Abstract: The decision to allocate time and energy to find multiple sexual partners or raise children is a fundamental reproductive trade-off. The Strategic Pluralism Hypothesis argues that human reproductive strategies are facultatively calibrated towards either investing in mating or parenting (or a mixture), according to the expression of features dependent on the individual's condition. This study seeks to test predictions derived from this hypothesis in a sample of 242 young men (M ± SD = 22.12 ± 3.08) from Chile’s 5th Region (33֯ south latitude). Specifically, two predictions were considered that raise questions about the relationship between traits related to physical and psychological attractiveness (fluctuating facial asymmetry and self-perception of attractiveness) and competitive skills (baseline testosterone and self-perception of fighting ability) with short-term reproductive strategies. Our results indicate that psychological features related to the self-perception of physical attractiveness are related to short-term reproductive strategies. However, no evidence was found that fluctuating facial asymmetry, basal levels of testosterone and self-perception of fighting ability were related to short-term reproductive strategies. These results support the existing evidence of the importance of physical attractiveness in calibrating men’s reproductive strategies but cast doubts about the role of fluctuating facial asymmetry. They also suggest that traits related to physical attractiveness, in comparison to competitive capabilities, play a more important role in calibrating men’s short-term reproductive strategies.
Discussion
The Strategic Pluralism Hypothesis explains the conditionality of human reproductive strategies and the resolution of the trade-off between investment in multiple partners and investment in parental care [1]. This hypothesis considers that there are biological, psychological and anthropometric factors that calibrate reproductive behavior according to the context in which the individual faces the aforementioned trade-off. This study proposes two predictions that were mainly not sustained as only an effect of self-perceived physical attractiveness on short-term sociosexual orientation was found. Our results emphasize the role of physical attractiveness in men on the unfolding of unrestricted reproductive strategies (short-term strategies at the scale of sociosexual orientation). The main result indicates that the traits of attractiveness have an effect on unrestricted reproductive strategies whereas fighting abilities do not.
The first prediction sought to determine if there is a positive relationship between traits associated with physical attractiveness and traits associated with competitive abilities with unrestricted reproductive strategies. Also, we postulated that these effects should be moderated by psychological variables related to self-perception of physical attractiveness and fighting ability, respectively. Our results suggest that only self-perceived attractiveness does affect unrestricted sociosexual orientation when evaluated with the full data set. However, we failed to show the expected effect of fluctuating facial asymmetry on unrestricted reproductive strategy either as a main effect or moderated by self-perception of physical attractiveness. Conversely to our results, some studies found evidence that fluctuating facial asymmetry is associated with the implementation of short-term reproductive strategies [20], with the number of sexual partners over one’s lifetime [50, 51], and with the perception of attractiveness [14]. Several lines of evidence may explain our contrasting results. First, despite that symmetry is associated with attractiveness, this association is weak and other facial features like averageness may play a more important role in perceived attractiveness [52]. Also, facial fluctuating asymmetry is assumed to underlie variation in facial symmetry between individuals being an indirect measure of overall symmetry. This circumstance may lessen its relationships with attractiveness. And more importantly, there exists controversy about the relationship between evolutionary relevant features and levels of fluctuating facial asymmetry [21]. If it is the case that fluctuating asymmetry is not an accurate proxy of developmental instability, the rationale about the importance of fluctuating facial asymmetry as a trait related to short-term mating strategies weakens and other variables as muscularity or strength could be better predictors of an unrestricted sociosexual orientation than fluctuating facial asymmetry [42, 53]. However, this is an unresolved issue as positive evidence about the importance of fluctuating asymmetry as a proxy of health and mating success was also reported [14]. An alternative explanation of our results is that fluctuating facial asymmetry affects unrestricted sociosexual orientation but this effect is mediated rather than moderated by psychological features. In this regard, previous investigations have found that the effects of morphological features on the psychology of unrestricted male sociosexual behavior were mediated by self and third-party perceptions of physical attractiveness [23, 54]. However, our cross-sectional design precluded us to investigated mediation relationships in an accurate way [55].
