An adolescent orangutan called Rocky was able to copy human sounds, an international team of researchers found. When the team asked Rocky to imitate the vowel-like calls, they found that the orangutan was able to copy the pitch and tone of the sounds they made.

As stated in the study published on July 27 in the journal Scientific Reports, this proves that orangutans can control their voices, contrary to what was previously assumed. This could also shed light into how modern human speech evolved from hominins that lived before apes and human lineages split.

The study, led by Adriano Lameira from Durham University in the UK, was conducted between April and May 2012 in the Indianapolis Zoo, Indiana, USA. The researcher made random sounds with different tones and pitches, which Rocky then copied.

The research team compared Rocky’s sounds with other orangutan sounds available in the database. The sound collection includes 12, 000 hours of observations of more than 120 orangutans selected from the wild and in captivity.

They found that Rocky’s sounds were different from the ones on the database. This showed that Rocky was capable of learning new sounds and control his voice in a way that it seemed like he is conversing with a human.

The findings echo a previous one that was also led by Lameira when he was still based at the University of Amsterdam. Published in January 2015, the researcher found that Tilda, a female orangutan in Cologne Zoo in Germany, produced sounds that were almost similar to human consonants and vowel-like calls at the same rhythm and pace as human speech.

“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,” Lameira says. “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.