Less sexual functioning problems with frequent pornography use, more functioning problems with problematic pornography use

Are sexual functioning problems associated with frequent pornography use and/or problematic pornography use? Results from a large community survey including males and females. Beáta Bőthe et al. Addictive Behaviors, Volume 112, January 2021, 106603. https://doi.org/10.1016/j.addbeh.2020.106603

Highlights
• PPU had positive, moderate links to sexual function problems in males and females.
• FPU had negative, weak links to sexual function problems in males and females.
• FPU and PPU should be discussed separately concerning its links to sexual outcomes.

Abstract: There is much debate regarding whether pornography use has positive or negative associations with sexuality-related measures such as sexual functioning problems. The present study aimed to examine differential correlates between quantity (frequency of pornography use–FPU) and severity (problematic pornography use–PPU) of pornography use with respect to sexual functioning problems among both males and females. Multi-group structural equation modeling was conducted to investigate hypothesized associations between PPU, FPU, and sexual functioning problems among males and females (N = 14,581 participants; females = 4,352; 29.8%; Mage=33.6 years, SDage=11.0), controlling for age, sexual orientation, relationship status, and masturbation frequency. The hypothesized model had excellent fit to the data (CFI = 0.962, TLI = 0.961, RMSEA = 0.057 [95% CI = 0.056-0.057]). Similar associations were identified in both genders, with all pathways being statistically significant (p < .001). PPU had positive, moderate associations (βmales=0.37, βfemales=0.38), while FPU had negative, weak associations with sexual functioning problems (βmales=-0.17, βfemales=-0.17). Although FPU and PPU had a positive, moderate association, they should be assessed and discussed separately when examining potential associations with sexuality-related outcomes. Given that PPU was positively and moderately and FPU negatively and weakly associated with problems in sexual functioning, it is important to consider both PPU and FPU in relation to sexual functioning problems.

Keywords: Pornography use frequencyProblematic pornography useSexual dysfunctionSexual functioning problemsSexual problems

4. Discussion

Given seemingly inconsistent results concerning associations between pornography use and sexual outcomes (Grubbs and Gola, 2019, Vaillancourt-Morel et al., 2019), the aim of the present study was to examine potentially different roles for FPU and PPU with respect to relationships with sexual functioning problems among males and females. FPU had a weak, negative association with sexual functioning problems, and PPU had a moderate, positive association with sexual functioning problems. Although most studies of PPU have investigated males (Bőthe et al., 2020, Dwulit and Rzymski, 2019, Gola et al., 2016, Kraus and Rosenberg, 2014, Kraus et al., 2017)—especially when associations between PPU and sexual functioning problems have been examined (Grubbs and Gola, 2019, Landripet and Štulhofer, 2015, Prause and Pfaus, 2015, Wéry and Billieux, 2016)—the present results suggest that similar associations may be identified among females concerning associations between PPU, FPU, and sexual functioning problems. Implications are discussed below.

4.1. Differences between the quantity and severity of pornography use

Similarities and differences between FPU and PPU is an understudied field within behavioral addictions and problematic sexual behaviors (Gola et al., 2016, Grubbs et al., 2018, Grubbs et al., 2018). The results of the present study corroborate recent findings (Bőthe et al., 2020, Gola et al., 2016, Grubbs et al., 2018, Grubbs et al., 2018) suggesting that FPU and PPU are distinct yet related patterns of pornography consumption. In the present largescale cross-sectional study, although FPU and PPU were positively and moderately related, their associations with sexual functioning problems were in opposite directions. Therefore, the results suggest that FPU and PPU represent related yet distinct aspects of pornography use not only in the case of treatment-seeking populations (Gola et al., 2016) but also in community samples, particularly as they relate to sexual functioning problems.

These findings resonate with the “high engagement versus problematic engagement” model of potentially addictive behaviors (Billieux et al., 2019, Charlton and Danforth, 2007, Charlton, 2002). According to this model, some characteristics should be considered as “core” symptoms of problematic behaviors, while others represent “peripheral” symptoms that may be present in both frequent but non-problematic use and in problematic use, such as FPU (Billieux et al., 2019, Bőthe et al., 2020, Charlton and Danforth, 2007, Charlton, 2002). In other words, individuals may experience FPU but not necessarily PPU. In contrast, individuals with PPU may also report core and peripheral symptoms (including FPU) (Bőthe et al., 2020). As found here and elsewhere (Billieux et al., 2019, Charlton and Danforth, 2007, Charlton, 2002), when only FPU was present (i.e., a peripheral symptom), no major adverse consequences may be observed. However, when PPU is present (i.e., both core and peripheral symptoms), it is more likely that adverse and harmful consequences will be observed. Similar observations have been reported regarding other online behaviors with respect to measures of quantity/frequency and problematic use, such as internet use (Chak & Leung, 2004), Facebook use (Koc & Gulyagci, 2013), online gaming (Király et al., 2017, Orosz et al., 2018), and problematic television series watching (Tóth-Király et al., 2017, Tóth‐Király et al., 2019).

Taking findings together, while quantities of the aforementioned activities were often unrelated to maladaptive states and conditions, problematic engagement in these online behaviors has been related to maladaptive or harmful measures. Therefore, thorough examinations are needed when effects of potentially problematic online behaviors are investigated, taking into consideration not only the quantity of behaviors but also quality levels of engagement.

4.2. Differentiated roles for quantity and severity of pornography use in sexual functioning problems among males and females

While FPU had a weak, negative association with sexual functioning problems, PPU had a positive and moderate association, suggesting that FPU may be associated with fewer sexual functioning problems in some cases (Landripet & Štulhofer, 2015). Nevertheless, males reported using pornography significantly more frequently, and reported higher levels of PPU, compared to females. However, females reported significantly higher levels of sexual functioning problems than males.

Differentiated relationships with FPU and PPU may relate to several underlying biopsychosocial factors. Speculatively, FPU may stem from stronger sexual desire and relate to lower levels of sexual functioning problems, perhaps due to variety in pornographic material that could lead to easier and quicker responses to different offline sexual stimuli (Prause & Pfaus, 2015). FPU may facilitate sexual thoughts, which, in turn, may lead to quicker sexual responses in and thus not lead to sexual functioning problems assessed here (Watson & Smith, 2012). Another possible explanation concerning the negative association between FPU and sexual functioning problems could reflect familiarity generated from viewing pornographic materials (Griffiths, 2000, Kohut et al., 2017, Watson and Smith, 2012), whereby individuals with FPU may feel more sexual comfort when engaging in offline sexual activities because given pornography-related familiarity with sexual activities (Kohut et al., 2017). Based on qualitative analysis of males and females, the most frequently reported effect of pornography use was “no negative impacts”, followed by using pornography as an information source, for sexual experimentation, and for sexual comfort. Thus, higher levels of sexual comfort and self-acceptance, and lower levels of anxiety, shame, and guilt concerning sexual behaviors may be related to FPU. Increased arousal and orgasm response, interest in sex, and more acceptance towards different sexual activities and more sexual experimentation were also reported as positive effects of pornography use (Kohut et al., 2017). Alternate explanations include that individuals with poor sexual functioning may be less likely to engage in FPU, individuals may not be fully aware of pornography-use-related sexual problems and some sexual problems may not have been captured by the assessment instrument. Nevertheless, FPU explained only a very small amount of the variance related to sexual functioning problems in the present study, indicating that other factors are likely to play a more important role in the development and maintenance of sexual functioning (McCabe et al., 2016).

