Consistently over time, polygenic scores that predict higher earnings, education and health also predict lower fertility

Human Capital Mediates Natural Selection in Contemporary Humans. David Hugh-Jones & Abdel Abdellaoui. Behavior Genetics, Jul 6 2022. https://rd.springer.com/article/10.1007/s10519-022-10107-w

Abstract: Natural selection has been documented in contemporary humans, but little is known about the mechanisms behind it. We test for natural selection through the association between 33 polygenic scores and fertility, across two generations, using data from UK Biobank (N = 409,629 British subjects with European ancestry). Consistently over time, polygenic scores that predict higher earnings, education and health also predict lower fertility. Selection effects are concentrated among lower SES groups, younger parents, people with more lifetime sexual partners, and people not living with a partner. The direction of natural selection is reversed among older parents, or after controlling for age at first live birth. These patterns are in line with the economic theory of fertility, in which earnings-increasing human capital may either increase or decrease fertility via income and substitution effects in the labour market. Studying natural selection can help us understand the genetic architecture of health outcomes: we find evidence in modern day Great Britain for multiple natural selection pressures that vary between subgroups in the direction and strength of their effects, that are strongly related to the socio-economic system, and that may contribute to health inequalities across income groups.

Discussion

Previous work has documented natural selection in modern populations on variants underlying polygenic traits (Beauchamp 2016; Kong et al. 2017; Sanjak et al. 2018). We show that correlations between polygenic scores and fertility are highly concentrated among specific subgroups of the population, including people with lower income, lower education, younger first parenthood, and more lifetime sexual partners. Among mothers aged 22+, selection effects are reversed. Furthermore, the size of selection effects on a polygenic score correlates with that score’s association with labour market earnings. Strikingly, some of these results were predicted by Fisher (1930), pp. 253-254. The economic theory of fertility gives a parsimonious explanation for these findings. Because of the substitution effect of earnings on fertility, scores are selected for when they correlate with low human capital, and this effect is stronger at lower levels of income and education.

Polygenic scores which correlate with lower earnings and less education are being selected for. In addition, many of the phenotypes under positive selection are linked to disease risk. Many people would probably prefer to have high educational attainment, a low risk of ADHD and major depressive disorder, and a low risk of coronary artery disease, but natural selection is pushing against genes associated with these traits. Potentially, this could increase the health burden on modern populations, but that depends on effect sizes. Our results show that naïve estimates can be affected by sample ascertainment bias. There may be remaining sources of ascertainment bias after our weighting; if so, we expect that, like the sources of ascertainment we have controlled for, they probably bias our results towards zero. Researchers should be aware of the risks of ascertainment when studying modern natural selection.

We also do not know how estimated effect sizes of natural selection will change as more accurate polygenic scores are produced, or whether genetic variants underlying other phenotypes will show a similar pattern to those studied here. Also, effects of polygenic scores may be inflated in population-based samples, because of indirect genetic effects, gene-environment correlations, and/or assortative mating (Lee et al. 2018; Selzam et al. 2019; Kong et al. 2018; Howe et al. 2021), although we do not expect that this should change their association with number of offspring, or the resulting changes in allele frequencies. Although effects on our measured polygenic scores are small even after weighting, individually small disadvantages can cumulate to create larger effects. Lastly, note that our data comes from people born before 1970. Recent evidence suggests that fertility patterns may be changing (Doepke et al. 2022). Overall, it is probably too early to tell whether modern natural selection has a substantively important effect on population averages of phenotypes under selection.

Because selection effects are concentrated in lower-income groups, they may also increase inequality with respect to polygenic scores. For example, Figure 8 plots mean polygenic scores for educational attainment (EA3) among children from households of different income groups. The blue bars show the actual means, i.e. parents’ mean polygenic score weighted by number of children. The grey bars show the hypothetical means if all households had equal numbers of children. Natural selection against genes associated with educational attainment is stronger at the bottom of the income distribution, and this increases the differences between groups. Overall, natural selection increases the correlation of polygenic scores with income for 28 out of 33 polygenic scores, with a median percentage increase of 16.43% in the respondents’ generation (Appendix Table 5). If inequalities in polygenic scores are important for understanding social structure and mobility (Belsky et al. 2018; Rimfeld et al. 2018; Harden 2021), then these increases are substantive. Similarly, since many polygenic scores are predictive of disease risk, they could potentially increase health inequalities. In general, the evolutionary history of anatomically modern humans is related to disease risk (Benton et al. 2021); understanding the role of contemporary natural selection may help researchers to map the genetic architecture of health disparities.

