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Humans engage in this funny behaviour known as “language.” To be able to talk and write, humans need to have a few key abilities such as hearing, for example. Another pretty key ability is vocal learning.  Rather than just listening to another and copying them, vocal learning involves altering the sounds an individual produces in order to better imitate another and/or innovate a new call.

Although this has been show to exist in species to whom vocalisation is important – such as songbirds – no non-human primates are known to do it. This has some pretty interesting implications for the development of language, suggesting that this key component is a unique hominin behaviour. Perhaps this is why we don’t see chimps talking, which may be a good thing after all.

New research, however, is challenging the traditional view of whether vocal learning exists in primates. Researchers studied five populations of orang-utans from two different islands. They followed them throughout the day, recording when they made four different calls: nest smack, raspberry, harmonic uuh and throat scrapes (if you’ll pardon the pun, it sounds like they had fun naming these calls).

The nest smack and raspberry are typically produced whilst an individual is preparing a nest whilst the harmonic uhh and throat scrape are sounds mothers make towards their children. Nest building calls aren’t made by apes who are younger than 2/3 years old whilst the mothering sounds aren’t made by apes who aren’t made by mothers.

They found that different populations made different calls whilst in the same situation. One would make a harmonic uhh to get the attention of their offspring, another would make a throat scrape noise whilst the three other populations were silent. Similarly, one population made nest smacks whilst building a nest, two made raspberries and three were silent.

Since new calls are being produced vocal learning could be occurring. Changing the sounds they produce could have resulted in innovation, which may be the source of these different calls. Further, vocal learning could be used to better imitate these new calls, enabling young orang-utans to pick up on the calls of their “tribe.” However, for vocal learning to be responsible other factors, such as genetics, could not be. After all some groups are on different islands which could lead to genetic divergence.

See, there’s genetic variation!

If genetic variation was responsible for call variation then one would expect those two traits to be correlated. The two groups that made raspberries should be more closely related to each other than they are to the other groups which made nest smacks or remained silent.

However, their genetic analysis of the primates revealed that this was not the case. That there was no such link between genetics and call variation. As such it is very unlikely that these call cultures are the result of genes.

The other popular explanation for such variation is environmental differences. A group living in a different area would have to behave differently which could manifest in call variation. As such there needn’t be vocal learning going on, the orang-utans could just be picking it up from the environment.

Again, this explanation doesn’t seem to hold water. Whilst the populations are indeed split over two islands the environment in both is very similar. Further, some variation occurred between groups on the same island. Two populations from the same forest would give different calls in the same situation.

Genetic differences between pairs of sites. Note how there is no correlation.

Since genetics and environment don’t appear to be responsible for the call variation observed (or rather, heard) the researchers thus argue that the only explanation left is that vocal learning is occurring. Orang-utans are modifying their calls to better make the noises their group is supposed to make. However, this is only true provided that some other force the researchers didn’t/couldn’t control for isn’t influencing this call variation. As such this research is far from definitive and should be taken with a pinch of salt (although not dismissed entirely).

And if further research does indeed confirm primates are capable of vocal learning then this will also have some fascinating implications for human evolution. Previously the absence of vocal learning in non-human primates had made Homo sapiens‘  vocal learning seem rather out of place. It would seem that language is very distinct from the calls made by other primates.

This research serves to close the gap somewhat, making it plausible that one of the basic foundations of language was present in our ancestors.

Wich, Serge A., Michael Krützen, Adriano R. Lameira, Alexander Nater, Natasha Arora, Meredith L. Bastian, Ellen Meulman, et al. 2012. ‘Call Cultures in Orang-Utans?PLoS ONE 7 (5) (May 7): e36180. doi:10.1371/journal.pone.0036180.

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Jeroen van der Aa · 14th June 2012 at 11:36 am

This is not vocal learning, this is auditory learning. These two phenomena are very distinct, and all vertebrates are capable of auditory learning.

For example, see:
Jarvis, E.D. (2007) Neural systems for vocal learning in birds and humans: a synopsis. Journal of Ornithology, 148, S35-S44.

    Adam Benton · 14th June 2012 at 12:56 pm

    Thanks for pointing that out, I can’t recall exactly what was going through my mind at the time. Both the citation and introduction appear to be for a paper which may well show a form of vocal learning (orangs using tools to modify their speech so they sound deeper) yet the main body of what I wrote comes from another paper on orang cultures. For some bizarre reason, I seem to have switched between the two.

    I’ll try and get it fixed as soon as I can.

    Adam Benton · 17th June 2012 at 1:38 pm

    So I found the original paper, fixed the citation and rewrote the text a bit to better reflect what the research is actually saying.

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