The Importance of Physical Strength to Human Males


Fighting ability, although recognized as fundamental to intrasexual competition in many nonhuman species, has received little attention as an explanatory variable in the social sciences. Multiple lines of evidence from archaeology, criminology, anthropology, physiology, and psychology suggest that fighting ability was a crucial aspect of intrasexual competition for ancestral human males, and this has contributed to the evolution of numerous physical and psychological sex differences. Because fighting ability was relevant to many domains of interaction, male psychology should have evolved such that a man’s attitudes and behavioral responses are calibrated according to his formidability. Data are reviewed showing that better fighters feel entitled to better outcomes, set lower thresholds for anger/aggression, have self-favoring political attitudes, and believe more in the utility of warfare. New data are presented showing that among Hollywood actors, those selected for their physical strength (i.e., action stars) are more likely to believe in the utility of warfare.

Animals have complex adaptations that allow them to rapidly apply force to objects and to structure the physical world in ways that facilitate their survival and reproduction. In creatures with endoskeletons, such actions depend on a musculoskeletal system composed of strong, rigid, mineralized tissue (bones) connected to bundles of contractile fibers (muscles) laid out in stripes that shorten when stimulated by the nervous system. These systems allow the organism to manipulate and shape its environment in beneficial ways. Of course, other organisms are also out there lifting, pushing, pulling, throwing, and stacking the world in ways that are beneficial to them. Consequently, these conflicts of interest have generated powerful selection pressures that have contributed to the evolution of various complex organismic design features which function to win these conflicts. The most straightforward way to win a conflict of interest is to disable the functional machinery of the other organism—in other words, to inflict physical damage. For example, one could compromise the integrity of the oxygenating circulatory system, interrupt neural connections between the central nervous system and the peripheral musculature, disable the perceptual systems, or fracture load-bearing bones and hinder movement. Actions such as these, which involve the detrimental modification of another organism’s machinery, are typically described as acts of “aggression.”

Analyzed unemotionally and with the full range of animal species in mind, aggression is the disordering of another organism’s functional machinery—typically in a manner that disrupts that other organism’s ability to pursue its fitness interests at the expense of the aggressive animal. Of course the machinery that makes up an organism was selected precisely because its organizational structure aided in the replication of the genes comprising it, and thus genes that coded for design features that allowed an animal to resist the disordering attempts of their conspecifics, often by disordering said conspecific first, would be selected for. The deployment of mutually incompatible behavioral strategies designed to thwart organismic design can be succinctly called “combat.”

Animals have been differentially affected by selection pressures for combat, but evolutionary biologists and behavioral ecologists have found the concept of “fighting ability” (resource holding power/potential, formidability) to be a crucial variable when trying to explain numerous aspects of animal behavior and physiology, including the design of animal weaponry, the factors underlying dominance and status, the nature of aggression, sexual dimorphism and sexually differentiated life history strategies, the dynamics of territory and ownership, predator/prey relationships, mating competition and mate choice, and aggressive posturing and signaling.

Convergent evidence from multiple sciences shows that these same selection pressures have actively designed the phenotype of human beings, particularly that of the adult male. Both anthropological (Low 1988) and genetic (Hammer et al. 2008) evidence indicates that humans, like many other mammalian species, are effectively polygynous—in other words, there is greater fitness variance among males than among females. This means that the upper limit of a man’s potential reproductive success is far greater than a woman’s, but there is also a much greater chance that he will die without leaving any descendants at all. Consequently, there was stronger selection on males to be willing to get involved in violent, aggressive competition with other males (Daly and Wilson 1988) as the benefits of competition were proportionally larger and the costs of failure smaller. Moreover, in addition to shaping a male psychology that is willing to use risky aggression to resolve conflicts of interest with other males, the selection pressures associated with effective polygyny will also have favored the evolution of anatomical and physiological traits in males that are important for success in such encounters.

