In many animal populations, status in a social hierarchy is positively correlated with reproductive success (Ellis 1995; Strier 2003). Greater reproductive success may result from increased access to resources, decreased harassment by other group members, and the reduced risk of predation inherent in enhanced social status. In both sexes, this promotes reduced emotional stress and better health, leading to greater chances of copulation, conception, and birth of healthy offspring (Ellis 1995). This trend is evident in both preindustrial and contemporary Western human societies. Male status within communities such as the !Kung of the Kalahari and the Aché of Paraguay relates positively to number of surviving offspring, as does income in the contemporary United States and Britain (Buss 1989; Hopcroft 2006; Kaplan and Hill 1985; Nettle and Pollet 2008; Pennington and Harpending 1993).

Status is often determined by male-male competition (Altmann et al. 1995). Across a range of mammalian species, testosterone closely tracks the results of such dominance interactions (Zilioli and Watson 2012). Furthermore, increased testosterone levels may encourage dominant behavior intended to achieve or maintain high status. The changes in androgenization caused by competition may have consequences for future status-seeking behavior, as proposed by the reciprocal model of testosterone and status (Mazur and Booth 1998). As such, testosterone both affects and is affected by status-seeking competition. The reciprocal model may therefore illuminate both winning and losing streaks (Booth et al. 1989).

Among human males, testosterone levels generally show a relative increase following victory compared with defeat in both athletic and non-athletic contests, as observed in tennis, wrestling, chess, timed reaction tests, monetary competitions, tasks of chance, and the vicarious experience of winning amongst sports fans (Apicella et al. 2014; Archer 2006; Bernhardt and Dabbs 1997; Bernhardt et al. 1998; Booth et al. 1989; Elias 1981; Gladue et al. 1989; Mazur and Lamb 1980; Mazur et al. 1992; McCaul et al. 1992). Similar findings have recently been reported in non-industrialized human populations with respect to hunting success (Trumble et al. 2013) and in primates following a dominance interaction (Muller and Wrangham 2001). This relationship is not surprising since competitions have been described as formalized contests for status in which winners enjoy a status gain relative to losers (Edwards 2006). However, several investigations report nonsignificant differences in testosterone levels between winners and losers in both individual and team sports as well as video game contests (Gonzalez-Bono et al. 2000; Mazur et al. 1997; Salvador et al. 1987, 1990; Suay et al. 1999).

The Role of Testosterone in Male Mating Effort

According to the Immunocompetence Handicap Hypothesis (Folstad and Karter 1992), which builds upon Zahavi’s (1975) handicap hypothesis for the evolution of secondary sexual characteristics, testosterone mediates signals of underlying reproductive status and quality in humans. Male muscle mass, whose synthesis is enhanced by testosterone, may serve as such a signal in humans (Griggs et al. 1989; Kadi 2008). Muscular men are more sexually attractive than slender men and report more sexual partners as well as a younger age at first intercourse (Frederick and Haselton 2007; Gallup et al. 2007; Lavrakas 1975). Muscularity is advantageous in male intrasexual competition, as well as in provoking jealousy in male rivals (Bribiescas 2001; Dijkstra and Buunk 2002; Frederick and Haselton 2007). Testosterone therefore plays an important moderating role in the physiological aspects of male reproductive effort through increasing chances of successful male-male competition and also in attracting females.

Any signal that is expensive to construct and maintain from an energetic or otherwise fitness-related perspective will serve as an indicator of male quality (Andersson 1994). Selection may then favor the opposite sex being attracted to such signals (Graffen 1990; Zahavi 1975). Skeletal muscle mass is an expensive tissue to maintain, accounting for approximately 20% of human male basal metabolic rate (Elias 1992). Further burden is placed on the male through testosterone-induced suppression of the immune system (Folstad and Karter 1992). Elevated levels of testosterone have been linked to increased incidence of prostate cancer, oxygen radical production, reduced tissue and organ maintenance, and injury associated with aggressive confrontational behavior (see Lassek and Gaulin 2009; Muehlenbein 2006). The high energetic demands associated with muscle mass mean that during periods of energetic deficit there may be a suppression of testosterone levels. This leads to reduced somatic reproductive effort by decreasing muscle mass (Bribiescas 2001). However, although there is evidence for a direct link between testosterone and male musculature in nonhuman primates, similar evidence in humans is considered weak (Alvarado et al. 2015). Alvarado et al. (2015) present evidence suggesting that muscle mass and strength are enhanced by fatherhood, despite decreased testosterone levels. This “paternal provisioning hypothesis” predicts that men’s skeletal muscle mass is less dependent on testosterone than it is for nonhuman primates.

