Unterschiede in körperlicher Kraft und Selektionen auf Kampf bei Männern und Frauen

Eine interessante Studie untersucht die „Kampffähigkeiten“ der Geschlechter:

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.

Quelle: The Importance of Physical Strength to Human Males (PDF, Volltext)

Die Ausgangslage wird in dem Artikel wie folgt dargestellt:

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.

Das ist für Leser dieses Blogs nichts neues: Das Männer einer hohen intersexuellen Selektion und einer starken Konkurrenz unterliegen, war wiederholt Thema. Dazu findet sich auch eine interessante Passage in dem Artikel:

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.

Demnach finden sich in den verschiedensten Stämmen Anzeichen für Gewalt im Rahmen intrasexuellen Wettbewerbs und dies wird auch durch archäologische Funde gestützt. Zudem zeigen sich entsprechende Selektionen an den Menschen, wobei diese eben abzugrenzen sind zu den Selektionen für eine Jagd und der für Kämpfe gegen Menschen.

Interessant ist, welche Auswirkungen dieser Selektion man heute noch finden kann:

Körperliche Unterschiede zwischen Mann und Frau als Selektion auf Kampf

Körperliche Unterschiede zwischen Mann und Frau als Selektion auf Kampf

Ich hatte meinerseits auch schon einmal eine Liste zusammengestellt, die im wesentlichen damit übereinstimmt:

  • Männer wiegen etwa 15% mehr als Frauen
  • Männer sind im Schnitt 15 cm größer als Frauen
  • das Hüfte-Taile Verhältnis ist anders, Männer haben schmalere Hüften
  • Das Brust-Tailen Verhältnis ist anders: Männer haben normalerweise einen größeren Brustumfang
  • Der Oberkörper von Männern ist im Schnitt 40-50% stärker
  • der Unterkörper von Männern ist im Schnitt 30% stärker
  • Männer haben relativ zu ihrer Körpergröße mehr Lungenvolumen (ca. 30%)
  • Ellenbogen und Knie sind beim Mann c42-60% stärker
  • die Haut von Männern ist dicker und fettiger
  • Männer haben mehr Körperbehaarung als Frauen
  • Frauen haben einen höheren Körperfettanteil
  • Frauen haben einen niedrigeren Blutdruck, Frauenherzen schlagen dafür etwas schneller
  • Männer haben mehr androgene Hormone, Frauen mehr Estrogene
  • Männer haben im Schnitt 5,2 Millionen rote Blutkörperchen pro Kubikmililiter, Frauen 4,6 Millionen
  • Männer haben mehr Hämoglobin als Frauen und können daher mehr Sauerstoff speichern
  • Männer haben im Verhältnis zu ihrem Körper ein um 10% größeres Herz
  • Der Grundumsatz von Männern ist etwa 10% höher als der von Frauen
  • Männer haben stärkere Knochen
  • Frauen wandeln mehr ihrer Nahrung in Fett um, Männern mehr in Muskeln
  • Männer können mehr Hitze abgeben, weil sie mehr Schweißdrüsen haben
  • Frauen haben mehr weiße Blutkörperchen (bessere Imunabwehr)
  • Männer haben mehr Gerinnungsfaktoren und Inhibitoren im Blut (schnellere Wundheilung)

Im Text werden dann auch noch ein paar Zahlen genannt:

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

Die Studie geht dann noch darauf ein, inwieweit Körperkraft mit der Einstellung zu beispielsweise Krieg einhergeht. Dies wird wie folgt begründet:

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.

Das ist auch eine interessante Darstellung für Leute, die Beeinflussungen des Verhaltens aus der Biologie ablehnen: Bestimmte „Geisteszustände“ sind sozusagen „Konfigurationen“ des Körpers für bestimmte Situationen, die sich als evolutionär vorteilhaft herausgestellt haben: Stress mag zB „Fight or flight“ hervorrufen, Ärgerlich sein kann einem helfen seine Position zu verteidigen und nicht als zu leicht unterzubekommen angesehen zu werden, Angst hilft einem, sich zu schützen. Ich hatte dazu schon mal etwas geschrieben.

Die Studie weiter

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). (…)

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 theWestern world should be far greater than is warranted from a reasoned analysis.