Design for Aggression among Human Males

Contrary to common belief, human violence has been steadily declining over recorded history (Daly and Wilson 1988; Eisner 2001). The modern pacification of human beings has led scholars to underestimate the frequency of aggression in ancestral societies (Payne 2004). Indeed, it is difficult for the average citizen of the Western world, without anthropological training, to appreciate the pervasiveness of aggression and violence among the males of many small-scale societies. Lawrence Keeley (1996) shows that across a spectrum of contemporary foraging societies (e.g., Jivaro, Yanomamo, Mae Enga, Dugum Dani, Murngin, Huli, and Gubsi) the percentage of all male deaths that arise from violent confrontations with other males can average more than 30%. In contrast, in the modern United States homicide is only the fifteenth most common cause of death, accounting for 0.8% of male deaths in 2007 (Centers for Disease Control and Prevention 2010). To put this in perspective, if modern Western societies had homicide rates as high as some foraging peoples, a male graduate student would be more likely to be killed than to get a tenure-track position.

While modern foraging people are not the ancestors of modern humans, their lifestyles resemble those of our ancestors in important ways, including the lack of modern medicine, police, formalized written systems of law, nation-state militaries, and other features of modern society with implications for the possibility and utility of using physical aggression to resolve conflicts of interest (Kelly 1995). More direct evidence of the prevalence of combat during human evolutionary history comes from archaeological records and excavations from which forensic evidence has been gathered (Keeley 1996; Walker 2001). These show a high prevalence for physical aggression as well as the male bias in frequency. Similar findings emerge from examinations of the historical record going back hundreds of years (Daly and Wilson 1988).

The most compelling evidence that human males have undergone selection for the efficient deployment of physical aggression is the sheer number of features that (when compared with women) show evidence of special design for this purpose. Table 1 lists some of the documented sex differences that likely resulted from more intense selection on males for physical aggression. Because of the inherent similarities between damaging the phenotypes of prey and conspecific competitors, it is difficult to know how much of this design was the result of selection for hunting ability rather than success in aggressive encounters with conspecifics. Nonetheless, once a design feature had been favored by natural selection because of its benefits in one domain, the cost of participating in the other would be lowered: for example, if males evolved features that allowed for the efficient pursuit and subduing of prey, these same features would have lowered the costs of conspecific aggression, and vice versa.

Table 1 Sex differences that suggest male design for combat in humans

Fighting Ability and Upper-Body Strength

As Table 1 indicates, there are sex differences in many traits that likely contribute to fighting ability, including the ability to dissipate heat, perceive and respond rapidly to threats, estimate the trajectory of thrown objects, integrate perceptual systems rapidly, resist blunt-force trauma, and accurately intercept incoming objects. That said, few of these traits will be more predicative of fighting ability than the differential capacity to apply force to an object or adversary—in other words, physical strength. Ignoring for the moment the complicated nature of social conflict, the ability to disable a competitor will almost always require the application of force either directly, with one’s musculoskeletal system, or indirectly, using weapons. Humans appear to know this intuitively, as evidenced by the mental conflation of fighting ability and strength: subjects shown photographs or played voice samples of men and asked to rate “toughness in a fight” or “physical strength” will respond with almost perfectly correlated ratings regardless of the phrasing (r = 0.96 for photographs, r = 0.98 for voices; Sell et al. 2009, 2010).

An analysis of ancestral forms of aggression shows that upper-body strength is most crucial to fighting ability. This holds for ancestral combat with weaponry (Brues 1959) such as spears, bows, handaxes, clubs, and rocks, which would have been propelled using upper-body strength (indeed, no primitive weapon has ever been found that is primarily propelled by lower-body strength). Moreover, upper-body strength is also crucial for unarmed combat, particularly the wrestling, grappling, rending and choking that most likely characterized ancestral combat according to analyses of skeletal remains (Walker 1997). Consequently, it is intriguing to note that in modern humans sex differences in muscularity are most pronounced for the upper body, with males on average having 78% greater upper-arm muscle volumes than females while the difference for thigh muscle volumes is only 50% (Lassek and Gaulin 2009), and that these differences in muscle volume lead to predictable differences in strength. For example, Stoll et al. (2000) found that adult males are able to exert 77% more force across various measures of upper-limb strength, but only 58% more force on measures of lower-limb strength. In young adults specifically, Bohannon (1997) found sex differences in strength of 92% for upper- and only 58% for lower-limb muscle actions. These patterns are consistent with the idea that upper-body strength in particular has been of critical importance in male intrasexual competition. Finally, the literature on strength assessment demonstrates the importance of upper-body strength in judgments of fighting ability (see below).

