Abstract In order to determine how to act in situations of potential agonistic conflict, individuals must assess multiple features of a prospective foe that contribute to the foe's resource-holding potential, or formidability. Across diverse species, physical size and strength are key determinants of formidability, and the same is often true for humans. However, in many species, formidability is also influenced by other factors, such as sex, coalitional size, and, in humans, access to weaponry. Decision-making involving assessments of multiple features is enhanced by the use of a single summary variable that encapsulates the contributions of these features. Given both a) the phylogenetic antiquity of the importance of size and strength as determinants of formidability, and b) redundant experiences during development that underscore the contributions of size and strength to formidability, we hypothesize that size and strength constitute the conceptual dimensions of a representation used to summarize multiple diverse determinants of a prospective foe's formidability. Here, we test this hypothesis in humans by examining the effects of a potential foe's access to weaponry on estimations of that individual's size and strength. We demonstrate that knowing that an individual possesses a gun or a large kitchen knife leads observers to conceptualize him as taller, and generally larger and more muscular, than individuals who possess only tools or similarly mundane objects. We also document that such patterns are not explicable in terms of any actual correlation between gun ownership and physical size, nor can they be explained in terms of cultural schemas or other background knowledge linking particular objects to individuals of particular size and strength. These findings pave the way for a fuller understanding of the evolution of the cognitive systems whereby humans – and likely many other social vertebrates – navigate social hierarchies.

Citation: Fessler DMT, Holbrook C, Snyder JK (2012) Weapons Make the Man (Larger): Formidability Is Represented as Size and Strength in Humans. PLoS ONE 7(4): e32751. https://doi.org/10.1371/journal.pone.0032751 Editor: Thomas Claudepierre, Faculty of Medicine University of Leipzig, Germany Received: July 21, 2011; Accepted: February 3, 2012; Published: April 11, 2012 Copyright: © 2012 Fessler et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the United States Air Force Office of Scientific Research under Award #FA9550-10-1-0511. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.

Introduction Violent conflict with conspecifics is a fundamental factor influencing fitness in many social species, humans included. We can therefore expect that such species will possess adaptations that facilitate decision-making in potentially agonistic interactions, as the individual must determine whether is it best to fight, flee, or appease the prospective foe. The likelihood that the actor will prevail without incurring unsustainable costs is the product of many features of the actor and the foe, as attributes such as the potential combatants' relative size, strength, sex, age, health, and number of allies all play a role; in humans, access to weapons adds to the complexity of this calculation. Importantly, when multiple factors must be weighed, decision-making can be expedited by compiling said factors into a single summary representation. Here, we explore the hypothesis that, in situations of potential agonistic conflict, such a variable takes the form of a representation wherein conceptualized size summarizes the assessed resource-holding potential, or formidability, of the foe relative to that of the actor. Across diverse species, physical size and, relatedly, strength, are elementary determinants of formidability, and this is also true of humans [1]. The deep antiquity of the contributions of size and strength to formidability raises the possibility that, as species evolve more complex behavioral repertoires, with corresponding increases in the range of factors influencing formidability, size and strength may come to be employed as the core dimensions of a cognitive representation that summarizes diverse determinants of relative formidability, such that the greater the foe's formidability relative to that of the actor, the larger and stronger the foe is conceptualized as being, even when the foe's formidability does not derive from actual physical size or strength. Note that, while the phylogenetic thesis holds that the postulated system whereby relative formidability is represented is innate, in species capable of complex behavior, understanding the diverse determinants of formidability will often be partially or wholly dependent on learning – innate systems can process, and even rely on, learned input (e.g., about the lethal affordances of evolutionarily novel objects). Bolstering the likelihood that the representational system described above exists in humans, the aforementioned phylogenetic thesis is directly paralleled by a mutually compatible ontogenetic thesis. A wide variety of cognitive representations draw on bodily experience, often without explicit recognition of the relationship between representations and their sources [2]. This suggests that representations of relative formidability may be the product of lived events. Even in peaceful societies, from infancy onward, children inevitably have the recurrent experience that conflicts are won by the bigger, stronger person. Hence, over the course of development, size and strength may come to play a central role in representations of relative formidability. If representations of a potential foe employ conceptualized size and strength as a medium for summarizing formidability, then augmenting the foe's formidability should cause the actor's conception of the foe's size and strength to increase. In humans, weapons are a primary determinant of victory in dyadic violence, and the modern handgun is prototypic in this regard. We therefore sought to test the above prediction by exploring whether knowing that someone possesses a gun increases estimations of that person's size and strength. Before investigating this question, however, we first had to rule out a potential confound. Sell et al. [3] documented that human physical strength is correlated with the propensity to engage in coercive behavior (see also [4]). Although the authors found no effect of height in this regard, other results [5] suggest that this too may occur (see also [6], but see also [7]). It is therefore possible that, because guns enhance coercive capacity, being more prone to employ coercion, larger people may be more likely to purchase guns. If so, then demonstrating that knowing that someone possesses a gun increases participants' estimations of the target individual's size could not be taken as evidence supporting our representational hypothesis, as participants might simply be reporting correlations that they have previously observed. We therefore conducted a preliminary study in which we surveyed gun owners to ascertain whether they are taller than those who do not own guns.