Die Studie stellt dann fest, dass kräftigere Schauspieler eher dem Repubikanischen Lager nahestehen, weniger kräftigere eher den Demokraten und das sich Mitglieder dieser jeweiligen Lager im Schnitt eher für Fortsetzung kriegerischer Aktivitäten bzw. für deren Beendigung aussprechen. Da sind also einige Unsicherheiten drin, da eine reine Parteizuordung erfolgt und die Schauspieler nicht zu ihren Ansichten befragt worden sind.

Interessant ist vielleicht noch, dass sich durch die dort gebildeten Lager zieht: Aktionsstars sind ehe Republikaner, Dramadarsteller eher Demokraten, Komödianten auch, innerhalb dieser Lager sind die kräftigeren dann wieder eher Republikaner.

Die Schlußfolgerung der Studie:

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.

Einige der Schlußfolgerungen sind aus meiner Sicht etwas dünn. Aber die körperlichen Unterschiede lassen darauf schließen, dass hier eine Selektion in diese Richtung erfolgte. Nimmt man die Untersuchung über die Unterschiede im Gesicht und deren Selektion auf die Auswirkung von Gewalt hin, dann würde ich die Theorie, dass eine entsprechende Selektion erfolgt ist schon für sehr schlüssig halten. Mentale Selektionen in diese Richtung sind dann ebenfalls zu erwarten. Gleichzeitig ist ebenso damit zu rechnen, dass Männer Systeme entwickeln die Kosten von solchen Konfrontationen gering zu halten, etwa durch Hierarchien oder die Verlagerung von Konkurrenzkämpfen in einen unblutigen Bereich.

Geschlechterunterschiede im Gesicht als Anpassung an Kampf?

Eine Studie wirft die These auf, dass Unterschiede zwischen den Geschlechtern auf eine verstärkte Anpassung der Männer an Kämpfe beruhen könnte:

When humans fight hand-to-hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest increase in robusticity during the evolution of basal hominins. These bones are also the most sexually dimorphic parts of the skull in both australopiths and humans. In this review, we suggest that many of the facial features that characterize early hominins evolved to protect the face from injury during fighting with fists. Specifically, the trend towards a more orthognathic face; the bunodont form and expansion of the postcanine teeth; the increased robusticity of the orbit; the increased robusticity of the masticatory system, including the mandibular corpus and condyle, zygoma, and anterior pillars of the maxilla; and the enlarged jaw adductor musculature are traits that may represent protective buttressing of the face. If the protective buttressing hypothesis is correct, the primary differences in the face of robust versus gracile australopiths may be more a function of differences in mating system than differences in diet as is generally assumed. In this scenario, the evolution of reduced facial robusticity in Homo is associated with the evolution of reduced strength of the upper body and, therefore, with reduced striking power. The protective buttressing hypothesis provides a functional explanation for the puzzling observation that although humans do not fight by biting our species exhibits pronounced sexual dimorphism in the strength and power of the jaw and neck musculature. The protective buttressing hypothesis is also consistent with observations that modern humans can accurately assess a male’s strength and fighting ability from facial shape and voice quality.

Quelle: Protective buttressing of the hominin face

Protective Buttressing ist sozusagen das Einziehen besonderer Stützpfeiler in der Architektur, also ein Verstärken von besonders belasteten Bereichen. Die Studie führt einige interessante Unterschiede zwischen Männern und Frauen auf:

