Time-space-displaced responses in the orangutan vocal system

Chimpanzees utilize video as reference in a spatiotemporally distant search for hidden food

Referring to things that are displaced in space and time is one of the defining features of human language. In order to better understand the evolution of human language, it is therefore important to explore how widely the ability for displaced reference is shared in animal kingdom. In this study, we explored whether chimpanzees are capable of uzsing video as a displaced reference in a spatiotemporally distant task. We used video to inform chimpanzees about an otherwise unobservable food-hiding. We examined the extent to which chimpanzees would make use of video as a source of information to guide their retrieval of hidden food from a target container. We found that when the event of observing food-hiding and the event of retrieving hidden food were close in space and time within the same room, all chimpanzees solved the task. Some chimpanzees continued to solve the task even when the two events were distant and separated spatiotemporally, in which they had to move to the next room between the events. Our findings suggested that chimpanzees can uzse video as a displaced reference to retrieve hidden food later when solving real-life problems.

Open plains are not a level playing field for hominid consonant-like versus vowel-like calls

Africa's paleo-climate change represents an "ecological black-box" along the evolutionary timeline of spoken language; a vocal hominid went in and, millions of years later, out came a verbal human. It is unknown whether or how a shift from forested, dense habitats towards drier, open ones affected hominid vocal communication, potentially setting stage for speech evolution. To recreate how arboreal proto-vowels and proto-consonants would have interacted with a new ecology at ground level, we assessed how a series of orangutan voiceless consonant-like and voiced vowel-like calls travelled across the savannah. Vowel-like calls performed poorly in comparison to their counterparts. Only consonant-like calls afforded effective perceptibility beyond 100 m distance without requiring repetition, as is characteristic of loud calling behaviour in nonhuman primates, typically composed by vowel-like calls. Results show that proto-consonants in human ancestors may have enhanced reliability of distance vocal communication across a canopy-to-ground ecotone. The ecological settings and soundscapes experienced by human ancestors may have had a more profound impact on the emergence and shape of spoken language than previously recognized.

What we know and don't know about great ape cultural communication in the wild

Following the first descriptions of culture in primates, widespread agreement has developed that the term can be applied to nonhumans as group-specific, socially learned behaviors. While behaviors such as those involving extractive tool use have been researched intensively, we propose that behaviors that are more subtle, less likely to be ecologically constrained, and more likely to be socially shaped, such as cultural forms of communication, provide compelling evidence of culture in nonhuman primates. Additionally, cultural forms of communication can provide novel insights into animal cognition such as the capacity for conformity, conventionalized meanings, arbitrariness in signal forms, and even symbolism. In this paper we focus on evidence from studies conducted on wild great apes. First, we provide a thorough review of what exactly we do know, and by extension don't know, about great ape cultural communication. We argue that detailed research on both vocal and gestural communication in wild great apes shows a more nuanced and variable repertoire than once assumed, with increasing support for group-specific variation. Second, we discuss the relevance of great ape cultural communication and its potential for illustrating evolutionary continuity for human-like cultural attributes, namely cumulative culture and symbolism. In sum, a concerted effort to examine cultural forms of communication in great apes could reveal novel evidence for cultural capacities that have thus far been heavily debated in the literature and can simultaneously contribute to an improved understanding of the complex minds of our closest living relatives.

Animal thought exceeds language-of-thought

Quilty-Dunn et al. claim that all complex infant and animal reasoning implicate language-of-thought hypothesis (LOTH)-like structures. We agree with the authors that the mental life of animals can be explained in representationalist terms, but we disagree with their idea that the complexity of mental representations is best explained by appealing to abstract concepts, and instead, we explain that it doesn't need to.

