The pandemic exposes human nature: 10 evolutionary insights.

Humans and viruses have been coevolving for millennia. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, the virus that causes COVID-19) has been particularly successful in evading our evolved defenses. The outcome has been tragic-across the globe, millions have been sickened and hundreds of thousands have died. Moreover, the quarantine has radically changed the structure of our lives, with devastating social and economic consequences that are likely to unfold for years. An evolutionary perspective can help us understand the progression and consequences of the pandemic. Here, a diverse group of scientists, with expertise from evolutionary medicine to cultural evolution, provide insights about the pandemic and its aftermath. At the most granular level, we consider how viruses might affect social behavior, and how quarantine, ironically, could make us susceptible to other maladies, due to a lack of microbial exposure. At the psychological level, we describe the ways in which the pandemic can affect mating behavior, cooperation (or the lack thereof), and gender norms, and how we can use disgust to better activate native "behavioral immunity" to combat disease spread. At the cultural level, we describe shifting cultural norms and how we might harness them to better combat disease and the negative social consequences of the pandemic. These insights can be used to craft solutions to problems produced by the pandemic and to lay the groundwork for a scientific agenda to capture and understand what has become, in effect, a worldwide social experiment.

Endocrinological effects of social exclusion and inclusion: Experimental evidence for adaptive regulation of female fecundity.

When current conditions are probabilistically less suitable for successful reproduction than future conditions, females may prevent or delay reproduction until conditions improve. Throughout human evolution, social support was likely crucial to female reproductive success. Women may thus have evolved fertility regulation systems sensitive to cues from the social environment. However, current understanding of how psychological phenomena might affect female ovarian function is limited. In this study, we examined whether cues of reduced social support-social ostracism-impact women's hormone production. Following an in-lab group bonding task, women were randomly assigned to a social exclusion (n = 88) or social inclusion (n = 81) condition. After social exclusion, women with low background levels of social support experienced a decrease in estradiol relative to progesterone. In contrast, socially-included women with low background social support experienced an increase in estradiol relative to progesterone. Hormonal changes in both conditions occurred specifically when women were in their mid-to-late follicular phase, when baseline estradiol is high and progesterone is low. Follow-up analyses revealed that these changes were primarily driven by changes in progesterone, consistent with existing evidence for disruption of ovarian function following adrenal release of follicular-phase progesterone. Results offer support for a potential mechanism by which fecundity could respond adaptively to the loss or lack of social support.

Exposure to perceived male rivals raises men's testosterone on fertile relative to nonfertile days of their partner's ovulatory cycle.

The challenge hypothesis posits that male testosterone levels increase in the presence of fertile females to facilitate mating and increase further in the presence of male rivals to facilitate male-male competition. This hypothesis has been supported in a number of nonhuman animal species. We conducted an experiment to test the challenge hypothesis in men. Thirty-four men were randomly assigned to view high-competitive or low-competitive male rivals at high and low fertility within their partner's ovulatory cycle (confirmed by luteinizing hormone tests). Testosterone was measured upon arrival to the lab and before and after the manipulation. Based on the challenge hypothesis, we predicted that a) men's baseline testosterone would be higher at high relative to low fertility within their partner's cycle, and b) men's testosterone would be higher in response to high-competitive rivals, but not in response to low-competitive rivals, at high relative to low fertility within their partner's cycle. Contrary to the first prediction, men's baseline testosterone levels did not differ across high and low fertility. However, consistent with the second prediction, men exposed to high-competitive rivals showed significantly higher post-test testosterone levels at high relative to low fertility, controlling for pre-test testosterone levels. Men exposed to low-competitive rivals showed no such pattern (though the fertility by competition condition interaction fell short of statistical significance). This preliminary support for the challenge hypothesis in men builds on a growing empirical literature suggesting that men possess mating adaptations sensitive to fertility cues emitted by their female partners.

Changes in women's feelings about their romantic relationships across the ovulatory cycle.

