Having too many men – although sex ratio skew might increase competition and violence among some members of the population, overall levels of those same behaviors might decline

Ecological Sex Ratios and Human Mating. Jon K.Maner, Joshua M.Ackerman. Trends in Cognitive Sciences, December 28 2019. https://doi.org/10.1016/j.tics.2019.11.008

Abstract: The ratio of men to women in a given ecology can have profound influences on a range of interpersonal processes, from marriage and divorce rates to risk-taking and violent crime. Here, we organize such processes into two categories – intersexual choice and intrasexual competition – representing focal effects of imbalanced sex ratios.

Keywords: evolutionpsychologyrelationshipscognitionsexualitycompetition

SR = sex ratio

Conclusion
Although evolutionary psychology is sometimes viewed as focusing exclusively on phenomena assumed to be invariant across time, people, and cultures (psychological universals), several lines of research demonstrate the important role of ecological contingencies [12]. Humans display enormous flexibility, calibrating their behavior in a facultative manner to variables in the local environment [13]. Ecological SRs reflect a key variable to which men and women adjust their mating behavior. Those adjustments are highly strategic and are aimed at enhancing reproductive success given features of the mating environment and of the individual person. This last insight helps answer our opening question about the consequences of having too many men – although SR skew might increase competition and violence among some members of the population, overall levels of those same behaviors might decline. Identifying individual differences and situational factors that moderate SR effects, as well as proximate cognitive mechanisms that underlie those effects, provides a fertile ground for future research. Future work would also benefit from delineating more clearly the specific social cues and population boundaries that people use to assess SRs (Box 1).

Box 1. Unanswered Questions about Ecological SRs
• What specific cues and population boundaries do people use to assess SRs?
o Do people base their assessments on immediate interaction partners, their local communities, or broader social/ecological borders?
o How should researchers navigate difficulties associated with analysis of data aggregated at population levels (e.g., problems can arise when inferring individual processes from regionally aggregated data)? [7]

• What degree of SR skew is required to affect behavioral outcomes?
o Few systematic analyses of this question exist in humans. Do minor imbalances in SRs affect behavior, or are larger and more obvious imbalances required?

• When should various types of SRs (e.g., adult SR vs. operational SR) be distinguished theoretically and empirically?
o The ecological literature focuses primarily on adult SRs, but these sometimes include nonreproducing individuals less relevant for mating dynamics (e.g., elderly, sexual minorities).

• On what key ecological, cultural, and individual difference factors are SR effects contingent?
o Relatively little work has been done to address this question, but preliminary evidence supports certain factors (e.g., mate value, social status, conflict levels) and not others (e.g., life expectancy, wealth).

• When do SRs have effects beyond those immediately predicated on mating dynamics?
o What other downstream behaviors and cognitions are influenced by SR skew? Some evidence suggests, for example, that SRs affect distal outcomes including investment behavior, consumer spending, career choices, and health decisions.