F Rosa Rubicondior: Chimpanzee Gestures Confound Creationists

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.

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
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.

In a series of well-known children’s books, Doctor Dolittle was able to talk to nonhuman animals, but in reality, deciphering meaning in nonhuman communication presents a much bigger challenge. First, there is the question of whether animal signals can be said to have ‘meanings’ or merely ‘functions’. Functions are known for many animal signals: for example, various species are able to decode complex information from their conspecifics’ calls on the location or class of food or predators [14], level of risk [4,5], and size of predator [6]. However, for meaning, a signal needs to be produced intentionally—the signaller must aim to change the behaviour (first-order intentional) or the mental state (at least second-order intentional) of the recipient [79].

Mounting evidence shows that, unlike most nonhuman animals [10], great apes habitually engage in first-order intentional communication: great apes routinely direct their gestures towards a specific recipient; monitor that recipient’s attentional state and choose gestures appropriate to it; wait for the recipient to respond; and, if the recipient does not respond, they persist and elaborate with further gestures [1117]. These criteria demonstrate that the signaller has a specific outcome in mind and uses gestures to achieve that outcome [18]. It has also been argued that to have meaning, communication needs to be ostensive, drawing attention to the fact that it is being used to communicate [19]. In developmental psychology, eye gaze is taken as an ostensive cue; the audience checking performed by great apes before gesturing serves the same ostensive function [20]. Because great apes deploy gestures intentionally, it is appropriate to go beyond simply describing their function and enquire about the intended meaning that a signaller aims to achieve by gesturing [20]. Although we focus on gestural communication, it should be noted that great apes also appear to deploy some vocal signals intentionally [2123]. Moreover, we focus on a Gricean approach to meaning, rather than a semantic approach [24,25], given that few great ape gestures appear to be referential (but see [26]).

The second challenge is that gesture meanings must be deduced indirectly. Past studies have tackled the issue of meaning by looking at the context in which gestures occur [16,27], thereby showing that the same gesture may occur in several contexts. We have taken a different approach. By using the reaction that each gesture elicits, but only in cases where the signaller’s behaviour indicates that this reaction was their intended aim, we hope to pin down the signaller’s intended meaning for each specific gesture. The meaning of a gesture can thus be defined by the ‘Apparently Satisfactory Outcome’ (ASO), the reaction of the recipient that satisfies the signaller as shown by cessation of gesturing [28]. This method indicates the individual signaller’s intended meaning in each instance, and across many instances and individuals, one can examine the gesture’s general meaning(s) in a population. Aggregating the meanings represents population level patterns of meaning but does not infer that meanings are conventionalised nor indeed does it imply any particular ontogeny for gesture meanings.

Defining meaning by ASOs, wild chimpanzees use their gestures to achieve at least 19 ASOs; that is, their gestures achieve 19 types of behavioural response from the recipient [28]. Each gesture type has a distinct (set of) meaning(s) that is calculated by comparing the distribution of meanings for a gesture type to the distribution of meanings across all gesture types [28]. Using ASOs to define the meaning of gestures is a relatively new approach, so gesture meanings have not yet been defined for our other closest living relative—the bonobo (or ‘bilia’, as the species is locally known) [29]. Our study is the first to investigate meaning in the natural gestural repertoire of wild bonobos.

Once the meanings of bonobo gestures are defined, we can examine the gestural overlap of bonobos and chimpanzees. All species of nonhuman great ape share the majority of their gestural repertoire in terms of the gestures’ physical forms. The overlap for chimpanzees and bonobos is 88%–96% [30]; for chimpanzees and gorillas, 60% [31]; and for chimpanzees and orangutans, 80% [31]. But simply using the same actions does not mean that chimpanzees and bonobos share a communication system (that is, that a chimpanzee and bonobo would in principle be able to understand one another). Only if bonobo and chimpanzee gestures share the same meanings can they be said to share the same system of communication.

Deciding that issue is not straightforward. Ape gestural repertoires are large, with over 70 distinct gestures in the chimpanzee and bonobo catalogues. In captivity, large quantities of gestural data can be collected very quickly, but the majority of it occurs during play [32,33]. Data from the wild are needed to examine the full breadth of meaning expressed in nonplayful ape communication. Previous studies have used traditional analyses of variance or goodness of fit tests, demonstrating that different individuals within a chimpanzee group use the same gesture to achieve the same outcome [28]. However, despite data sets containing thousands of gesture cases, large repertoires and the regular use of only a subset of these gestures [34] limits the number of gesture types that can be examined in this way. Furthermore, those tests are not suited to data sets in which many of the possible outcomes never occur for each signal type, as we would expect in a system of communication in which specific signals are employed for specific outcomes. We have therefore adapted methods from numerical ecology to compare the similarity between the meanings of bonobo and chimpanzee gestures. In doing so, we offer the first analysis that examines whether the overlap in the physical form of bonobo and chimpanzee gestures extends to their meaning.

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

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.


What Makes You So Special? From The Big Bang To You

How did you come to be here, now? This books takes you from the Big Bang to the evolution of modern humans and the history of human cultures, showing that science is an adventure of discovery and a source of limitless wonder, giving us richer and more rewarding appreciation of the phenomenal privilege of merely being alive and able to begin to understand it all.

Available in Hardcover, Paperback or ebook for Kindle


Ten Reasons To Lose Faith: And Why You Are Better Off Without It

This book explains why faith is a fallacy and serves no useful purpose other than providing an excuse for pretending to know things that are unknown. It also explains how losing faith liberates former sufferers from fear, delusion and the control of others, freeing them to see the world in a different light, to recognise the injustices that religions cause and to accept people for who they are, not which group they happened to be born in. A society based on atheist, Humanist principles would be a less divided, more inclusive, more peaceful society and one more appreciative of the one opportunity that life gives us to enjoy and wonder at the world we live in.

Available in Hardcover, Paperback or ebook for Kindle


Thank you for sharing!

submit to reddit

No comments :

Post a Comment

Obscene, threatening or obnoxious messages, preaching, abuse and spam will be removed, as will anything by known Internet trolls and stalkers, by known sock-puppet accounts and anything not connected with the post,

A claim made without evidence can be dismissed without evidence. Remember: your opinion is not an established fact unless corroborated.

Web Analytics