Maestripieri et al. provide an important service in highlighting prosocial biases toward attractive people from a cross-disciplinary perspective. Here I comment on the conceptual and critical side of their review of evolutionary psychology studies. I propose that further work should be focused on understanding the role of signaling in prosocial behavior.

Maestripieri et al. pit evolutionary psychology against social psychological and economic perspectives in a winner-take-all empirical battle. In doing so, they risk positioning evolutionary psychology as an antagonistic subdisciplinary enterprise. We worry that such a framing may exacerbate tensions between “competing” scientific perspectives and limit evolutionary psychology's potential to serve as a unifying core theory.

According to cognitive averaging theory, preferences for attractive faces result from their similarity to facial prototypes, the categorical central tendencies of a population of faces. Prototypical faces are processed more fluently, resulting in increased positive affect in the viewer.

We adopt Tinbergen's (1963) “four questions” approach to strengthen the criticism by Maestripieri et al. of the non-evolutionary accounts of favouritism toward attractive individuals, by showing which levels of explanation are lacking in these accounts. We also use this approach to propose ways in which the evolutionary account may be extended and strengthened.

In our response, we review and address the comments on our target article made in the 25 commentaries. First, we review and discuss the commentaries that recognized the value of our approach, accepted the main premises and conclusions of our target article, and suggested further avenues for research on attractiveness-related biases. We then respond to commentators who either misinterpreted some parts of our target article or made statements with which we disagree. These commentaries provided us with an opportunity to clarify some aspects of our target article, for example, the fact that we address both the functional significance of attractiveness-related biases and their underlying mechanisms. We provide a rebuttal to two commentaries, in which we are accused of poor scholarship. We conclude our response by addressing two commentaries that discussed the societal implications of the occurrence of attractiveness-related biases in the labor market by briefly discussing the relationship between scientific research and social policy.

How does sign language compare with gesture, on the one hand, and spoken language on the other? Sign was once viewed as nothing more than a system of pictorial gestures without linguistic structure. More recently, researchers have argued that sign is no different from spoken language, with all of the same linguistic structures. The pendulum is currently swinging back toward the view that sign is gestural, or at least has gestural components. The goal of this review is to elucidate the relationships among sign language, gesture, and spoken language. We do so by taking a close look not only at how sign has been studied over the past 50 years, but also at how the spontaneous gestures that accompany speech have been studied. We conclude that signers gesture just as speakers do. Both produce imagistic gestures along with more categorical signs or words. Because at present it is difficult to tell where sign stops and gesture begins, we suggest that sign should not be compared with speech alone but should be compared with speech-plus-gesture. Although it might be easier (and, in some cases, preferable) to blur the distinction between sign and gesture, we argue that distinguishing between sign (or speech) and gesture is essential to predict certain types of learning and allows us to understand the conditions under which gesture takes on properties of sign, and speech takes on properties of gesture. We end by calling for new technology that may help us better calibrate the borders between sign and gesture.

Empirical evidence suggests a broad impact of communication mode on cognition at large, beyond language processing. Using a sign language since infancy might shape the representation of words and other linguistic stimuli – for example, incorporating in it the movements and signs used to express them. Once integrated into linguistic representations, this visuo-motor content can affect deaf signers’ linguistic and cognitive processing.

Goldin-Meadow & Brentari (G-M&B) outline several criteria for delineating the boundaries between (discrete) signs and (continuous) gestures. However, the complex links between linguistics forms and their phonetic realizations defy such heuristics. A systematic exploration of language structure by mouth and by hand may help get us closer to answering the important challenge outlined in this target article.

In contrast with two widely held and contradictory views – that sign languages of deaf people are “just gestures,” or that sign languages are “just like spoken languages” – the view from sign linguistics and developmental research in cognition presented by Goldin-Meadow & Brentari (G-M&B) indicates a more complex picture. We propose that neuroscience research suggests that a similar approach needs to be taken and offer some examples from research on the brain bases of sign language perception.

