High income men are more likely to marry, less likely to divorce, if divorced are more likely to remarry, & are less likely to be childless; income is not linked with the probability of marriage for women

High income men have high value as long-term mates in the U.S.: personal income and the probability of marriage, divorce, and childbearing in the U.S. Rosemary L. Hopcroft. Evolution and Human Behavior, March 23 2021. https://doi.org/10.1016/j.evolhumbehav.2021.03.004

Abstract: Using data from the first Census data set that includes complete measures of male biological fertility for a large-scale probability sample of the U.S. population (the 2014 wave of the Study of Income and Program Participation-N = 55,281), this study shows that high income men are more likely to marry, are less likely to divorce, if divorced are more likely to remarry, and are less likely to be childless than low income men. Men who remarry marry relatively younger women than other men, on average, although this does not vary by personal income. For men who divorce who have children, high income is not associated with an increased probability of having children with new partners. Income is not associated with the probability of marriage for women and is positively associated with the probability of divorce. High income women are less likely to remarry after divorce and more likely to be childless than low income women. For women who divorce who have children, high income is associated with a lower chance of having children with new partners, although the relationship is curvilinear. These results are behavioral evidence that women are more likely than men to prioritize earning capabilities in a long-term mate and suggest that high income men have high value as long-term mates in the U.S.

Keywords: Evolutionary psychologyFertilityMarriageChildlesnessDivorceSex differences

Stronger negative feelings (i.e., more disturbed, upset, & frustrated) when encountered others who, in our view, hold false beliefs, compared to when we think that others’ beliefs are merely different from our own

Molnar, Andras and Loewenstein, George F., Thoughts and Players: An Introduction to Old and New Economic Perspectives on Beliefs (March 16, 2021). The Science of Beliefs: A multidisciplinary Approach (provisional title, to be published in October 2021). Cambridge University Press. Edited by Julien Musolino, Joseph Sommer, and Pernille Hemmer. SSRN: http://dx.doi.org/10.2139/ssrn.3806135

Abstract: In this chapter we summarize how economists conceptualize beliefs. Moving both backward and forward in time, we review the way that mainstream economics currently deals with beliefs, as well as, briefly, the history of economists’ thinking about beliefs. Most importantly, we introduce the reader to a recent, transformational movement in economics that focuses on belief-based utility. This approach challenges the standard economic assumption that beliefs are only an input to decision making and examines implications of the intuitive idea that people derive pleasure and pain directly from their beliefs. We also address the question of when and why people care about what other people believe. We close with a discussion of the implications of these insights for contemporary social issues such as political polarization and fake news.

Keywords: Anticipatory Emotions, Belief-based Utility, Cognitive Dissonance, False Beliefs, Homophily, Motivated Reasoning, Polarization, Self-esteem, Theory of Mind

JEL Classification: A11, B12, B21, D83, D91

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In our own recent research, however (Molnar & Loewenstein, 2020), we have been advancing a subtly, but we believe crucially, different perspective. Our own view is that it is not awareness that other people have different beliefs than our own which causes discomfort. Rather, it is the belief that others hold, and act on, beliefs that we perceive to be wrong. This idea is also captured by “Cunningham’s Law”—named after Ward Cunningham, the developer of the first wiki—which states that “the best way to get the right answer on the internet is not to ask a question; it’s to post the wrong answer.”5 At the heart of this rather witty “law” lies the intuition that people have a strong desire to correct others’ beliefs when they deem those beliefs to be false. Aligned with the above anecdotal evidence, our own research demonstrates that participants express stronger negative feelings (i.e., are more disturbed, upset, and frustrated) when they encounter others who—from the participant’s point of view—hold false beliefs, compared to when participants think that others’ beliefs are merely different from their own (Molnar & Loewenstein, 2020). These strong negative emotions can then, based on the situation and the type of relationship, either trigger approach (e.g., confronting the other person, attempting to persuade them) or avoidance behaviors (e.g., blocking the other person online).

The subject of these false beliefs can be anything: beliefs about the individual (e.g., misunderstanding one’s intentions), about relationships (incorrectly believing that someone’s partner had been cheating on them), economic outcomes (tax cuts on the rich ultimately “trickle down” to help the poor), or even global phenomena (climate change is unrelated to human activity). What matters more is not the domain of belief, rather, the conviction that someone else holds an incorrect view of the individual, relationships, outcomes, or the world. The more convinced people are that others hold false beliefs, the more upset they will be (Molnar & Loewenstein, 2020), and the more likely they will take some action (either confront these others, or making extra effort to avoid them).

We find that men remain active in the dating and sexual marketplace longer than women

Dating and sexualities across the life course: The interactive effects of aging and gender. Lisa R. Miller, Justin R. Garcia, Amanda N. Gesselman. Journal of Aging Studies, Volume 57, June 2021, 100921. https://doi.org/10.1016/j.jaging.2021.100921

Highlights

• The authors investigate whether aging differentially impacts single women's and men's dating and sexual attitudes and behaviors

• The authors find that aging has greater effects on women's than men's dating and sexual attitudes and behaviors

• Gender differences in dating and sexuality are only found in specific stages of the life course

• Age is central to understandings of gendered heterosexuality

Abstract: Research on aging and sexuality has proliferated in recent years. However, little is known about the gender-specific effects of aging on dating and sexuality. Using survey data from the 2014 wave of Singles in America (SIA), a comprehensive survey on adult singles' experiences with dating and sexuality, we examine whether age differentially affects heterosexual women's and men's dating and sexual attitudes and behaviors and whether gender differences persist across the life course. We find that men remain active in the dating and sexual marketplace longer than women. Although main effects of gender differences are documented in dating and sexual attitudes and behaviors, the results show that gender does not operate the same across the life course. Notably, gender differences shrink or are eliminated in attitudes and behaviors surrounding partnering in midlife and late adulthood, suggesting that age is integral to understanding gendered heterosexuality.

Keywords: GenderSexualitiesAgingIntimate relationshipsLife course

Over and above other Big Five personality domains, both conscientiousness & agreeableness were negatively correlated with alcohol consumption, risky/hazardous drinking, & negative drinking-related consequences

Lui, P. P., Michael Chmielewski, Mayson Trujillo, Joseph Morris, and Terri Pigott. 2021. “Linking Big Five Personality Domains and Facets to Alcohol (mis)use: A Systematic Review and Meta-analysis.” PsyArXiv. March 17. doi:10.31234/osf.io/x2yta

Abstract

Aims: The goal of this investigation was to synthesize (un)published studies linking Big Five personality domains and facets to a range of alcohol use outcomes. Meta-analyses were conducted to quantify the unique associations between alcohol use outcomes and each Big Five personality domains over and above other domains. Within each domain, meta-analyses also were conducted to examine the unique contribution of each personality facet in alcohol use outcomes.

