While science continues to uncover the many interesting ways animals communicate with each other, we humans have long considered ourselves distinct from our most recent ancestors, thanks to our powers of elocution. Our range of vocal abilities is unique; it evolved after human lineage split off from our ape relatives.
Or so we thought.
As it turns out, Rocky the Orangutan can control his voice, too.
Research published Wednesday in the journal Scientific Reports demonstrates how Rocky, a resident of the Indianapolis Zoo, can control his vocal folds to produce sounds in response to random stimuli that are distinctive from native orangutan calls.
While this amounts, more or less, to a series of grunts, this finding also suggests that our current models of the evolution of human speech may need a bit of a rewrite.
The research “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,” lead researcher Adriano Lameria of the University of Durham in Britain, told the New Scientist. Dr. Lameria sees this research as a jumping-off point for further study.
Lameria was building off research that he had done at the University of Amsterdam, where he observed another orangutan whose sound patterns kept a rhythm similar to that of human speech.
With Rocky, researchers used a simple test and then an exhaustive cross-referencing process to establish evidence that the ape could indeed control his own vocal cords.
The first test for Rocky was an imitation “do-as-I-do” game with a human demonstrator making specific sounds for Rocky to repeat. If he copied the sound correctly on the first try, he was rewarded. The sounds included both vowel and constant-like calls, as well as variations in pitch.
Recordings from these trials were then cross-referenced with a database of orangutan calls, compiled from over 12,000 hours across multiple and varied orangutan populations. This was to verify that the sounds that Rocky was making were novel for his species.
The results showed that “a nonhuman great ape can achieve levels of volitional voice control qualitatively comparable to those manifested in humans,” such as “real-time, dynamic and interactive” vocal control “beyond the species-specific vocal repertoire,” the researchers wrote.
While this is not the first great ape language project to have attempted to teach apes speech, the researchers say that their trial is different because their evidence is empowered by the database. That resources allows them to compare the Rocky's replies in the experiment with orangutan's natural noises. Unlike the earlier studies, this one compares apes to themselves, not to humans. It's an important distinction, the scientists suggest, because it now appears the ape vocal system was evolving parallel to the human one.
The researchers call for earlier experiments to be re-evaluated and for more study to explore the new path that they (and Rocky) have opened up: Given that this evidence challenges the long-held views about “genetic and ecological divergence,” they write that there is a new imperative to explore how vocal capacities and spoken language ability evolved within our family tree.