PPU may be associated with increased masturbation and pornography “binges” (i.e., using pornography multiple times or hours per day), based on results from a ten-week long diary study with treatment-seeking males (Wordecha et al., 2018). Therefore, males who excessively view pornographic materials may be more likely to be in a refractory period when trying to engage in sexual activities with their partner, potentially leading to sexual functioning problems (Ley et al., 2014). For some, sexual intercourse with one’s partner may not be as stimulating as online pornographic material (e.g., it may not provide as much novelty as online pornography). Furthermore, clinical and case reports suggest that pornography use may alter arousal templates (Brand, Blycker, & Potenza, 2019). These potential impacts should be considered in future studies. Additional possible explanations exist. For example, among men seeking treatment for compulsive sexual behaviors, severity of PPU was associated positively with sexual anxiety and negatively with sexual satisfaction (Kowalewska, Kraus, Lew-Starowicz, Gustavsson, & Gola, 2019); as these factors may impact sexual dysfunction, further study is warranted.

As males and females with compulsive-pornography-use profiles (likely PPU) reported lower levels of sexual functioning problems than individuals with a highly distressed non-compulsive profile (Vaillancourt-Morel et al., 2017), stress may impact sexual functioning problems (McCabe et al., 2016). Stress reduction and emotion regulation are frequently reported motivations in PPU, and interventions involving training in emotion regulation (e.g., mindfulness) may be effective in reducing PPU (Bőthe et al., 2020, Levin et al., 2012, Wéry and Billieux, 2016, Sniewski and Farvid, 2019). Individuals experiencing high levels of stress may engage in PPU, leading to sexual functioning problems, which, in turn, could result in further stress. Further studies should examine this possibility and relationships between stress, PPU and sexual functioning problems generally.

In sum, different mechanisms may underlie FPU and PPU. Such mechanisms may both directly and indirectly relate to sexual functioning problems in complex manners. When assessing relationships between pornography use and sexual functioning problems, future research should consider both FPU and PPU and other aspects of pornography and specific aspects of sexual functioning problems.

4.3. Limitations and future studies

Study findings should be considered alongside limitations. Self-report methods have biases (e.g., underreporting and overreporting). Causality cannot be inferred from cross-sectional studies. The internal consistency of the SFS was less than optimal (perhaps related to diversity of the 4 domains assessed), and this may have affected findings, as could have the limited number of domains and lack of specificity. For example, context specificity is not detailed in the SFS (e.g., partnered versus solitary sexual activities), and individuals with hypersexuality have reported sexual functioning problems during partnered sex but not during pornography use (Voon et al., 2014).

Moral incongruence and religiosity were not assessed, which may limit generalizability. Moral incongruence and religiosity may relate to PPU (Grubbs and Perry, 2019, Grubbs et al., 2019, Grubbs et al., 2020, Grubbs et al., 2020, Lewczuk et al., 2020), with individuals with higher levels of morality and religiosity perhaps showing stronger associations between FPU and PPU than those with lower levels of morality and religiosity (Grubbs, Lee, Hoagland, Kraus, & Perry, 2020). As such, future studies should include assessments of moral incongruence in relation to pornography content (e.g., aggressive sexual behaviors often targeted towards women (Bridges, Wosnitzer, Scharrer, Sun, & Liberman, 2010), particularly Black women (Fritz, Malic, Paul, & Zhou, 2020), and rape, incest and other pornography genres (Rothman, Kaczmarsky, Burke, Jansen, & Baughman, 2015)and other domains in which people may experience morality-related conflicts. The present study examined a general, community sample. Given that stronger associations may be present between FPU and PPU in treatment-seeking and clinical populations (Bőthe et al., 2018, Bőthe et al., 2020, Brand et al., 2011, Gola et al., 2016, Gola et al., 2017, Grubbs et al., 2015, Grubbs et al., 2019, Lewczuk et al., 2017, Twohig et al., 2009, Voon et al., 2014), the findings of the present study concerning the associations between FPU, PPU, and sexual functioning problems may not generalize to treatment-seeking or clinical populations.

Longer-term longitudinal studies are needed to examine further the nature of the relationships and how they may change over time among both males (Grubbs & Gola, 2019) and females. Individuals who may have developed sexual functioning problems that could have been related to prior pornography viewing (before past-year) may potentially contribute to weakening relationships between FPU and sexual functioning problems. Also, individuals with sexual functioning problems may fear performance failure. Consequently, they may choose online pornography viewing instead of engaging in offline sexual behaviors with their partners (Miner et al., 2016). Additionally, while quantity and FPU are typically related, they are not equivalent and may relate differently to clinically relevant aspects of pornography use (e.g., when trying to abstain; (Fernandez, Tee, & Fernandez, 2017). Qualitatively analyzing narratives of the development and maintenance of one's PPU (Wordecha et al., 2018) and sexual functioning problems may be fruitful in identifying possible mediator and moderator variables such as moral incongruence (Brand et al., 2019, Grubbs and Perry, 2019), accessibility of pornography (Rissel et al., 2017), and other factors (Vaillancourt-Morel et al., 2019).

Pleasant sleep paralysis was found to be a fairly common experience (23%); episodes were emotionally complex, with pleasant episodes often involving some admixture of fear

Could sleep paralysis be pleasant? Monika Kliková  Brian A. Sharpless  Jitka Bušková. Journal of Sleep Research, August 31 2020. https://doi.org/10.1111/jsr.13154

Abstract: Sleep paralysis is an inability to move at sleep onset or upon awakening. It is often a distressing experience that can be associated with significant clinical consequences. Few studies have focussed on pleasant sleep paralysis episodes. The present study aimed to determine the relative prevalence of pleasant episodes of sleep paralysis as well as variables that may make them more likely to occur. Participants (N = 172) with recurrent episodes of sleep paralysis completed a battery of questionnaires investigating sleep paralysis episodes, trauma symptoms, life satisfaction, and Big Five personality traits. Pleasant sleep paralysis was found to be a fairly common experience (i.e. 23%). Episodes were emotionally complex, with pleasant episodes often involving some admixture of fear. In terms of hallucinations, pleasant episodes were more likely to involve vestibular‐motor sensations (i.e. illusory body movements) and some individuals reported an ability to induce these hallucinations. Contrary to expectation, neither lower trauma symptomatology nor higher levels of reported life satisfaction predicted pleasant sleep paralysis. However, the ability to lucid dream and higher levels of trait openness to new experiences appeared to make pleasant episodes more likely. Clinical implications are discussed.

Being more happy (more positive affect) was associated with heavy alcohol use

Daily associations between affect and alcohol use among adults: The importance of affective arousal. Dusti R. Jones et al. Addictive Behaviors, September 1 2020, 106623. https://doi.org/10.1016/j.addbeh.2020.106623

Abstract
Objective: Little is known about whether level of affective arousal (i.e., high vs. low) is associated with alcohol use and whether this relationship differs by valence (i.e., positive vs. negative affect) among adults.

Methods. Participants were n=93 self-reported current drinkers (ages 25-65) who reported positive (PA) and negative affect (NA) seven times a day and alcohol use once a day for seven consecutive days. For each individual, mean levels of high arousal PA (e.g., excited), low arousal PA (e.g., satisfied), high arousal NA (e.g., frustrated), and low arousal NA (e.g., sad) were computed for each day.

Results. Alcohol use was reported on 30% of person-days, with an average of 2.3 drinks consumed on drinking days. Heavy episodic drinking (4+/5+ drinks for women/men) occurred on 4% of days. After covarying for age, gender, and weekday, days with higher-than-usual levels of high arousal PA were associated with a 52% increase in the odds of consuming any alcohol and a 105% increase in the odds of engaging in heavy episodic drinking. Individuals reporting more low arousal PA on average had a 77% increase in the odds of heavy episodic drinking. No significant associations between high or low arousal NA and alcohol use were found.