Ethics Statement All studies reported here were examined and approved by the University of California, Los Angeles Institutional Review Board. As per said approvals, in each study, participants were initially presented with a web-based written information sheet describing the study procedures, any potential risks or discomforts, the identity and contact information of the first author, and compensation, if any. Participants indicated their consent to participate by clicking on a web link so marked. As participation was anonymous in all studies, signed informed consent was not collected.

Pre-study Participants Three hundred and forty-four adults living in the United States were recruited in multiple U.S. cities via Craigslist.org to participate in an unpaid online study titled “Traits of Gun Owners—a 2-minute Study;" advertisements explicitly solicited participation by gun owners. Data were pre-screened for incomplete or frivolous responses (e.g., participants who stated that they had not answered truthfully, etc.), leaving a final sample of 338 adults (114 females) with a mean age of 39.28 years (SD=13.96). The ethnicity of the sample was 92.4% White, 1.5% Hispanic/Latin American, and 6.1% other or mixed ethnicities. 60.2% of female participants and 85.8% of male participants owned guns. Materials and Methods The survey consisted of demographic questions, including items addressing gun ownership and participant height. In this and subsequent studies, participants' self-reported ethnic identities were collected to provide a rough measure of the extent to which recruitment protocols reached multiple audiences in the U.S. Also included in the Pre-study were questions concerning individual differences (e.g., political orientation) designed to explore research questions orthogonal to the present enterprise. Results and Discussion Gun Ownership and Height. All tests of significance reported in this paper are two-tailed. ANOVAs of data segregated by gender revealed no significant difference between the heights of participants who owned firearms and those who did not (ps>.15). Having determined that it is unlikely that perceptions of gun possessors as larger could be driven by real-world correlations between gun ownership and physical size, we proceeded to a series of studies in which participants were asked to judge the size and strength of target men on the basis of photographs depicting only their hands holding either a handgun or various construction tools having a pistol-like handle. Because men are more likely to own guns than are women [8], and are larger and stronger than women, in order to ensure that any perceived differences in size were not due to spurious perceived differences in the sex of the models holding the objects, in this study we selected comparison objects likely to be as strongly associated with men as are guns. The construction trades primarily employ men, hence construction tools were selected as a comparison group.

Study 2 Participants One hundred and eight adults living in the United States were recruited via the website MechanicalTurk.com to participate in an online study titled “Your Impressions of Everyday Objects" in exchange for $0.50 compensation. Data were screened prior to analysis for incomplete or frivolous responses (e.g., rating the handgun as ‘not at all dangerous’). The final sample consisted of 102 adults (46 female), with a mean age of 34.71 years (SD=12.57). Materials and Methods In a within-subjects design, participants were asked to rate the harmfulness of the objects used in Study 1 if employed as weapons, using a 9-point Likert scale (1=Not at all harmful, 5=Moderately harmful, 9=Extremely lethal). The objects were presented using images taken from Study 1, with all objects held by the same hand model; in light of the effects of the small handsaw in Study 1, an additional photo, using the same model, depicted a large handsaw. The objects were presented in fixed order: caulking gun, small handsaw, power drill, large handsaw, .45 caliber handgun. The handgun image was included as an attention check, as the lethality of firearms is not in question. Participants were then asked demographic questions, thanked, and debriefed. Results and Discussion Effects of Sex. A MANOVA revealed significant effects of participant sex on ratings of the dangerousness of the objects; sex was therefore controlled for in subsequent analyses. Perceptions of Object Danger. A repeated measures ANCOVA controlling for sex revealed a significant main effect of object condition for ratings of harmfulness, F(4, 400)=223.67, p<.000001, η2 p =.69 (see Table 2 for means). As predicted, planned contrasts revealed that the handgun was rated as more dangerous than all of the other objects (ps<.000001). In contrast, the small handsaw was not rated as significantly more or less dangerous than the drill. Lastly, the large handsaw, though far below the handgun, was nevertheless rated as significantly more dangerous than the other objects (ps<.01) (of potential relevance here, the latest film in the Saw horror movie series was heavily advertised in the U.S., and enjoying commercial success, at the time that these studies were conducted). PPT PowerPoint slide