Goldin-Meadow & Brentari (G-M&B) challenge the traditional separation between gestural and categorical language by modality, but they retain a binary distinction. However, multiple dimensions, particularly discreteness and combinatoriality, better carve up the range of linguistic and nonlinguistic human communication. Investigating transformation over time along these dimensions will reveal how the nature of language reflects human minds, rather than the world to which language refers.

Goldin-Meadow & Brentari (G-M&B) are implicitly going against the dominant paradigm in language research, namely, the “speech as written language” metaphor that portrays vocal sounds and bodily signs as means of delivering stable word meanings. We argue that Heinz Werner's classical research on the physiognomic properties of language supports and complements their view of sign and gesture as a unified system.

Bimodal bilingual language provides further evidence for the viewpoint advocated by Goldin-Meadow & Brentari (G-M&B) that sign, speech, and gesture work together to create a single proposition, illustrating the potential in each set of articulators for both imagistic and categorical components. Recent advances in formal semantics provide a framework for incorporating both imagistic and categorical components into a single compositional system.

The target article highlights the utility of new technology to study sign language and gesture. Research in special populations – specifically, individuals with autism spectrum disorder, ASD – may further illuminate sign/gesture similarities and differences and lead to a deeper understanding of the mechanisms of growth and change. Even verbally fluent speakers with ASD display distinctive qualities in sign and gesture.

Linguistic and psycholinguistic tests will be more useful than motion capture technology in calibrating the borders between sign and gesture. The analogy between motion capture (mocap) technology and the spectrograph is flawed because only vocal articulators are hidden. Although information about gradience and variability will be obtained, the technology provides less information about linguistic constraints and categories. Better models are needed to account for differences between co-speech and co-sign gesture (e.g., different degrees of optionality, existence of beat gestures).

We draw parallels between emoticons in textual communication and gesture in signed language with respect to the interdependence of codes by describing two contexts under which the behavior of emoticons in textual communication resembles that of gesture in speech. Generalizing from those findings, we propose that gesture is likely characterized by a nuanced interdependence with language whether signed, spoken or texted.

In our commentary, we raise concerns with the idea that location should be considered a gestural component of sign languages. We argue that psycholinguistic studies provide evidence for location as a “categorical” element of signs. More generally, we propose that the use of space in sign languages comes in many flavours and may be both categorical and imagistic.

In their target article, Goldin-Meadow & Brentari (G-M&B) discuss several observations suggesting that the use of space is imagistic and may not form part of the categorical properties of sign languages. Specifically, they point out that (1) the number of locations toward which agreeing verbs can be directed is not part of a discrete set, (2) event descriptions by users of different sign languages and hearing nonsigners exhibit marked similarities in the use of space, and (3) location as a phonological parameter is not categorically perceived by native signers. It should be noted that G-M&B acknowledge that categorical properties of location and movement may simply not have been captured yet because the proper investigative tools are not yet readily available.

The target article's emphasis on distinguishing sign from gesture may resolve one important objection to gesture-first theories of language evolution. However, this approach risks undervaluing the gradual progression from nonlanguage to language over hominin evolution, and in emerging sign systems today. I call for less emphasis on drawing boundaries and more emphasis on understanding the processes of change.

Gesture and sign form an integrated communication system, as do gesture and speech. Communicative acts in both systems combine categorical linguistic (words or signs) with imagistic (gestures) components. Additionally, both sign and speech can employ modifying components that convey iconic information tied to a linguistic base morpheme. An accurate analysis of communicative acts must take this third category into account.

The target article is consistent with seeing languages as semiotically heterogenous, using categorial, depictive, and analogic semiotic signs. “Gesture,” used in the target article, is shown to be vague and not useful. Kendon's view, criticised in the target, is restated. His proposal for comparative semiotic analyses of how visible bodily action is used in utterance production is reexplained.

Mismatch occurs when there is a discrepancy between produced gestures and co-occurring speech. In this commentary, I explore why research on mismatch might be called into question by changing views of what constitutes a gesture. I argue that the experimental procedure for producing mismatch, through its coding methods, is blind to the tight temporal coordination of gesture and affiliated talk.