Physical Strength and Assessment Mechanisms in Humans

In nonhuman animals the ability to assess the fighting ability of conspecifics has been widely documented. For example, auditory cues alone are sufficient to reveal fighting ability in red deer (Clutton-Brock and Albon 1979), common loons (Mager et al. 2007), toads (Davies and Halliday 1978), owls (Hardouin et al. 2007) and feral horses (Rubenstein and Hack 1992). Additional evidence comes from aggressive conflicts in which animals assess fighting ability using aggressive displays rather than engaging directly in potentially more lethal forms of conflict. For example, red deer will parallel walk, roar, and finally antler wrestle but do not stab each other from behind or from the side with their antlers (Clutton-Brock and Albon 1979). Cichlid fish engage in parallel swimming, mouth wrestling, and tail beating before engaging in highly damaging combat (Enquist and Leimar 1983; Enquist et al. 1990). These interactions provide individuals with important information about the physical formidability of rivals—information that can be used by assessment mechanisms in the brains of each organism to estimate the probability of winning more intensive combat and therefore triggers facultative escalation or retreat as appropriate.

Given the frequency and selective importance of aggression and combat during human evolutionary history, it would be surprising if humans had not been tailored by selection to assess the fighting ability of conspecific males. Indeed, evidence from four distinct cultures, including hunter-horticulturalists, industrialists, and pastoralists, shows that cues of physical strength are present in the body, face and voice, and that these cues can be extracted and assessed rapidly and accurately (Sell et al. 2009, 2010; Fig. 1). In addition to this simple test, there is evidence of complex functional design in the assessment system showing that judgments of strength are dependent on cues that convey specific information about the kind of strength most relevant to fighting ability: upper-body strength in males. For example, ratings of strength tracked physical strength independently of height and weight even when rating a voice or face. Furthermore, upper-body strength was more closely tracked by ratings than was lower-body strength. In all cases, the physical strength of males was more accurately assessed than that of females, even when females were doing the ratings.

Fig. 1

Accuracy of strength assessment from the male body, face, and voice (Sell et al. 2009, 2010)

Physical Strength as a Calibrator of Mental Adaptations

A central nervous system enables animals to engage in complex regulation and structuring of motor activity. Muscle movements are therefore contingent on information that can be stored internally, and thresholds of behavior can be regulated in a facultative manner according to new information acquired about the physical and social environment. The kinds of information that animals will assess and store will depend on the fitness consequences that such information had in the environments in which that animal’s species has evolved. As has already been noted, the efficiency with which an individual can render its opponents unable to function is a crucial variable particularly for human males, so much so that humans develop the ability to assess this variable through at least three separate channels (body, face, and voice). Information about relative formidability would be useless if it were not influencing other psychological adaptations involved in the regulation of behavior. Consistent with this, fighting ability as measured by upper-body strength has been predicted and shown to correspond to the functional modification of behavior in a host of evolutionarily relevant domains.

Strength and Anger

According to the recalibrational theory of anger, anger is an adaptation designed by natural selection to regulate conflicts of interest in ways that lead the target of anger to increase the weight placed on the interests of the angry individual when making decisions (Sell 2005, 2011; Sell et al. 2009). The anger system responds to cues indicating that the target does not value the angry individual’s welfare very highly: for example, the target imposes large costs on the angry individual for trivial benefits; the target thinks the angry individual is weak, ineffectual, or unworthy of trust; or the target is uninterested in the wants or needs of the angry individual. Once triggered, the anger system then deploys negotiative tactics such as cost imposition and benefit withdrawal that incentivize the target to recalibrate the weight they will put on the angry individual’s welfare in the future. Because cost infliction is one tactic that anger deploys to bargain for better treatment, and because personal fighting ability is one subcomponent of one’s ability to impose costs generally, it follows that males who are better fighters will have more power to bargain for better treatment. This increase in bargaining power will make anger more effective for better fighters (all else being equal), and lead better fighters to feel entitled to better treatment from others, deploy anger more readily, use physical aggression more frequently, and succeed more in conflicts. These relationships have been shown empirically in multiple U.S. samples (Sell et al. 2009) and among non-Westerners such as East Indians (Archer and Thanzami 2007), the Aka of the Central African Republic (Hess et al. 2010), and the Tsimane of Bolivia (Sell et al. 2012).