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larger image TIFF original image Download: Table 2. Ratings of Object Lethality ( Ratings of Object Lethality ( Study 2 ). https://doi.org/10.1371/journal.pone.0032751.t002 Having clarified that the effect of the small handsaw on perceived size found in Study 1 was likely due to the small size of the saw rather than its affordances as a weapon, we sought to replicate and extend the results of Study 1 without the confounding effects of the small handsaw. We therefore replaced the images depicting this item with images depicting a large handsaw, using the same hand models employed in Study 1. To ensure that the handgun effect found in Study 1 could not similarly be explained as owing to the comparatively large size of the hand relative to the object, we paralleled this change by replacing the images of the .45 caliber handgun with images of a (much larger) .357 magnum handgun, again using the same hand models (see Figure 2, Panel B). These changes maximized the likelihood that estimations of height or overall size would derive from perceived formidability, rather than from the relative scale effects of holding small objects. To explore our notion that representations of relative formidability employ a combination of conceptualized size and strength, we added a measure of perceptions of the muscularity of the target men. Lastly, to replicate the Pre-study, we also included questions about gun ownership and participant height.

Study 4 Participants One hundred participants (57 female) living in the United States were recruited via the website MechanicalTurk.com to participate in a study titled “Perceptions of Everyday Objects" in exchange for $0.35 compensation. The mean age of the sample was 37.09 years (SD=12.85). The ethnicity of the sample was 90.9% White, 1% Hispanic/Latin American, 3% Black/African American, and 5.1% other or mixed ethnicities. Materials and Methods The design and framing paralleled Study 2. Participants viewed images of adult male hands holding, respectively, a paintbrush, a squirt gun, and a kitchen knife, in that order (see Figure 2, Panel C). For each image, participants were asked to rate the harmfulness of each object, using a 9-point Likert scale (1=Not at all dangerous, 5=Moderately dangerous, 9=Extremely dangerous). For each image, participants were also asked which type of person would be most associated in their minds with the given object, with answers constrained to four fixed categories (adult women, adult men, young girls, or young boys). Participants were then asked demographic questions, thanked, and debriefed. Results and Discussion Perceptions of Object Danger. A preliminary MANOVA revealed no effects of participant sex on ratings of object danger. Repeated measures ANOVAs with a Greenhouse-Geisser correction revealed a significant main effect of object condition for ratings of harmfulness, F(2.63, 257.74)=671.85, p<.000001, η2 p =.87. As predicted, planned contrasts revealed that the kitchen knife (M=7.65, SD=1.49) was rated as more dangerous than the paintbrush (M=1.63, SD=.86) or the squirt gun (M=2.42, SD=1.22). Object Associations. Seventy-one percent of the sample rated the kitchen knife to be most associated with adult women, 92% of the sample associated the paintbrush with adult men, and 96% of the sample associated the squirt gun with young boys. Having documented that kitchen knives are indeed associated with women, paintbrushes are indeed associated with men, and squirt guns are indeed associated with young boys, and having demonstrated that kitchen knives are indeed perceived as vastly more dangerous than paintbrushes or squirt guns, we then employed the same objects in a design directly paralleling that of Study 1 and Study 3.

