Orangutans Provide Insight into Human Speech Development

New research, led by scientists from the Indianapolis Zoo and the University of St Andrews, shows that great apes can control their voice in a similar way to humans, giving a unique insight to the evolution of human language.

The research, in collaboration with the University of Durham, published in Scientific Reports, reveals how orangutans can control their voice in a similar way to humans. Working alongside animal care staff and researchers at the Indianapolis Zoo, the team studied then 11-year-old Rocky and 36-year-old Knobi, analyzing how the orangutans used their voice to play a basic musical instrument.

“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 Indianapolis Zoo President Dr. Rob Shumaker. “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.” 

The team of researchers developed a diagnostic test for active voicing in orangutans, by using a membranophone: a musical instrument, such as a kazoo, where a player’s voice flares a membrane’s vibration through oscillating air pressure. This musical instrument was chosen because it is strictly activated by the player’s voice.

Active voicing, which requires voluntary control over vocal fold oscillation, is essential for speech. While traditionally presumed to be uniquely human, there is currently a growing volume of multidisciplinary data evidencing voice control in great apes.

“Language defines human communication, but its evolution defies scientific explanation,” said lead researcher Dr. Adriano R. Lameira, from the School of Psychology and Neuroscience at the University of St Andrews. “Great apes, our closest relatives, may hold the key to how language evolved in our lineage. 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.”

By asking the apes to use the kazoo, researchers were able to determine that our nearest ape relatives have good levels of voice control, allowing them to produce voiced sounds beyond their natural repertoire. This basic capacity is what allows humans to learn the vowels of our mother tongues and the new voiced sounds of second languages.

Membranophone activation was successful within minutes after first exposure, precluding that it developed out of training or conditioning. The research demonstrated that novel vocalzsations in orangutans is indeed the product of vocal fold action and that orangutans can adjust their voice frequency and duration features rapidly and meaningfully. This research demonstrates that voice control in great apes is only different from humans’ in degree, not kind. 

At the Indianapolis Zoo

The Simon Skjodt International Orangutan Center at Indianapolis Zoo is home to one of the largest groups of orangutans in any American zoo. In addition to collaborating with international scientists, researchers at the Simon Skjodt International Orangutan Center offer the apes computer-based cognitive tasks on a daily basis. These opportunities for learning and problem solving are conducted in a demonstration format with visitors. By directly witnessing the intelligence of orangutans, the Zoo inspires and empowers people to advance great ape conservation. Orangutans are critically endangered and only found in the wild on the islands of Borneo and Sumatra. The loss of habitat due to non-sustainable palm oil production is devastating wild orangutan populations. The Zoo supports orangutan conservation in Borneo’s Kutai National park. The project studies orangutans living in the park and plants trees in areas where forests have been depleted. Guest who visit the Simon Skjodt International Orangutan Center are able to make a donation to support tree planting in Kutai.