Human expression is open-ended, versatile, and diverse, ranging from ordinary language use to painting, from exaggerated displays of affection to micro-movements that aid coordination. Here we present and defend the claim that this expressive diversity is united by an interrelated suite of cognitive capacities, the evolved functions of which are the expression and recognition of informative intentions. We describe how evolutionary dynamics normally leash communication to narrow domains of statistical mutual benefit, and how expression is unleashed in humans. The relevant cognitive capacities are cognitive adaptations to living in a partner choice social ecology; and they are, correspondingly, part of the ordinarily developing human cognitive phenotype, emerging early and reliably in ontogeny. In other words, we identify distinctive features of our species' social ecology to explain how and why humans, and only humans, evolved the cognitive capacities that, in turn, lead to massive diversity and open-endedness in means and modes of expression. Language use is but one of these modes of expression, albeit one of manifestly high importance. We make cross-species comparisons, describe how the relevant cognitive capacities can evolve in a gradual manner, and survey how unleashed expression facilitates not only language use, but also novel behaviour in many other domains too, focusing on the examples of joint action, teaching, punishment, and art, all of which are ubiquitous in human societies but relatively rare in other species. Much of this diversity derives from graded aspects of human expression, which can be used to satisfy informative intentions in creative and new ways. We aim to help reorient cognitive pragmatics, as a phenomenon that is not a supplement to linguistic communication and on the periphery of language science, but rather the foundation of the many of the most distinctive features of human behaviour, society, and culture.

Before claiming major differences between the communication systems of humans and other species, it is necessary to (1) overcome methodological limitations in the comparative study of communicative intentions; (2) account for mechanisms other than epistemic vigilance that may also sustain complex forms of communication; and (3) better differentiate between motivational and cognitive factors potentially affecting the emergence of open-ended communication.

Unleashed expressions for cooperation are mainly based on the expected perceptual effects of behaviours and not the behaviours themselves. From an evolutionary viewpoint, this goal-directed mechanism allows for a comprehensive story for the theory proposed by Heintz & Scott-Phillips. Over the past 2 million years, this situated mechanism has been reused for tool use and the language development for hominids.

Heintz & Scott-Phillips's account of human expression leaves a number of central issues unclear – not least, whether the lack of expression in nonhuman species is attributable to their lack of the relevant metarepresentational abilities, an absence of trust, or a consequence of other factors. In place of their view, we propose a gradualistic account of the origins of human expression.

Heintz & Scott-Phillips propose that the partner choice ecology of our ancestors required Gricean cognitive pragmatics for reputation management, which caused a tendency toward showing and expecting prosociality that subsequently scaffolded language evolution. Here, we suggest a cognitively leaner explanation that is more consistent with comparative data and posits that prosociality and eventually language evolved along with cooperative breeding.

While the metarepresentational structure of ostensive communication may explain the unleashing of human expression, it neither explains the open-endedness of the thoughts expressed/communicated, nor how the multiply embedded nature of the metarepresentational structure invoked arose. These both require the recursivity of human language, a capacity which must be distinguished from external (public) languages and their use in communication.

We agree with Heintz & Scott-Phillips that pragmatics does not supplement, but is prior to and underpins, language. Indeed, human non-linguistic communication is astonishingly rich, flexible, and subtle, as we illustrate through the game of charades, where people improvise communicative signals when linguistic channels are blocked. The route from non-linguistic charade-like communication to combinatorial language involves (1) local processes of conventionalization and grammaticalization and (2) spontaneous order arising from mutual constraints between different communicative signals.

Homesign is a visual–gestural form of communication that emerges between deaf individuals and their hearing interlocutors in the absence of a conventional sign language. I argue here that homesign conversations form a perfect testcase to study the extent to which pragmatic competence is foundational rather than derived from our linguistic abilities.