Fig. 8

Mean polygenic score for educational attainment (EA3) of children by household income group. Blue is actual. Grey is hypothetical in the absence of selection effects (Color figure online)

Full size image

Existing evidence on human natural selection has led some to “biocosmic pessimism” (Sarraf and Feltham 2019). Others are more sanguine, and argue that natural selection’s effects are outweighed by environmental improvements, like those underlying the Flynn effect (Flynn 1987). The evidence here may add some nuance to this debate. Patterns of natural selection have been relatively consistent across the past two generations, but they are not the outcome of a single, society-wide phenomenon. Instead they result from opposing forces, operating in different parts of society and pulling in different directions.

Any model of fertility is implicitly a model of natural selection, but so far, the economic and human genetics literatures have developed in parallel. Integrating the two could deepen our understanding of natural selection in modern societies. Economics possesses a range of theoretical models on the effects of skills, education and income (see Hotz et al. 1997; Lundberg and Pollak 2007). One perennial problem is how to test these theories in a world where education, labour and marriage markets all interact. Genetic data, such as polygenic scores, could help to pin down the direction of causality, for example via Mendelian randomization (Smith and Shah 2003). Conversely, economic theories and empirical results can shine a light on the mechanisms behind natural selection, and thereby on the nature of individual differences in complex traits and disease risk.

For both women and men, higher education predicted a high masturbation frequency and sexual dissatisfaction

A Seemingly Paradoxical Relationship Between Masturbation Frequency and Sexual Satisfaction. Nantje Fischer & Bente Træen. Archives of Sexual Behavior, Jul 5 2022. https://rd.springer.com/article/10.1007/s10508-022-02305-8

Abstract: Despite many benefits related to masturbation, we know surprisingly little about how solo sex is associated with sexual satisfaction. Using questionnaire data from a probability-based sample of 4,160 Norwegians aged 18–89 years, we explored subgroups of women and men that differed in their masturbation–sexual satisfaction typology and examined whether sociodemographic, psychological, and sexual behavioral characteristics were associated with distinct masturbation–satisfaction patterns. A cluster analysis revealed four similar groupings for women and men, reflecting sex lives characterized by high masturbation/sexual satisfaction, low masturbation/sexual satisfaction, high masturbation/sexual dissatisfaction, or low masturbation/sexual dissatisfaction. While being younger, higher pornography consumption, and sexual variety were primarily associated with increased masturbation frequency, sexual distress and a negative body and genital self-image were more clearly associated with sexual dissatisfaction. Predicting different masturbation–satisfaction groupings also revealed some gender-specific findings in the use of pornography, and in the association between masturbation and intercourse frequency, which suggested a complementary pattern for women and a compensatory pattern for men. Our findings emphasize that the linkage between masturbation and sexual satisfaction warrants closer focus.

Discussion

Previous studies have focused on linear relationships between sexual satisfaction and masturbation frequency, without considering the possibility that women and men might vary in their masturbation–sexual satisfaction relationships. The clustering in this study revealed four groupings, with men’s and women’s sex life being characterized by either HmS, LmS, HmD, or LmD. Further, we assessed whether sociodemographic, psychological, and sexual behavioral factors predicted distinct masturbation–satisfaction patterns.

Two interesting patterns emerged. Psychological factors (sexual distress, body image and genital self-image) were more clearly related to sexual dissatisfaction, while age and sexual behavioral factors (pornography use, sexual experience and desires) were mainly linked to masturbation frequency. A possible reason for the fragmented findings may reflect that masturbatory behavior only partly contributes to a person’s overall sex life satisfaction. For example, Philippsohn and Hartmann (2009) found that masturbation was considerably less central in explaining women’s overall sexual satisfaction than sexual intercourse activity. Moreover, qualitative data from focus groups with 50 heterosexual men reveal that, compared to partnered sexual activities, masturbation was not fully integrated into men’s sense of being sexual (Janssen et al., 2008). These studies indicate that, although overlapping, sexual satisfaction from solitary and partnered sexuality might be different. Similarly, qualitative data from focus groups with 73 queer and heterosexual women showed that solitary and partnered sexual pleasure were largely distinct constructs, with only some overlap (Goldey et al., 2016). Future studies should therefore consider defining and measuring solitary and partnered sex life satisfaction as distinct concepts.

A Compensatory or Complementary Pattern?

Women with higher sexual intercourse frequency were more likely to report high masturbation and satisfaction (HmS) than any other group (LmS, HmD, LmD). Also, more sexual experimentation among women was associated with more masturbation and satisfaction (HmS), compared to participants with LmS. Both findings support a complementary pattern for women, as it implies that frequent solo sex enhances partnered sex and is more widespread among adults with a sexualized personality pattern (e.g., increased sexual experimentation and desires) (Das et al., 2009).

