Chimpanzee accents have spurred debate among scientists, following a study published in February which had claimed the primates adjust the pitch of their vocalizations based on their companion.
The initial research, led by Dr. Katie Slocombe, lecturer in psychology at the University of York, analyzed a group of 9 chimps which had inhabited Beekse Bergen Safari Park, in the Netherlands. In 2010, these animals were moved to Edinburgh Zoo, to live alongside 9 other adult members of the same species.
At first, when the two groups were fed apples, the Dutch chimps expressed their enthusiasm using high-pitched sounds, whereas the old residents only gave out a low-pitched grunt showing disinterest.
In 2011, when the primates were observed again, it was determined that the calls had remained dissimilar, since the two communities didn’t interact much and preferred their former companions.
However, in 2013, when the analysis was conducted again, it was revealed that group had finally become cohesive, with close bonds and friendships between the newcomers and the older Scotland-raised chimpanzees.
At the same time, the vocalizations had also changed, with the Dutch primates adopting lower-pitched grunts when being given apples, although they had remained just as keen on the fruit as before.
Researchers claimed in their study that this suggests that “referential calls” can change and be re-learnt, as chimpanzees try to adapt themselves to life in the presence of new companions.
The vocalizations aren’t in fact mere emotional reactions provoked by a stimulus, but they become part of a shared language, employed in order to establish closer relationships. This is very similar to the way humans acquire vocabulary and communication skills, by being taught in their social circle, by family and peers.
Now however, three experts have challenged these findings, in a letter addressed to the journal Current Biology, where the results were initially published. As they explain, their mission isn’t to negate the merits of the authors, but simply to air out disagreements regarding this widely publicized research.
According to Dr. James Higham, at New York University, the investigators in the contested study have misrepresented their data, and their methods weren’t accurate. In reality, the calls pertaining to the two groups weren’t that dissimilar to begin with.
In their first responses to apples, both categories of animals had used high-pitched and low-pitched sounds, and the change that was produced throughout the study period was “statistically significant but biologically weak”.
On the other hand, Warwick University’s Dr. Simon Townsend, one of the authors of the original paper, stands by the claims formulated in the research, and says that the team has re-analyzed data and reached the same conclusions.
As he explained, there was a growing preference for lower grunts as the community became more close-knit, and this was especially detectable among well-integrated chimpanzees.
Another point made by detractors is that the high-pitched sounds at the beginning were only signs of apprehension and excitement felt by the newcomers, but that argument can be combated since the changes took years to appear, and any anxiety would’ve subdued much quicker.
Critics however still insist that even if vocalizations really did suffer a transformation, this is due to “social modulation”. This means that the process can’t be compared to learning a new word, and instead is more similar to adopting the majority’s behavior in order to fit in.
In response to this, study authors admit that it’s difficult to differentiate between the two instances, but whichever the case may be the findings reveal a variation in sounds across time which hadn’t been identified before among chimps.
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