According to the dual mating hypothesis, women possess two overlapping suites of mate-choice mechanisms: one leading to preferences for sexually desirable men who have high-fitness genes and one leading to preferences for men who are able to invest in a woman and her children. Evidence increasingly demonstrates that women's preference for sexual desirability (but not investment attractiveness) increases when women are most fertile within the ovulatory cycle. Little is known, however, about the implications of these preference shifts for women's relationships with their long-term partners. Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner's faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women's commitment to their relationship. Therefore, partner sexual desirability predicts women's high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women's reproductive hormones play an important role in relationship dynamics.

Sexual regret: evidence for evolved sex differences.

Regret and anticipated regret enhance decision quality by helping people avoid making and repeating mistakes. Some of people's most intense regrets concern sexual decisions. We hypothesized evolved sex differences in women's and men's experiences of sexual regret. Because of women's higher obligatory costs of reproduction throughout evolutionary history, we hypothesized that sexual actions, particularly those involving casual sex, would be regretted more intensely by women than by men. In contrast, because missed sexual opportunities historically carried higher reproductive fitness costs for men than for women, we hypothesized that poorly chosen sexual inactions would be regretted more by men than by women. Across three studies (Ns = 200, 395, and 24,230), we tested these hypotheses using free responses, written scenarios, detailed checklists, and Internet sampling to achieve participant diversity, including diversity in sexual orientation. Across all data sources, results supported predicted psychological sex differences and these differences were localized in casual sex contexts. These findings are consistent with the notion that the psychology of sexual regret was shaped by recurrent sex differences in selection pressures operating over deep time.

Does breastfeeding offer protection against maternal depressive symptomatology?: A prospective study from pregnancy to 2 years after birth.

Mothers who breastfeed typically exhibit lower levels of depressive symptomatology than mothers who do not. However, very few studies have investigated the directionality of this relationship. Of the prospective studies published, all but one focus exclusively on whether maternal depression reduces rates of subsequent breastfeeding. This study again examines this relationship, but also the reverse-that breastfeeding might predict lower levels of later depression. Using multilevel modeling, we investigated the relationship between breastfeeding and self-reported depressive symptomatology in 205 women followed prenatally and at 3, 6, 12, and 24 months after birth. Consistent with previous research, women with prenatal depressive symptomatology weaned their infants 2.3 months earlier, on average, than women without such symptomatology. We also found, however, that women who breastfed more frequently at 3 months postpartum showed greater subsequent declines in depressive symptomatology over time compared to women who breastfed less frequently, resulting in lower absolute levels of depressive symptoms by 24 months postpartum, controlling for important confounds. In sum, these findings are consistent with a bidirectional association between breastfeeding and depression, with prenatal depression predicting less breastfeeding soon after birth and breastfeeding predicting declines in maternal depression up to 2 years after birth. We discuss mechanisms that could potentially explain these associations and avenues for future research.

Body odor attractiveness as a cue of impending ovulation in women: evidence from a study using hormone-confirmed ovulation.

Scent communication plays a central role in the mating behavior of many nonhuman mammals but has often been overlooked in the study of human mating. However, a growing body of evidence suggests that men may perceive women's high-fertility body scents (collected near ovulation) as more attractive than their low-fertility body scents. The present study provides a methodologically rigorous replication of this finding, while also examining several novel questions. Women collected samples of their natural body scent twice--once on a low-fertility day and once on a high-fertility day of the ovulatory cycle. Tests of luteinizing hormone confirmed that women experienced ovulation within two days of their high-fertility session. Men smelled each woman's high- and low-fertility scent samples and completed discrimination and preference tasks. At above-chance levels, men accurately discriminated between women's high- and low-fertility scent samples (61%) and chose women's high-fertility scent samples as more attractive than their low-fertility scent samples (56%). Men also rated each scent sample on sexiness, pleasantness, and intensity, and estimated the physical attractiveness of the woman who had provided the sample. Multilevel modeling revealed that, when high- and low-fertility scent samples were easier to discriminate from each other, high-fertility scent samples received even more favorable ratings compared with low-fertility scent samples. This study builds on a growing body of evidence indicating that men are attracted to cues of impending ovulation in women and raises the intriguing question of whether women's cycling hormones influence men's attraction and sexual approach behavior.