Wild orangutans can simultaneously use two independent vocal sound sources similarly to songbirds and human beatboxers

Speech is among the most complex motoric tasks humans ever perform. Songbirds match this achievement during song production through the precise and simultaneous motor control of two sound sources in the syrinx. Integrated and intricate motor control has made songbirds comparative models par excellence for the evolution of speech, however, phylogenetic distance with humans prevents an improved understanding of the precursors that, within the human lineage, drove the emergence of advanced vocal motor control and speech. Here, we report two types of biphonic call combination in wild orangutans that articulatorily resemble human beatboxing and that result from the simultaneous exercise of two vocal sound sources: one unvoiced source achieved through articulatory maneuvering of the lips, tongue, and jaw as typically used for consonant-like call production, plus one voiced source achieved through laryngeal action and voice activation as typically used for vowel-like call production. Orangutan biphonic call combinations showcase unappreciated levels of, and distinct neuromotor channels for, vocal motor control in a wild great ape, providing a direct vocal motor analogy with birdsong based on the precise and simultaneous co-control of two sound sources. Findings suggest that speech and human vocal fluency likely built upon complex call combination, coordination and coarticulation capacities that involved vowel-like and consonant-like calls in an ancestral hominid.

Life of p: A consonant older than speech

Which sounds composed the first spoken languages? Archetypal sounds are not phylogenetically or archeologically recoverable, but comparative linguistics and primatology provide an alternative approach. Labial articulations are the most common speech sound, being virtually universal across the world's languages. Of all labials, the plosive 'p' sound, as in 'Pablo Picasso', transcribed /p/, is the most predominant voiceless sound globally and one of the first sounds to emerge in human infant canonical babbling. Global omnipresence and ontogenetic precocity imply that /p/-like sounds could predate the first major linguistic diversification event(s) in humans. Indeed, great ape vocal data support this view, namely, the only cultural sound shared across all great ape genera is articulatorily homologous to a rolling or trilled /p/, the 'raspberry'. /p/-like labial sounds represent an 'articulatory attractor' among living hominids and are likely among the oldest phonological features to have ever emerged in linguistic systems.

Flexible signalling strategies by victims mediate post-conflict interactions in bonobos

Compared to other animals, humans supposedly excel at voluntarily controlling and strategically displaying emotional signals. Yet, new data shows that nonhuman great apes' emotion expressions may also be subject to voluntary control. A key context to further explore this is during post-conflict (PC) periods, where signalling by distressed victims may influence bystander responses, including the offering of consolation. To address this, our study investigates the signalling behaviour of sanctuary-living bonobo victims following aggression and its relation to audience composition and PC interactions. Results show that the production of paedomorphic signals by victims (regardless of age) increased their chances of receiving consolation. In adults, the production of such signals additionally reduced the risk of renewed aggression from opponents. Signal production also increased with audience size, yet strategies differed by age: while immatures reduced signalling in proximity of close-social partners, adults did so especially after receiving consolation. These results suggest that bonobos can flexibly adjust their emotion signalling to influence the outcome of PC events, and that this tendency has a developmental trajectory. Overall, these findings highlight the potential role that flexible emotion communication played in the sociality of our last common ancestor with Pan. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Are ape gestures like words? Outstanding issues in detecting similarities and differences between human language and ape gesture

Opinion piece: ape gestures are made intentionally, inviting parallels with human language; but how similar are their gestures to words? Here we ask this in three ways, considering: flexibility and ambiguity, first- and second-order intentionality, and usage in interactive exchanges. Many gestures are used to achieve several, often very distinct, goals. Such apparent ambiguity in meaning is potentially disruptive for communication, but-as with human language-situational and interpersonal context may largely resolve the intended meaning. Our evidence for first-order intentional use of gesture is abundant, but how might we establish a case for the second-order intentional use critical to language? Finally, words are rarely used in tidy signal-response sequences but are exchanged in back-and-forth interaction. Do gestures share this property? In this paper, we examine these questions and set out ways in which they can be resolved, incorporating data from wild chimpanzees. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Sociality predicts orangutan vocal phenotype

