Evolution
The ability to produce new sounds, so-called vocal fold control, was critical to the evolution of spoken language. It has, however never been demonstrated directly in a non-human primate. This has led some to believe that great apes –our closest relatives – could not learn to produce new sounds and because speech is a learned behaviour therefore could not have originated from them.
Mimicking sounds
Rocky was studied at Indianapolis Zoo, Indiana, USA, where he is currently housed, between April and May 2012, and all steps were taken to ensure his routine and environment were not disrupted. During the study, a researcher made random sounds with variations in the tone or pitch of her voice which Rocky then mimicked. The research team compared these sounds against the largest available database of orangutan calls collected from over 12,000 hours of observations of more than 120 orangutans from 15 wild and captive populations.
Based on their comparison, they were able to conclude that the sounds made by Rocky were different compared to the sounds on the database, showing that he was able to learn new sounds and control the action of his voice in a ‘conversational’ context.
Vocal control
‘It’s not clear how spoken language evolved from the communication systems of the ancestral great apes’, says Dr Adriano Lameira, lead author of the study.
‘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. 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.’
Serge Wich, professor by special appointment of Conservation of the Great Apes at the UvA, adds: ‘Our findings indicate that the excellent vocal control that humans exhibit likely derives from an evolutionary ancestor with similar capacities in terms of voice control as those found in orang-utans, and possibly in all great apes more generally. Based on these findings, science can now start to reconstruct the vocal capacities of an early hominid, estimated to have lived before the split between the orang-utan and the human lineages, and examine the following steps in the evolution of the vocal system towards full-blown speech.’
The research involved the Pongo Foundation (Netherlands); Max Planck Institute for Evolutionary Anthropology (Germany); Liverpool John Moores University (UK); University of Amsterdam (Netherlands); Indianapolis Zoo (USA); George Mason University (USA); Indiana University (USA).
