The Question of Capacity: Why Enculturated and Trained Animals have much to Tell Us about the Evolution of Language

Great ape interaction: Ladyginian but not Gricean

Nonhuman great apes inform one another in ways that can seem very humanlike. Especially in the gestural domain, their behavior exhibits many similarities with human communication, meeting widely used empirical criteria for intentionality. At the same time, there remain some manifest differences, most obviously the enormous range and scope of human expression. How to account for these similarities and differences in a unified way remains a major challenge. Here, we make a key distinction between the expression of intentions (Ladyginian) and the expression of specifically informative intentions (Gricean), and we situate this distinction within a "special case of" framework for classifying different modes of attention manipulation. We hence describe how the attested tendencies of great ape interaction-for instance, to be dyadic rather than triadic, to be about the here-and-now rather than "displaced," and to have a high degree of perceptual resemblance between form and meaning-are products of its Ladyginian but not Gricean character. We also reinterpret video footage of great ape gesture as Ladyginian but not Gricean, and we distinguish several varieties of meaning that are continuous with one another. We conclude that the evolutionary origins of linguistic meaning lie not in gradual changes in communication systems, but rather in gradual changes in social cognition, and specifically in what modes of attention manipulation are enabled by a species' cognitive phenotype: first Ladyginian and in turn Gricean. The second of these shifts rendered humans, and only humans, "language ready."

Joyful by nature: approaches to investigate the evolution and function of joy in non-human animals

The nature and evolution of positive emotion is a major question remaining unanswered in science and philosophy. The study of feelings and emotions in humans and animals is dominated by discussion of affective states that have negative valence. Given the clinical and social significance of negative affect, such as depression, it is unsurprising that these emotions have received more attention from scientists. Compared to negative emotions, such as fear that leads to fleeing or avoidance, positive emotions are less likely to result in specific, identifiable, behaviours being expressed by an animal. This makes it particularly challenging to quantify and study positive affect. However, bursts of intense positive emotion (joy) are more likely to be accompanied by externally visible markers, like vocalisations or movement patterns, which make it more amenable to scientific study and more resilient to concerns about anthropomorphism. We define joy as intense, brief, and event-driven (i.e. a response to something), which permits investigation into how animals react to a variety of situations that would provoke joy in humans. This means that behavioural correlates of joy are measurable, either through newly discovered 'laughter' vocalisations, increases in play behaviour, or reactions to cognitive bias tests that can be used across species. There are a range of potential situations that cause joy in humans that have not been studied in other animals, such as whether animals feel joy on sunny days, when they accomplish a difficult feat, or when they are reunited with a familiar companion after a prolonged absence. Observations of species-specific calls and play behaviour can be combined with biometric markers and reactions to ambiguous stimuli in order to enable comparisons of affect between phylogenetically distant taxonomic groups. Identifying positive affect is also important for animal welfare because knowledge of positive emotional states would allow us to monitor animal well-being better. Additionally, measuring if phylogenetically and ecologically distant animals play more, laugh more, or act more optimistically after certain kinds of experiences will also provide insight into the mechanisms underlying the evolution of joy and other positive emotions, and potentially even into the evolution of consciousness.

Is Conceptual Diversity an Advantage for Scientific Inquiry? A Case Study on the Concept of 'Gesture' in Comparative Psychology

Growing scientific fields often involve multidisciplinary investigations in which the same concepts may have different meanings. Here, we examine the case of 'gesture' in comparative research to depict how conceptual diversity hidden by the label 'gesture' can lead to consistently divergent interpretations in humans and nonhuman primates. We show that definitions of 'gesture' drastically differ regarding the forms of a gesture and the cognitive processes inferred from it, and that these differences emerge from implicit assumptions which have pervasive consequences on the interpretations claimed by researchers. We then demonstrate that implicit assumptions about scientific concepts can be made explicit using a finite set of operational criteria. We argue that developing theoretical definitions systematically associated with operational conceptual boundaries would allow to tackle both the challenges of maintaining high internal coherence within studies and of improving comparability and replicability of scientific results. We thus offer an easy-to-implement conceptual tool that should help ground valid comparisons between studies and serve scientific inquiry.