Hierarchical competition and the ethology of sexual dimorphism in humans

sexual dimorphism

In many species, males are the ones who dispute the group supremacy and fight for a high hierarchical position that grants them more resources and access to females. Because the genes of the most powerful and aggressive males pass on from one generation to another, the new generations of males are, at their turn, aggressive and combative. Therefore, the fighting never diminishes in its intensity for there is a natural selection that biases the hierarchical aggressiveness. It is true that tussles are often ritualized, meaning that the males try to prove their powers by grappling with one another, without seriously injuring or killing one another; the simple demonstration of physical potential is also practiced by comparing the volume of the voice or that of the body.

But even during such duels, those who are weak and careless run the risk of getting themselves killed. For example, during the tussles between red deer males (Cervus elephus), that takes place during the breeding season, between 13% and 29% of males involved are killed, which represents a very large number [Clutton-Brock, Albon, 1982]. Generally speaking, the higher the stake of the competition is, that is, the higher the risks of not having access to women, food and territory is, the fiercer the intra-male duels are. We could detect species in which the stake of intra-sexual competition is high by analyzing the physical differences between males and females.

In elephant seals, for example, the males are polygamous and must fight for females. The most powerful males, also known as alpha males, gain the control of a harem that contains over 50 females; beta males get a smaller harem, and the weakest males that lose all fights are banished to the periphery of the colony, where they are left as well without any females, as without a safe shelter. A study carried on a colony of elephant seals has shown that only 28.8% of males have had offsprings, and 89.6% of them had harems. Practically speaking, the males that are incapable of forming a harem are getting dropped out of the reproductive chain [Fabiani et al., 2004].

Inside this species, the more massive and the fiercer is the male, the more chances he has for victory, and this is why bigger and bigger males have passed on from one generation to another, while females, due to the fact that they didn’t fight among themselves, didn’t face such pressure that was coming from the sexual selection. Presently, the difference between a male and a female is striking (see the picture below): males can reach six and a half meters in length, while females can reach only three meters and a bit; males weight 3.5 tones, while females barely reach 900 kg [1].

competition sexual demorphism
The sexual dimorphism, presented on a pair of elephant seals; the male (on the right) is much more massive than the female, because the natural selection favors the male that are stouter and more powerful when it comes to hierarchical fights.
Source: http://travelwild.com/antarctica-wildlife/southern-elephant-seal

In gorillas, males weigh 135 to 180 kg while adult females usually weigh half as much as adult males at 68–113 kg. Adult males are 1.7 to 1.8 m tall, with an arm span that stretches from 2.3 to 2.6 m. Female gorillas are shorter with smaller arm spans [2]. In humans, the sexual dimorphism is not so obvious, but nonetheless, the difference in volume, weight and force is noticeable. Men have 120% of women’s weight. They are higher and have a better developed musculature. This is already a clear proof that men are much more involved in hierarchical competitions than women [Bohannon, 1997; Abe et al., 2003, apud Goetz, 2010, p. 16].

It also proves the role of the hunter that was attributed to men. The studies conducted upon the men from the African tribe Hazda have shown that their hands’ developed musculature is correlated with their hunting success, as well as with their reputation and reproductive success. Strong arms are considered to be the most important physical trait for hunting and it is very likely that the natural selection has biased men with a more imposing musculature [Apicella, 2014]. More powerful men have higher chances of becoming leaders in hunter-gatherer tribes [Rueden et al., 2014].

Even in well developed Western societies, taller and stronger men have a prominent reproductive success. In particular, it was shown that Dutch men are so high because there was a sexual selection for tall individuals. Dutch men added about 20 cm in height from the last 150-200 years [Stulp et al., 2015]. Therefore, it is the hierarchical competition and the role of hunters, warriors and guardians of the tribe that contributed to the apparition of the sexual dimorphism inside the human species. The masculinity and developed musculature have evolved alongside with the more combative character.

This is why many young people choose to enroll in various sports sections, to practice martial arts, to increase muscle mass, to be more physically rugged and corresponds to the role of male warrior, hunter and protector. The desire to have a solid body, to be strong and be able to protect themselves and the loved ones is one of the main reasons underlying the passion of boys and men for contact sports and gym. Often it happens that men who failed in his youth to develop a muscular body, choose to play sports in adulthood, especially with the arrival of so-called “midlife crisis”.

Evolutionist writer Jonathan Gottschall, married and father of two daughters, decided to seriously deal with martial arts around the age of 38 years and published a book about his motivation and experience entitled (“The Professor in the Cage: Why Men Fight and Why We Like to Watch”). In the book, the author explains the evolving nature of battles and duels between men as a way of claiming hierarchical rank and establishing social order in archaic groups [Gottschall, 2015].

In an interview dedicated to his book Gottschall testifies: ”I was a very late bloomer as a kid. I came into my adult size and muscle very late. Whenever I was confronted in the schoolyard, I found some way to avoid the fight. I ran for it. I backed down. Psychologically and emotionally, that isn’t a low-cost course of action for most boys. You avoid a physical beating, but you pay a real social and psychological cost for it. Those moments of walking away from fights, even though I knew it was the rational and civilized thing to do, cost me tremendously. I think that’s why I finally got in that cage to fight” [3].

It was found that, among men, the ones who are more massive and have a more prominent musculature are more prone to cause conflict situations, more inclined to express emotions of anger and have the tendency to impose themselves through acts of physical violence in relation to other individuals [Lemieux et al., 2002]. The more men assess their own physical condition (their stature, their might), the more they will be inclined to underestimate the one that their potential opponents have [Fessler et al., 2014]. Men that have a massive size are more assertive as regarding the claiming of their economic interests [Petersen et al., 2013].

