In their article, Goldin-Meadow & Brentari (G-M&B) assert that researchers must differentiate between sign/speech and gesture. We propose that this distinction may be useful if situated within a two-systems approach to theory of mind (ToM) and discuss how drawing upon perspectives from bilingualism and acting can help us understand the role of gesture in spoken/sign language.

Research into nonhuman primates’ gestures is often limited by the lack of clear criteria to define a gesture and by studying gestures separately from other communicative means. Despite the fundamental differences between the gestural communication of humans and other primates, I argue that sign language research might benefit from the lessons learned from these drawbacks and the current developments in primate communication research.

State-of-the-art methods of analysis of video data now include motion capture and optical flow from video recordings. These techniques allow for biological differentiation between visual communication and noncommunicative motion, enabling further inquiry into neural bases of communication. The requirements for additional noninvasive methods of data collection and automatic analysis of natural gesture and sign language are discussed.

The extent to which early motor patterns represent antecedents to later communicative functions, and the emergence of gesture and/or sign as potential communicative acts in neurodevelopmental disorders (NDDs), are research questions that have received recent attention. It is important to keep in mind that different NDDs have different neurological underpinnings, with correspondingly different implications for their conceptualization, detection, and treatment.

Understanding the relationship between gesture, sign, and speech offers a valuable tool for investigating how language emerges from a nonlinguistic state. We propose that the focus on linguistic status is problematic, and a shift to focus on the processes that shape these systems serves to explain the relationship between them and contributes to the central question of how language evolves.

Goldin-Meadow & Brentari (G-M&B) rely on a formalist approach to language, leading them to seek objective criteria by which to distinguish language and gesture. This results in the assumption that gradient aspects of signs are gesture. Usage-based theories challenge this view, maintaining that all linguistic units exhibit gradience. Instead, we propose that the distinction between language and gesture is a categorization problem.

We applaud Goldin-Meadow & Brentari's (G-M&B's) significant efforts to consider the linkages between sign, gesture, and language. Research on deaf children and sign language acquisition can broaden the G-M&B approach by considering how language readiness is also a social phenomenon and that distinctions between imagistic and categorical formats rely on language practices and contexts.

We observe a tension in the target article as it stresses an integrated gesture-speech system that can nevertheless consist of contradictory representational states, which are reflected by mismatches in gesture and speech or sign. Beyond problems of coherence, this prevents furthering our understanding of gesture-related learning. As a possible antidote, we invite a more dynamically embodied perspective to the stage.

Vocal laughter fills conversations between speakers with normal hearing and between deaf users of American Sign Language, but laughter rarely intrudes on the phrase structure of spoken or signed conversation, being akin to punctuation in written text. This punctuation effect indicates that language, whether vocal or signed, is dominant over laughter, and that speech and manual signing involve similar mechanisms.

Whether in sign or speech, language is more integrative than the target article suggests. A more integrative view embraces not only sign/speech and co-sign/speech gesture, but also indicative gestures irrespective of modality, and locations along with movements in the signed modality, as suggested by both linguistic acquisition and pathologies. An extended integrative view also proves advantageous in terms of conceptual coherence.

Semantic work on sign language iconicity suggests, as do Goldin-Meadow & Brentari (G-M&B) in their target article, that “sign should be compared with speech-plus-gesture, not speech alone” (sect. 7.1). One key question is whether speech-plus-gesture and sign-with-iconicity really display the same expressive resources. This need not be the case, because gestural enrichments are typically not at-issue, whereas iconic enrichments in sign language can often be at-issue. Future research should thus focus on the “projection” properties of different sorts of iconic enrichment in both modalities.

Goldin-Meadow & Brentari (G-M&B) argue that, for sign language users, gesture – in contrast to linguistic sign – is iconic, highly variable, and similar to spoken language co-speech gesture. We discuss two examples (telicity and absolute gradable adjectives) that challenge the use of these criteria for distinguishing sign from gesture.

The claim that gesture is primarily imagistic, analog, and holistic is challenged by the presence of abstract diagrammatic gestures, here points and lines, that represent point-like and line-like concepts and are integrated into larger constituents.

The commentaries have led us to entertain expansions of our paradigm to include new theoretical questions, new criteria for what counts as a gesture, and new data and populations to study. The expansions further reinforce the approach we took in the target article: namely, that linguistic and gestural components are two distinct yet integral sides of communication, which need to be studied together.

Worldwide there are substantial differences within and between countries in aggression and violence. Although there are various exceptions, a general rule is that aggression and violence increase as one moves closer to the equator, which suggests the important role of climate differences. While this pattern is robust, theoretical explanations for these large differences in aggression and violence within countries and around the world are lacking. Most extant explanations focus on the influence of average temperature as a factor that triggers aggression (The General Aggression Model), or the notion that warm temperature allows for more social interaction situations (Routine Activity Theory) in which aggression is likely to unfold. We propose a new model, CLimate, Aggression, and Self-control in Humans (CLASH), that helps us to understand differences within and between countries in aggression and violence in terms of differences in climate. Lower temperatures, and especially larger degrees of seasonal variation in climate, call for individuals and groups to adopt a slower life history strategy, a greater focus on the future (vs. present), and a stronger focus on self-control. The CLASH model further outlines that slow life strategy, future orientation, and strong self-control are important determinants of inhibiting aggression and violence. We also discuss how CLASH differs from other recently developed models that emphasize climate differences for understanding conflict. We conclude by discussing the theoretical and societal importance of climate in shaping individual and societal differences in aggression and violence.

Life history theory serves as the foundation for the CLimate, Aggression, and Self-control in Humans (CLASH) model of aggression. However, this model embodies several misunderstandings of life history constructs and principles. The CLASH model does not recognize that environmental harshness and environmental unpredictability are unique theoretical constructs, rendering predictions and implications from the model suspect.

Contrary to one assumption of CLASH, we suggest that colder rather than warm climates are the harsh, unpredictable ones, thus requiring greater self-control. We propose shifting emphasis from predictability to utility of prediction. Northern climates may be less predictable than tropical ones, making predictions and planning far more important, insofar as they can prevent fatalities and promote other pragmatic benefits.

The CLASH model is not convincing for two reasons. First, it ignores prior research proposing very similar ideas in a more compelling fashion. Second, it dismisses the role of genetic factors in shaping criminal propensities across population groups, opting for a facultative view of life history evolution that does not seem to square with current evidence.

Planning for the future may encourage apparently “impulsive” behaviour when the future is anticipated to be bleak. Thus, a seeming failure of self-control in reactive violence could be caused not by a disinclination to plan ahead, but by virtue of this ability. Furthermore, we point to empirical and theoretical shortcomings in the authors' case, such as a failure to distinguish proximate and ultimate explanations.

We argue that the CLASH model makes a number of questionable assumptions about the harshness and unpredictability of low-latitude environments, calling into question the life history strategy approach used, and that it is inconsistent with more nuanced global patterns of violence. We suggest an alternative account for less violence at high latitudes, based on a greater need for cooperation.