Conclusions. Greater PA, but not NA, was associated with heavy alcohol use at both the within- and between-person levels, perhaps attributable to social and enhancement drinking motives. Results differed by arousal, highlighting the importance of considering a wide range of affective states when examining alcohol use behavior.

Keywords: positive affectnegative affectaffective arousalalcohol use

Men’s decision to augment their masculinity via full beardedness occurs under conditions characterised by stronger inter-sexual and intra-sexual selection (competition)

Cross-Cultural Variation in Men’s Beardedness. Barnaby J. W. Dixson & Anthony J. Lee. Adaptive Human Behavior and Physiology (2020). Sep 1 2020. https://link.springer.com/article/10.1007/s40750-020-00150-4

Abstract
Objectives To test whether cross-cultural variation in men’s facial hair conforms to patterns predicted by processes of inter-sexual and intra-sexual selection.

Methods Data were taken from the PEW Research Center’s World’s Muslims’ project that collected information from 14,032 men from 25 countries. An Independent Factor Analysis was used to analyse how suites of demographic factors predict men’s beardedness.

Results Analyses replicated those from past research using the PEW data, showing that beardedness was more frequent under prevailing conditions of lower health and higher economic disparity.

Conclusions These findings contribute to evidence that men’s decision to augment their masculinity via full beardedness occurs under conditions characterised by stronger inter-sexual and intra-sexual selection.

Check also Mothers are sensitive to men's beards as a potential cue of paternal investment. Barnaby J. W. Dixson, Siobhan Kennedy-Costantini, Anthony J. Lee, Nicole L. Nelson. Hormones and Behavior, Volume 113, July 2019, Pages 55-66. https://www.bipartisanalliance.com/2019/05/preferences-for-beards-when-judging.html

The belief that “my side” sees the world objectively while the “other side” sees it through the lens of its biases (the “objectivity illusion”), was strong & persistent among Trump and Clinton supporters before the election

The objectivity illusion and voter polarization in the 2016 presidential election. Michael C. Schwalbe, Geoffrey L. Cohen, and Lee D. Ross. Proceedings of the Royal Society, September 1, 2020 117 (35) 21218-21229; https://doi.org/10.1073/pnas.1912301117

Significance: Political polarization increasingly threatens democratic institutions. The belief that “my side” sees the world objectively while the “other side” sees it through the lens of its biases contributes to this political polarization and accompanying animus and distrust. This conviction, known as the “objectivity illusion,” was strong and persistent among Trump and Clinton supporters in the weeks before the 2016 presidential election. We show that the objectivity illusion predicts subsequent bias and polarization, including heightened partisanship over the presidential debates. A follow-up study showed that both groups impugned the objectivity of a putative blog author supporting the opposition candidate and saw supporters of that opposing candidate as evil.

Abstract: Two studies conducted during the 2016 presidential campaign examined the dynamics of the objectivity illusion, the belief that the views of “my side” are objective while the views of the opposing side are the product of bias. In the first, a three-stage longitudinal study spanning the presidential debates, supporters of the two candidates exhibited a large and generally symmetrical tendency to rate supporters of the candidate they personally favored as more influenced by appropriate (i.e., “normative”) considerations, and less influenced by various sources of bias than supporters of the opposing candidate. This study broke new ground by demonstrating that the degree to which partisans displayed the objectivity illusion predicted subsequent bias in their perception of debate performance and polarization in their political attitudes over time, as well as closed-mindedness and antipathy toward political adversaries. These associations, furthermore, remained significant even after controlling for baseline levels of partisanship. A second study conducted 2 d before the election showed similar perceptions of objectivity versus bias in ratings of blog authors favoring the candidate participants personally supported or opposed. These ratings were again associated with polarization and, additionally, with the willingness to characterize supporters of the opposing candidate as evil and likely to commit acts of terrorism. At a time of particular political division and distrust in America, these findings point to the exacerbating role played by the illusion of objectivity.

Keywords: intergroup conflictpolarizationcognitive biaspolitical psychology

Liking for foods high in salt and fat is associated with a lower diet quality but liking for foods high in sugar is not

Liking for foods high in salt and fat is associated with a lower diet quality but liking for foods high in sugar is not – Results from the Predise study. Elise Carbonneau et al. Food Quality and Preference, September 1 2020, 104073. https://doi.org/10.1016/j.foodqual.2020.104073

Highlights
• Liking for sweet foods is not associated with Canadian Healthy Eating Index (C-HEI).
• Liking for salty foods is associated with lower consumption of healthy foods.
• Liking for salty foods is inversely associated with C-HEI in men.
• Liking for salty foods is inversely associated with C-HEI in less educated women.

Abstract: The research aimed at examining how liking for foods high in salt and fat and for foods high in sugar are associated with overall diet quality and how these associations differ according to individual characteristics (i.e., sex, age, education, income, nutrition knowledge, and energy reporting status) in French-speaking adults from the Province of Quebec, Canada. As part of the web-based cross-sectional PREDISE study, 1096 men and women completed online questionnaires. The Food Liking Questionnaire assessed reported liking for a variety of salty foods (high in salt and fat) and sweet foods (high in sugar and either high-fat or low-fat) on a scale from 1 to 9. The Canadian Healthy Eating Index (C-HEI) was computed based on data collected using 24-hour food recalls. Women (vs. men) reported lower liking for salty foods (5.97±1.34 vs. 6.58±1.16, p<0.0001) and for sweet foods (5.52±1.36 vs. 5.71±1.25, p=0.015). Multiple linear regressions showed that liking for sweet foods was not associated with C-HEI (B=-0.10, p=0.78). Given a significant sex interaction in the association between liking for salty foods and C-HEI (p interaction=0.0218), subsequent analyses were stratified by sex. Multiple linear regressions supported that liking for salty foods was more strongly inversely associated with C-HEI in men (B=-3.37, p<0.0001) than women (B=-1.46, p=0.0035). In conclusion, a strong liking for salty foods may interfere with healthy eating, especially in men. Building on these results, future studies should investigate the potential of interventions designed to improve the healthiness of food habits in individuals with strong liking for these foods.

Keywords: Food likingsalty foodssweet foodsdiet qualityHealthy Eating IndexPREDISE study

Rolf Degen summarizing... A majority of laypersons mistakenly believe that people can be trained to become highly accurate judges of truth and deception ("truth wizards")

The psychology of confessions: A comparison of expert and lay opinions. Fabiana Alceste  Timothy J. Luke  Allison D. Redlich  Johanna Hellgren  Aria D. Amrom  Saul M. Kassin. Applied Cognitive Psychology, August 16 2020. https://doi.org/10.1002/acp.3735

Summary: Despite a body of confessions research that is generally accepted in the scientific community, courts often exclude experts on the ground that such testimony would not assist the jury, which can use its common sense. To examine whether laypeople know the contents of expert testimony on confessions, we asked 151 lay participants to indicate their beliefs about 30 confession‐related statements used in a recent survey of 87 confession experts (Kassin et al., American Psychologist, 2018, 73, 63–80). Participants agreed with experts on only 10 of the 30 propositions, suggesting that much of the psychology of confessions is not common knowledge and that expert testimony can assist the trier of fact.