Furthermore, the same pattern of effects was found between measured strength and anger as was found in the assessment literature on perceived strength: physical strength that was most combat-relevant drove the effect. As in the assessment literature, physical strength and not height or weight accounted for the relationship between strength and anger (Sell et al. 2009: see the supporting information at doi:10.1073/pnas.0904312106). And again, as in the assessment literature, it was upper- rather than lower-body strength that predicted anger. When performance on upper- and lower-body weightlifting machines (leg press and chest press) are regressed on anger, the only effect is from chest strength (std. β = 0.33, p = 0.08), not leg strength (std. β =0.02, p = 0.93). The same effect is found when upper- and lower-body strength are regressed on scales measuring the use of physical aggression (chest strength, std. β = 0.31, p = 0.08; leg strength, std. β = 0.09, p = 0.64) (from data published in Sell et al. 2009). Finally, again mirroring the assessment literature, the effect of physical strength on anger was reliably found only in males (though see Hess et al. 2010).

In contrast to the situation in ancestral environments, interpersonal physical aggression is rarely used within modern Western societies to resolve conflicts of interests. However, if human males evolved facultative mechanisms that are calibrated by assessments of their own fighting ability and the fighting ability of others, then these processes are predicted to continue to exert effects on behavior in contemporary environments in ways that are not rational. Just as human phobias are calibrated for ancestral dangers (Marks and Nesse 1994), our faculties that govern interpersonal conflicts, feelings of entitlement, political decision-making, sexual attitudes, and a host of other domains of human interaction were designed in an environment in which violence was much more common than today. In such an environment, one’s probability of successfully imposing one’s will on another and the probability of resisting another’s will were partly a function of one’s personal fighting ability and the fighting ability of those one could count as allies. This idea, that decision-making mechanisms and motivational systems evolved as solutions to problems faced by our ancestors in past environments, and that consequently they may not necessarily produce optimal outcomes in contemporary environments, is a core element to the evolutionary psychological approach (e.g., Tooby and Cosmides 1990).

If ancestral males could benefit from making facultative adjustments to their sense of entitlement and willingness to impose on others according to assessments of their own personal fighting ability, then we should expect evidence for such mechanisms to persist in modern humans. Specifically, this predicts that in our modern world, even when the rational effect of upper-body strength has been minimized owing to modern weaponry, comparatively low rates of violent interpersonal aggression, the existence of large and well-regulated police forces and judicial systems, and the extinction of or markedly reduced exposure to natural predators, a man’s mental faculties will still respond in predictable ways to his personal fighting ability. In other words, the effect of physical strength on the minds of modern men in the Western world should be far greater than is warranted from a reasoned analysis.

Research programs now underway indicate the far-reaching effects of physical strength for modern men on such diverse topics as attitudes toward crime and punishment (Petersen et al. 2010), calibration of extraversion and other personality variables (Lukaszewski and Roney 2011), attitudes toward egalitarianism (Price et al. 2011), and endorsement of various political attitudes (Sell et al. 2009).

Strength and Political Attitudes

Attempts to explain the distribution of political attitudes in modern populations by reference to rational choice have met with limited success. For a given topic, such as attitudes about income redistribution, those who benefit from the particular policy (e.g., the poor) are often no more in favor of it than those who are hurt by the policy (e.g., the rich) (Kumlin 2007). This makes little sense if one expects modern political attitudes to stem from reasoned consideration of evidence and the careful selection of policies that are likely to benefit oneself if implemented. On the other hand, if modern political attitudes arise from psychological mechanisms that evolved to guide behavior in ancestral environments, then one would expect a modern cost-benefit analysis to have limited success in explaining voting behavior. Consequently, if it is the case that social decision-making mechanisms evolved to respond to ancestrally relevant variables such as fighting ability, then an understanding of how these mechanisms function could help shed light on individual differences in political attitudes that are otherwise difficult to explain.