Study 5 Participants Six hundred and forty-seven participants living in the United States were recruited via the website MechanicalTurk.com to participate in exchange for $0.50 compensation. Screening using the same criteria employed in Studies 1 and 3 left a sample of 541 (336 female) with a mean age of 33.73 years (SD=12.1). The ethnicity of the sample was 80.2% White, 3.3% Hispanic/Latin American, 5.7% Asian, 6.5% Black/African American, and 4.3% other or mixed ethnicities. Materials and Methods The design and framing paralleled Study 3. Three adult men having hands very similar in size and appearance served as models; the hand of each model was photographed holding a kitchen knife, a paintbrush, and a squirt gun. The photographs were then combined into three sequences such that, within a given sequence, each object was held by a different model, and each sequence presented the objects in a different order. Participants were again randomly assigned to view one of the three sequences of images. Results and Discussion Effects of Object Order and Sex. MANOVAs revealed significant effects of participant sex on estimations of size and muscularity. As in Study 3, these effects were minor and inconsistent across objects; sex was therefore controlled for in subsequent analyses of these variables. A MANOVA also revealed significant effects of the order of image presentation on height, overall size, and muscularity estimates; once again, these effects were neither substantial nor patterned, and hence order of presentation was also controlled for in all subsequent analyses. Height Estimates. Repeated measures ANCOVAs with a Greenhouse-Geisser correction controlling for order revealed a significant main effect of object condition for estimations of height, F(1.95, 1,048.93)=52.32, p<.000001, η2 p =.088 (see Table 4 for means). As predicted by our representation-of-formidability hypothesis, planned contrasts revealed that the men holding the kitchen knife were estimated to be taller than the men holding the paintbrush (p<.0001) and the squirt gun (p<.000001). Consistent with the notion that the squirt gun holders would be estimated as shortest due to a simple association with children, the men holding the squirt gun were estimated to be shorter than the men holding the paintbrush (p<.01). PPT PowerPoint slide

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larger image TIFF original image Download: Table 4. Estimated Height, Size, and Muscularity ( Estimated Height, Size, and Muscularity ( Study 5 ). https://doi.org/10.1371/journal.pone.0032751.t004 Size Estimates. A repeated measures ANCOVA controlling for order of object presentation and sex of participant revealed a significant main effect of object condition for estimations of size, F(1.93, 938.59)=9.21, p<.001, η2 p =.02 (see Table 4 for means). As predicted, planned contrasts revealed that the men holding the kitchen knife were estimated to be larger than the men holding the paintbrush (p<.03) or the squirt gun (p<.000001). Consonant with the height estimates, the men holding the squirt gun were estimated to be smaller than the men holding the paintbrush (p<.01). Muscularity Estimates. A repeated measures ANCOVA with a Greenhouse-Geisser correction controlling for order of object presentation and sex revealed a main effect of object condition for estimations of muscularity, F(1.96, 1,045.19)=21.79, p<.000001, η2 p =.039 (see Table 4 for means). As predicted, planned contrasts revealed that the men holding the kitchen knife were estimated to be more muscular than the men holding the paintbrush (p<.01) or the squirt gun (p<.0001). Breaking with the height and size estimations, the men holding the squirt gun and those holding the paintbrush were not estimated to differ from one another in muscularity (p>.45). In Study 5, participants estimated men to be larger and stronger when the target individual possessed a kitchen knife, an object principally associated with women, and one that does not require strength to use effectively. This finding indicates that the core results of Studies 1 and 3 are not primarily explicable in terms of cultural schemas involving associations between guns and large, muscular men, nor are they explicable in terms of associations stemming from the strength needed to properly handle a large handgun. Participants in Study 5 did estimate men to be shorter and smaller when the target possessed a toy squirt gun, an object associated with children, thus indicating that schematic cultural associations between objects and categories of persons likely do play some role in estimations of this type. Compellingly, however, comparison of the effects of the kitchen knife (associated with women) with those of the paintbrush (associated with men) indicate that, when lethal affordances characterize an object that is associated with a comparatively shorter, smaller, and physically weaker class of individuals, the impact of said lethal affordances overrides any influence of schematic associations, leading to a net magnification of estimations of the size and strength of the object's possessor.