Similar as in women, we found that men with higher intercourse frequency were more likely to be sexually satisfied (HmS), than those belonging to a sexually dissatisfied cluster (HmD or LmD). This is a finding that corresponds to previous studies that have found a positive relationship between partnered sex and sexual satisfaction (Brody & Costa, 2009; Byers & Rehman, 2014; Schoenfeld et al., 2017). However, when comparing men with high sexual satisfaction (HmS versus LmS), those with more partnered sex were more likely to report no or low masturbation (LmS). This finding supports a compensatory pattern in men, as it suggests that masturbation is regarded as unnecessary if one has highly satisfying and frequent sex with a partner (Regnerus et al., 2017). The gendered finding, revealing a compensatory pattern among men and a complementary pattern among women, is consistent with prior work supporting gender-specific models (Carvalheira & Leal, 2013; Fischer et al., 2022; Gerressu et al., 2008; Regnerus et al., 2017).

Pornography Use Predict HmS

Another notable finding was that both women and men with frequent pornography use were more likely to report high masturbation and sexual satisfaction (HmS) than those belonging to a cluster characterized by no or low masturbation (LmS or LmD). This finding is similar to previous studies that have found a positive relationship between pornography use and masturbation (Baćak & Štulhofer, 2011; Carvalheira et al., 2015; Richters et al., 2014) and emphasizes that pornography functions as an aid for masturbation (Prause, 2019).

Apart from this, we found a link between pornography use, high masturbation, and sexual satisfaction in men (but not in women). When comparing men characterized by relatively high masturbation frequency (HmD vs. HmS), those with greater pornography use were more likely to report being sexually dissatisfied (HmD). This finding is consistent with a recent meta-analysis (Wright et al., 2017), which documented a negative association between men’s pornography use and sexual satisfaction, but no overall or global association between women’s pornography consumption and sexual satisfaction.

Evaluative Factors Associated with Specific Masturbation-Satisfaction Typologies

Among both genders, a more negative body image was associated with being sexually dissatisfied (HmD in women and men; LmD in women), compared to participants in the reference cluster (HmS). This is consistent with previous evidence, implicating important links between body image and sexual satisfaction (Træen et al., 2016; Woertman & van den Brink, 2012). Interestingly, genital self-image was only linked to male cluster’s. In particular, a negative genital self-image was associated with being sexually dissatisfied (HmD and LmD), compared to the reference cluster (HmS). These findings echo those of a recent study, which revealed that when accounting for all body attitudes (body fat, genitals, muscularity, and height), only negative attitudes toward one’s own genitals were significantly associated with sexual dissatisfaction in men (van den Brink et al., 2018). The fact that men’s genitalia play an important role in defining masculinity in terms of appearance (e.g., penis size) and performance (e.g., erection) might explain the influences of men’s genital self-image on their sexual satisfaction.

Another central finding of the present study was that women and men who experienced distressing sexual problems were more likely to be dissatisfied with their sex life (HmD and LmD), compared to the reference cluster (HmS). This is in line with previous research indicating that sexual distress and sexual satisfaction are closely related (Stephenson & Meston, 2010).

Links Between Sociodemographic Factors and Masturbation-Satisfaction Typologies

Some sociodemographic factors predicted specific masturbation-satisfaction typologies. Interestingly, although accounting for sexual intercourse frequency, relationship status remained an important predictor of high masturbation frequency and sexual satisfaction. Specifically, those who were married/cohabitant or in a registered partnership were less likely to report high masturbation and satisfaction than falling into a cluster characterized by LmS, HmD, LmD. This resembles findings of a recent large-scale study, which documented a negative association between being partnered and recent masturbation (Regnerus et al., 2017). As Regnerus et al. controlled for sexual frequency and sexual contentment, this was a surprising finding, providing “evidence that the effect of partnered status is not simply the effect of stable access to sex” (p. 2117).

For both women and men, higher education predicted a high masturbation frequency and sexual dissatisfaction (HmD). This finding dovetails with previous findings documenting a positive relationship between higher education and more masturbation (Gerressu et al., 2008; Kaminsky-Bayer, 2020; Kontula & Haavio-Mannila, 2003; Richters et al., 2014). However, previous research also seems to indicate that education does not play a major role in sexual satisfaction (Byers & Rehman, 2014). It is thus unclear why higher education was related to less sexual satisfaction among those who frequently masturbate. Finally, consistent with prior studies on age-related decreases in masturbation activity (Fischer et al., 2022; Lee et al., 2016; Schick et al., 2010a, 2010b), older age was related with a sex life characterized by low masturbation (LmS in women and men; LmD in men).