Methods: Systematic literature reviews were performed in PsycINFO and PubMed using keywords related to alcohol use and personality. Peer-reviewed and unpublished studies were screened and coded for the meta-analyses. Eighty independent samples were subjected to correlated effects meta-regressions.

Results: Over and above other Big Five personality domains, both conscientiousness and agreeableness were negatively correlated with alcohol consumption, risky/hazardous drinking, and negative drinking-related consequences. Facet-level analyses indicated that deliberation and dutifulness were uniquely associated with alcohol (mis)use over and above other conscientiousness facets, and compliance and straightforwardness were uniquely associated with alcohol (mis)use over and above other agreeableness facets. Extraversion—namely excitement seeking—was correlated with alcohol consumption, whereas neuroticism—namely impulsiveness and angry hostility—was correlated with negative drinking-related consequences.

Conclusions: Personality characteristics are robust correlates of alcohol (mis)use. Examining relevant narrowband traits can inform mechanisms by which personality affects drinking behaviors and related problems, and ways to enhance clinical interventions for alcohol use disorder. Gaps in this literature and future research directions are discussed.

From 2019... Educational attainment impacts drinking behaviors and risk for alcohol dependence: results from a two-sample Mendelian randomization study with ~780,000 participants

From 2019... Educational attainment impacts drinking behaviors and risk for alcohol dependence: results from a two-sample Mendelian randomization study with ~780,000 participants. Daniel B. Rosoff, Toni-Kim Clarke, Mark J. Adams, Andrew M. McIntosh, George Davey Smith, Jeesun Jung & Falk W. Lohoff. Molecular Psychiatry volume 26, pages1119–1132. Oct 2019. https://www.nature.com/articles/s41380-019-0535-9

Rolf Degen's take: The genetic instruments associated with higher educational attainment are linked to reduced binge drinking, reduced amount of alcohol consumed per occasion, but to increased frequency of alcohol intake, especially of wine

Abstract: Observational studies suggest that lower educational attainment (EA) may be associated with risky alcohol use behaviors; however, these findings may be biased by confounding and reverse causality. We performed two-sample Mendelian randomization (MR) using summary statistics from recent genome-wide association studies (GWAS) with >780,000 participants to assess the causal effects of EA on alcohol use behaviors and alcohol dependence (AD). Fifty-three independent genome-wide significant SNPs previously associated with EA were tested for association with alcohol use behaviors. We show that while genetic instruments associated with increased EA are not associated with total amount of weekly drinks, they are associated with reduced frequency of binge drinking ≥6 drinks (ßIVW = −0.198, 95% CI, −0.297 to –0.099, PIVW = 9.14 × 10−5), reduced total drinks consumed per drinking day (ßIVW = −0.207, 95% CI, −0.293 to –0.120, PIVW = 2.87 × 10−6), as well as lower weekly distilled spirits intake (ßIVW = −0.148, 95% CI, −0.188 to –0.107, PIVW = 6.24 × 10−13). Conversely, genetic instruments for increased EA were associated with increased alcohol intake frequency (ßIVW = 0.331, 95% CI, 0.267–0.396, PIVW = 4.62 × 10−24), and increased weekly white wine (ßIVW = 0.199, 95% CI, 0.159–0.238, PIVW = 7.96 × 10−23) and red wine intake (ßIVW = 0.204, 95% CI, 0.161–0.248, PIVW = 6.67 × 10−20). Genetic instruments associated with increased EA reduced AD risk: an additional 3.61 years schooling reduced the risk by ~50% (ORIVW = 0.508, 95% CI, 0.315–0.819, PIVW = 5.52 × 10−3). Consistency of results across complementary MR methods accommodating different assumptions about genetic pleiotropy strengthened causal inference. Our findings suggest EA may have important effects on alcohol consumption patterns and may provide potential mechanisms explaining reported associations between EA and adverse health outcomes.

Discussion

Using large summary-level GWAS data and complementary two-sample MR methods, we show that EA has a likely causal relationship with alcohol consumption behaviors and alcohol dependence risk in individuals of European Ancestry. More specifically, higher EA reduced binge drinking (six or more units of alcohol), the amount of alcohol consumed per occasion, frequency of memory loss due to drinking, distilled spirits intake, and AD risk. EA increased the frequency of alcohol intake, whether alcohol is consumed with meals, and wine consumption. We found evidence that our results may be driven by genetic pleiotropy in only two of the eight alcohol consumption behaviors (average weekly beer plus cider intake and alcohol usually taken with meals) and significance remained after additional analysis using EA instruments with SNPs nominally associated with either cognition or income suggest that EA may be an important factor responsible for variation in alcohol use behaviors. Consistency of our results across MR methods also strengthens our inference of causality.

Educated persons generally have healthier lifestyle habits, fewer comorbidities, and live longer than their less educated counterparts [52], and our results suggest EA is causally associated with different likelihoods of belonging to variegated alcohol consumer typologies. We found that an additional 3.61 years of education reduced the risk of alcohol dependence by ~50%, which is consistent with results from small community samples [53], and the two most recent alcohol dependence GWASs findings strong inverse genetic correlations with educational attainment [27, 54]. Notably, binge drinking significantly increases the alcohol dependence risk [55], and distilled spirits and beer consumption account for the majority of hazardous alcohol use [56]. Furthermore, compared to wine drinkers, beer and spirits drinkers are at increased risk of becoming heavy or excessive drinkers [57], for alcohol-related problems and illicit drug use [58, 59], and AD [57]. Our findings related to alcoholic drink preferences, when combined with our results showing increased binge drinking, memory loss due to alcohol, and a suggestive relationship with remorse after drinking, imply a pattern of alcohol consumption motivated to reduce negative emotions or becoming intoxicated [14].