Also, grandiose and physically attractive men are more egocentric and less willing to accept the egalitarianism. It is a legacy that has come to us from times when men with an imposing physique were acting more prevailingly and had greater chances of obtaining resources by means of fighting and of defeating their adversaries. In other words, the social inequality benefited them [Price et al., 2015]. To be trained means to have a greater fighting ability, a condition that is indispensable for survival during different confrontations that appeared during the evolution of species; and, up to this day, a superior physical shape induces self confidence in men, therewith rendering them more socially aggressive and combative.

Muscular men are more likely to approve military interventions in their countries; even Hollywood actors that act in action movies and have a grandiose physique have, to a certain degree, radical rightist, pro interventionist political views [Sell et al., 2012]. By the way, talking about the support offered to interventionist politics by action movies’ actors, it is worth noting the case of Mikhail Porechenkov, a massive man who, in October 2014, has visited the camp of the separatists from Donetsk and has shot from a machine gun towards the camp of the Ukrainian army as a gesture of support of the Russian policy in the region [4].

Therefore, our minds still work according to the standards that were set by the warlike tribal life and the muscular mass continues to correlate with the assertiveness of men in interpersonal conflicts, this correlation being universally valid for the most diverse human cultures and societies. Besides, we do have an amazing capacity of evaluating the physical states of other individuals and the muscular and well-trained guys from around us have the advantage of impressing solely through their aspect.

It is curious the fact that, if a man is armed (with a gun or a knife), the other individuals will see him as being bigger, higher and physically scary. This perception appears on an unconscious level and is based on an old cognitive mechanism; throughout human evolution, the attributes of a warrior were directly associated with power and have had, therefore, an important role in the hierarchical competition [Fessler et al., 2012].

This impression is created not only by the corporal aspect, by also by the facial one, the one that in shaped by faces’ bones and musculature. Men whose facial width-to-height ratio’s indexes are more inclined towards width usually have a more aggressive behavior. The ratio is calculated by measuring the distance between the right and the left cheek and between the lower lip and the intersection of superciliary arches. It has been found that a wide face is usually associated with a higher level of testosterone [Carré, McCormick, 2008; Carré et al., 2009, 2010].

And the men whose indexes indicate a wider face are usually perceived as being more aggressive [Geniole et al., 2012]; and they really behave more aggressively [Haselhuhn et al., 2015]. Not only among soldiers, gangsters, athletes, but also among CEOs and heads of state is the high percentage of men with wider faces; facial features correlate with more competitive drive, with combativeness and with readiness to protect own group [5].

And women’s faces can be characterized as being more feminine and more masculine, judging by the form of their maxillary, their lips, the position of their cheeks (and excluding such elements as their hairstyle, their makeup or their accessories). It is surprising that, depending on the type of their face, women can have different political predilections. Psychological studies conducted on female politicians in US have shown that women with a typical feminine face are supporters of The Republican Party (which is more conservative and patriarchal), and the women with a less feminine face would rather support The Democratic Party (which is more liberal and supports gender equality) [Carpinella, Johnson, 2013].

It is probable that the hormonal factor is involved; in case of women with typical feminine faces, they have more estrogen (and less testosterone), a combination that is correlated with supporting a more conservative or patriarchal policy that are being dominated by men. But additional studies are required for a true cause of these distinctions to be established.

Returning to the relationship between facial traits and aggressiveness, we can notice that we unwillingly associate even an angry face with more physical force. Anger, as we all know, is one of the main precursors of aggressiveness and it is associated with an individual’s readiness towards force usage, therefore it is assumed that he is powerful. Those men who displayed more anger were creating the impression of having more chances to achieve success during interpersonal conflicts.

The ability to display these facial signs is inherited; we also inherit the ability to decipher and understand the meaning of non-verbal messages that are being sent by others. Anger, as a form of emotional expression, is considered, by scientists, to be an evolutionary adaptation that has benefited individuals in intragroup hierarchical competition; when it comes to emotional reactions, men are usually more furious than women [Sell et al., 2009; Hess et al., 2010; Sell et al., 2014].

Likewise, men with a stronger voice are considered to be more dominating and stouter; there is a correlation between the voice deepness and the physical size of the individual [Sell et al., 2010; Doll et al., 2014; Pisanski et al., 2014]. It is interesting that the quality of voice changes in people who reach high functions, both men and women. In other worlds, together with the hierarchical ascent, the voice becomes more grandiose as if it would correlate with an individual’s status, and those around him are capable of detecting these changes [Ko et al., 2014]. As in other species of animals, the voice can be an indirect indicator of an individual’s physical capacities in humans and it represents an important factor in hierarchical competitions and in natural selection as a whole, including the sexual one.

© Dorian Furtună, ethologist

Sources:
Photo: 2008 World’s Strongest Man Competition / Flickr / https://www.flickr.com/photos/jasonscottmeans/2843905735

1. Southern elephant seal // http://travelwild.com/antarctica-wildlife/southern-elephant-seal/
2. Gorilla // http://en.wikipedia.org/wiki/Gorilla#Physical_characteristics
3. Fighting. A Conversation between Sam Harris and Jonathan Gottschall // Sam Harris.org. April 13, 2015 / http://www.samharris.org/blog/item/fighting
4. Russian action star Mikhail Porechenkov caught firing a machine gun towards Ukraine // SBS. 3 Nov 2014 / http://www.sbs.com.au/news/article/2014/11/03/russian-action-star-mikhail-porechenkov-caught-firing-machine-gun-towards-ukraine
5. Temperament: Men, Testosterone, Wide Faces and Hockey Players // by INTJ. TemperamentMatters. November 16, 2013 / http://temperamentmatters.com/2013/11/16/temperament-men-testosterone-wide-faces-and-hockey-players/

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