Implications

The clusters characterized by no or low masturbation frequency and sexual satisfaction (HmS) were the largest clusters in both genders. This is interesting and may changes supposing the sexual scripts toward masturbation become more pronounced and positive in the future. The smallest clusters were those that included individuals dissatisfied with their sex life (HmD and LmD). To create a more masturbation-friendly society, future sexual health initiatives should focus on promoting masturbation and positive attitudes toward masturbation (Kontula & Haavio-Mannila, 2003).

Study Limitations

Several limitations should be addressed. First, the item used to assess masturbation frequency lacked an explicit definition and contextualization of the term masturbation. As the measure does not solely refer to masturbation in unpartnered situations, it is possible that participants used varied definitions when responding to the question. Accordingly, we cannot rule out that some also referred to masturbation during sexual intercourse. However, recent evidence indicates that the common script for sexual self-pleasure incorporates solo rather than partnered masturbation (Kirschbaum & Pederson, 2018). Specifically, the absence of a partner and having an orgasm seem to be central aspects of labeling a sexual act as masturbation. Second, although the use of single-item indicators is standard practice and indicates good convergent validity with sexual satisfaction scales (Mark et al., 2014; Štulhofer et al., 2010), the psychometric properties of multiple-item scales are preferable. However, because many individuals seem to fill out online questionnaires on their mobile phones (in this study 51%), we had to prioritize single items to minimize response fatigue. Third, no information about attitudes toward masturbation and feelings associated with sexual self-pleasure was collected. Thus, third-variable problems cannot be ruled out. Assessing negative and positive perceptions of masturbation would have allowed for more differentiated clustering. Another limitation pertains the presumption of binary gender/sex in some questions. Also, because the results from this study are based on cross-sectional data, it is not feasible to draw any causal conclusions. Further, the possibility of social desirability bias and volunteer bias may affect our findings and limit the generalizability of the study findings (Boughner, 2010). A final limitation pertains to the low response rate. In the past decades, scientific research has experienced a steady decrease in participation rates (Galea & Tracy, 2007). This applies also to Norwegian surveys, where response rates have been declining from 63% in 1987, to 48% in 1992, 38% in 1997, 34% in 2002, and 23% in 2008 (Træen & Stigum, 2010). One reason for much higher refusal rates nowadays may be the growing number of instances people are asked to participate in studies (Galea & Tracy, 2007). Because this survey was carried out during the COVID-19-related lockdown, which was imposed on 12 March in Norway, it is possible that some Web Panel members were less receptive to participate in a study on sexual behavior. Moreover, it is uncertain how the COVID-19-related restrictions may have influenced our findings. Another explanation for the low response rate may pertain to the length of the questionnaire. According to Kantar, response rates for surveys drawn from the Gallup Panel vary between 46 and 51%. An estimated timeframe of 15–20 min for our survey was probably too long, especially because 51% of the respondents were answering on their mobile devices.

Openness to experience, extraversion and neuroticism correlated with a higher frequency of sexual dreams; agreeableness showed a negative relationship

Personality correlates of the self-rated frequency of erotic dreams. Anja S. Göritz. International Journal of Dream Research, Vol 15, No 1 (April 2022). https://doi.org/10.11588/ijodr.2022.1.86903

Abstract: Erotic dreams have been of interest for researchers and the public alike. Although, the gender difference in the frequency of erotic dreams is well documented with men reporting erotic dreams more often than women, studying other factors, for example, personality traits, in relationship with erotic dreaming is scarce. Overall, 1711 participant estimated the percentage of erotic dreams with regard to all their remembered dreams and also completed a Big Five Personality inventory. The findings indicate that four of the Big Five personality factors were related to the frequency of erotic dreams; although the effects sizes of these associations were small. As expected, openness to experience correlated with a higher frequency of sexual dreams, as this personality trait is related to more frequent positive sexual cognitions and pornography consumption. Whereas extraversion and neuroticism were also positively related to erotic dream frequency, agreeableness showed a negative relationship. These kinds of studies help to understand how waking life sexuality affect erotic dreams, and in more general terms, how waking life is reflected in dreams.

Toward a Deeper Understanding of Prolific Lying: The more that people lied, the more they believed that others lied as well

Toward a Deeper Understanding of Prolific Lying: Building a Profile of Situation-Level and Individual-Level Characteristics. David M. Markowitz. Communication Research, July 4, 2022. https://doi.org/10.1177/00936502221097041

Abstract: Prior work suggests those who lie prolifically tend to be younger and self-identify as male compared to those who engage in everyday lying, but little research has developed an understanding of prolific lying beyond demographics. Study 1 (N = 775) replicated the prior demographic effects and assessed prolific lying through situation-level (e.g., opportunistic cheating) and individual-level characteristics (e.g., dispositional traits, general communication patterns) for white and big lies. For these two lie types, prolific lying associated with more opportunistic cheating, the use of fewer adjectives, and being high on psychopathy compared to everyday lying. Study 2 (N = 1,022) replicated these results and observed a deception consensus effect reported in other studies: the more that people deceived, the more they believed that others deceived as well. This piece develops a deeper theoretical understanding of prolific lying for white and big lies, combining evidence of situational, dispositional, and communication characteristics.