In contrast to the often-reported positive association between EA and total amount of alcohol consumption reported from observational studies [18, 60], we found little evidence of a causal relationship. This null finding may be reconciled by the opposing influences on alcohol intake frequency and total alcohol consumed per occasion, which, while not leading to an overall change in total consumption, nonetheless significantly affect the pattern. Our null finding regarding total consumption does support similar results from Davies et al. [52], who used the 1972 mandated increase in school-leaving age in the UK as a natural experiment instrumental variable design to investigate the causal effects of staying in school on total alcohol consumption (from individuals in the UKB sample who turned 15 in the first year before and after the schooling age increased). Davies et al. may have found a significant effect of staying in school had they included the disaggregated behavioral dimensions of alcohol consumption behaviors. Nevertheless, even if no EA-total alcohol consumption relationship exists, studies have reported that both the specific alcoholic beverage and the pattern with which it is consumed, controlling for total consumption, independently contribute to risky health behaviors [61, 62].

Natural experiments [52, 63], and twin studies have found that differences in EA, even after controlling for shared environmental factors, still significantly impact mortality risk [64,65,66], and recent large Mendelian randomization studies have demonstrated inverse relationships between EA on smoking behaviors [35] and coronary heart disease (CHD) risk [34] add to the growing body of literature, suggesting a causal effect of increased EA on health and mortality. Other observational studies have linked alcohol consumption patterns to health, disease, and mortality risk [67,68,69]. In particular, binge drinking may have dramatic short-term consequences, including motor vehicle accidents, alcoholic coma, cerebral dysfunction, and violent behavior [70], as well as long-term effects such as hypertension, stroke, and other cardiovascular outcomes [71]. A recent MR study showed that smoking mediates, in part, the effect of education on cardiovascular disease [72], and our results suggest that differences in alcohol consumption patterns may also be another mediator. Health consequences incur significant costs with binge drinking accounting for ~77% of the $249 billion alcohol-related costs (lost workplace productivity, health care expenses, law enforcement, and criminal justice expenses, etc.) in the United States in 2010 [55].

While we do not fully understand the underlying biological mechanisms through which the instrument SNPs influence EA, they are primarily found in genomic regions regulating brain development and expressed in neural tissue. These SNPs demonstrate significant expression throughout the life course, but exhibit the highest expression during development [36]. For example, rs4500960, which was associated with reduced EA, is an intronic variant in the transcription factor protein, T-box, Brain 1 (TBR1), that is important for differentiation and migration of neurons during development [36], while rs10061788 is associated with cerebral cortex and hippocampal mossy fiber morphology [36]. It is, however, important to note that interpreting these SNPs as representing “genes for education” may be “overly simplistic” since EA is strongly affected by environmental factors [36]. Our results remained when using an EA instrument with SNPs nominally associated with income removed, suggesting that an individual’s genetics may impact behavior development, which then increases EA [73]. Conversely, genetic estimates of EA and its correlations with other complex social phenotypes using population-based samples may be susceptible to biases, such as assortative mating and dynastic effects that provide pathways alternate to direct biological effects [40]. For example, EA-associated genetic influence on parental behavior could causally affect the child’s environment [73]. Using polygenic scores for EA, Belsky et al. [73] recently found the mothers’ EA-linked genetics actually predicted their children’s social attainment better than the child’s own EA-linked genetics, suggesting an effect mediated by environmental effects. While policies are not able to change children’s genes, or their inherited social status, they can provide resources [73], and our results suggest that interventions to increase education may help improve health outcomes through changing alcohol consumption patterns.

Notably, there was evidence for some causal effects of alcohol consumption patterns on EA, and the divergent effects again demonstrate the importance of separating drinking variables. However, we failed to find evidence that total alcohol consumed, binge drinking, or AD impacts EA, which is in line with observational studies finding no, or small effects [21], and suggests that other studies findings a negative effect [21] may be due to confounding. Alternatively, EA may not be sensitive enough to detect changes in schooling, e.g., grade point average [21], falling behind in homework and other academic difficulties that also reported association  with heavy drinking [74]. Further, there are currently no adolescent drinking behavior GWAS, so the temporal sequence of these analyses should be considered during their interpretation. Our findings, therefore, need replication when GWAS on adolescent alcohol consumption patterns becomes available.

Exploratory sex-specific analyses revealed differences in certain aspects of the relationship between EA and alcohol consumption. For men, the relationship between their consumption of red wine, beer, and whether they drink with meals was more sensitive to changes in EA than for women. Conversely, the reduction in binge drinking with increased EA may be driven by its effect for women since its effect on men was not significant. In addition, in women the negative effect of EA on spirit consumption was more than double its effect on men. We found no differences among the AUDIT question.

There are noted gender gaps in alcohol use and associated outcomes due to a combination of physiological and social factors [39]. Notably, Huerta et al. [75] found sex-specific effects of EA and academic performance on the odds of belonging to different alcohol consumption typologies (ranging from “Abstainer” to “Regular Heavy Drinker with Problems”). The absence of any association in males may be due to their inability to model binge drinking [75]; however, our results suggest otherwise. Additionally, the recent Clarke et al. [28] total weekly alcohol GWAS found sex-specific genetic correlation differences with an rg = 0.1 in men and 0.33 in women. Taken together, our findings suggest EA may partially account for some of these observed gender gaps in alcohol consumption, but not others. We should note that the only available sex-specific EA GWAS had significant overlap ( ≥18.9%) with the outcome datasets, so our exploratory sex-specific analysis used the same EA GWAS combining men and women. The lack of available sex-specific AD GWAS also meant we were unable to examine differences in AD risk. Notably, the sex-specific EA GWAS demonstrated nearly identical effect sizes between men and women, which support the validity of the estimates derived from the combined-sex EA GWAS, but future studies using sex-specific instruments are required.

