turn taking.
What is Small Talk to Monkeys?
One aspect, however, that monkeys left researchers guessing was the contents of their conversations. On one hand, these calls may simply be a way to reduce stress, and taking turns confirms that there’s somebody listening on the other side, as opposed to random vocalisations. However, what sounds like very simple calls may actually contain important information about the other individual, like age and gender. If this is the case, the lack of interruption may allow marmosets to understand the message, especially in a noisy forest environment.
Do Marmosets Need to Learn this Behaviour?
In the future, the team is hoping that their approach using marmoset monkeys will help reveal more about how our conversation skills develop, and what could be at fault in human communication disorders. Preliminary studies already show that, like with any child, “it seems to be mum or other care-giver that reinforces the vocal behaviour,” according to Dr Ghazanfar, and “marmosets learn over the course of time not to interrupt when other individual is speaking.”
D Takahashi, D Narayanan & A Ghazanfar. Coupled Oscillator Dynamics of Vocal Turn-Taking in Monkeys. (2013). Current Biology. Accessed October 20, 2013.
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