Keywords: lying, deception, prolific lying, automated text analysis, Dark Triad, deception consensus effect

The Effect of Labor Market Liberalization on Political Behavior and Free Market Norms: The kibbutz liberalization in the 1990s

The Effect of Labor Market Liberalization on Political Behavior and Free Market Norms. Ran Abramitzky, Netanel Ben-Porath, Shahar Lahad, Victor Lavy & Michal Palgi. NBER Working Paper 30186, Jun 2022. DOI 10.3386/w30186

Abstract: We study the effects of labor market liberalization on political behavior and attitudes towards free-market capitalism and socialism, exploiting a reform whereby the Israeli socialist communities called kibbutzim shifted from equal sharing to market-based wages. Our identification strategy relies on this reform's sharp and staggered implementation in different kibbutzim. We first examine changes in behavior associated with this labor market liberalization and document that the reform led to a shift in electoral voting patterns, resulting in decreased support for left-wing political parties and increased support for the center and right parties in national elections. Using annual survey data on attitudes over 25 years, we show that the reform led to increased support for free-market policies such as full privatization and differential wages. Moreover, it decreased support for socialist policies such as the joint ownership of production means. Yet, the reform increased support for the safety net to support weak members through mutual guarantee. These effects appear to be driven by an increase in living standards and work ethics that resulted from the reform. We conclude that introducing market-based wages led to a shift in attitudes towards a market economy with compassion, revealing a change in members’ support from their traditional democratic socialist model to a social democratic model.

Political Conservatives and Political Liberals Have Similar Views about the Goodness of Human Nature

Political Conservatives and Political Liberals Have Similar Views about the Goodness of Human Nature. Eric Schwitzgebel with Nika Chegenizadeh. Monday, July 04, 2022. schwitzsplinters.blogspot.com/2022/07/political-conservatives-and-political.html

Back in 2007, I hypothesized that political liberals would tend to have more positive views about the goodness of human nature than political conservatives. My thinking was grounded in a particular conception of what it is to say that "human nature is good". Drawing on Mengzi and Rousseau (and informed especially by P.J. Ivanhoe's reading of Mengzi), I argued that those who say human nature is good have a different conception of moral development than do those who say it is bad.

[...]

Those who say human nature is bad have, in contrast, an outward-in model of moral development. On this view, what is universal to humans is self-interest. Morality is an artificial social construction. Any quiet voice of conscience we might have is the result of cultural learning. People regularly commit evil and feel perfectly fine about it. Moral development proceeds by being instructed to follow norms that at first feel alien and unpleasant -- being required to share your toys, for example. Eventually you can learn to conform whole-heartedly to socially constructed moral norms, but this is more a matter of coming to value what society values than building on any innate attraction to moral goodness.

Thus, a liberal style of caregiving, which emphasizes children exploring their own values, fits nicely with the view that human nature is good, while a conservative style of caregiving, which emphasizes conformity to externally imposed rules, fits nicely with the view that human nature is bad.

Data: Schwitzgebel, Eric. 2022. “Do Political Liberals Have More Optimistic Views about the Goodness of Human Nature?” OSF. June 27. osf.io/ys6nj

Environmental harshness and unpredictability, life history, and social and academic behavior of adolescents in nine countries

Chang, L., Lu, H. J., Lansford, J. E., Skinner, A. T., Bornstein, M. H., Steinberg, L., Dodge, K. A., Chen, B. B., Tian, Q., Bacchini, D., Deater-Deckard, K., Pastorelli, C., Alampay, L. P., Sorbring, E., Al-Hassan, S. M., Oburu, P., Malone, P. S., Di Giunta, L., Tirado, L. M. U., & Tapanya, S. (2019). Environmental harshness and unpredictability, life history, and social and academic behavior of adolescents in nine countries. Developmental Psychology, 55(4), 890–903. https://doi.org/10.1037/dev0000655

Abstract: Safety is essential for life. To survive, humans and other animals have developed sets of psychological and physiological adaptations known as life history (LH) tradeoff strategies in response to various safety constraints. Evolutionarily selected LH strategies in turn regulate development and behavior to optimize survival under prevailing safety conditions. The present study tested LH hypotheses concerning safety based on a 6-year longitudinal sample of 1,245 adolescents and their parents from 9 countries. The results revealed that, invariant across countries, environmental harshness, and unpredictability (lack of safety) was negatively associated with slow LH behavioral profile, measured 2 years later, and slow LH behavioral profile was negatively and positively associated with externalizing behavior and academic performance, respectively, as measured an additional 2 years later. These results support the evolutionary conception that human development responds to environmental safety cues through LH regulation of social and learning behaviors.