Strengths and limitations

We note several strengths. We have analyzed multiple alcohol-related behavioral phenotypes, which support the consistency of our results. We have implemented multiple complementary MR methods (IVW, Egger, weighted median, and weighted mode MR) and diagnostics. Consistency of results across MR methods (accommodating different assumptions about genetic pleiotropy) strengthens our causal interpretation of the estimates [76]. We also used the largest publicly available GWASs for both exposure and outcome samples; large summary datasets are important for MR and other genetic analysis investigating small effect sizes [77]. We also note limitations and future directions. There is minimal sample overlap between the exposure SSGAC GWAS and the outcome PGC GWAS (AD), but there may still be individuals participating in multiple surveys, which event we cannot ascertain with available summary-level GWAS statistics. Further, the GWASs cohorts are from Anglophone countries, where beer is the preferred drink [78]; therefore, applicability to other countries with different alcohol preferences may be limited. Further still, it has been reported the UKB sample is more educated, with healthier lifestyles, and fewer health problems than the UK population [79], which may limit the generalizability to other populations. Replication of these findings using alcohol use information from different ethnicities is necessary. EA only measured years of completed schooling; determining how various aspects of education differentially impact alcohol consumption was not possible but should be a topic of future work. Finally, alcohol consumption is not stable over time [15]; however, the alcohol consumption outcomes correspond to current drinking behavior, which may have led to the misclassification of some individuals. The current drinking also impacts the temporal relationship of our bidirectional analyses, since the current alcohol intake likely occurred after maximum educational attainment for most of the participants. Future GWAS that evaluate drinking behavior during adolescence, or other longitudinal studies are necessary to confirm these findings and better elucidate the impact of alcohol intake on EA.

In adolescents, we found sex differentiation in jealousy responses to infidelity scenarios at all ages from 16 to 19; males found the sexual aspect of imagined infidelity more distressing than adolescent females did

Investigating the emergence of sex differences in jealousy responses in a large community sample from an evolutionary perspective. Per Helge H. Larsen, Mons Bendixen, Trond Viggo Grøntvedt, Andrea M. Kessler & Leif Edward Ottesen Kennair. Scientific Reports volume 11, Article number 6485. Mar 22 2021. https://www.nature.com/articles/s41598-021-85997-7

Abstract: Sex differences in jealousy responses to sexual and emotional infidelity are robust in samples of heterosexual adults, especially in more gender egalitarian nations. However, investigations of when and how these differences develop have been scant. We applied two forced choice infidelity scenarios in a large community sample of high school students (age 16–19, N = 1266). In line with previous findings on adults using the forced choice paradigm, adolescent males found the sexual aspect of imagined infidelity more distressing than adolescent females did. Nevertheless, there was no effect of age on the jealousy responses, and age did not moderate the sex difference. There were neither any effects of three covariates (having had first sexual intercourse, being in a committed romantic relationship, and sociosexuality), neither as markers of pubertal maturation nor as psychosocial environmental stimuli. Future research needs to investigate even younger samples in order to specify at what age the sex difference in jealousy responses emerges.

Discussion

In a large community sample of adolescents, we found sex differentiation in jealousy responses to infidelity scenarios at all ages from 16 to 19. The jealousy responses were neither affected by sexual or romantic experiences nor by respondent sociosexual orientation. Prior to this study, it was known that in adult heterosexual samples there is a sex difference in responses to jealousy scenarios using a forced choice paradigm1. This sex difference has proven especially robust in Scandinavian young adult samples4,14,15. Previously only Shackelford et al.29 and de Visser et al.19 have considered the sex difference in romantic jealousy among adolescents. However, Shackelford et al.29 only included a small number of participants younger than 20 and de Visser et al.19 focused primarily on life-span development. None of these considered the ontogenetic development and emergence of the sex difference in romantic jealousy during adolescence specifically and in detail. The current study therefore set out to discover when these sex differences emerge in a large community adolescent sample. Further, we considered how relationship status, sexual debut and sociosexuality might moderate the development of the sex difference in romantic jealousy – indicators of both psychological and pubertal maturation or life history52 and relevant experiences3.

Although our sample represents the largest group of young adolescents yet studied, we were unable to detect at what age the sex difference comes online. There was no interaction with age. Further, despite what evolutionary theories predict3, there was neither any effect of relationship status, sexual status, nor sociosexuality on the development of sex differentiation of jealousy responses. None of our predictions were supported. The sex difference appears to develop earlier than age 16, and it is fully established at that age.

Suggesting that these results were obvious a priori is not convincing. The analyses of de Visser et al.19 and Shackelford et al.29 do not really allow for any extrapolation to the age group considered here, due to low number of participants in the relevant age and no specific attention to processes in the ages 16 to 19. The current data were also collected prior to de Visser et al.19. Nevertheless, an evolutionary perspective suggests that adaptations develop or come online strategically, just prior to being adaptive relevant32.

This leaves us with some evolutionary developmental conundrums. The increased male heterosexual sexual jealousy response seems to be present at an early age and not contingent upon the specific domain relevant experiences we measured in this study. What function this specific emotional response to sexual infidelity might have played in young males in an evolutionary context is therefore unclear. None of the current evolutionary psychology approaches has specified any function for increased male sexual jealousy in adolescents too young to be troubled with cuckoldry, which is the main function of male, heterosexual sexual jealousy. The acquisition of committed, long-term partners that young men were able to defend from older, more formidable rivals with higher status was most likely evolutionary rare35. Further, at lower ages, it is unclear what, if any function early adolescent males’ increased focus on physical aspects of their romantic partners’ infidelity should serve. It is possible that the developmental appearance of sexual jealousy simply prepares the individual for later life, serving no function during adolescence. However, the current findings warrant further theoretical development. If anything, increased emotionality in young males might put them in harm’s way from older, more formidable men, rather than improving any relevant paternal certainty. Nevertheless, at some point when moving towards younger ages, the responses the participants would be reporting on might not be the functional jealousy of adults, but some form of a proto-sexual jealousy, with other possible specific or deferred functions. This might also be reflected in “puppy love”53 or other roleplay type of love bonds between children.

Finally, our community sample evinced adequate variance in the different sexual and relationship experiences to detect any conditional developmental effects in jealousy responses. At this point we would need further studies of early puberty to address the question of the emergence and development of this sex difference. Based on these results, our preliminary conclusion must be that increased heterosexual male sexual jealousy matures primarily as part of puberty, independent of specific experiences. However, the function of this response at this age remains unclear, as it would seem it serves no anti-cuckolding function, while retaining, especially in concert with Young Male Syndrome tendencies54, the cost of violent conflict with more formidable older males.

Limitations and future research

While this is the largest, youngest adolescent sample to be studied with the forced choice paradigm, we were unable to discover the point in development when the sex difference emerges. Future studies therefore need to investigate jealousy responses in even younger samples. However, doing so would introduce ethical and methodological challenges. As we consider continually lower ages, the scenarios will at some age stop being meaningful, or developmentally relevant to the participants. We need to consider the possibility that the males’ increased proto-sexual jealousy develops early in puberty. Future studies should possibly also go beyond self-report and investigate specific design features of jealousy and their development in men and women using longitudinal designs, including other developmentally relevant factors. Such a design might better address causality than our cross-sectional design. However, in this first in-depth of the emergence of the sex difference of jealousy responses, our focus was not primarily on causes, but on at what age this difference appears. Also, the community sample consisted of four representative age cohorts55, and therefore ought to be adequate to address age trends. Further, the current approach to the development of jealousy is limited to test a specific set of predictions and does not address several other socio-cultural and intrapsychic factors, that may be of interest in future studies.