I propose that the evolution of teaching has been central in extending manipulative intentions. Demonstrating may be the evolutionarily first form of expression that is productive, ostensive, and involves informative intention. Demonstration also involves theory of mind. Then pantomime goes a step further and involves a communicative intention. Pantomime can thereby function as displaced communication used for more complex expressions.

We use screams to explore ideas presented in the target article. Evolving first in animals as a response to predation, screams reveal more complex social use in nonhuman primates and, in humans, uniquely, are associated with a much greater variety of emotional contexts including fear, anger, surprise, and happiness. This expansion, and the potential for manipulation, promotes listener social vigilance.

We challenge the proposal that partner-choice ecology explains the evolutionary emergence of ostensive communication in humans. The good fit between these domains might be because of the opposite relation (ostensive communication promotes the evolution of cooperation) or because of the dependence of both these human-specific traits on a more ancient contributor to human cognitive evolution: the use of technology.

As Heintz & Scott-Phillips rightly argued, pragmatics has been too commonly considered as a supplement to linguistic communication. Their aim to reorient the study of cognitive pragmatics as the foundation of many distinctive features of human behavior finds echo in the neuropsychological literature on tool use, in which the investigation of semantic dementia challenges the classical semantics versus pragmatics dissociation.

The target article highlights the sources of open-endedness of human communication. However, the authors' perspective does not account for the structure of particular communication systems. To this end, we extend the authors' perspective, in the spirit of evolutionary extended synthesis, with a detailed account of the sources of constraints imposed upon expression in the course of child development.

Heintz & Scott-Phillips's hypothesis that the topic range and type diversity of human expressive communication gains support from consilience with prior accounts of market exchange as fundamental to unique human niche construction, and of mindshaping as much more important than mindreading. The productivity of the idea is illustrated by the light it might shed on why elephants seem to engage in continuous social communication for little evident purpose.

This commentary presents two illustrations, from the world of poker, of the continuity between linguistic and non-linguistic communication and expression, in support of Heintz & Scott-Phillips's account of the evolution of human expression and communication. I also come across the presumption of relevance in the context of a poker table.

The problem of generating generally capable agents is an important frontier in artificial intelligence (AI) research. Such agents may demonstrate open-ended, versatile, and diverse modes of expression, similar to humans. We interpret the work of Heintz & Scott-Phillips as a minimal sufficient set of socio-cognitive biases for the emergence of generally expressive AI, separate yet complementary to existing algorithms.

Heintz & Scott-Phillips provide a useful synthesis for constructing a bridge between work by both cognitive scientists and evolutionary biologists studying the diversity of human communication. Here, we aim to strengthen their bridge from the side of evolutionary biology, to argue that we can best understand ostensive communication as a scaffold for more complex forms of intentional expressions.

We applaud Heintz & Scott-Phillips's guiding metaphor of “unleashing leashed expression,” and we value the unified explanation for the emergence of not only language, but also other forms of unleashed expression, such as multimodal communication. We are more critical of the authors' discussion of the selection pressures acting towards unleashed expression, which are proposed to hinge on partner choice ecology.

The authors present an ambitious attempt to outline the gradual evolution of the cognitive foundations of ostensive communication. We focus on three problematic aspects of the distinction between expression and communication: ambiguity in the distinction's central principle of “complementary mechanisms,” inconsistencies in the application of the distinction across taxa, and the dismissal of mentalizing in nonhuman primates.

One of our main goals with “Expression unleashed” was to highlight the distinctive, ostensive nature of human communication, and the many roles that ostension can play in human behavior and society. The commentaries we received forced us to be more precise about several aspects of this thesis. At the same time, no commentary challenged the central idea that the manifest diversity of human expression is underpinned by a common cognitive unity. Our reply is organized around six issues: (1) languages and their cultural evolution; (2) the pervasiveness of expression in human behavior; (3) artificial intelligence and ostensive communication; (4) communication in other animals; (5) the ecology and evolution of ostensive communication; and (6) biolinguistics and pragmatics.