Keywords: fast and slow life history strategy; environmental harshness; unpredictability; externalizing; academic performance; child and adolescent development

It seems impulsivity doesn't evolve in response to childhood environmental harshness

Can impulsivity evolve in response to childhood environmental harshness? Atsushi Kometani, Yohsuke Ohtsubo. Evolutionary Human Sciences, Volume 4, May 24 2022, e21. DOI: https://doi.org/10.1017/ehs.2022.22

Abstract: Previous studies have suggested that human impulsivity is an adaptive response to childhood environmental harshness: individuals from families of low socioeconomic status (SES) tend to be more impulsive. However, no studies have tested the evolvability of this reaction norm. This study examined whether (a) impulsivity is associated with higher fitness among individuals from low SES families, while (b) it is associated with lower fitness among individuals from high SES families. We assessed three indices of impulsivity (temporal discounting, risk taking and fast/slow life history strategy), childhood SES and five proxy indices of fitness (number of children, lifelong singlehood, annual household income, subjective SES and life satisfaction) of 692 middle-aged participants (40–45 years old). None of the results supported the evolvability of the impulsivity reaction norm, although low childhood SES was associated with lower fitness on every proxy measure. Impulsivity (operationalised as the fast life history strategy) was associated with lower fitness regardless of childhood SES.

Discussion

We examined the evolvability of the impulsivity reaction norm. Although the results confirmed the basic presumption that childhood economic harshness adversely influenced participants’ later fitness, none of the other results supported the impulsivity reaction norm's evolvability: when operationalised as risk-taking tendency, impulsivity was associated with higher fitness among individuals with high, but not low, childhood SES (this pattern, however, was not replicated in our subsequent unpublished study including only male participants). When operationalised by Mini-K score, it was associated with lower fitness regardless of childhood SES.

The present study failed to replicate the results of previous studies (Griskevicius et al., Reference Griskevicius, Ackerman, Cantú, Delton, Robertson, Simpson and Tybur2013). In particular, childhood SES was not significantly associated with either risk taking or temporal discounting. Given the robust association between childhood SES and BCD (Pepper & Nettle, Reference Pepper and Nettle2017), the present study's operationalisation of impulsivity might have provided inadequate indices of impulsivity. For example, one could argue that the temporal discounting and risk-taking tasks should have been incentivised (but see Amir et al., Reference Amir, Jordan and Rand2018, which reported no systematic differences between incentivised and non-incentivised risk-taking tasks). Mishra et al. (Reference Mishra, Barclay and Sparks2017) recently proposed a model of risk-taking (relative state model) that distinguishes two types of risk-taking behaviours, need-based and ability-based risk-taking; the former is motivated by poor environments, while the latter is motivated by superior abilities (i.e. the prospect of successful risk-taking). In future studies, it is worthwhile not only to incentivise risk-taking tasks but also to distinguish subtypes of risk-taking and impulsivity based on such a nuanced model.

One limitation is that we assessed fitness in a modern, industrialised society that is largely different from the environment of evolutionary adaptedness (EEA). For example, if low SES conditions in contemporary Japan are still more benign compared with harsh conditions in EEA, the present study may not be a fair test of the hypothesised phenotypic plasticity. Nonetheless, it is worth noting that childhood SES was in fact positively associated with every measure of fitness in this study. Moreover, careful analyses revealed some comparability of the modern and ancestral environments (i.e. positive association between wealth and the number of children in both modern and ancestral environments; Nettle & Pollet, Reference Nettle and Pollet2008). Nevertheless, this particular result does not necessarily imply that the comparability between the modern and ancestral environments extends to other aspects. For example, one could argue that impulsivity is an effective strategy for disadvantaged individuals only in EEA but not in the modern environment. Since there is a wide range of differences between the modern environment and EEA, or the so-called evolutionary mismatch problem (Li et al., Reference Li, van Vugt and Colarelli2018), it is informative to replicate this study in populations that maintain traditional lifestyles.

We admit that this study does not disprove the evolvability of human reaction norms as a whole. This study only tested the evolvability of impulsivity in response to childhood economic harshness. There are other independent and dependent variables that have attracted researchers’ attention in the context of life history theory in psychology. For example, timing of puberty and parental strategies are oft-studied life history traits (i.e. dependent variables), and childhood mortality/morbidity and unpredictability are oft-studied environmental (independent) variables (Ellis et al., Reference Ellis, Figueredo, Brumbach and Schlomer2009). Therefore, future studies need to include a wider range of measures of childhood environments and life history traits in order to fully test the evolvability of any form of phenotypic plasticity in response to early environments.