Although humans are generally viewed as exhibiting low to moderate levels of sexual dimorphism (McHenry, 1994; Plavcan, 2001, 2012; Reno et al., 2003), the relatively low body mass dimorphism of humans is largely a consequence of human females having substantial fat stores (Pond & Mattacks, 1987). When fat-free masses are compared, men are 41% more massive (Mayhew & Salm, 1990; Lassek & Gaulin, 2009) and have 48–65% more muscle mass than women (Illner et al., 2000; Abe, Kearns & Fukunaga, 2003; Kim et al., 2004; Shen et al., 2004). As in gorillas (Zihlman & McFarland, 2000) and australopiths (McHenry, 1986, 1991, 1996), the upper body of humans exhibits more sexual dimorphism in size and strength than do the legs (Abe et al., 2003; Raadsheer et al., 2004; Lassek & Gaulin, 2009; Price et al., 2012). Among young adults, the muscles of the arm are 69–109% stronger in males than in females, whereas strength dimorphism of leg muscles range from only 23 to 66% (Bohannon, 1997). The most sexual dimorphic part of the human body, in terms of muscular strength, may be the neck. Maximum moments produced by the muscles of the neck are 100–150% greater in men than in women (Vasavada, Li & Delp, 2001). Pronounced sexual dimorphism in cervical muscles is surprising given that humans do not fight by biting with the jaws. However, as discussed above, energy absorption by the muscles of the neck can protect against concussion when the head is struck. Thus, humans do show very high levels of sexual dimorphism in the parts of the postcranial musculoskeletal system that appear to be most important in fighting (Lassek & Gaulin, 2009; Puts, 2010; Carrier, 2011; Sell, Hone & Pound, 2012; Morgan & Carrier, 2013).

Because sexual dimorphism is often greatest in those characters that enhance a male’s capacity to dominate other males (Clutton-Brock & Harvey, 1977; Parker, 1983; Andersson, 1994), the observation that the face is the primary target when males fight leads to the expectation of sexual dimorphism in buttressing of the human face (Puts, 2010). The protective buttressing hypothesis predicts that the most dimorphic parts of the hominin skull will be those that are most frequently injured during fighting, namely the mandible, nasal region, zygomatic arch, orbit and maxilla.

Also erheblich mehr Muskeln bei Männern, aber auch an Stellen, an denen sie eigentlich nur zum Auffangen von Energie Sinn machen.

As predicted, the parts of the human facial skeleton that exhibit marked sexual dimorphism are also the parts of the skull that most frequently fracture when people fight (Table 1). First, as described above, the face of humans exhibits much more sexual dimorphism than the neurocranium and fractures of the face as a result of fighting are much more common than fractures of the neurocranium (Shepherd et al., 1990; Boström, 1997). Second, although relative frequency of fracture type varies among the studies included in Table 1, the sites of facial fracture are the same in each study. Of the mandibular fractures in the Bristol study, 25.4% were to the condyle or coronoid, 35.6% were to the ramus, 35.6% to the angle, and 3.4% to the symphysis. Additionally, the nasal region, zygoma and orbit are also sites of frequent injury and exhibit relatively high sexual dimorphism. Thus, a dramatic correspondence exists between the parts of the skull that are most sexually dimorphic and the parts that most frequently fracture during fighting.

Es zeigen sich also gerade dort mehr Unterschiede, wo zur Vermeidung eines Kampfes Verstärkungen notwendig waren.

Given that humans have relatively small canine teeth, exhibit low canine sexual dimorphism (Frayer & Wolpoff, 1985; Wood et al., 1991; Plavcan & van Schaik, 1997) and rarely bite during fighting (Shepherd et al., 1990; Boström, 1997), it is puzzling that humans exhibit significant sexual dimorphism in the strength of their jaw adductor muscles. Five studies that measured maximum bite force in men and women indicate that, on average, men produce 34.3 ± 10.5% (mean ± S.D.) greater forces than women (Klatsky, 1942; Waltimo & Könönen, 1993; Braun et al., 1995; Raadsheer et al., 2004; van der Bilt et al., 2008). This level of sexual dimorphism is only 7–20% below estimated sexual dimorphism in bite force of gorillas and orangutans (Demes & Creel, 1988; Eng et al., 2013); species in which biting is an important male fighting behaviour. The human masseter muscle also exhibits substantial gender differences in the proportion of fast-twitch (type II) muscle fibres. The average cross-sectional area of type II fibres in the masseter muscle averages 66.9% in males and only 8.3% in females (Tuxen, Bakke & Kenrad, 1992; Tuxen, Bakke & Pinholt, 1999). Type II muscle fibres shorten faster and generate force more quickly when stimulated than type I fibres (Close, 1967). Although human sexual dimorphism in adductor muscle strength and fibre type cannot be explained by aggressive biting behaviour during fighting or by mastication, because diets of human males and females are largely similar, the observed human dimorphism is consistent with the hypothesis of protective buttressing of the face. If the jaw adductor muscles do function to protect against mandibular dislocation and fracture, as suggested above, greater muscle strength and shorter force activation times in males would be expected because of their higher incidence of fighting and facial injury.