Testosterone administration increases the audience effect & further buttress the social status hypothesis (which posits that testosterone promotes status-seeking behaviour in a context-dependent manner)

Exogenous testosterone increases the audience effect in healthy males: Evidence for the social status hypothesis. Yin Wu et al. Proceedings of the Royal Society: Biological Sciences, July 2020. https://royalsocietypublishing.org/doi/10.1098/rspb.2020.0976

Abstract: Several studies have implicated testosterone in the modulation of altruistic behaviours instrumental to advancing social status. Independent studies have also shown that people tend to behave more altruistically when being watched (i.e. audience effect). To date, little is known about whether testosterone could modulate the audience effect. In the current study, we tested the effect of testosterone on altruistic behaviour using a donation task, wherein participants were asked to either accept or reject a monetary transfer to a charity organization accompanying a personal cost either in the presence or absence of an observer. We administered testosterone gel or placebo to healthy young men (n = 140) in a double-blind, placebo-controlled, mixed design. Our results showed that participants were more likely to accept the monetary transfer to the charity when being observed compared to when they completed the task alone. More importantly, this audience effect was amplified among people receiving testosterone versus placebo. Our findings suggest that testosterone administration increases the audience effect and further buttress the social status hypothesis, according to which testosterone promotes status-seeking behaviour in a context-dependent manner.


Electronic supplementary material: https://doi.org/10.6084/m9.figshare.c.5046800

Women show pre-copulatory mating preferences for human leucocyte antigen-dissimilar men; a possibility is that the ultimate mating bias towards HLA-dissimilar partners could occur after copulation, at the gamete level

Post-copulatory genetic matchmaking: HLA-dependent effects of cervical mucus on human sperm function. Annalaura Jokiniemi, Martina Magris, Jarmo Ritari, Liisa Kuusipalo, Tuulia Lundgren, Jukka Partanen and Jukka Kekäläinen. Proceedings of the Royal Society: Biological Sciences, August 2020. https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1682

Abstract: Several studies have demonstrated that women show pre-copulatory mating preferences for human leucocyte antigen (HLA)-dissimilar men. A fascinating, yet unexplored, possibility is that the ultimate mating bias towards HLA-dissimilar partners could occur after copulation, at the gamete level. Here, we explored this possibility by investigating whether the selection towards HLA-dissimilar partners occurs in the cervical mucus. After combining sperm and cervical mucus from multiple males and females (full factorial design), we found that sperm performance (swimming velocity, hyperactivation, and viability) was strongly influenced by the male–female combination. This indicates that sperm fertilization capability may be dependent on the compatibility between cervical mucus (female) and sperm (male). We also found that sperm viability was associated with partners' HLA dissimilarity, indicating that cervical mucus may selectively facilitate later gamete fusion between immunogenetically compatible partners. Together, these results provide novel insights into the female-mediated sperm selection (cryptic female choice) in humans and indicate that processes occurring after copulation may contribute to the mating bias towards HLA-dissimilar partners. Finally, by showing that sperm performance in cervical mucus is influenced by partners' genetic compatibility, the present findings may promote a deeper understanding of infertility.

4. Discussion

Our results show that along with sperm intrinsic quality (male effect) and cervical mucus identity (female effect), sperm performance was also strongly dependent on male–female combination (interaction), explaining 8.5–32.3% of the total variation in measured sperm traits. In other words, females had a stronger effect on the sperm of some males than the others. We also observed that both the number of different HLA alleles and the Grantham pairwise amino acid distance of HLA alleles affected sperm viability: sperm had higher survival rates in HLA-dissimilar male–female combinations than in more similar combinations. Conversely, we found that HLA-allele sharing did not affect sperm motility, but the Grantham distance was negatively associated with sperm swimming velocity and hyperactivation in one of the three time points (180 min). In other words, sperm motility was higher in male–female combinations that had low HLA amino acidic divergence in comparison to more dissimilar combinations. However, the observed effect was male-dependent, indicating that the effect of the Grantham distance on sperm motility varies across males. None of the measured sperm traits was associated with male–female genome-wide similarity. Although all the male subjects were diagnosed as normozoospermic it is possible that reproductive physiology of the study subjects may partly differ from that of the average male and/or female population. Consequently, some caution should be applied to generalize our findings and future research should ideally aim to test whether the same mechanisms are widespread in the human population.

The female reproductive tract allows only a minute subset of spermatozoa to reach the site of fertilization [49,75,76], but the mechanisms and function of this stringent sperm selection have remained ambiguous. It has been suggested that the functional incompatibility between cervical mucus and sperm could play an important role in the process [62,66], but to the best of our knowledge none of the earlier studies have experimentally tested this possibility. The present results demonstrate that the chemical composition of the cervical mucus may selectively maintain sperm viability of HLA-dissimilar males, indicating that cervical mucus could mediate post-copulatory choice towards the sperm of immunologically compatible males. Furthermore, given that sperm performance in cervical mucus predicts fertilization success [62], these results raise the novel possibility that immunological compatibility between sperm and cervical mucus plays an important role in determining the reproductive success of the partners. While previous studies have reported an effect of MHC-dissimilarity on egg-sperm fusion [6,17–19,21], to our knowledge, this is the first study to show that MHC-based cryptic female choice could be mediated by fluids of the female reproductive tract in mammals.

Earlier studies have demonstrated that cervical mucus is capable of conserving sperm function [62] and it has been hypothesized that cervical crypts could serve as sperm reservoirs [77], where sperm motility is restrained to enhance longevity, such as in the sperm storage sites of the oviduct [78,79]. Besides demonstrating that cervical mucus likely preserves sperm viability of HLA-dissimilar males, we also found evidence that cervical mucus may simultaneously restrict sperm motility of these males. This could indicate that one key function of cervical mucus is to selectively store the sperm of immunologically compatible males, possibly for later use in fertilization. Alternatively, our results raise the intriguing possibility that females (via cervical mucus) may reduce the survival of sperm of (overly) HLA-similar males on the one hand and slow down the sperm of (overly) HLA-dissimilar ones on the other. Such a search for intermediate MHC dissimilarity may facilitate ‘production' of intermediately heterozygous offspring at MHC loci, which, according to the optimal MHC-heterozygosity hypothesis, may have better immunocompetence than more heterozygous individuals [80]. In fact, while highly heterozygous individuals at MHC loci are able to present more antigens to the immune system, they are likely to have smaller T-cell repertoires following thymic selection [80]. Supporting the optimal heterozygosity hypothesis, Jacob et al. [81] showed that women prefer the body odour of men with whom they share few HLA alleles over the more similar and dissimilar men [36]. However, since observed sperm motility associations were present only at one time point and were not consistent across males, further studies are required to investigate the relative importance of these alternative functions of cervical mucus. Furthermore, since performed cervical mucus dilution likely altered sperm motility patterns, we encourage future studies to confirm whether our results can be replicated in undiluted cervical mucus to fully account for its natural viscoelastic features.

The observed effects of partners' HLA dissimilarity on sperm function could potentially arise at least through two evolutionary mechanisms. First, as highlighted above, cervical mucus -mediated selection towards HLA-dissimilar males may represent an evolutionary strategy that ensures the ‘production' of offspring that have broad (or optimal) antigen recognition capability and thus better ability to fight against infections [82]. Supporting this possibility, pathogens have been widely assumed to be the strongest selective agent in human evolution (e.g. [9]). Alternatively, it is possible that HLA-associated sperm preferences represent a gamete-level inbreeding avoidance mechanism that prevents mating between close relatives [10]. In the present study, however, we found that overall (genome-wide) genetic similarity was not associated with sperm performance, indicating that observed findings are more likely to be a direct consequence of HLA-dependent sperm selection, instead of inbreeding avoidance based on HLA-independent cues. Although detailed molecular-level mechanisms behind our findings remain to be described, we envisage that sperm surface HLA molecules and/or HLA-linked olfactory receptors [83] may play an important role in the demonstrated sperm selection process.

