An orangutan has displayed the ability to make vowel-like calls, mimicking the tone and pitch of sounds made by researchers — a development that could provide insight into the origins of human language.

In the scientific community, it has been an established fact that speech is a learned behavior — one that evolved through the mastery of our own vocal cords. As such, since apes hadn't demonstrated the ability to learn new vocalizations, scientists concluded that spoken language evolved after we split from the apes.

Now, thanks to Rocky, an 11-year-old orangutan from the Indianapolis Zoo, scientists have a lot to reconsider.

The study, published in the journal Scientific Reports, details how researchers attempted to teach him new sounds without disrupting his environment or schedule by engaging him in copycat games, where he was challenged to mimic new vocalizations that varied greatly in tone and pitch in order earn snacks.

Much to their surprise, Rocky was able to move his vocalizations up and down in pitch and tone to match researchers, as well as make calls that resembled both consonants and vowels. This wasn't a fluke, either, as the scientists compared Rocky's exclamations against a database of more than 12,000 hours of various orangutan calls and found that none of them matched, meaning they were entirely new.

The results were clear: apes are able to achieve levels of voice control that is comparable to those in humans.

"Instead of learning new sounds, it has been presumed that sounds made by great apes are driven by arousal over which they have no control, but our research proves that orangutans have the potential capacity to control the action of their voices," Adriano Lameira, an anthropologist at Durham University, said in a news release. "This indicates that the voice control shown by humans could derive from an evolutionary ancestor with similar voice control capacities as those found in orangutans and in all great apes more generally."

Rocky's performance in the game suggests that voice control isn't limited to specific species and is likely indicative of broader capabilities among all orangutans — and potentially all great apes. Until now, it had been assumed that their cognitive abilities far outstripped their vocal ones, but these results suggest both abilities are equally sophisticated.

"[This opens] up the potential for us to learn more about the vocal capacities of early hominids that lived before the split between the orangutan and human lineages to see how the vocal system evolved towards full-blown speech in humans," Lameira concluded.

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