King Louie once sang "I wanna walk like you, talk like you, too", but his real-life sisters and brothers aren't as far off as you might think – at least if a new study published in Scientific Reports is anything to go by. While orangutans have not yet mastered jazz, scientists at the University of St Andrews and Indianapolis Zoo have shown that they have the capacity to control their voice in a similar way to humans, using a kazoo.
"Language defines human communication, but its evolution defies scientific explanation. Great apes, our closest relatives, may hold the key to how language evolved in our lineage," Adriano Lameira from the University of St Andrews said in a statement.
"Our results provide the first positive diagnostic test of vocal production learning in great apes, namely active voicing, during novel voiced vocal production in orangutans."
Up until quite recently, it was believed that non-human great apes were unable to produce new vocalizations. However, new research is challenging that assumption. In 2016, researchers taught an adolescent orangutan called Rocky an imitation "do-as-I-do" game. He impressed the team with his ability to mimic human sounds and learn "new" sounds – showing it was possible for orangutans to control their voice in a way previously unthought of and develop "speech" beyond their natural repertoire.
The crux of the issue comes down to a process called active voicing (i.e. the ability to voluntarily control vocal fold oscillation), which is essential for speech and was believed to be unique to humans. This is where the kazoo comes in.
Unlike, say, a flute, a kazoo can only be activated by a player's voice. Blowing into the instrument isn't enough to create a sound. A player's voice, on the other hand, creates oscillating air pressure, which makes the kazoo's membrane vibrate and produces noise.
Six orangutans of different sexes and ages (including Rocky) were presented with a kazoo to play around with for an hour. Three of the apes involved had already developed individualized vocalizations that are species atypical.
Two of the orangutans in the latter group (including Rocky) were able to produce sounds from the kazoo in a relatively short space of time – 11 and 34 minutes – using their individualized vocalizations. Interestingly, the pair adopted opposite strategies (ingressive versus egressive airflow) to change their voice duration and frequency to best suit the kazoo, demonstrating plastic voice control. The study authors say that the results show voice control in orangutans is "only different from humans' in degree, not kind".
The fact that active voicing was reported in two unrelated apes suggests the skill is not a one-off but, most likely, lies latent yet mobilizable in the genus. While it is true the sample size was small, we can think of Nassim Taleb's black swan – just one black swan is enough to prove not all swans are white. Likewise, the achievements of these two primates seem to prove that active voicing is possible in orangutans.
"This important study redefines our understanding of how spoken language may have evolved. It also demonstrates that the abilities of orangutans, and likely all great apes, have been greatly underestimated," said Rob Shumaker, president of Indianapolis Zoo.
"This new knowledge compels us to have a stronger conservation ethic at a time when all wild great ape populations face serious threats to their survival."