If viewed from the perspective of a forager without nation-states and complicated taxation systems, the issue of income redistribution looks very different. There were no anonymous “rich” who could be taxed, only recognizable neighbors and acquaintances who could look at you while you attempted to lay claim to their resources and with whom you would most likely interact for years to come. Likewise, the “poor” would not have been a distant and relatively unknown group of people in need, but neighbors and acquaintances who could benefit from resources that you owned and may or may not turn to violence if they did not get what they wanted. In this context, the costs and benefits of laying claim to resources (your own or others’) depended heavily on your ability to defend your own interests, one component of which would have been physical strength and fighting ability. Formidable men who are high in SES could defend themselves against those who would confiscate their resources and therefore should be opposed to income redistribution. Price and his colleagues (2010) confirmed this prediction by showing a significant negative relationship between upper-body musculature and attitudes toward income redistribution among undergraduates at a prestigious English university. No effect of musculature was found for women, who ancestrally were much less likely to use their own personal fighting ability to defend their resources. An ongoing project is testing the corollary prediction that strong men who are low in SES will be in favor of income redistribution.

The same type of analysis applies to attitudes about warfare. Ancestrally, wars were fought with weapons that depended on upper-body strength for the bulk of their destructive force. In such conditions, a man’s probability of surviving and benefitting from armed conflict would have depended, to a large extent, on his personal fighting ability. Moreover, men may evaluate the utility of warfare using mechanisms that evolved to assess the costs and benefits of interpersonal violence. Consequently, to the extent that our modern political attitudes arise from mechanisms that respond to ancestrally relevant cues rather than to modern rational analyses, one would predict that a man’s personal fighting ability should still be a powerful predictor of his attitudes about the utility of war. All else being equal, strong men should believe that warfare makes us safer by punishing and deterring our enemies. Weaker men should be more swayed by arguments that warfare puts us in greater danger by encouraging and provoking our enemies. These basic predictions have now been confirmed (Sell et al. 2009).

The effects of formidability have also been shown in experiments on voting behavior. There is no rational basis for the physical strength of a candidate to be important when it comes to elections in nation-states, and yet evidence shows that it is (Little et al. 2007). Viewing the human mind through the lens of our ancestral lifestyle, however, brings these behaviors into sharper focus. A physically dominant leader would not have been sent to a legislature far away but would be an active member of the community and could wield significant power in numerous social interactions. Supporting a physically dominant leader would generate both costs and benefits as a result of his increased status. On one hand, physically dominant men are better able to deter rivals, more skilled and presumably more willing to both attack enemies and aggressively defend their allies. On the other hand, physically dominant men demand better treatment and thus may be more likely to impose costs on lower-status individuals (see Boehm 1999). This means that in ancestral conditions, the benefit of having a physically dominant leader would depend on the likelihood of warfare at that time. This is precisely what Little and his colleagues found. Subjects preferred to elect physically-dominant-looking men when imagining a time of war, but this preference reversed when imaging a time of peace (Little et al. 2007).

These lines of research demonstrate the pervasive effect of upper-body strength on the minds of modern men. The results suggest that many decisions in large nation-states are being made by men whose attitudes and decision-making processes are informed by an ancestral calculus that weighs one’s personal fighting ability as a relevant variable even when discussing national military action.

Warfare and the Hollywood Action Star

If attitudes about warfare are causally tied to a man’s own sense of fighting ability, we would expect professions, industries, and coalitions of strong, powerful men to be more likely to endorse attitudes about the utility of political aggression as a means of resolving conflicts of interest. More interestingly, even among professions that are typically left-leaning with respect to attitudes about war,Footnote 1 we should expect to find exceptions among those who are physically formidable. We tested for this pattern among a small group of physically strong men, Hollywood action stars, who work and reside in a culture that is left-leaning compared with contemporary America, particularly when it comes to views on the utility of warfare. If physical strength in men leads to more positive views of the utility of war, then even in a population with predominately leftist attitudes, such as Hollywood actors, those actors known for their physical strength and formidability should be more likely to be supportive of military action.