Besides clarifying the mechanistic basis of female-induced sperm selection in humans, our findings may have novel implications for the deeper understanding of infertility and for the development of new contraceptives. Infertility affects about 15% of couples globally and currently remains unexplained in 30–40% of cases [84]. Furthermore, a reliable diagnosis of infertility is extremely challenging, and the accuracy of diagnoses is low when compared to several other areas of medicine [85,86]. According to current clinical practice, infertility problems are partitioned into male- and female-derived pathological factors and are thus thought to represent a disease of the reproductive system [87]. Our results indicate that this may represent an overly simplistic view, since it does not consider the fact that some male–female (or their gamete) combinations may be immunologically more compatible than others. Consequently, gamete-level incompatibility may reduce the probability of conception and may help to understand fertilization problems, especially in couples that are diagnosed with unexplained infertility.

In conclusion, our results show that chemical factors in the cervical mucus preferentially conserve sperm viability (and possibly constrain sperm motility) of HLA-dissimilar males. This indicates that one of the key functions of cervical mucus may be to selectively facilitate gamete fusion between immunogenetically compatible partners and this way facilitate optimization of offspring immunocompetence. Immunological mechanisms of sperm selection have remained virtually unexplored in mammals and internally fertilizing species, in general. The present results provide novel insights into MHC-based post-copulatory sperm selection in humans and may be potentially applied to many other species. Furthermore, a more pervasive integration of the demonstrated ‘gamete compatibility' concept into current infertility diagnostic guidelines may facilitate development of more personalized infertility diagnostics and increase accuracy of the diagnoses.

Positive relationship between intolerance & perceived homosexuality; The more a given gender-role violation is thought to implicate homosexuality, the more negatively/less positively people tend to react to the violation

Differential Reactions to Male and Female Gender-Role Violations: Testing the Sexual Orientation Hypothesis. Ursula A. Sanborn-Overby & Kimberly K. Powlishta. Archives of Sexual Behavior (2020). Aug 31 2020. https://link.springer.com/article/10.1007/s10508-020-01803-x

Abstract: Previous research has found that gender-atypical males are evaluated more negatively than gender-atypical females. According to the sexual orientation hypothesis, this asymmetry in evaluations occurs because the feminine characteristics taken on by males when they violate gender roles are more closely tied to perceived sexual orientation than are the masculine characteristics of gender-atypical females. The current series of studies were designed to confirm the existence and generality of the asymmetry phenomenon (Study 1), the preconditions for testing the sexual orientation hypothesis (Study 2), and then to test the hypothesis itself (Study 3). Study 1 found that, as predicted, adults (N = 195, females = 97) displayed more intolerance of males than of females committing gender-role violations across a wide variety of characteristics within multiple domains, although the existence of asymmetry varied somewhat depending on the domain. Study 2 revealed that, as predicted, adults (N = 196, females = 117) believed that gender-role violations indicate homosexuality more so for males than for females overall and across all four domains studied (occupation, activity, trait, and appearance). Study 3 directly tested the sexual orientation hypotheses by examining the relationship between intolerance of specific gender-role violations (scores from Study 1) and the perceived homosexuality associated with those violations (scores from Study 2). Overall, there was a positive relationship between intolerance and perceived homosexuality, indicating that the more a given gender-role violation is thought to implicate homosexuality, the more negatively/less positively people tend to react to the violation, consistent with the sexual orientation hypothesis.

We find a ‘good-looking giver’ effect–that more physically attractive people are more likely to engage in giving behaviors, and vice versa

The Good-looking Giver Effect: The Relationship Between Doing Good and Looking Good. Sara Konrath, Femida Handy. Nonprofit and Voluntary Sector Quarterly, August 28, 2020. https://doi.org/10.1177/0899764020950835

Abstract: Evidence exists that beautiful is seen as good: the halo effect wherein more physically attractive people are perceived to be good, and the reverse halo that good is seen as beautiful. Yet research has rarely examined the evidence linking the beautiful with the good, or the reverse, without the halo effect. We examine the relationship between physical attractiveness (beauty) and giving behaviors (good), where ratings of attractiveness are independent of giving behaviors. We use three U.S. datasets: (a) a nationally representative sample of older adults (NSHAP), (b) a nationally representative longitudinal study of adolescents (ADD Health), and (c) the 54-year Wisconsin Longitudinal Study (WLS), to present evidence that these two characteristics (attractiveness and giving) are indeed correlated without the halo effect. We find a ‘good-looking giver’ effect–that more physically attractive people are more likely to engage in giving behaviors, and vice versa. Thus, in ecologically valid real-world samples, people who do good are also likely to look good.

Keywords: physical attractiveness, halo effect, beauty, prosocial behavior, giving behaviors

Expressions of Sexual Deviance in Black Serial Killers: The number of Black serial killers has increased, but empirical studies have not focused on this unique population

Expressions of Sexual Deviance in Black Serial Killers. Lucia J. Weatherall. PhD Thesis, Walden Univ, 2020. https://search.proquest.com/openview/a63d166c2c056fc6a67b09ea54899371/1?pq-origsite=gscholar&cbl=18750&diss=y

Abstract: The number of Black serial killers (BSKs) has increased, but empirical studies have not focused on this unique population, including their expressions of sexual deviance. The purpose of this case study was to understand the common socialization experiences and the expressions of sexual deviance in BSKs. Two conceptual frameworks were used to identify the concepts to explore: Bandura’s social learning theory of aggression and Agnew’s general strain theory. Data collected came from archival court and police records in Texas. A content-analysis approach was used to analyze the archival data, organized by criminal background, sexual deviance, familial data, and social development. The results identified rape and sadism as the primary expressions of sexual deviance in BSKs. The level of aggression and trauma experienced during childhood was consistent across all cases. The results, while limited by the lack of interviews with family and law enforcement, indicated that BSKs present a social problem and have an adaptive skill not hindered by mental impairments or limited education. The results suggested empirical research needs to explore aggression and strain on African American children, the possible connection to the lack of paternal involvement, and expressions of sexual deviance in BSKs. Future research on BSKs can help create an accurate profile to assist law enforcement agencies identify predators.

Implications

The unique and consistent findings offer a meaningful contribution to the forensic
psychology community and adding to the literature on BSKs. The common theme of
negative parental support (and associated strain) with childhood trauma indicates a
potential connection to aggression, sexual deviance, and serial murder as an adult. The
data confirmed the presence of aggression during social development of the 14 BSKs
either during childhood or expressed at an adult. I plan to use the result for presentations
to law enforcement agencies at the local, state, and federal level. Providing law
enforcement with additional data could assist with the pursuit and capture of this
population. I plan to give presentations, discussing the negative familial exposure and
strain during childhood, focused at the juvenile justice system.
Furthermore, the implications of this study can assist various law enforcement
agencies. Presentations can assist agencies with investigation practices and techniques to
help identify victims of BSKs, who would otherwise go unnoticed or unidentified as
victims of a serial killer. For example, law enforcement agencies should review the
procedures in place when responding to missing persons reports or deaths of the missingmissing
population. Far too often, agencies dismiss the reports as a voluntary choice
when the individual lives a transient lifestyle, allowing BSKs longer crime sprees. The
lack of a comprehensive investigations into the cause of deaths for the missing-missing,
as in Case #14, suggested a dismissive approach in providing closure for the victims and
their families. Law enforcement agencies, using systems to capture forensic evidence and
search DNA profiles compared to cold cases, increased the number of BSKs identified.
The lack of communication between law enforcement agencies in sexual assaults,
missing persons, and murders allowed BSKs to prey upon women, elderly, and the
missing-missing. Additional implication included increased communications between
jurisdictions, and sharing of information on criminal activities, to identify patterns more
quickly.

