Wednesday, 28 February 2018

Chimpanzee Gestures Confound Creationists

Bonobo and chimpanzee gestures overlap extensively in meaning

The thing about evolutionary biology is that researchers can't help providing evidence for it. It's not intentional; it's not as though there is any doubt, it's just that the reality is that species evolved from common ancestors. So, inevitably, reality shows the evidence.

Take, for example, this piece of research published yesterday on the subject of bonobo (Pan paniscus) and chimpanzee (P. troglodytes) and their use of non-verbal communications or gestures which both use extensively to communicate with others of their species. It turns out that there is an approximate 90% overlap between the two species. This is far more than chance alone could account for. The research was conducted by scientists based at the Department of Psychology, University of York, York, United Kingdom and the School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom.

Since there is almost zero probability that the two species could interact and learn from one another, there has to be another explanation.

Abstract
Cross-species comparison of great ape gesturing has so far been limited to the physical form of gestures in the repertoire, without questioning whether gestures share the same meanings. Researchers have recently catalogued the meanings of chimpanzee gestures, but little is known about the gesture meanings of our other closest living relative, the bonobo. The bonobo gestural repertoire overlaps by approximately 90% with that of the chimpanzee, but such overlap might not extend to meanings. Here, we first determine the meanings of bonobo gestures by analysing the outcomes of gesturing that apparently satisfy the signaller. Around half of bonobo gestures have a single meaning, while half are more ambiguous. Moreover, all but 1 gesture type have distinct meanings, achieving a different distribution of intended meanings to the average distribution for all gesture types. We then employ a randomisation procedure in a novel way to test the likelihood that the observed between-species overlap in the assignment of meanings to gestures would arise by chance under a set of different constraints. We compare a matrix of the meanings of bonobo gestures with a matrix for those of chimpanzees against 10,000 randomised iterations of matrices constrained to the original data at 4 different levels. We find that the similarity between the 2 species is much greater than would be expected by chance. Bonobos and chimpanzees share not only the physical form of the gestures but also many gesture meanings.

Author summary
Bonobos and chimpanzees are closely related members of the great ape family, and both species use gestures to communicate. We are able to deduce the meaning of great ape gestures by looking at the ‘Apparently Satisfactory Outcome’ (ASO), which reflects how the recipient of the gesture reacts and whether their reaction satisfies the signaller; satisfaction is shown by the signaller ceasing to produce more gestures. Here, we use ASOs to define the meaning of bonobo gestures, most of which are used to start or stop social interactions such as grooming, travelling, or sex. We then compare the meanings of bonobo gestures with those of chimpanzees and find that many of the gestures share the same meanings. Bonobos and chimpanzees could, in principle, understand one another’s gestures; however, more research is necessary to determine how such gestures and gesture meanings are acquired.


There was so much commonality between them that it seems likely the two species could communicate fairy effectively with one another.

The overlap in gesture meanings between bonobos and chimpanzees is quite substantial and may indicate that the gestures are biologically inherited.

Dr Kirsty Graham, Lead author
Research Associate, Department of Psychology University of York
The explanation is, of course to be found in the evolution of the two closely-related species which diverged between one and two million years ago, shortly after their common ancestor diverged from the hominin line. In fact, it shows that these gestures were present in that common ancestor.

The fact that humans too use gestures, especially when communicating at a distance and that these gestures in humans, unlike verbal communication, is universal, suggests that gesturing was also present in the common ancestor we share with bonobos and chimpanzees.

The simple use of gestures and their commonality, like shared anatomy, physiology, genetics, etc, simply reinforce the clear message that evolution happens. We don't need to go looking for it; it shouts out to us wherever we look.

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