Testosterone has also been implicated in the behavioral aspects of male mating effort (see Roney and Gettler’s 2016 review of the role of testosterone in mating effort). Underscoring the motivational role of male sexual desire, Darwin noted that “males. . . are almost always the more active and most often, the initiators of sexual interactions” (Darwin 1871). Although sexual desire, or libido, is a concept that has evaded precise definition (Bancroft 1988), many studies have attempted to understand how it is generated. Despite the literature being somewhat mixed, and recent work suggesting no significant association between testosterone and desire in men (Van Anders 2012), androgens appear to play an important role in its production (Baumeister et al. 2001). In addition to impacting sexual motivation when a threshold is reached (Bagatell et al. 1994), androgens regulate the competitive behavioral components of male mating effort as well as mediating confidence and assertiveness in social situations—qualities deemed to be beneficial in male mating effort (Bagatell et al. 1993; Ellison 2003; Morley 2003). Consequently, higher levels of testosterone have been found to be associated with a greater number of sexual partners (Bogaert and Fisher 1995) and mating success (defined as the number of sexual partners an individual has had; Peters et al. 2008). Furthermore, men who are single or have multiple sexual partners have been shown to have higher testosterone levels than men in committed monogamous relationships (McIntyre et al. 2006; Van Anders et al. 2007; Van Anders and Watson 2007). Therefore, in addition to influencing libido, high testosterone levels seem to facilitate heightened competition for female mates, the adoption of short-term strategies, and the subsequent pursuit of multiple mates. The present study aims to build on previous work (van der Meij et al. 2012), which demonstrated that elevated testosterone levels following male-male competition may be followed by increased affiliative behavior toward women, such as increased smiling and eye contact. This will enhance understanding of whether human short-term fluctuations in testosterone reveal analogous behavioral effects of male mating effort at the intraindividual level.

Variations in Testosterone and Parenting Effort

Life history theory predicts trade-offs in energetic investment in key physiological processes such as reproduction, maintenance, and growth (Charnov 1993; Roff 1992; Stearns 1992). Reproductive effort is the sum of mating (time and energy invested in attraction, pursuing mates, and competition) and parental effort (all forms of energy and time invested in offspring). The trade-off between mating and parental effort may be one of the most common life history trade-offs (McGlothlin et al. 2007). In addition to varying across species, the outcome of this trade-off may also vary within species and individuals depending on age and environmental conditions. In species with biparental care, such as humans and birds, males confront a trade-off between the acquisition of mates and investment in offspring since these activities compete for time and energy given limited budgets. In these species, variations in testosterone levels between males appear to reflect different allocations of mating versus parental effort.

There is convincing evidence that testosterone levels are reduced in men who are in love, married, or otherwise pair bonded relative to those of single men (Booth and Dabbs 1993; Burnham et al. 2003; Gettler et al. 2011a; Gray et al. 2002, 2004a, 2007a; Marazziti and Canale 2004; Mazur and Michalek 1998; McIntyre et al. 2006). In addition, studies in a variety of human populations show that the transition to, or the attainment of, fatherhood is marked by a decrease in testosterone (although there are exceptions—fathers with older, or more than four, children do not exhibit this reduction in testosterone; e.g., Alvergne et al. 2009; Berg and Wynne-Edwards 2001; Fleming et al. 2002; Gettler et al. 2011b; Gray et al. 2004b, 2006, 2007b; Kuzawa et al. 2009; Muller et al. 2009; Perini et al. 2012; Pollet et al. 2013; Storey et al. 2000).