Des weiteren wurde auch untersucht, ob aus dem Gesicht Rückschlüsse auf die Eigenschaften als Kämpfer hergeleitet werden können:

The facial features that allow observers to assess a male’s strength, fighting ability and propensity to behave aggressively include the ratio of facial width to height (Carré et al., 2009, 2010), face width, chin breadth, eyebrow prominence and nose size (Windhager et al., 2011; Třebický et al., 2013). These metrics represent aspects of the skull that experience high rates of fracture due to interpersonal violence and are features that increased in robusticity coincident with the evolution of hand proportions that allow the formation of a fist (discussed above). Generally, facial masculinity is viewed as an honest signal conveying information about formidability (Sell et al., 2009; Puts et al., 2012b; Třebický et al., 2013). Puts (2010) proposed that, in addition to acting as a signal, the greater facial robusticity of males may have evolved to protect the face from injury when males fight, as we are suggesting here. It is also likely that masculine features of the face convey direct information about the degree to which the face, the primary target during interpersonal violence, is vulnerable to injury. Male contest competition involves both offence and defence and a robust facial skeleton may make an individual more formidable simply because he is less susceptible to serious injury.

Das wäre für Männer durchaus eine wichtige Information.

Es ist aber auch unter dem Gesichtspunkt der Partnerwahl interessant: Viele Aspekte, die innerhalb des intrasexuellen Konkurrenzkampfes einen Vorteil bieten, werden auch in der intersexuellen Selektion wichtig, denn entsprechende genetische Informationen werden dann auch an einen Sohn weitergegeben. Das könnte erklären, warumfür Frauen ein markantes, kräftiges Kinn attraktiv sein kann: Es spricht eben für ein robusteres Gesicht.

George Clooney

George Clooney

Wenn es eine sexuelle Selektion auf diesen Umstand gegeben hätte, dann hätte das diesen Zugang noch zusätzlich verstärkt.

Sportliche Männer haben mehr Sex

Eine Studie beleuchtet die Kurzzeitpartnerwahlstrategien von Frauen:

Evolutionary scientists propose that exaggerated secondary sexual characteristics are cues of genes that increase offspring viability or reproductive success. In six studies the hypothesis that muscularity is one such cue is tested. As predicted, women rate muscular men as sexier, more physically dominant and volatile, and less committed to their mates than nonmuscular men. Consistent with the inverted-U hypothesis of masculine traits, men with moderate muscularity are rated most attractive. Consistent with past research on fitness cues, across two measures, women indicate that their most recent short-term sex partners were more muscular than their other sex partners (ds = .36, .47). Across three studies, when controlling for other characteristics (e.g., body fat), muscular men rate their bodies as sexier to women (partial rs = .49-.62) and report more lifetime sex partners (partial rs = .20-.27), short-term partners (partial rs = .25-.28), and more affairs with mated women (partial r = .28).

Quelle: Why Is Muscularity Sexy? Tests of the Fitness Indicator Hypothesis


Natürlich hilft Aussehen in diesem Bereich sehr. Ein sportlicher Körper macht alles einfacher. Zwar meine ich, dass man mit Game vieles überbrücken kann, aber man muss dann eben um so besser sein um so schlechter der eigene Körper ist. Natürlich macht das eigentlich heute keinen Sinn mehr. Schließlich ist ein muskulöserer Mensch nicht unbedingt besser im Bett oder gefühlvoller etc. Aber Muskeln sind eben ein gutes Anzeichen für viele Fitnessindikatoren. Zum einen braucht es eine regelmäßige und gute Ernährung über eine lange Zeit um sie aufzubauen. Zum anderen bieten sie (zumindest bis zu einem gewissen Grad) Vorteile bei der Jagd (zB dem Werfen eine Speers) und auch beim Kampf (male-male-competition), was in der Steinzeit von Vorteil gewesen ist und diesbezügliche Attraktivitätsmerkmale der Frauen sinnvoll macht.

Also: Wer mehr One-Night-Stands haben will sollte am Besten ab ins Fitnessstudio.