In humans, individuals' social setting determines which and how language is acquired. Social seclusion experiments show that sociality also guides vocal development in songbirds and marmoset monkeys, but absence of similar great ape data has been interpreted as support to saltational notions for language origin, even if such laboratorial protocols are unethical with great apes. Here we characterize the repertoire entropy of orangutan individuals and show that in the wild, different degrees of sociality across populations are associated with different 'vocal personalities' in the form of distinct regimes of alarm call variants. In high-density populations, individuals are vocally more original and acoustically unpredictable but new call variants are short lived, whereas individuals in low-density populations are more conformative and acoustically consistent but also exhibit more complex call repertoires. Findings provide non-invasive evidence that sociality predicts vocal phenotype in a wild great ape. They prove false hypotheses that discredit great apes as having hardwired vocal development programmes and non-plastic vocal behaviour. Social settings mould vocal output in hominids besides humans.

Orangutan information broadcast via consonant-like and vowel-like calls breaches mathematical models of linguistic evolution

The origin of language is one of the most significant evolutionary milestones of life on Earth, but one of the most persevering scientific unknowns. Two decades ago, game theorists and mathematicians predicted that the first words and grammar emerged as a response to transmission errors and information loss in language's precursor system, however, empirical proof is lacking. Here, we assessed information loss in proto-consonants and proto-vowels in human pre-linguistic ancestors as proxied by orangutan consonant-like and vowel-like calls that compose syllable-like combinations. We played back and re-recorded calls at increasing distances across a structurally complex habitat (i.e. adverse to sound transmission). Consonant-like and vowel-like calls degraded acoustically over distance, but no information loss was detected regarding three distinct classes of information (viz. individual ID, context and population ID). Our results refute prevailing mathematical predictions and herald a turning point in language evolution theory and heuristics. Namely, explaining how the vocal–verbal continuum was crossed in the hominid family will benefit from future mathematical and computational models that, in order to enjoy empirical validity and superior explanatory power, will be informed by great ape behaviour and repertoire.

Experience-Specific Dimensions of Consciousness (Observable in Flexible and Spontaneous Action Planning Among Animals)

The multidimensional framework to the study of consciousness, which comes as an alternative to a single sliding scale model, offers a set of experimental paradigms for investigating dimensions of animal consciousness, acknowledging the compelling urge for a novel approach. One of these dimensions investigates whether non-human animals can flexibly and spontaneously plan for a future event, and for future desires, without relying on reinforcement learning. This is a critical question since different intentional structures for action in non-human animals are described as served by different neural mechanisms underpinning the capacity to represent temporal properties. And a lack of appreciation of this variety of intentional structures and neural correlates has led many experts to doubt that animals have access to temporal reasoning and to not recognize temporality as a mark of consciousness, and as a psychological resource for their life. With respect to this, there is a significant body of ethological evidence for planning abilities in non-human animals, too often overlooked, and that instead should be taken into serious account. This could contribute to assigning consciousness profiles, across and within species, that should be tailored according to an implemented and expansive use of the multidimensional framework. This cannot be fully operational in the absence of an additional tag to its dimensions of variations: the experience-specificity of consciousness.

Chimpanzee lip-smacks confirm primate continuity for speech-rhythm evolution

Speech is a human hallmark, but its evolutionary origins continue to defy scientific explanation. Recently, the open-close mouth rhythm of 2-7 Hz (cycles/second) characteristic of all spoken languages has been identified in the orofacial signals of several nonhuman primate genera, including orangutans, but evidence from any of the African apes remained missing. Evolutionary continuity for the emergence of speech is, thus, still inconclusive. To address this empirical gap, we investigated the rhythm of chimpanzee lip-smacks across four populations (two captive and two wild). We found that lip-smacks exhibit a speech-like rhythm at approximately 4 Hz, closing a gap in the evidence for the evolution of speech-rhythm within the primate order. We observed sizeable rhythmic variation within and between chimpanzee populations, with differences of over 2 Hz at each level. This variation did not result, however, in systematic group differences within our sample. To further explore the phylogenetic and evolutionary perspective on this variability, inter-individual and inter-population analyses will be necessary across primate species producing mouth signals at speech-like rhythm. Our findings support the hypothesis that speech recruited ancient primate rhythmic signals and suggest that multi-site studies may still reveal new windows of understanding about these signals' use and production along the evolutionary timeline of speech.