Why women choose divorce: An evolutionary perspective.

In Western dual-educated, male-female marriages, women who divorce face greater burdens because of decreased income and primary or sole responsibility for caring for children than men who divorce. Why, then, do these women initiate divorce more and fare better psychologically after a divorce than men? Here, we articulate an evolutionary mismatch perspective, informed by key findings in relationship science. We argue that mismatches between women's evolved preferences and configurations of modern marriage often clash, producing dissatisfaction. Women's unprecedented career ascendance also affords women ever more freedom to leave. We discuss pressures from social expectations for men and women that contribute to or compound these vulnerabilities. We conclude with key questions for future research, which can contribute to strategies for mitigating relationship dissatisfaction and the profound loss and pain that results from divorce.

Achieving Status and Reducing Loneliness during the Transition to College: The Role of Entitlement, Intrasexual Competitiveness, and Dominance.

Although many emerging adults struggle to gain status and develop social relationships, particularly during the college transition, it remains unclear whether certain personality traits facilitate this transition. Using a longitudinal design, we investigated whether status-related traits-namely, entitlement, intrasexual competitiveness, and dominance-related to the development of status in 91 first-year college students (M age=18.15, SD=0.44) transitioning to a novel college environment. We also examined whether personality traits moderated the degree to which status related to loneliness. As hypothesized, only students high in intrasexual competitiveness experienced increases in subjective dorm status across the year. In addition, students exhibiting average or low entitlement experienced decreases in loneliness over time, whereas high entitlement was related to consistently low loneliness. Finally, higher subjective dorm status was related to lower loneliness only for less dominant students, as assessed by both self-ratings of trait dominance and raters' judgments of facial dominance from photographs. Using a real-world context of status development, these results suggest that personality traits may influence students' ability to experience higher status and modulate the relation between subjective status and loneliness.

Psychological Science in the Wake of COVID-19: Social, Methodological, and Metascientific Considerations.

The COVID-19 pandemic has extensively changed the state of psychological science from what research questions psychologists can ask to which methodologies psychologists can use to investigate them. In this article, we offer a perspective on how to optimize new research in the pandemic's wake. Because this pandemic is inherently a social phenomenon-an event that hinges on human-to-human contact-we focus on socially relevant subfields of psychology. We highlight specific psychological phenomena that have likely shifted as a result of the pandemic and discuss theoretical, methodological, and practical considerations of conducting research on these phenomena. After this discussion, we evaluate metascientific issues that have been amplified by the pandemic. We aim to demonstrate how theoretically grounded views on the COVID-19 pandemic can help make psychological science stronger-not weaker-in its wake.

Kin affiliation across the ovulatory cycle: females avoid fathers when fertile.

A commonplace observation in humans is that close genetic relatives tend to avoid one another as sexual partners. Despite the growing psychological research on how antierotic attitudes develop toward relatives, few studies have focused on actual behavior. One prediction, stemming from parental investment theory, is that women should be more vigilant of reproduction-compromising behaviors, such as inbreeding, during times of peak fertility than during times of low fertility. Indeed, females of other species avoid interactions with male kin when fertile-but the corollary behavior in humans has yet to be explored. Here we fill this gap. Using duration and frequency of cell-phone calls, an objective behavioral measure that reflects motivations to interact socially, we show that women selectively avoid interactions with their fathers during peak fertility. Avoidance specifically targeted fathers, which rules out alternative explanations. These data suggest that psychological mechanisms underlying mating psychology regulate sexual avoidance behaviors, and in women they fluctuate according to fertility status.

Cues of Social Status: Associations Between Attractiveness, Dominance, and Status.