To test whether action stars were significantly more likely to believe in the utility of warfare, we gave individual surveys to 36 undergraduates at UCSB and 13 faculty and staff members of the Department of Anthropology and asked them to list four Hollywood actors of each of the following categories: action, dramatic, and comedic. Any actor who was listed more than once in a given category was included in our analysis. If an actor was mentioned in more than one category, he was placed only in the category for which he was mentioned most frequently. This process produced a list of 80 actors (see Supporting Information to this article).

Each actor was then put into one of two political categories regarding the utility of warfare: left-wing (i.e., warfare leads to more problems) or right-wing (i.e., warfare solves problems). Because the actors were largely American citizens and working in America during the late twentieth century, the “antiwar” position was indicated by support of the Democratic Party, which, to a large extent, opposed the Vietnam and Iraq wars, America’s most significant foreign military actions in the latter part of the century. The complications of history make this a simplification, but for the purposes of this study what matters is the public perception of the parties’ platforms. The Democratic Party has been the party supported by those who wish to end foreign incursions and the Republican Party has been the party supported by those who wish to use the U.S. military to attack America’s enemies (Aldrich et al. 2006). The actor’s political affiliation was assessed using a five-step ordered procedure:

  • if the actor had run for office as a member of a political party, he was classified as a supporter of that party. One actor was classified by this criterion.

  • if the actor’s political donations to one party were more than double those to another, he was classified as a supporter of that party. Thirty-eight actors were classified by this criterion.

  • if the actor made direct statements regarding a military action by the United States he was categorized accordingly. Eight actors were classified by this criterion.

  • if the actor made direct statements of support for a party or a politician, or if they spoke at a party fund raiser or convention, they were categorized accordingly. Eleven actors were classified by this criterion.

  • finally, if not classified by any previous criteria, actors were classified by any stated support they had for left-wing or right-wing causes. Only three actors were classified according to this criterion based on support of these left-wing causes: desire for more regulation of free market capitalism, support for Che Guevera, and preference for government-provided universal health care.

Of the original 80 actors, 61 were categorized by one of these criteria and included in our analyses. Of the 19 actors who could not be classified according to support for a U.S. political party, 16 were non-U.S. citizens for at least part of their lives. Only three U.S. citizens were not classifiable. As expected, Hollywood actors are generally more supportive of left-wing politics and politicians, with 47 of the actors (77.0%) being categorized as left-wing and 14 (23.0%) as right-wing. Despite that general pattern, a chi-square test indicated significant differences in the distribution of political attitudes between different categories of actors (χ2 = 15.0; df = 2; p < 0.001). As shown in Fig. 2, actors known for their physical strength and formidability—action stars—were the exception. More than half of Hollywood action stars in our sample (56.3%) were right-wing according to our categorization process. These included such imposing figures as Arnold Schwarzenegger, Bruce Willis, Chuck Norris, Clint Eastwood, Sylvester Stallone, Dwayne Johnson (“the Rock”), and Charlton Heston. Post-hoc comparisons indicated that right-wing categorizations were significantly more common (χ2 = 13.9; df = 1; p < 0.001) among action actors (56.3%) than dramatic actors (4.2%). Similarly, right-wing categorizations were more common (χ2 = 5.5; df = 1; p < 0.05) among action actors than comedic actors (19.0%).

Fig. 2

Political attitudes among different categories of Hollywood actors

Consistent with the hypothesis that physical strength is linked to positive views of the utility of warfare, many of the action stars categorized as left-wing were indeed physically less imposing than their right-wing counterparts. For example, Nicholas Cage, Tom Cruise, Pierce Brosnan, and Keanu Reeves are prominent left-wing action stars but do not appear to have the same physiques as Schwarzenegger, Stallone, or Chuck Norris. Furthermore, several of the right-wing comedic and dramatic stars were also physically formidable, such as Matthew McConaughey and Vince Vaughn. Though they were not mentioned repeatedly by our subjects, and thus did not contribute to our analysis, many other physically formidable actors contributed to or supported right-wing political causes, including James Earl Jones, Tom Selleck, LL Cool J, Lorenzo Lamas, Dean Cain, Mickey Rourke, Clint Walker, Clancy Brown, Chuck Conners, Ronald Reagan, “Hulk Hogan,” and Kurt Russell.Footnote 2