According to a number of researchers (e.g., Gray et al. 2002; Storey et al. 2000), lower testosterone facilitates paternal caregiving and increased investment in offspring by decreasing competing energetic expenditures in competition and additional mating (which could include extra-pair bonding). In addition to varying according to marital status, testosterone also appears to vary in conjunction with men’s reported ongoing behavioral and emotional investment in parenting effort. Mascaro et al. (2013) found that both testosterone levels and testes volume were negatively correlated with paternal caregiving in fathers, as determined from mothers’ responses on measures of parental responsibility and activity. Similarly, low morning testosterone levels of Senegalese men and low evening levels of testosterone in Filipino men had the highest spouse- and self-report investment in childcare. In addition, Fleming et al. (2002) report that fathers felt more sympathy and experienced a greater need to respond to infant cries if they had lower testosterone levels.

Taken together these findings suggest that the regulation of male reproductive trade-offs through the endocrine system may be a common feature of human populations (Archer 2006). Whether this androgenic regulation is accompanied by complementary psychological changes is much less well studied or established. We might expect, however, that both the physiology and the psychology of human males may reflect facultative trade-offs between mating and parenting effort. Moreover, psychological changes may underlie or mediate the relationship between endocrine function and reproductive behavioral outcomes.

To date, it is unclear whether the transient testosterone surges following victory, which may have implications for male reproductive effort, emerge in conjunction with the physical effort of winning, or as a result of the social perception of winning. An experimental design in which the competition outcome is manipulated would disentangle the two possibilities (similar to the work of Gladue et al. 1989), allowing consideration of the effects of perceived competition outcome separately from the physical act of winning or losing.

Trade-Offs between Mating and Parental Effort as a Function of Perceived Mate Value

Rationally speaking, the optimal reproductive strategy for human males is to seek multiple shorter-term relationships with reduced investment in offspring (Bateman 1948; Trivers 1972). This is due to the positive relationship between copulation frequency and reproductive success, and the lower level of parental investment minimally required of men (Buss 1989). However, as a result of the heightened requirements imposed by women on casual mates, many men have reduced opportunities to engage in short-term mating strategies (Buss and Schmitt 1993; Gangestad and Simpson 2000). Although the majority of men may have the ability to provide at least some care for children or some level of ongoing resources, fewer have possessed the level of attractiveness to consistently qualify them as short-term mates. Therefore, for many men, the pursuit of a long-term mating strategy with a focus on a single mate and their progeny is their best option. Only those men most attractive to women may be successful in pursuing casual sexual relationships. Therefore trade-offs between mating and parenting effort may vary as a function of men’s SPMV, with higher levels increasing male initiative in seeking partners and mating opportunities versus engaging in relationships associated with investment in children.

Human males and females appear to possess some awareness of their own value as a mate, with one’s self-perceived mate value (SPMV) potentially motivating or mediating mating strategies and effort (Landolt et al. 1995; Surbey and Brice 2007). To test this possibility, Surbey and Brice (2007) experimentally enhanced men’s SPMV resulting in an increase in behavioral intentions to pursue casual over long-term relationships. The attitudinal component of the Sociosexuality Orientation Inventory (SOI, Simpson and Gangestad 1991), a gauge of one’s orientation toward engaging in casual, uncommitted sexual relationships, was similarly heightened. Results further showed that increased SPMV drove these changes in mating strategy rather than a rise in global self-esteem, a psychological characteristic also associated with men’s mating preferences and SPMV (Goodwin et al. 2012; Kiesler and Baral 1970; Surbey and Brice 2007). However, SPMV may be a distinct component of self-esteem especially involved in mating contexts (e.g., Brase and Guy 2004; Kirkpatrick et al. 2002; Webster and Kirkpatrick 2005) and not functionally equivalent to global measures of self-esteem. Moreover, it appears to be a partly inherent, but dynamic, psychological attribute that fluctuates opportunistically in men (e.g., Yong and Li 2012). That SPMV may also be manipulated as a result of male-male competition, or contests between men, including athletic contests typically found to increase testosterone levels in victors, was thus explored.