Conclusion

In summary, the purpose of the study described the expressions of sexual
deviance in BSKs. The study determined BSKs rape their victims as the most common
expression in sexual deviance. The study also suggested BSKs do not always murder the
victims they rape, and instead express sexual deviance through sadistic acts. The results
of the study determined BSKs remain out of the social spotlights and off the radar of law
enforcement agencies. The study suggested that BSKs prey upon all levels of society, and
across racial demographics. Although the missing-missing remain a vulnerable and easily
forgotten victims, BSKs kills women, children, and men. BSKs who committed murders
over extended time used various methods to kill their victims as an adaptive method to
avoid detection.
The results of the study suggested BSKs have a common pattern during
childhood. BSKs exposed to abuses, aggression, and violence within their families and
social development did not receive attention or a proper outlet. The underreporting of
psychological interventions of African American boys could result from the belief
systems that do not encourage weakness (Lester & White, 2014; Voison et al., 2013).
BSKs with a limited education or intellect demonstrated an adaptability to aid with their
criminal activities. The socially adaptive behaviors and criminally adaptive skills
demonstrated by BSKs with lower IQ suggested a level of planning, premeditation, and
deception. The finding conflicted with profiles on serial killers. This misconception
benefited the BSKs population as they continued to navigate below the radar; until DNA
matches (found by computers) caught up to them. The potential for a connection in
expressions of sexual deviance and a lack of paternal figures during childhood requires
the consideration of future studies.
The research on WSKs provided law enforcement agencies and researchers with a
vast pool of data to profile perpetrators and reduce the number of their victims.
Documentaries on WSKs (i.e. Ted Bundy, Jeffery Dahlmer, and Todd Kohlhepp)
provided intrigued audiences hours of information into their lives, motives, and victims.
Meanwhile, BSKs (like their White counterparts) also have the appearance of normalcy
(Arndt et al., 2004; Beasley, 2004; Hickey, 2015; Kraemer et al., 2004) and continued to
thrive undetected by law enforcement, family, friends, and co-workers. Case #11 lived a
normal life, working as a waiter and taking care of his family. His common-law wife
found it hard to believe she lived with a serial murderer; until DNA evidence linked him
to a series of rapes and murders near their home. Case #14 methodically and with malice
murdered almost 100 women, for almost four decades, across the United States.
Black men commit serial murder. BSKs present a social problem that requires
more research and law enforcement consideration. Empirical research needs to explore
the effects of exposure to aggression, violence, and strain during childhood on African
American. Additionally, studies on the expressions of sexual deviance in BSKs, and the
possible connection to paternal involvement. The results of the case study demonstrated
BSKs possess an adaptive skill, a flexibility with victim selection, and variation of
expressions in sexual deviance; not hindered by mental impairments or limited education.
Last, research on BSKs would allow for a more accurate profile to assist law enforcement
agencies. The social aggression and strain experienced during childhood manifest into
actions, including rape and sadistic violence. Additional research on BSKs would provide
beneficial information to develop interventions for at risk youths. Addressing the
aggression and strain experienced during childhood might provide a healthy outlet. Left
unaddressed we have a society at risk of finding a place on the carrousel of victims,
spinning in the mind of a predator.

Imagination, the Brain’s Default Mode Network, and Imaginative Verbal Artifacts

Carroll J. (2020) Imagination, the Brain’s Default Mode Network, and Imaginative Verbal Artifacts. In: Carroll J., Clasen M., Jonsson E. (eds) Evolutionary Perspectives on Imaginative Culture. Springer, August 29 2020. https://doi.org/10.1007/978-3-030-46190-4_2

Abstract: The purpose of this chapter is to explain how imaginative verbal artifacts are produced by the imagination and in turn influence the imagination. Assimilating recent neuroscientific research on the evolution of modern brain shape and on the brain’s default mode network, we can now say with confidence that the imagination is a neurological reality, that it is lodged in specific parts of the brain, that it consists of an identifiable set of components and processes, that these components and processes have adaptive functions, and that in fulfilling its functions imagination has been a major causal factor in making Homo sapiens the dominant species on earth. The first section of the chapter defines the main terms in this argument. The second section describes the evolution of modern brain shape and suggests the role imagination has played in producing the complex of behaviors that characterize neurologically modern Homo sapiens. The third section describes the current neuroscientific understanding of the brain’s default mode network—the neurological locus of imagination. The fourth section describes three core processes of imagination used in constructing imaginative verbal artifacts: simulation, mental time travel, and perspective taking (also known as “Theory of Mind” and “mentalizing”). The three processes are illustrated with reference to a modern American novel, Wallace Stegner’s Angle of Repose. The fifth section describes four specialized forms of imagination that deploy the core processes: dreaming, mind-wandering, autobiographical narratives, and counterfactual thinking. That section explains how these forms are involved in writing or reading literature and identifies a few literary works that illustrate them. The final section sums up the argument for the adaptive functions of literature.

Keywords: Imagination Globular brain Default mode network Literature Simulation Mental time travel Perspective taking Spontaneous thought Literary theory

The Role of Aesthetic Style in Alleviating Anxiety About the Future

Carney J. (2020) The Role of Aesthetic Style in Alleviating Anxiety About the Future. In: Carroll J., Clasen M., Jonsson E. (eds) Evolutionary Perspectives on Imaginative Culture. Springer, August 29 2020.  https://doi.org/10.1007/978-3-030-46190-4_8

Abstract: Though few would dispute that aesthetic style is a vehicle for cognitive effects, there is little systematic work that views style from anything other than a historical perspective. This chapter will outline how style, broadly conceived, can be understood as an attempt to avoid anxiety by gaining predictive traction on the future. The central claim will be that style evolved as complexity reduction device, to the extent that it is a predictive scheme that balances explanatory simplicity against model accuracy. I shall show that every given style achieves this by saturating the perceptual environment with evidence for a particular model of the world. This account of style explains several features of its target phenomenon, including its normative character, its polemical nature, and its transitory duration. It also allows for style to be seen as continuous with other complexity reduction strategies on the part of biological agents more generally. The discussion will be supported by a historical appreciation of how style has been theorized in the past, but my overall framework will be provided by information theory.

Keywords: Anxiety Style Prediction Aesthetics Cognition Model building

Women's wellbeing and fertility in rural Tanzania: Overall, women's wellbeing was highest in husband-older marriages, but among women married to older men, spousal age gap was unrelated to wellbeing

Shared interests or sexual conflict? Spousal age gap, women's wellbeing and fertility in rural Tanzania. David W. Lawson et al. Evolution and Human Behavior, August 29 2020. https://doi.org/10.1016/j.evolhumbehav.2020.08.009

Highlights
• We explore whether husband-older spousal age gaps are costly or beneficial to women.
• Women frequently married older men than their stated ideal spousal age gaps.
• Spousal age gap was unrelated to the risk of divorce or to women's fertility.
• Overall, women's wellbeing was highest in husband-older marriages.
• However, among women married to older men, spousal age gap was unrelated to wellbeing.

