Blue Eyes Help Men Reduce the Cost of Cuckoldry

Men with light eyes lack the dominant gene allele that codes for dark-brown eyes. Pairing with a woman who lacks the same allele must increase paternity confidence in these men, because any children with dark eyes would be extremely unlikely to have been fathered by them. This notion implies that men with light (blue or green) eyes should (1) prefer light-eyed women, especially in a long-term context, and (2) feel more threatened by light-eyed than by dark-eyed rivals. Yet because choosiness is costly and paternity concerns are entirely driven by the prospect of paternal investment, any such inclinations would be adaptive only in men who expect to invest in their children. Here I test these ideas using the data of over 1000 men who rated the facial attractiveness of potential partners, and the threat of potential rivals, whose eye color had been manipulated. Light-eyed men liked light-eyed women better (particularly as long-term companions), and feared light-eyed rivals more, than did dark-eyed men. An exploratory analysis showed that these large, robust effects disappeared in men who had felt rejected by their fathers while growing up—suggesting that such men are not expecting to invest in their own children either.

Stepfather Investment and Reproductive Outcomes Among US Couples

Although paternal investment in humans is highly variable, many males invest heavily in offspring. Biological fathers invest more in children than stepfathers, yet stepfathers do invest in their stepchildren, possibly to gain mating access to the mother. Stepfathers are also more likely to be abusive and antagonistic towards their stepchildren than biological fathers. Most previous research quantifies the investment of stepfathers in relation to biological fathers. However, no studies have explored how investment and relationship quality influences reproductive outcomes for stepfathers. I examine how stepfathers’ relationship quality with stepchildren associates with stepfathers’ reproductive success (number of biological children born to the couple) by utilizing the National Survey of Families and Households longitudinal survey of American couples. I also examine how mother’s financial autonomy may moderate the relationship between investment and reproductive success. Results show some evidence that stepfather investment can improve reproductive success, but these results are not particularly strong and may be difficult to interpret.

Kin recognition and step-paternal investment: the effect of childhood co-residence duration

Evolutionarily relevant nepotistic kin investment requires reliable kin detection. Evolutionary scholars have argued that childhood co-residence is one of the most important indirect cues for kinship. While childhood co-residence duration has been found to correlate with kin investment in intragenerational studies (i.e., among siblings), intergenerational investigations considering the association between childhood co-residence duration and kin investment have been scarce. Here, we investigate whether the investment of biological and stepfathers is correlated with childhood co-residence duration. We used data from adolescents and adults (aged 17–19, 27–29, and 37–39 years) from the German Panel Analysis of Intimate Relationships and Family Dynamics (Pairfam), wave 2, collected in 2010–2011. Paternal investment was measured as financial and practical help, emotional support, intimacy, and emotional closeness. We found that while stepfathers invested less than biological fathers, both biological and stepfathers’ investments increased with increased childhood co-residence duration in most measures. Financial help correlated with childhood co-residence in stepfathers but not in biological fathers who helped financially more than stepfathers regardless of childhood co-residence duration. Emotional support, intimacy, and emotional closeness were correlated with childhood co-residence in both biological fathers and stepfathers. Practical help did not correlate with co-residence in either father. Thus, our results partially support the hypothesis that childhood co-residence duration serves as a kin detection cue and directs intergenerational altruism.

Phenotypic Mimicry Distinguishes Cues of Mating Competition From Paternal Investment in Men’s Conspicuous Consumption

Evolutionary psychologists propose that men’s conspicuous consumption facilitates mate attraction because it predicts resource investment in offspring. This article elaborates on the ultimate functions of men’s luxury displays based on Life History Theory. Three studies provide evidence for phenotypic mimicry, in which consumer product features mimicking male secondary sex characteristics indicate investment in mating competition, at the expense of paternal investment. Men owning shirts with larger luxury brand logos were rated higher on mating effort, lower on parental investment, higher on interest in brief sexual affairs, lower on interest in long-term committed romantic relationships, higher in attractiveness to women for brief sexual affairs, lower in attractiveness to women for long-term committed relationships, and higher in developmental environment unpredictability compared with men owning shirts displaying a smaller logo. Participants recognized the strategic use of luxury display properties across social contexts but did not consistently associate product properties with owners’ physiological characteristics.

Elevated temperature, but not decreased pH, impairs reproduction in a temperate fish

Fish reproductive success is linked to the ability of couples to mate and produce clutches that successfully hatch. Environmental stressors like high temperature and low pH can jeopardize this energetically costly process. In this study, exposure to high temperature and low pH was tested on a marine temperate species, Gobiusculus flavescens, to evaluate effects on reproductive performance. Breeding pairs were assigned to different temperatures (+ 0 °C, + 3 °C relative to in situ temperature) and pH levels (8.0, 7.6), in a cross-factorial design for a 3-month period. Reproduction activity, success, and paternal investment were measured throughout the exposure period. Results show reproduction is impaired by elevated temperature, while low pH had little impact. Breeding pairs under high temperature had 3% to 10% hatching success, up to 30% less eggs and eggs up to 20% smaller. Although paternal investment was not affected by tested parameters, males of breeding pairs exposed to elevated temperature had smaller gonadosomatic indexes, which might indicate a lack of investment in the reproductive process. Overall, results show that elevated temperature, expected more frequently in the near future, as a consequence of global warming, may impair key processes like reproduction in temperate fish, with potential consequences for fitness and population replenishment.