Conclusions from a Norwegian sample are admittedly culturally limited, to some degree56—and in any case subject to evolutionary mismatch57. Known cultural and socioecological variation that contribute to variation in jealous responses include more parental investment and less extramarital sex, which predict more severe jealousy responses across cultures12. Despite the importance of cultural and socioecological factors, similar forced-choice patterns have been found in cultures as diverse as China40, Korea58, Japan12,58, Sweden14, Norway4, England, Romania59, Germany, Netherlands60, Spain61, India, and among the Hadza, Himba, Karo Batak, Mayangna, Mosuo, and the Shuar12.

Finally, the current study suffers from the same limitations that hold true for all hypothetical scenarios, and the forced choice paradigm. Continuous measures and experienced jealousy may also be studied in the future in this age group.

Interesting images/1

 

No date, no place

Coping with mortality: responses of monkeys and great apes to collapsed, inanimate and dead conspecifics

Coping with mortality: responses of monkeys and great apes to collapsed, inanimate and dead conspecifics. Arianna De Marco, Roberto Cozzolino & Bernard Thierry. Ethology Ecology & Evolution, Mar 21 2021. https://doi.org/10.1080/03949370.2021.1893826

Abstract: It was long assumed that only humans can distinguish the living from the dead. Renewed interest in this question over the last decade has led several authors to assert that non-human primates are also aware of death. We investigate this issue by comparing the behaviours of monkeys and great apes toward helpless conspecifics, basing our analysis on published reports. We first examine the behaviours of mothers towards the body of their dead offspring. They may carry the corpse for days or more before abandoning it. They groom, inspect and protect it, sometimes allowing group members to explore it, and rare cases of cannibalism have been reported. No significant difference is observed in the way that monkeys and great apes treat the bodies of infants. We then examine responses to collapsed (still able to move and react) and inanimate (unresponsive or dead) conspecifics. Monkeys and great apes guard, care for and inspect their helpless partners, and also manipulate and mobilise them. Through these actions, individuals may inform themselves about the state of their partners, test their responsiveness and/or attempt to rouse them. It appears that only chimpanzees and gorillas show violent action such as display behaviours and the rough treatment of bodies. They can also make distress calls, and periods of “stunned silence” sometimes occur in chimpanzees, indicating that they are experiencing intense emotion. Finally, we argue that while both monkeys and great apes detect body dysfunction through the victims’ inability to wake up and move, only great apes can understand that something serious has happened. The signs of emotional disturbance reported in them indicate that they may believe that inanimate conspecifics have entered a state of “dormancy”, meaning that they are unlikely to regain wakefulness. However, there is no evidence that any non-human primates are aware of mortality.

Keywords: deathemotiondistressempathymental representationepimeletic behaviourprimate

RECOGNITION OF DYSFUNCTION AND AWARENESS OF MORTALITY

Since death is the cessation of life, it may seem necessary to know what primates understand about life in order to know what they understand about death. Animals are defined by their animacy, and it has been shown in several animal species, including primates, that individuals are able to distinguish between animate and inanimate as human infants do: they can separate entities that engage in self-generated motion from those that do not (Opfer & Gelman 2011; Tsutsumi et al. 2012; Abdai et al. 2021). Some authors have proposed that animals and humans are endowed with several innate systems of “core knowledge” that are designed to build representations with specific contents. One system would serve to represent (inanimate) objects and their mechanical effects, while another would serve to represent (animate) agents and their actions (Spelke & Kinzler 2007; Carey 2009). On the basis of this theoretical framework, Gonçalves and colleagues (Gonçalves & Biro 2018; Gonçalves & Carvalho 2019) hypothesize that when a living being dies, its body becomes an object, thus activating both the object and agency core systems in bystanders. This would create a perceptual mismatch in them, resulting in an “animacy detection malfunction”.

It is sound to consider that an inanimate body can present contradictory clues that do not meet the expectations of conspecifics, and hinder their ability to recognize its state. However, it is probably too early to assert that the perception of a corpse induces a conflict between an object representation system and something like a life representation system. We are far from knowing what dynamic clues subjects use to assess animacy, and as Gonçalves and Carvalho (2019) acknowledge, agency involves much more than animacy: agents are capable of attentional states, goal-directed movements and interactions with others; primate species probably vary in their ability to identify these different components of agency. Moreover, subjects can also identify living beings like animals using morphological features such as the presence of a face, eyes, limbs or species-specific characteristics, and we do not know how dynamic and morphological clues are integrated at the brain level (Opfer & Gelman 2011; Fisher & Freiwald 2015). We should add to these multiple clues the past interactions and social relationships that a subject may have memorized about a given conspecific, which would also contribute to the subject’s representation of this individual.

Rather than starting from theoretical constructs about the recognition of life by primates, it seems more productive for the time being to address what they understand about the state of their inanimate conspecifics. However, discriminating inanimate individuals from perceptual features is not the same as knowing what it means to be dead (Allen & Hauser 1991; Monsó 2020). In what follows, we will examine in turn whether monkeys and great apes detect conspecific dysfunction, show signs of disturbance, and exhibit some awareness of mortality.

Detection of dysfunction

Although death is usually regarded as an event, it is more accurate to think of it as a process in which one organic function fails after another. In principle, it would thus be possible to detect the dysfunction of a body using different clues: cardiorespiratory arrest, cessation of eye movements, and the inability to move and react.

