Testosterone, facial symmetry and cooperation in the prisoners' dilemma

Abstract

Recent research has analyzed how individual characteristics, like the exposure to different hormones and symmetry, affect decision-making and strategic behaviour. The present article investigates the effect of symmetry, of exposure to testosterone (T) in utero and during puberty and of current T on cooperation in a Prisoners' Dilemma Game (PDG). T is a hormone with well known effect on males' behaviour, and that promotes activities that seek to increase reproductive success. Fluctuating Asymmetry (FA) reflects the ability of the organism to maintain a stable development and it is usually employed as a variable reflecting genetic quality (low FA values are thought to signal higher genetic quality). Our results show that subjects with intermediate levels of second to fourth digit ratio (a proxy of exposure to T in utero) and with high FA cooperate more often in the PDG. We also observe that the latter effect is due to the fact that FA has an impact on subjects' expectations about the behaviour of their counterpart in the game. These results reinforce the described link between markers related to genetic quality and cooperative behaviour. This possible linkage of individual condition and pro-social behaviour in humans clearly merits further attention.

Do risk and time preferences have biological roots?

“…Development or examination of accurate but more applicable methods of measuring hormonal levels can help researchers assess the robustness of our findings related to the biology of risk and time preferences. (Bröder & Hohmann, 2003;Burns, 2006;Buser, 2010;Buser, 2011;Chen et al, 2009;Da Silva et al, 2011;Pearson & Schipper, 2011;Schipper, 2011a;Wozniak et al, 2011) Indirect measures of prenatal exposure to hormones (D2:D4 ratio) (N=19) (Apicella et al, 2008;Apicella et al, 2011;Brañas-Garza & Rustichini, 2011;Buser, 2011;Coates & Page, 2009;Da Silva et al, 2011;Dreber & Hoffman, 2007;Garbarino et al, 2011;Guiso & Rustichini, 2011;Millet & Dewitte, 2006;Millet & Dewitte, 2008;Millet & Dewitte, 2009;Pearson & Schipper, 2012;Sanchez-Pages & Turiegano, 2010;Sapienza et al, 2009;Schipper, 2011a;Trahms et al, 2010;van den Bergh & Dewitte, 2006) Direct measures of hormones (saliva or blood samples) (N=11) (Apicella et al, 2008;Apicella et al, 2011;Burnham, 2007;Coates & Herbert, 2008;Sanchez-Pages & Turiegano, 2010;Sapienza et al, 2009;Schipper, 2011a;Schipper, 2011b;White et al, 2006;…”

“…Obviously the literature involves a wider variety of tasks and games including self-selection into competitive environments (Apicella et al, 2011;Buser, 2010;Wozniak et al, 2011), explorations of the Allais paradox (Da Silva et al, 2011), bidding behavior in auctions (Pearson & Schipper, 2012), decision making in trust, ultimatum, dictator, public good and prisoners' dilemma games (Burnham, 2007;Buser, 2011;Eisenegger et al, 2010;Kosfeld et al, 2005;Millet & Dewitte, 2006;Millet & Dewitte, 2009;Sanchez-Pages & Turiegano, 2010;van den Bergh & Dewitte, 2006;Zak et al, 2005a;Zak et al, 2005b;Zak et al, 2007;Zethraeus et al, 2009) as well as entrepreneurship decisions (White et al, 2006). A critical synthesis of the above mentioned studies that would explain differences in methods, findings etc.…”

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…Several studies have examined whether facial asymmetry is related to whether faces are rated as attractive by the subjects themselves or by other viewers, and some found a significant association [57,249,295,374], whereas others found no association [102,105] or a weak association only for male but not female faces [247]. Some analyses showed an association between fluctuating asymmetry and facial femininity or masculinity in humans [375], but others did not [102,374], nor was there a correlation between femininity or masculinity of skull shape and fluctuating asymmetry in baboons, chimpanzees, and gorillas [110]. Also, no correlation was found between facial fluctuating asymmetry and the ratio of second to fourth digits, which relates to prenatal exposure to sex hormones [375,376].…”

“…Some analyses showed an association between fluctuating asymmetry and facial femininity or masculinity in humans [375], but others did not [102,374], nor was there a correlation between femininity or masculinity of skull shape and fluctuating asymmetry in baboons, chimpanzees, and gorillas [110]. Also, no correlation was found between facial fluctuating asymmetry and the ratio of second to fourth digits, which relates to prenatal exposure to sex hormones [375,376]. By contrast, short-term effects of hormonal levels on asymmetry have been shown, as the asymmetry of facial shape changes during the menstrual cycle of individual women [294].…”

Is sociopolitical egalitarianism related to bodily and facial formidability in men?

“…Price et al (2015) also found that men with more attractive bodies are less egalitarian on a variety of behavioural and psychological measures, but found no relationship between bodily formidability and these egalitarianism measures. Several experimental economic studies (Sanchez-Pages & Turiegano, 2010;Shinada & Yamagishi, 2014;Takahashi, Yamagishi, Tanida, Kiyonari, & Kanazawa, 2006;Zaatari & Trivers, 2007) have demonstrated that relatively inegalitarian resource distribution decisions are made by men who possess traits that are judged as more attractive by others, and/or who possess more symmetrical faces and bodies (symmetry being a putative indicator of attractiveness, health, and underlying genotypic quality [Møller, 2006]). Finally, Holtzman, Augustine, and Senne (2011) reported that bodily/facial symmetry relates negatively to prosocial personality traits, including some related to egalitarianism (e.g., fairness, empathy), in both men and women.…”