A multinational team of researchers report that orangutans can invent arbitrary calls that become shared in populations through social learning, a characteristic that was previously ascribed only to humans.
The last decade has seen an explosion of studies in the field of ‘cultural primatology’. These studies have been of enormous influence on theories for the evolution of human culture, but have not yet touched upon one of humans’ most unique cultural aspects, namely language. This is likely the result of a widespread consensus that non-human primates (hereafter primates) are largely incapable to learn new calls and are stuck in a species-fixed repertoire without geographic variation and thus without a call culture.
The researchers wanted to examine potential variation in call cultures in non-human primates, especially since finding such variation would have major implications for theories on the evolution of human language. This led them to study whether wild orangutans have call cultures.
The study was recently published in the peer-reviewed scholarly journal PLoS ONE.
The researchers studied the vocal repertoire of five wild orangutan populations in Indonesia for more than 50,000 observation hours and found that in two behavioral contexts (nest-building and mother-infant travel) there is geographic variation in the calls that are given. The reported variation clearly shows that the calls in the different populations are not subtle variants of each other, but represent completely new calls. "Our findings are especially striking because the calls used by one population do not occur at all in some other populations and thus are not simply a case of using the same call in a different context," said Dr Serge Wich at the Anthropological Institute and Museum, Zurich, and the first author in the study. "Such variation has major implications for theories on the evolution of human language," added Dr Wich.
A female orangutan and her offspring in Tuanan (Kalimantan). Image Credit: Dr. Serge Wich.
At the same time as these researchers collected the call data, they also collected a large number of genetic samples from these populations. Because for the first time extensive genetic data are in hand for all the populations involved, their analyses, according to the researchers, now firmly exclude genetic differences that might explain this variation, in addition to ecological ones.
The significance of these findings are that they indicate that orangutans posses the basic ability of inventing arbitrary calls that become shared in populations through social learning. In primates, this capacity is traditionally only ascribed to humans. This claimed human uniqueness for this capability has made it difficult for theories of the evolution of human language to explain the transition from fixed-genetically canalized primate vocal systems to socially learned human language. "The results presented here provide a bridge for this transition because they are the first evidence for ‘call cultures’ in a non-human primate species," Dr. Wich told SciGuru.com.
In summary, the results of the new study indicate that there was a pre-existing foundation in the great apes for vocal learning, which was extensively exploited in human evolution and has led to our rich variation in languages.