As previously reported, monkeys and great apes have been observed inspecting the face and/or mouth of collapsed or inanimate partners, and Anderson et al. (2010) wrote that the companions of a dying chimpanzee “appeared to test for signs of life by closely inspecting her mouth and manipulating her limbs (test for pulse or breath)”. However, nobody ever saw a monkey or an ape move their ear close to the mouth of another to listen to his/her breathing; nobody ever saw a monkey or an ape put their hand on the chest of another to feel his/her heartbeat. Not only would the contrary imply expectations about the need for breathing and heartbeats, but it is even hard for humans to be certain that the lungs and heart have stopped, especially in weakened individuals (Stewart 2003). Historically, people waited for signs of putrefaction to confirm death. Until a few centuries ago, tests for respiratory ventilation consisted for example of placing a feather under the nose, or holding a mirror before the mouth to detect condensation; it was only with the invention of the stethoscope in the 19th century that medical practitioners were able to determine with a reasonable degree of certainty whether the heart had ceased to function (President’s Commission 1981; Powner et al. 1996; Whetstine 2008). Against this background, it seems unlikely that primates other than humans have the ability to use soundless breathing, heart rate or pulse to assess the state of their conspecifics.

Another long-established medical sign of decease has been the fixity of the eyes (President’s Commission 1981; Whetstine 2008). This is understandable given the normal animation of the eye area, which includes gaze orientation, pupillary reflex, and eyelid movements. Experimental studies in humans and other primates have shown that they are disproportionally interested in the eye area; they are highly sensitive to the attention and gaze direction of others, and are able to adjust their behaviour to get a partner to attend to them (Emery 2000; Bourjade et al. 2014; Liebal et al. 2014; Tomasello & Call 2019). Correspondingly, monkeys and great apes often inspect the face and/or eyes of collapsed and recently deceased conspecifics (Tables 1–2). It is safe to assume that they are able to detect the absence of eye movement. The inability to make eye contact and get attention may warn them that something is going wrong with their companion. We can note that the eyes of inanimate individuals may be open or closed, but this information is not found in scientific reports. Fingering or picking at the eyes or eyelids has sometimes been observed in monkeys (Yerkes 1915; Fashing et al. 2011). According to a second-hand account, chimpanzees were once seen opening the eyes of a dead companion (Bekoff 2007).

Even if animacy is a main attribute of animals, it is common for primates to encounter motionless conspecifics. They regularly experience periods of immobility, which are first and foremost due to sleep phases. It is not the lack of animacy per se that must seem odd to observers of motionless individuals, but rather their inability to regain animacy: they are expected to wake up when someone acts on them, and the problem arises when they fail to do so. Assessing the responsiveness of partners and probing or stimulating them may account for many of the behaviours of primates towards collapsed and inanimate conspecifics. Although observing and sniffing can provide initial information, it is only by touching and above all handling partners that group members can test their reactivity or attempt to rouse them – with rough treatments producing the same effects. Whatever the exact goals of the intervening individuals, their actions can inform them if their partners were previously asleep or if something is going wrong. This is not an issue for collapsed partners, as they may still show some movement; we have indeed found that manipulative actions were mainly reported for inanimate partners, further indicating that monkeys and great apes are able to discriminate between these two conditions (Table 2). Note that we would expect the opposite trend for mobilising actions that specifically seek to lift a partner and restore him/her to an upright position: if the performers are able to distinguish between the two conditions, these actions should be applied to apparently wakeful – i.e. collapsed – partners rather than to inanimate ones. As already mentioned, only two unambiguous cases of this type of helping behaviour have been described. In the first instance a mountain gorilla attempted to pull a juvenile into a sitting position while the latter was still reactive (Watts 2020: case 1). In contrast, the second instance concerns a rhesus macaque who tried to lift a partner when the partner was inanimate, and did so again when the partner was beginning to regain consciousness after fainting (see Supplemental Material). There are too few cases to be able to draw firm conclusions.

The termination of breathing, heartbeat, eye movements and any reflex or motor response is referred to by medicine as negative signs of life. They are later followed by positive signs of death: cooling of the body, stiffening, putrid odours and changes in skin colour that result from the decomposition process. These different alterations gradually take the body away from its living appearance, which could contribute to the information – or confusion – of those who inspect it (Gonçalves & Biro 2018). However, positive signs of death do not appear until several hours or even more than a day after death, so in many cases group members have assessed the state of the affected partner long before this time.

It may be expected that the more experienced individuals are better at detecting unresponsiveness and other signs of death. Three studies have compared the duration of dead infant carrying in females of different age and maternal experience. This yielded contradictory results that provided little support for the hypothesis that younger and/or first-time mothers would carry their dead infant for longer periods of time than other mothers (Sugiyama et al. 2009; Das et al. 2019; Lonsdorf et al. 2020). Besides, younger chimpanzees tend to exhibit more exploratory behaviours toward corpses than adults (Teleki 1973a; Stewart et al. 2012; van Leeuwen et al. 2016; Jakucińska et al. 2020), and it is not rare for them to play with the bodies of dead infants (see above). However, little quantitative data are available in primates about the tendency of different age-and-sex categories to examine the body of affected conspecifics (see De Marco et al. 2020).

Signs of disturbance

In the foregoing, we deliberately used the vague expression “something is going wrong” to account for what primates can infer when faced with a conspecific’s inability to respond to their actions. The question now is whether this can cause concern to subjects. Not understanding something is not necessarily a reason for worry. On the contrary, if primates understand that something serious has happened, it can be disturbing to them and can be reflected in their behaviour.

Several authors have claimed that the occurrence of affiliative behaviours towards collapsing or dying conspecifics is a mark of compassion (Bezerra et al. 2014; Yang et al. 2016; Gonçalves & Carvalho 2019). However, the affected individuals in these situations can move and emit sounds, so partners may respond to their signs of distress without the need for a mental representation of their emotional states. If compassion implies an understanding of distress that involves empathic perspective-taking or the sharing of feelings (Cheney & Seyfarth 2007; Boesch 2012; Adriense et al. 2020), then responses to the behavioural expression of distress are not proof of compassion. On the other hand, there is converging evidence that great apes such as chimpanzees are capable of targeted helping and empathic perspective-taking, and can thus apprehend the suffering of conspecifics (de Waal 2008; Boesch 2012; Pérez-Manrique & Gomila 2018; Sato et al. 2019). Nevertheless, when chimpanzees display affiliation towards a dying conspecific, it is difficult to justify any assumption that this a caretaking behaviour anticipating an approaching death (Anderson et al. 2010): an individual who is collapsing or dying is by definition still alive; we have no reason to believe that others can predict she/he is going to die, and they may actually perceive her/him as rescuable. Stringent conditions are necessary to examine whether a companion’s physical condition may disturb partners, regardless of the occurrence of any communicative cues. We must rule out reactions to collapsed conspecifics and focus on reactions to inanimate conspecifics. We must also exclude cases where the presence of a danger in the surroundings can elicit distress or warning calls from bystanders (e.g. Mohnot 1980; Gupta 2000; Perry & Manson 2008: Maní/Pobrecito; Riley et al. 2015; Campbell et al. 2016: case 4).