In summary, this study does not reveal any evidence of the evolvability of the impulsivity reaction norm in response to childhood economic harshness. Therefore, we urge researchers to critically assess the impulsivity reaction norm, especially whether the adaptationist explanation is better supported by empirical data than by-product explanations.

Global sex differences in hygiene norms and their relation to sex equality

Global sex differences in hygiene norms and their relation to sex equality. Kimmo Eriksson,Thomas E. Dickins, Pontus Strimling. PLOS Glob Public Health 2(6): e0000591. June 21, 2022. https://doi.org/10.1371/journal.pgph.0000591

Abstract: Strict norms about hygiene may sometimes have health benefits but may also be a burden. Based on research in the United States, it has been suggested that women traditionally shoulder responsibility for hygiene standards and therefore tend to have stricter views on hygiene. However, there is little systematic research on sex differences in hygiene norms at the global scale. We set up two hypotheses: (1) Stricter hygiene norms among women than among men is a global phenomenon. (2) The size of this sex difference varies across nations with the level of sex equality. We examine these hypotheses using data from a recent international survey (N = 17,632). Participants in 56 countries were asked for their views of where it is not appropriate for people to spit and in which situations people should wash their hands. As a measure of sex equality, we use an existing country-level measure of attitudes to equality between the sexes, available for 49 nations in the study. Stricter hygiene norms among women than among men are observed almost everywhere, but there are a few exceptions (most notably Nigeria and Saudi Arabia). The size of the sex difference in hygiene norms varies strongly with the level of sex equality, but in a non-linear way. The sex difference is most pronounced in moderately egalitarian countries with the highest recorded difference being in Chile. In more egalitarian parts of the world, more sex equality is associated with a smaller sex difference in hygiene norms. In the less egalitarian parts of the world, the opposite relation holds. We offer an interpretation in terms of what different levels of sex equality mean for the content of sex roles.

Discussion

Using data in 56 countries, the current study provided a comprehensive analysis of the sex difference in hygiene strictness. We studied a set of norms about when you should wash your hands and where you should not spit. Globally, we found norms about handwashing to be slightly stricter among women than among men. The direction of this sex difference is consistent with findings in many single-country behavioral studies of handwashing [11–15]. We found even more substantial sex differences in the strictness of spitting norms. This is an important novel finding as no prior studies have examined sex differences in spitting. Perhaps it is related to men producing more saliva than women do [31], as this might create a stronger preference in favor of spitting. It is possible that spitting elicits a stronger disgust response in women by association because spitting is an innate behavioral response to remove noxious material from the mouth [32]. But there are also differences in the types of norms the two behaviors are involved in. For one thing, handwashing norms are prescriptive while norms about spitting are proscriptive. For another, handwashing is primarily a private good while strictness about spitting is primarily a public good. Moreover, the handwashing norms we studied were concerned with when you should wash your hands whereas the spitting norms were concerned with where you should not spit. This could play a role as culture may restrict women’s access to certain locations (e.g., soccer pitches). Future work may examine the specific roles of these factors.

Our first hypothesis was that the sex difference in hygiene strictness would be observed everywhere. In our dataset, we observed the sex difference in most countries but not all. Two countries, Saudi Arabia and Nigeria, were clear exceptions in that men reported stricter hygiene norms than women. To validate this finding, we searched for prior studies of hygiene in any of these countries that report results separately for men and women. We found two such studies for Saudi Arabia, both of which indeed reported stricter hygiene among men than among women [33, 34]. Thus, our findings are consistent with prior literature. We conclude that sex difference in hygiene strictness is nearly universal but that the presence of clear exceptions demonstrates that there is some cultural moderator that needs to be understood.