Abstract: The marriage of older men to younger women is common across cultures. On one hand, husband-older marriage may serve the interests of both sexes, a conclusion broadly consistent with reported gender differences in mate preferences. On the other hand, men alone may benefit from such marriages at a cost to women if seniority enables men to exert dominance in conflicts of interest. Indeed, in public health large spousal age gaps are generally deemed “pathological”, both a cause and consequence of gender inequalities harmful to women. We investigate these alternative models of spousal age gap using data from a cross-sectional survey of women in Mwanza, northwestern Tanzania (n = 993). Consistent with the notion that spousal age gaps are a product of sexual conflict, women typically married with a larger age gap than stated ideals. However, adjusting for potential confounds, spousal age gap was not associated with fertility or the risk of divorce. Furthermore, women's mental health and autonomy in household decision-making was higher in husband-older marriages compared to rare cases of same-age or wife-older marriage. Beyond this comparison, the magnitude of spousal age gaps was unrelated to either measure of women's wellbeing among the overwhelming majority of marriages where the husband was older. Together these findings suggest husband-older marriage does not influence marital stability, relatively large spousal age gaps are neither especially costly nor beneficial to women, and that alternative sociodemographic factors are more important in driving variation in women's wellbeing and reproductive success in this context. Our results support neither a model of mutual benefits, nor a “pathological” conceptualization of spousal age gaps. We conclude by both encouraging evolutionary human scientists to engage more fully with models of sexual conflict in future studies of marriage and mating, and suggesting that public health scholars consider more neutral interpretations of spousal age differences.

Keywords: Spousal age differenceEmpowermentMental healthMarriageTanzaniaSexual conflict

Kin-Avoidance in Cannibalistic Homicide

Kin-Avoidance in Cannibalistic Homicide. Marlies Oostland and Michael Brecht. Front. Psychol., August 31 2020. https://doi.org/10.3389/fpsyg.2020.02161

Abstract: Cannibalism in the animal kingdom is widespread and well characterized, whereas the occurrence of human cannibalism has been controversial. Evidence points to cannibalism in aboriginal societies, prehistory, and the closely related chimpanzees. We assembled a non-comprehensive list (121 offenders, ~631 victims) of cannibalistic homicides in modern societies (since 1900) through internet-searches, publications, and expert questioning. Cannibalistic homicides were exceedingly rare, and often sex-related. Cannibalistic offenders were mainly men and older than offenders of non-cannibalistic homicides, whereas victims were comparatively young. Cannibalistic offenders typically killed manually (stabbing, strangulating, and beating) rather than using a gun. Furthermore, they killed more strangers and fewer intimates than conventional offenders. Human cannibals, similar to cannibalism in other species, killed and ate conspecifics, occasionally vomited and only rarely (2.5% of victims) ate kin. Interestingly, cannibalistic offenders who killed their blood relatives had more severe mental problems than non-kin-cannibals. We conclude that cannibalistic homicides have a unique pattern of murder methods, offenders, and victims.

Discussion

Cannibalistic homicides were very rare, often violent, manual and sex-related crimes. Victims were younger and offenders were older than in conventional homicide offenses. Cannibalistic offenders only rarely consumed kin and most who did suffered from serious mental problems.

Our data set consists of 121 offenders with approximately 631 victims. This is a very large number of victims, but note that we are dealing with the entirety of easily accessible cannibalism cases in modern societies since 1900. The case numbers in the US and Germany might be of particular relevance, because, in these two countries, we made a special attempt for a complete coverage of cases. Unsurprisingly, cannibalistic homicide is an exceedingly rare crime, accounting for a minute fraction of homicides. For the US in the period 1960–2018, we estimated the fraction of cannibalistic homicides, being the number of cannibalistic homicides divided by the total homicides [Uniform Crime Reporting (UCR) Program Federal Bureau of Investigation, 2020], to be 0.01%.

The cannibalistic homicides described here had many hundreds of victims but included only one cannibalized neonate. The two other children 2 years or younger killed by cannibalistic offenders were not cannibalized. Since in non-cannibalistic homicides the killing of children 2 years or younger is quite common (accounting for ~2.6% of homicides as reported in FBI data), it appears that this victim population is largely missing in cannibalistic offenses, i.e., we would have expected >15 cases. From a biological perspective, the absence of cannibalistic neonaticide in humans is surprising. Human neonaticide shares many features of cannibalistic neonaticide in rodents and lagomorphs (Sawin et al., 1960; DeSantis and Schmaltz, 1984). In humans, neonaticide, as defined by the killing of a neonate on the day of its birth by his/her own mother, incidence varied from 0.07 to 8.5 per 100,000 births (Tanaka et al., 2017). This behavioral pattern is strongly promoted by maternal stress and intrusion by novel partners or detection of predators. Thus, even though neonaticide has been suggested to be a prototypical “biologically” predetermined behavior (Hausfater and Hrdy, 2017), it still shows differences between rodents and humans.

Our data suggest kin-avoidance in cannibalistic homicide. About 97.5% of the victims were non-kin, a statistical difference to occurrence of kin-homicides in conventional homicides (Figure 6). The consanguinity of victim-offender pairs was very low. This conclusion agrees with findings from two other large-scale studies on cannibalistic homicides (Rajs et al., 1998; Lester et al., 2015). A diverging result with a large fraction of kin-cannibalism was only observed in one study with only five cases (Raymond et al., 2019). We think these discrepancies reflect different sampling of cases, i.e., while our internet search sampled mostly cases by news coverage, Raymond et al. (2019) focused on psychiatric patients. Indeed, in our sample the cannibalistic offenders with the most obvious mental problems killed more kin (Figure 6D). This reduced kin avoidance in offenders with mental problems might not be limited to cannibalistic homicides. Offenders of conventional homicides in Scotland targeted three times more kin when they had a psychiatric diagnosis at the time of trial. The fraction of kin victims for offenders with a psychiatric diagnosis at the time of trial was 30.9%, compared to a kin victim rate of 11.3% for mentally healthy offenders (Gillies, 1976).

The fact that mental problems can reduce kin-selectivity in cannibalistic homicides does not argue against the existence of strong anti-kin-ingestion mechanisms, whether such mechanisms are a result of nature, nurture, or a combination of both. In rats, there are kin-responsive neurons in the lateral septum (Clemens et al., 2020), which might point to a possible biological basis of kin recognition at least in rodents. Humans use stable psychosocial cues to distinguish different types of kin from non-kin, and the cues used for kin detection depends on the specific dyad (Lieberman et al., 2007; Tal and Lieberman, 2008; Antfolk et al., 2018; Billingsley et al., 2018). One such cue is early co-residence between purported siblings as suggested by Westermarck (i.e., the hypothesis of Westermarck, 1922). It might be that this system of kin detection is affected in offenders with a psychiatric diagnosis and thereby prevents the offenders from recognizing and avoiding kin.

Spitting out conspecifics or parts of them is a characteristic behavior of cannibalistic animals and humans. We found five such throwing up /spitting out events, which may not sound like a lot in 631 victim cases, but our documentation is not comprehensive and it is important to keep in mind that many humans may eat a thousand meals a year without any one such throw up event. In sticklebacks, a strongly cannibalistic fish species, spitting out of newly hatched fish has been carefully documented and referred to as “testing” (Bruijn and Sevenster, 1982). Similarly, the cannibalistic spadefoot tadpoles have been seen to nip at and spit out conspecifics (Pfennig et al., 1993), a behavior referred to as “tasting”. Our observations on humans and a review of the animal literature suggest, however, that it is very unlikely that spitting out meat from cannibalistic events indeed reflects a sensory discriminatory behavior or gustatory “tasting”. The reasons, why we reject the tasting/testing hypothesis are the following: (i) Stickleback, spadefoot tadpoles, and humans have potent non-gustatory kin-discrimination mechanisms. In stickleback (Mehlis et al., 2008) and in salamander tadpoles (Pfennig et al., 1994), such mechanisms are olfactory in nature and in humans and apes (Parr and de Waal, 1999) such mechanisms are presumably visual; (ii) when tested intadpoles by nare occlusion, olfactory mechanisms were necessary for kin discrimination, whereas the remaining gustatory mechanism (after nare occlusion) were insufficient for kin-discrimination (Pfennig et al., 1994); (iii) human gustatory kin-discrimination appears highly implausible from our screening of cannibalism reports. On numerous occasions, human meat was sold (and probably eaten) by cannibals as ostrich, pork, horse, or tenderloin, mostly without any customer complaints reported. For instance, J.R.M. sold meat of his victims as special barbecue meat in a stand next to his trailer. He mixed the meat together with pork, which he claims tastes very similar to human meat, so that nobody could tell the difference (Serial killer who “cut up victims and sold them as BBQ” dies, 2017). If humans cannot discriminate human meat from beef, how could humans or animals taste kin? (iv) “Testing” behavior in stickleback is strongly dependent on the state of satiation (Bruijn and Sevenster, 1982); it is not obvious why a sensory discriminatory behavior should strongly depend on the state of satiation; and (v) in interviews with human cannibalistic offenders, they do not report that kin had a bad taste. We propose an alternative explanation for cannibalistic spitting-out: We suggest that this behavior is driven by internally generated repulsion and reflects a conflict between kin-protective, anti-cannibalistic drives, and predatory/consumptive systems. This explanation makes sense, because (i) we do not assume gustatory kin-discrimination, (ii) it is consistent with strong dependence on internal variables like hunger, and (iii) it fits with reports from cannibalistic offenders. In our explanation we explain a contradictory behavior (spitting out, a reversion of the decision to ingest), by an internal contradiction (preying vs. protection of potential kin).