Hierarchies naturally emerge in social species, and judgments of status in these hierarchies have consequences for social relationships and health. Although judgments of social status are shaped by appearance, the physical cues that inform judgments of status remain unclear. The transition to college presents an opportunity to examine judgments of social status in a newly developing social hierarchy. We examined whether appearances-as measured by raters' judgments of photographs and videos-provide information about undergraduate students' social status at their university and in society in Study 1. Exploratory analyses investigated whether associations differed by participants' sex. Eighty-one first-year undergraduate students (Mage = 18.20, SD = 0.50; 64.2% female) provided photographs and videos and reported their social status relative to university peers and relative to other people in society. As hypothesized, when participants were judged to be more attractive and dominant they were also judged to have higher status. These associations were replicated in two additional samples of raters who evaluated smiling and neutral photographs from the Chicago Faces Database in Study 2. Multilevel models also revealed that college students with higher self-reported university social status were judged to have higher status, attractiveness, and dominance, although judgments were not related to self-reported society social status. Findings highlight that there is agreement between self-reports of university status and observer-perceptions of status based solely on photographs and videos, and suggest that appearance may shape newly developing social hierarchies, such as those that emerge during the transition to college.

An agent-based model of the female rivalry hypothesis for concealed ovulation in humans.

After half a century of debate and few empirical tests, there remains no consensus concerning why ovulation in human females is considered concealed. The predominant male investment hypothesis states that females were better able to obtain material investment from male partners across those females' ovulatory cycles by concealing ovulation. We build on recent work on female competition to propose and investigate an alternative-the female rivalry hypothesis-that concealed ovulation benefited females by allowing them to avoid aggression from other females. Using an agent-based model of mating behaviour and paternal investment in a human ancestral environment, we did not find strong support for the male investment hypothesis, but found support for the female rivalry hypothesis. Our results suggest that concealed ovulation may have benefitted females in navigating their intrasexual social relationships. More generally, this work implies that explicitly considering female-female interactions may inspire additional insights into female behaviour and physiology.

Early life stress, subjective social status, and health during late adolescence.

Objective: Both lower subjective social status (SSS)-or viewing oneself as having lower status relative to others-and greater early life stress consistently relate to poorer health in adolescence. Early life stress can also negatively influence one's social relationships and may thereby shape social status. The present studies investigated how early life stress relates to the development of SSS and how SSS relates to health across the transition to college.Design: In Study 1, 91 older adolescents (Mage = 18.37) reported early life stress, society SSS, and school SSS, and they reported their society SSS and school SSS again 2 years later. In Study 2, 94 first-year college students (Mage = 18.20) reported early life stress and society SSS at study entry and reported their dorm SSS, university SSS, and mental health monthly throughout the year.Results: Greater early life stress was related to lower society SSS, but not school SSS, in both studies. In Study 2, dorm and university SSS and early life stress were uniquely related to mental health, although associations weakened over time.Conclusion: Early life stress may predispose people to have low society SSS, and both low school SSS and high early life stress may increase risk for poorer health during transition periods.

Do women expose themselves to more health-related risks in certain phases of the menstrual cycle? A meta-analytic review.

Researchers have increasingly examined the menstrual cycle as a potential source of day-to-day variation in women's cognitions, motivations, and behavior. Within this literature, several lines of research have examined the impact of the menstrual cycle on women's engagement in activities that could negatively affect their health (alcohol and tobacco consumption, sexual behavior, risk recognition). However, findings have been mixed, leaving it unclear whether women may expose themselves to more health-related risks during certain phases of the cycle. We conducted a meta-analysis of 22 published and four unpublished studies (N = 7529, https://osf.io/xr37j/). The meta-analysis revealed shifts across the menstrual cycle in women's sexual behavior with others and risk recognition (higher in ovulatory phase), whereas there was no consistent pattern of difference for alcohol and cigarette consumption. These findings help to clarify the proximate physiological and evolutionary mechanisms underlying women's health-related risk-taking and may inform new interventions.

Falling in love is associated with immune system gene regulation.