The display behaviours and rough treatments that chimpanzees and gorillas show towards their inanimate conspecifics are among the most dramatic responses reported in animals (Table 2). Males are primarily responsible for these actions, which in some cases were repeated over several hours (Fossey 1983; Stewart et al. 2012). Even though rough treatments may contribute to test or awaken the partner, the energy devoted to violent behaviours indicates that the individuals’ motivations go beyond these goals. Regardless of whether this behaviour expresses frustration due to incomprehension or a lack of acceptance of the partner’s state, it at least informs us that individuals find the situation serious enough to engage in such heated action. The alternation of periods of quiet attendance and periods of excitement is another hallmark of the chimpanzee response. Emotional displays may include warning and distress calls, while stillness may pervade the entire group in cases of stunned silence (see above). Here again, signs of intense emotional disturbance in chimpanzees indicate that they attribute a special meaning to the unresponsiveness of their companion. No comparable periods of stunned silence have been recorded in gorillas, but it is difficult to make inferences about this difference with chimpanzees because gorilla temperament is characterized by high emotional stability (Schaeffer & Steklis 2014; Eckhardt et al. 2015). No conclusions can be drawn for bonobos and orang-utans due to the lack of documented reports in these species.

The comparison of monkey behaviour with that of chimpanzees and gorillas is illuminating. No rough treatment of corpses was reported in monkeys. Display behaviours were observed once in Hanuman langurs, but they were not directed at the body of the dead individual (Mohnot 1980). Monkey responses to inanimate conspecifics are generally unremarkable. In one well-documented case in brown capuchins, for example, group members quietly inspected and handled the body of a recently deceased female in turn, and even her sister and offspring did not exhibit any signs of distress (De Marco et al. 2020). In another instance in rhesus macaques, a male made sustained efforts to revive an unconscious partner by mobilising and lifting him, and although the intervening male yawned a few times, indicating a significant degree of tension (see Maestripieri et al. 1992; Deputte 1994), he showed no evidence of being alarmed (see Supplemental Material). Likewise, the other reported cases showed no signs of distress (Table 2; see also Takeshita et al. 2020). There were two types of situation in which distress vocalisations were heard, but they do not actually contravene the previous statement. In the first case, infants cried and screamed following their mother’s death (Mohnot 1980; Fashing et al. 2011); however, these behaviours also occur as part of normal mother-offspring interactions when a female does not attend to her infant. The second situation involves mothers emitting warning, distress or contact calls when they lose the body of their dead infant. Here, the triggering event is not the infant’s lack of response, but the absence of the infant’s body, as already mentioned (Altmann & Altmann 1970: Shorty; Smuts 1985: Zandra/Zephyr; Perry & Manson 2008: Abby/Omni; Li et al. 2012: case 1; Botting & van de Waal 2020: Nurks; Carter et al. 2020: cases 1 and 5). Although monkeys sometimes display signs of tension or anxiety such as restlessness, scratching and yawning when confronted with the unresponsiveness of a conspecific (Campbell et al. 2016: case 1; Carter et al. 2020; De Marco et al. 2020; Supplemental Material), they do not show any signs of the intense emotional disturbance observed in chimpanzees and gorillas. The communicative signals that only monkeys send to non-responding conspecifics may represent a further consequence of their inability to realize the severity of their state, whereas chimpanzees and gorillas could be aware that any attempt to communicate is pointless.

Awareness of mortality

We came to the conclusion that monkeys and great apes are able to understand that “something is going wrong” when confronted with an inanimate conspecific. We also reached the conclusion that at least great apes such as chimpanzees and gorillas can also understand that “something serious has happened”. However, the question remains as to whether they are aware of what it means when a partner remains permanently inert, and whether we can gain any insight into this question. Research studies in developmental psychology have shown that the understanding of death in human children can be defined and measured through several dimensions (Speece & Brent 1984; Kenyon 2001; Slaughter 2005; Longbottom & Slaughter 2018). From 4 to 10 years of age, children successively master four main dimensions related to the concept of mortality: (1) Irreversibility: a dead individual cannot return to life, (2) Universality: all living beings must eventually die, (3) Cessation: all bodily and mental functions cease upon death, (4) Causation: the breakdown of bodily functions is due to external and internal causes.

Irreversibility is probably the easiest dimension of mortality to grasp, as it is the first dimension that children successfully master. Several authors have expressed the opinion that primates are capable of understanding the permanence of death (de Waal 2013; Anderson 2018; Gonçalves & Carvalho 2019). de Waal (2013) reports an anecdote where a film was projected to a group of captive chimpanzees. The film showed a male from the group who had died a few years earlier, and his appearance on the screen provoked a strong emotional reaction from his former rivals. Gonçalves and Carvalho (2019) argue that their reaction was evidence of a violation of expectation regarding the irreversibility of death. However, this event is by no means conclusive, as it could just as well be used to support the view that chimpanzees accept that dead individuals can return to life, and be touched if this appears to happen. Other researchers claim that the weakening of the mother’s attachment to her dead infant and her eventual abandonment of the corpse prove her awareness of the irreversibility of death (Das et al. 2019; Lonsdorf et al. 2020; Monsó 2020). If it were true, however, this explanation would be tantamount to asserting that mothers of any animal species who give up the putrefying body of their offspring are aware of the irreversibility of death. One might just as well reason ad absurdum that chimpanzee females are among the least cognitively gifted primates since more than half of them in the Gombe population carry their dead offspring (see Lonsdorf et al. 2020). It is more straightforward to say that mothers have no other choice but to abandon the corpses after some time, and that this behaviour tells us nothing about death awareness in primates.