Self-perception of fighting ability was not related to unrestricted sociosexual orientation. In this regard, other studies have established a relationship between fighting and mate value [43], which is defined as “the complete set of characteristics that an individual has in a given moment and in a particular context that affects his capacity to successfully find, attract and keep a partner” [56]. According to Muñoz-Reyes et al. [43], fighting ability is associated with the mate value of a partner, which implies a positive relationship between this variable and men’s assessments of their chances of finding partners, and therefore of employing intrasexual competition strategies, which implies a high degree of self-confidence in the search for partners. It has been established that the self-perception of fighting ability is also associated with aggressive behavior [25]. These findings indicate that it is plausible to support that fighting ability is a conflict resolution mechanism in situations of intrasexual competition, which is consistent with studies that have found a positive association between traits associated with fighting abilities and reproductive success [23, 43, 57]. Despite the above evidence, our null results may indicate that self-perception of fighting ability when evaluated jointly with self-perception of attractiveness is not an important factor related to unrestricted strategies. That can be explained if we assume that mate choice or indirect competition through showing off attractive features may be more important in industrialized societies rather than the direct competition through fights.
No effect was found for baseline testosterone levels on short-term reproductive strategies. Studies have associated testosterone with the search for social status [58], self-confidence in competitive situation [39] and the adoption of dominant roles in economic environments [29]. Consequently, testosterone can be considered a social hormone associated with status-seeking and not so much with aggression in itself. Status in turn could be related to different reproductive strategies according to the way it is acquired. The relationship between testosterone and reproductive strategies has been explored in other studies and evidence has been found that favors the role of testosterone as a promoter of short-term strategies. For example, Edelstein et al. [32] found an interaction between unrestricted sociosexuality and the relational status of men and established that men in relationships with partners, but that have interest in extramarital relationships, have similar testosterone levels as those of single men, producing a positive attitude about unrestricted strategies. Puts et al. [38] established that there is a negative relationship between the number of sexual partners and baseline testosterone levels, and a positive relationship between high levels of baseline testosterone and unrestricted sociosexual psychology (desire and attitudes). Although this investigation employed a reduced version of the sociosexual orientation questionnaire [59], a relationship was found between baseline testosterone levels and an orientation toward short-term strategies. The reduced sample in the model that assesses the effect of baseline testosterone on reproductive strategies could explain the null result with respect to this variable.
Based on the second prediction, a relationship was expected between attractiveness and competitive abilities on unrestricted strategies. We failed to find that association as the effect of self-perception of attractiveness was not moderated by self-perception of fighting abilities. This result further suggests that fighting abilities do not play a major role in unrestricted sociosexual orientation both directly or moderating the effects of physical attractiveness. In addition, it is important to consider that self-perception of fighting ability may not necessarily be related to the willingness to compete for new mates, but may be also associated with the willingness to protect a current mate and the offspring. In this regard, that feature is expected to be related to more restricted sociosexual orientation reflecting a higher inversion in parental care [6].
Among the limitations of this research is the inclusion of only one anthropometric measurement (fluctuating facial asymmetry), which, although a common measurement to study physical attractiveness, could be complemented with others that are also considered attractive features and, in some cases, more important in explaining facial attractiveness [52]. Another limitation was the loss of data due to the storage of samples and handling of the testosterone kit, despite following protocols tested in other investigations. In addition, our null results of the effect of basal testosterone on sociosexuality do not preclude a potential relationship between testosterone changes elicited on a mating context and sociosexuality. Changes in testosterone levels and additional anthropometric variables associated with unrestricted strategies should be included in future research, such as facial masculinization [35], height [e.g. 60] and body mass [e.g. 42]. Finally, individuals in our study expected to participate in a competitive game and to be paid according to their performance. Despite that these tasks were performed after the measures taken for the current study; they may introduce some noise in the study.
In conclusion, the present study contributes some evidence that supports the Strategic Pluralism Hypothesis as we found that psychological features of attractiveness are related to unrestricted reproductive strategies among men. However, our results are not conclusive about the potential role of competitive skills (measured by basal levels of testosterone and self-perception of fighting ability) and the role of fluctuating facial asymmetry in explaining unrestricted reproductive strategies. These findings encourage further research on traits that may be affecting the cost-benefits balance in the reproductive trade-off that men have between maximizing the number of sexual partners and investing in parental care, and designs that allowed to investigate mediation relationships considering the importance of the relationship among anthropometric features on the self-perception (that is, psychological features) of subjects when the reproductive trade-off is solved.
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