Understanding Language Evolution: Beyond Pan-Centrism

Language does not fossilize but this does not mean that the language's evolutionary timeline is lost forever. Great apes provide a window back in time on our last prelinguistic ancestor's communication and cognition. Phylogeny and cladistics implicitly conjure Pan (chimpanzees, bonobos) as a superior (often the only) model for language evolution compared with earlier diverging lineages, Gorilla and Pongo (orangutans). Here, in reviewing the literature, it is shown that Pan do not surpass other great apes along genetic, cognitive, ecologic, or vocal traits that are putatively paramount for language onset and evolution. Instead, revived herein is the idea that only by abandoning single-species models and learning about the variation among great apes, there might be a chance to retrieve lost fragments of the evolutionary timeline of language.

Temporal representation and reasoning in non-human animals

Hoerl & McCormack argue that comparative and developmental psychology teaches us that "neither animals nor infants can think and reason about time." We argue that the authors neglect to take into account pivotal evidence from ethology that suggests that non-human animals do possess a capacity to represent and reason about time, namely, work done on Sumatran orangutans' long travel calls.

Orangutans show active voicing through a membranophone

Active voicing - voluntary control over vocal fold oscillation - is essential for speech. Nonhuman great apes can learn new consonant- and vowel-like calls, but active voicing by our closest relatives has historically been the hardest evidence to concede to. To resolve this controversy, a diagnostic test for active voicing is reached here through the use of a membranophone: a musical instrument where a player's voice flares a membrane's vibration through oscillating air pressure. We gave the opportunity to use a membranophone to six orangutans (with no effective training), three of whom produced a priori novel (species-atypical) individual-specific vocalizations. After 11 and 34 min, two subjects were successful by producing their novel vocalizations into the instrument, hence, confirming active voicing. Beyond expectation, however, within <1 hour, both subjects found opposite strategies to significantly alter their voice duration and frequency to better activate the membranophone, further demonstrating plastic voice control as a result of experience with the instrument. Results highlight how individual differences in vocal proficiency between great apes may affect performance in experimental tests. Failing to adjust a test's difficulty level to individuals' vocal skill may lead to false negatives, which may have largely been the case in past studies now used as "textbook fact" for great ape "missing" vocal capacities. Results qualitatively differ from small changes that can be caused in innate monkey calls by intensive months-long conditional training. Our findings verify that active voicing beyond the typical range of the species' repertoire, which in our species underpins the acquisition of new voiced speech sounds, is not uniquely human among great apes.

The antiquity and evolution of the neural bases of rhythmic activity

The evolution of the anatomy and neural circuits that regulate the rhythm of speech can be traced back to the Devonian age, 400 million years ago. Epigenetic processes 100 million years later modified these circuits. Natural selection on similar genetic processes occurred during the evolution of archaic hominins and humans. The lungs and larynx-anatomy that produces the rhythmic fundamental frequency patterns of speech-have a deep evolutionary history. Neural circuits linking the cortex, basal ganglia, and other subcortical structures plan, sequence, and execute motor as well as cognitive acts. These neural circuits generate the rhythm of speech, singing, and chanting. The human form of the transcription factor FOXP2 increased synaptic connectivity and plasticity in basal ganglia circuits, enhancing motor control and cognitive and linguistic capabilities in humans as well as Neanderthals. The archeological record also suggests that Neanderthals passed spoken language. Homologous circuits existed in amphibians. In songbirds, the avian form of FOXP2 acted on similar neural circuits allowing birds to learn and produce new songs. Current studies point to natural selection on genetic events enhancing these and other neural circuits to yield fully human rhythmic speech, and motor, cognitive, and linguistic capabilities, rather than the saltation proposed by Noam Chomsky.