Our second hypothesis examined a proposed cultural moderator: the level of sex equality in society. We operationalized societal sex equality by the average attitude to sex equality with respect to participation in the job market, in politics, and in higher education. Such attitudes can be taken as a proxy for the strength, or weakness, of sex roles. Some authors have attributed stricter hygiene norms among women to sex roles [2, 21]. However, a more complex picture emerged in our data. The sex difference in hygiene strictness was often larger in countries with above-average levels of sex equality than in countries with below-average levels of sex equality. This finding is in keeping with many behavioral and somatic sex difference results and Schmitt has argued that biological sex differences can be moderated and facilitated by specific cultural contexts [16]. To our knowledge it has not be shown for the contents of normative beliefs. Within these groups of countries, the sex difference in hygiene strictness varied with the level of sex equality in different ways. Among countries with above-average sex equality, the sex difference in handwashing strictness showed no relation with sex equality whereas the sex difference in spitting strictness showed a negative relation with sex equality. Thus, the hypothesis was partially supported in this group of countries. Results looked very different in the group of countries with below-average levels of sex equality. In this group, the expected sex difference was most pronounced at the high end of sex equality, that is, at global average levels of sex equality. In countries with greater inequality, the sex difference in hygiene strictness disappeared and even became reversed at extreme levels of inequality (Saudi Arabia and Nigeria). This reversal suggests a flexible connection, if any, between hygiene norms and established sex differences in disgust sensitivity. But it is possible that the underlying asymmetry in inclusive fitness costs is something that can drive either male or female custodianship of hygiene, and hence difference in hygiene strictness, dependent upon key social ecological factors. Our analyses strongly supported that sex equality is a key factor. Specifically, while prior research has found that pathogen prevalence and religiosity may be more important factors behind sex differences in other domains [16], we found the level of sex equality do be a much stronger predictor of sex differences in hygiene.

In sum, we have found that there is substantial cultural variability in the extent to which women have stricter hygiene norms than men do, and it is quite strongly related to sex equality—but in a non-linear way. A possible interpretation of this unexpected finding is that the full spectrum of sex inequality encompasses several distinct phenomena. If we hold on to the notion that the sex difference is due to sex roles giving women a greater responsibility for maintaining hygiene in society, how could this responsibility vary across different levels of gender inequality? In moderately unequal societies, both women and men are fully responsible, but they tend to have different responsibilities. Women and men are seen as working together in a family unit where she is responsible for raising the children and keeping the home clean while he is responsible for bringing home most of the income. It is in these societies we would expect women to be more responsible for hygiene. As societies become more egalitarian, these sex roles weaken, and we would expect a decline in the sex difference in hygiene. In the most unequal societies, however, it is arguably men that have the responsibility in that they make decisions about the whole family’s behavior and are held responsible for the behavior of their wives or daughters. As a case in point, all women in the extremely unequal society of Saudi Arabia have a legal male guardian who is responsible for them [35]. Among other things, this ultra-low level of women’s responsibility means a lower level of responsibility for hygiene. Sex segregation in Saudi Arabia also implies that women are allowed less mobility and thereby potentially less exposure to situations and things that may motivate hygiene norms, in this way moderating any underlying biological sex differences [16]. This could be examined in future research.

Limitations

Limitations of the data were discussed by Eriksson et al. [8]. Most importantly, as the data are limited to hand washing and spitting norms, we cannot say whether the sex difference in hygiene strictness generalizes to other hygiene-related behaviors, such as washing the whole body, washing clothes, coughing, sneezing, and urinating. Other limitations include that African countries and small countries were undersampled, that socioeconomic stratification within countries is not measured, and that samples per country are sometimes quite small and not necessarily representative. However, these may not be major concerns, as prior analyses of data from these samples successfully replicate country-level variation in cultural values found in representative samples [22, 36]. Another limitation is that we do not have data on participants’ knowledge of objective benefits of hygiene.

Dominance judgments—important across numerous psychological domains, like attractiveness, leadership, & legal decision-making—accurately predict the likelihood with which a potential mate, ally, or rival can incapacitate their adversaries

Caton, Neil R., Lachlan M. Brown, Amy Zhao, and Barnaby Dixson. 2022. “Human Male Body Size Predicts Increased Knockout Power, Which Is Accurately Tracked by Conspecific Judgments of Male Dominance.” PsyArXiv. June 29. doi:10.31234/osf.io/3jny4

Abstract: Humans have undergone a long evolutionary history of violent agonistic exchanges, which would have placed selective pressures on greater body size and the psychophysical systems that detect them. The present work showed that greater body size in humans predicted increased knockout power during contests (Study 1a-1b: total N = 5,866; Study 2: N = 44 openweight fights). In agonistic exchanges reflective of ancestral size asymmetries, heavier combatants were 300% more likely to win against their lighter counterparts solely because they were 300% more likely to knock them out (Study 2). Greater body size afforded no other fighting performance advantages other than increased knockout power (Studies 1-2). Human dominance judgments (total N = 500 MTurkers) accurately tracked the frequency with which men (N = 516) had knocked out similar sized adversaries (Study 3). Humans were able to directly perceive a man’s knockout power solely because they were attending to cues of a man’s body size. Human dominance judgments—which are important across numerous psychological domains, including attractiveness, leadership, and legal decision-making—accurately predict the likelihood with which a potential mate, ally, or rival can incapacitate their adversaries.