Although falling in love is one of the most important and psychologically potent events in human life, the somatic implications of new romantic love remain poorly understood. Psychological, immunological, and reproductive perspectives offer competing predictions of the specific transcriptional regulatory shifts that might accompany the experience of falling in love. To characterize the impact of romantic love on human genome function, we conducted genome-wide transcriptome profiling of 115 circulating immune cell samples collected from 47 young women over the course of a 2-year longitudinal study. Analyses revealed a selective alteration in immune cell gene regulation characterized by up-regulation of Type I interferon response genes associated with CD1C+/BDCA-1+ dendritic cells (DCs) and CLEC4C+/BDCA-2+ DCs, and a reciprocal down-regulation of α-defensin-related transcripts associated with neutrophil granulocytes. These effects emerged above and beyond the effects of changes in illness, perceived social isolation, and sexual contact. These findings are consistent with a selective up-regulation of innate immune responses to viral infections (e.g., Type I interferons and DC) and with DC facilitation of sexual reproduction, and provide insight into the immunoregulatory correlates of one of the keystone experiences in human life.

Subjective social status and inflammatory gene expression.

OBJECTIVE: There exists a well-established link between low perceived social status and poorer health outcomes. However, the molecular mechanisms associated with this link remain unclear. This study begins to fill this gap by investigating the effects of low perceived subjective social status on health-related gene expression. METHOD: Participants were 47 healthy heterosexual women (mean age 20.5 years) from a large American university. Participants gave 10 mL of peripheral blood and completed questionnaires assessing subjective social status (SSS), perceived childhood socioeconomic status (SES), health, and relevant demographics. Putatively associated genes were subject to TELiS promoter-based bioinformatic analysis to assess activity of proinflammatory, anti-inflammatory, and antiviral transcription factors. RESULTS: In analyses controlling for perceived childhood socioeconomic status (SES) and other covariates, 84 transcripts showed >1.5-fold difference in average expression across the range of SSS. TELiS bioinformatics analyses implicated the proinflammatory transcription factors, NF-κB and AP-1, in driving expression of genes that were up-regulated in low-SSS individuals. Results also indicated increased activity of CREB family transcription factors but no differential activity of the anti-inflammatory glucocorticoid receptor of interferon response factors. Transcript origin analysis implicated monocytes and dendritic cells as cellular mediators. CONCLUSION: In this first study examining the molecular correlates of SSS, experiences of low social status are associated with transcriptional effects similar to those previously observed for objective adversity conditions such as low SES, social isolation, and chronic stress. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Sex Differences in Detecting Sexual Infidelity : Results of a Maximum Likelihood Method for Analyzing the Sensitivity of Sex Differences to Underreporting.

Despite the importance of extrapair copulation (EPC) in human evolution, almost nothing is known about the design features of EPC detection mechanisms. We tested for sex differences in EPC inference-making mechanisms in a sample of 203 young couples. Men made more accurate inferences (φmen = 0.66, φwomen = 0.46), and the ratio of positive errors to negative errors was higher for men than for women (1.22 vs. 0.18). Since some may have been reluctant to admit EPC behavior, we modeled how underreporting could have influenced these results. These analyses indicated that it would take highly sex-differentiated levels of underreporting by subjects with trusting partners for there to be no real sex difference. Further analyses indicated that men may be less willing to harbor unresolved suspicions about their partners' EPC behavior, which may explain the sex difference in accuracy. Finally, we estimated that women underreported their own EPC behavior (10%) more than men (0%).

Changes in women's choice of dress across the ovulatory cycle: naturalistic and laboratory task-based evidence.

The authors tested the prediction that women prefer clothing that is more revealing and sexy when fertility is highest within the ovulatory cycle. Eighty-eight women reported to the lab twice: once on a low-fertility day of the cycle and once on a high-fertility day (confirmed using hormone tests). In each session, participants posed for full-body photographs in the clothing they wore to the lab, and they drew illustrations to indicate an outfit they would wear to a social event that evening. Although each data source supported the prediction, the authors found the most dramatic changes in clothing choice in the illustrations. Ovulatory shifts in clothing choice were moderated by sociosexuality, attractiveness, relationship status, and relationship satisfaction. Sexually unrestricted women, for example, showed greater shifts in preference for revealing clothing worn to the laboratory near ovulation. The authors suggest that clothing preference shifts could reflect an increase in female-female competition near ovulation.