Although physical height, compared with upper-body strength, is a less powerful predictor of anger, aggression, and entitlement in men (Sell et al. 2009); less closely tracked when subjects rate “fighting ability” from the body, face (Sell et al. 2009), and voice (Sell et al. 2010); and less sexually dimorphic (Lassek and Gaulin 2009), it is nonetheless an objective measure that covaries with physical strength and predicts, to some extent, fighting ability. Because the height of actors is reported online from various sources,Footnote 3 this allows for an additional test of the hypothesis that actors who are physically more formidable are more likely to be right-wing with respect to the utility of war. A simple independent t-test compared the height of right-wing actors (mean = 72.7 inches) with the height of left-wing actors (mean = 70.3 inches) on our list and showed that the right-wing actors were significantly taller: t 59 = 2.8, p = 0.007. This is noteworthy since, unlike degree of muscularity, height is not subject to behavioral modification (e.g., through resistance training). Although men with positive beliefs about the utility of violence could be more motivated to develop their upper-body strength through training, an association between height and views on the utility of warfare could not arise in such a way.


Upper-body strength in adult males is a crucial variable that appears to have impacts on a wide range of mental mechanisms that were designed by natural selection at a time when personal physical aggression was far more common and individual differences in fighting ability were far more relevant for the resolution of conflicts, the deployment of anger and aggression, the calibration of political attitudes, and the consequences of warfare. Despite the steady decline in physical aggression and violent deaths that have accompanied Western civilization, the human mind is still designed for ancestral environments (Tooby and Cosmides 1990), and this is evidenced by many lines of research. Sex differences in body size and strength, perceptual and spatial abilities, and physiological systems still show combat design in adult men. The existence of assessment mechanisms in the minds of men and women that track and respond to cues of upper-body strength also testify to the importance fighting ability had for our ancestors. And finally the persistence of associations between upper-body strength and psychological and behavioral variables in modern men shows how powerful the selection pressures were: physically stronger men have been shown to feel more entitled to better outcomes, to set a lower threshold for the triggering of anger and physical aggression, to have more self-favoring attitudes about income redistribution, and to believe more in the utility of warfare.


  1. 1.

    Where the terms “left” and “right” are used in the present manuscript they are intended to refer to their commonly understood meanings in the contemporary United States, where “left-leaning” refers to beliefs typically associated with the Democratic Party, including a more “dovish” approach to war, whereas “right-leaning” refers to beliefs associated with the Republican Party, including a more “hawkish” approach to war.

  2. 2.

    As with every human subject, Hollywood actors will have far more nuanced beliefs than can be captured in any dichotomous coding scheme. Kurt Russell and Clint Eastwood, for example, identify as libertarians, Bruce Willis has repudiated the religious right’s influence on the Republican Party, and Terry Bollea (“Hulk Hogan”) supported Obama and describes himself as “middle of the road” though he feels that the United States should have continued the 1990 Gulf War until Iraq was conquered. These variations may be obscured when averages or categorizations are used in statistical testing, but it is important to keep in mind (particularly because actors are identifiable public figures) that individual beliefs and attitudes will vary considerably within categories.

  3. 3.

    These measurements stem from various reports of unknown reliability and need to be treated cautiously until replicated.


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We would like to thank Jane Lancaster and three anonymous reviewers for helpful insights and comments. We also thank the Key Centre for Ethics, Law, Justice and Governance for support.

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Correspondence to Aaron Sell.

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Sell, A., Hone, L.S.E. & Pound, N. The Importance of Physical Strength to Human Males. Hum Nat 23, 30–44 (2012).

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  • Physical strength
  • Evolutionary psychology
  • Aggression
  • Anger
  • Warfare
  • Income redistribution
  • Hollywood actors
  • Political attitudes