Anderson (2011, 2018) points out that chimpanzees have many opportunities to learn that inanimate individuals generally do not wake up, not only because they are exposed to deceased conspecifics – infant death being the most common event – but also because they regularly capture animals that they may kill and handle for a period of time before consuming them. Indeed, these different experiences are likely to inform individuals that subjects who remain immobile for extended periods of time generally do not recover. It should be noted however that small animals of a wide range of taxa follow death-feigning anti-predator strategies in which they go into tonic immobility when captured (Humphreys & Ruxton 2018). This means that it is not uncommon for primates to encounter motionless animals, some of which can subsequently resume activity. It should also be remembered that witnessing sleeping and awakening sequences in others is a daily reality for them. Furthermore, individuals may have also seen unconscious partners who later recover, because they were temporarily ill or had passed out. For example, falling from a tree is a continuing risk for tree-dwelling animals (see Table 2); primates cannot avoid occasionally landing on a dead branch, and if they fail to catch hold of a lower branch, they may pass out or die when they hit the ground, depending on the distance they fall and the nature of the ground. Waking up is instantaneous in a sleeping partner, whereas it may seem delayed in an unconscious partner. The consequence is that it is always difficult for primates to predict what will happen to an inanimate conspecific because the possibility that she/he may recuperate can rarely be excluded. The occurrence of visitations points in the same direction. By returning to a body they have previously left, they can check if their companion is still in the same state.

Children grow in a world of cultural symbols and conventions, and the representations embodied in the human language help them to form abstract categories (Tomasello 1999; Carey 2009). The words “death” and “dead” are offered to them as tools that are passed on from one generation to the next (Renfrew 2016). Yet it takes years for them to understand that terms such as “never”, “always” or “definitely” can have absolute meaning (Kuczaj 1974; Hoffner et al. 1990). In comparison, animals are solipsist thinkers, meaning that they learn by themselves. They receive no support from others that would help them to conceptualize the absolute dimensions of death. While great apes can learn that unresponsive companions may not recover, this is probabilistic knowledge and not the absolute knowledge implied by words such as “irreversibility” and “permanence”. Rather than asserting that great apes may be aware of the irreversibility of death, it seems more appropriate to echo Boesch’s (2012) formulation that chimpanzees may be able to “realize dead individuals do not move or need help anymore, and that they will remain inanimate”. This knowledge involves some uncertainty; it may reflect the belief that these individuals have fallen into a state where they seem to remain asleep indefinitely. We propose to call this state “dormancy”, which means that the individual is in a prolonged state of immobility that is not normal sleep, with no rule specifying that recovery is excluded. In terms of the conceptualization abilities required, belief in dormancy is a less costly hypothesis than an awareness of the irreversibility of death.

Like irreversibility, the second dimension of mortality, universality, has an absolute meaning. We cannot question primates directly like we do with children, and there is no indication to date that they are able to know that death happens to everyone, whether they are conspecifics or individuals of other species (Anderson 2018). The third and fourth dimensions of mortality are the last to be mastered by children because they involve basic knowledge about the biological properties of living beings and the body functions that maintain life (Slaughter 2005). Some authors assume that primates recognize death as the cessation of bodily functions, basing their reasoning on the fact that mothers handle and defend the body of their dead infant (Das et al. 2019), or on changes in maternal behaviour such as atypical carrying postures, distancing from the corpse and its final abandonment (Lonsdorf et al. 2020). However, the first argument ignores the fact that mothers also handle and defend their live infants (Gonçalves & Carvalho 2019), and the second fails to distinguish between detection of dysfunction and awareness of mortality: mothers may be able to recognize that something is going wrong with their non-responding infant without necessarily understanding what has happened (see above). The fourth main dimension of mortality, causation, is particularly demanding on the cognitive level since it requires subjects to infer causal relations, i.e. formulate hypotheses about the mechanisms involved in the breakdown of the functioning of the organism. It has been suggested that prey killing and lethal attacks on conspecifics may help individuals to gain insight into the causes of death (Anderson 2018), and also that the investigation of inanimate bodies would enable the understanding of these causes (Das et al. 2019). However, it should be clear that inspecting corpses or even inflicting death on others – as all predators do – is by no means proof that they realize how death occurs. Several authors have argued, based on a limited number of cases, that individuals react differently to deceased partners depending on the cause of death, but the views expressed by these authors are conflicting. According to Anderson and collaborators (Anderson 2011; Yang et al. 2016; Pettitt & Anderson 2020), sudden and traumatic deaths resulting from an accident or a killing would trigger more alarm and violent behaviours than deaths due to non-apparent causes such as illness. In contrast, Boesch (2012) proposes that bodies with wounds generate fewer signs of fear and alarm in chimpanzees than those of individuals who die from unexplained causes such as illness. Whatever the case, the accumulation of reports in chimpanzees and other species indicates that none of these expectations have been confirmed, either for dead infants (Rajpurohit 1997; Watson & Matsuzawa 2018), or other inanimate conspecifics (Table 2).

While the absence of evidence is not evidence of absence, the burden of proof rests on the person who asserts that something exists, and not on the person who denies it. Monsó (2020) looked for behaviours that would demonstrate that animals understand death, but she only proposed signs of emotional disturbance and ways to detect the dysfunction of the body. To date, there is no evidence that primates, including great apes, have an absolute concept of death, whatever the dimension considered, be it irreversibility, universality, cessation or causation. At this point, it is important to notice that irreversibility differs from the other three dimensions in two major respects. First, irreversibility can be reduced to a more concrete notion such as dormancy. To bystanders, a dormant conspecific may appear to be a sleeping individual who fails to wake up despite repeated interactions with her/him, and who remains in this state for an indefinite period of time. It is also conceivable that experienced individuals may have learned that it is common for a dormant body to cool down, smell, be surrounded by flies, and gradually lose its shape. Second, the awareness of the mortal condition of all living beings or the biological functions involved in the cessation of life and the causation of death is very abstract knowledge with little emotional content. These three dimensions of mortality cannot account for the strong emotional commitment revealed by the behaviour of great apes such as chimpanzees and gorillas. On the contrary, the ability to conceive of irreversibility or dormancy may explain that they understand something serious has happened. Realizing that the inanimate individual in front of them is unlikely to come out of sleep, unlikely to revert to the way she/he was, and must be left behind, can induce intense emotional disturbance. This may explain the display behaviours and rough treatments that have been recorded in chimpanzees and gorillas, reflecting a lack of comprehension and/or acceptance that their companion remains in an inanimate state. This may also explain the distress calls and episodes of stunned silence reported in chimpanzees. Some authors consider that such behaviours indicate an awareness of the irreversibility of death (Anderson 2017; Monsó 2020). As discussed earlier, we find it more accurate to attribute these responses to the belief that their partner has gone into a dormant state. Belief in dormancy represents a more parsimonious explanation that does not require the involvement of concepts of mortality that may be too abstract to belong to the cognitive realm of great apes.