Discussion Knowing that an individual possesses a potentially lethal object, be it a handgun or a kitchen knife, led our U.S. participants to generally conceptualize the target individual as taller and larger in overall body size and muscularity. Our auxiliary investigations indicate that these patterns are not explicable in terms of cultural schemas linking bodily properties to the objects at issue, nor can they be explained in terms of background knowledge regarding the actual properties of gun owners. These findings constitute preliminary evidence in support of the hypothesis that conceptualized size and strength act as key dimensions in a cognitive representation that summarizes the formidability of a potential foe, where possession of a weapon is one factor contributing to said formidability. As discussed in the Introduction, both phylogenetic and ontogenetic considerations predict the existence of the hypothesized representational system. The phylogenetic thesis and the ontogenetic thesis are mutually compatible, as experiences that predictably occur during ontogeny often serve as the avenue whereby evolved adaptations develop. However, it is also possible that either a) the postulated representational system is entirely innate, and hence is independent of experience, or b) the postulated representational system is entirely the product of experience processed by a domain-general learning system, and hence does not reflect a discrete evolved adaptation. Given the positive affordances for solving adaptive problems provided by the prolonged period of human maturation (see, for example, [10]), we think that (a) is unlikely. Likewise, because the crucial adaptive problem of assessing relative formidability vastly predates mammalian sociality and altriciality, we think that (b) is also unlikely. We therefore favor a hybrid thesis that postulates the existence of an evolved adaptation, the successful functioning of which is at least partially contingent on predictably recurrent experiences during development. Nevertheless, we recognize that the results presented here are compatible with all three of these possibilities. Lastly, although both the phylogenetic thesis and the ontogenetic thesis logically apply to many social species, as we have investigated this hypothesis only in humans, applications to other species remain speculative, awaiting the development of experimental methods for assessing size estimation in nonhumans. Prior work in humans indicates that information regarding an individual's social status also influences perceptions of the individual's size (reviewed in [11]; see also [12] and [13]). Recently, Marsh, Yu, Schechter, and Blair [14] demonstrated that nonverbal cues associated with social status exercise a similar influence. In humans, status can reflect either dominance (i.e., position achieved through force or the threat thereof), prestige (i.e., position achieved through deference freely granted by others in light of accomplishments), or a combination of these factors [15] and [16]. While dominance is a universal feature of status hierarchies in social animals, prestige is thought to be unique to humans [15] and [16]. This suggests that the psychological mechanisms with which humans navigate status hierarchies initially evolved to address dominance, and were subsequently modified in our lineage to also address prestige (cf. [17]). We can therefore expect that the human representational systems that address status, having evolved from systems concerned with formidability, likely employ physical size to summarize diverse factors affecting social position. Viewed in this light, the aforementioned existing findings likely accurately capture the manner in which status is conceptually represented in humans. However, while we find this account compelling, we also recognize that previous findings linking status and perceived size may also owe to an alternative explanation. Height is correlated with actual social position and corresponding social influence – taller people achieve greater professional success, are paid more, are more likely to be elected, and so on (reviewed in [13] and [14]). Accordingly, participants may perceive high-status individuals as taller simply due to prior knowledge regarding the correlation between height and status. Likewise, cues of social superiority may lead to increases in perceived size [14] because participants may know that taller people often occupy elevated positions in the social hierarchy, and hence indications of high rank may lead to inferences of above-average height. Importantly, however, Duguid and Goncalo [18] have recently presented evidence that both militates against such an inferential explanation and is consonant with our thesis that relative formidability is represented in part using the dimension of size. In an elegant series of studies, the authors demonstrate that manipulating participants' perceptions of their ability to exercise power over others (either via unspecified means, or via a managerial position in a corporation) leads participants to a) increase estimates of their own physical height, b) decrease estimates of another person's physical height, and c) increase the height of a computerized avatar selected to represent themselves. Our findings are not readily explained in terms of participants' inferences derived from their prior observations of simple associations in the world, as gun owners are not taller than non-owners, and kitchen knives are associated with women, yet knowing that a man possesses a gun or a kitchen knife leads people to assess him as larger and more muscular. In conjunction with prior work, our studies thus provide strong preliminary evidence that the conceptual dimensions of size and strength are employed to represent relative formidability. In the future, we aim to arrive at similar clarity regarding the direction of causality in the relationship between overall social status and perceptions of size, a key step in exploring the evolution of the psychology of social hierarchy in humans.

Acknowledgments We thank Leonid Tiokhin, Rob Boyd, the members of the UCLA XBA Lab, and two anonymous reviewers for helpful feedback, and we thank our many RAs for assistance.

Author Contributions Conceived and designed the experiments: DF CH JKS. Performed the experiments: CH JKS. Analyzed the data: CH. Wrote the paper: DF.