Forensic awareness could be another explanation for the kin-avoidance observed in our study. Accordingly, cannibalistic offenders would avoid eating kin in order to escape prosecution, which is conceivably more likely for kin offenses. While we think forensic awareness is an important consideration, we do not think this hypothesis can fully explain our data. In particular, we do not see any evidence for a differential “forensic awareness” of cannibalistic and conventional offenders. Instead, many cannibalistic offenders enjoyed the celebrity emanating from their deeds; indeed, cannibal P.K. sends a letter to the press detailing the whereabouts of the grave of one of his victims, an action not speaking to forensic awareness. Also, other considerations do not align with the forensic awareness hypothesis. Offenders of cannibalistic crimes who showed forensic awareness were excluded from this study. For example, it is thought that the “confession” of cannibalism by E.K. is the result of forensic awareness, and he is, therefore, excluded from this study on the grounds of not enough evidence for cannibalism (Supplementary Data Sheet 3). However, we cannot exclude that other offenders still included in our study had a similar tactic unknown to us. It could be that offenders with forensic awareness will target strangers more often than family to dismiss any suspicions which might fall on them. In that case, one might argue that a reduced mental health also likely reduces the forensic awareness and that that could explain our finding that offenders with reduced mental health targeted kin more often. While we can not exclude this theory, we deem it unlikely because (i) this would then also be true for non-kin relatives such as intimate partners, and this is not the case (Figure 6E), and (ii) we excluded cases with suspicions of forensic awareness, and in first-hand reports by cannibals included in this study, they claim to really kill and eat for the purpose of pleasure, and (iii) cannibalistic offenders, who had enough forensic awareness to never be detected, are also not included in this study for the obvious reason that they are unknown. According to the theory above, uncaught cannibalistic offenders would target strangers more often than family, and those cannibals are missing from our study. Thus, if this is true, we are missing more strangers victims but we are not missing as many kin victims, in which case the actual effect size would be even larger than reported here.

War and hunger related cases of cannibalism appear to share features of cannibalistic homicide identified here. In war crimes, it is often the enemy which is cannibalized (Tanaka, 2018). In hunger-related cannibalism there are also indications of kin-avoidance. In the famous Uruguayan Air Force flight 571 incident, where starving victims of the plane crash fed on meat from deceased co-passengers to survive, it is said that at least some survivors made efforts to avoid eating kin (Arijón, 2008). Specifically, when one of them could only eat his kin for survival, he decided to cross the Andes to search for help instead (Parrado and Rause, 2013), which is the journey which eventually led to their rescue. Internally generated disgust is evident in such cases, i.e., the plane crash victims were appalled by eating human meat.

To achieve a correct interpretation of the results reported here, it is necessary to consider the limitations of our data set. Cannibalistic homicide is a secretive crime and our study is based on second hand and potentially distorted information. Thus, despite the best of our efforts, some errors are inevitable and we expect that our data set may contain mistakes about homicides, offenders, victims, and victim-offender relationships. The case of cannibalistic offender J.K. provides a warning. No less than five putatively innocent people were arrested for his crimes (three of whom committed suicide and a fourth was wrongly convicted of murder). Furthermore, some homicide offenders may give a calculated “confession” of cannibalism in order to use an insanity plea, as is suspected to be the case with E.K. (who for this reason has been excluded from this study, see Supplementary Data Sheet 3). In anthropology, the mere existence of human cannibalism in, for example, aboriginal cultures has been questioned on grounds of sensationalistic reporting in travelogs (Arens, 2004). Does this mean that one can dismiss our evidence about cannibalistic homicides, because these crimes seldom have eyewitnesses or video evidence and, without exception, incidents have been hyped by the press? We think the answer is a resounding no. The hundreds of cases documented in our report leave no room for doubt. We acknowledge, however, that our worldwide collection of cases is subject to a variety of sampling biases.

Limitations of Our Approach

The value of the data provided in our study might be limited by the following weaknesses:

1. The secretive nature of cannibalistic homicide. Cannibalistic homicide is nothing that can be openly performed in modern societies. The vast majority of cannibalistic homicides described here have been performed secretively and often there have been considerable efforts by offenders to destroy evidence. Hence, this paper largely describes deeds that nobody witnessed and cannibalism – the defining characteristic of what is talked about here – has rarely been directly established.

2. The need for estimates. Given the secretive nature of cannibalistic homicide, many details of the offenses described here can only be estimated. Many of these estimates are based on excellent evidence such as confessions, post-mortem examinations, or strongly suggestive circumstance (a child’s hand cooking in salted water on the stove), but nevertheless the evidence remains inferential.

3. Sampling biases. Perhaps the biggest problem of the data presented here is that our “news-based” search for cannibalistic incidents is subject to sampling biases. In particular, the data presented here will be biased towards particularly newsworthy cases with high victim numbers or gruesome case details.

4. Outright distortions. Sensationalism in the press might also lead to inflated presentation of evidence and distortion of the facts.

5. Reliance on second hand information. Our data set relies largely on web and newspaper reports and less so on official documents (original verdicts, interviews, letters and notes from the cannibal offender, autobiographies by offenders, and the like). Hence, verification of incident details is largely indirect.

6. Unintentional mistakes. Our data set is very large and unquestionably contains mistakes. Such mistakes would happen less in official documents double-checked and based on primary crime evidence but are unavoidable in our type of analysis.

7. Language barriers. We decided for a worldwide search of cannibalism cases, which allowed us amassing a large sample, but led us to encounter language problems. In several instances we used tools such as Google Translate to check local news sources. Such tools are powerful, but imperfect.

Strengths of Our Approach

1. Numbers. The biggest strength of the worldwide internet-based search for cannibalistic homicides is the sheer number of cases it returns.

2. Substantial coverage. The news coverage of cannibalistic cases is substantial. In a contemporary society, it is therefore simply unlikely that a cannibalistic homicide is not covered, unless (a specific detail of) a case is prohibited to be covered by the press.

3. Rich detail. Our data set contains very detailed information about cannibalistic homicides.

4. Good estimates. A lot of the evidence presented here is inferential, but many of the estimates presented here are good estimates. In modern societies an immense amount of effort is made to clear up homicides. Thus, a lot of the estimates about the deeds of serial murderers presented come from police investigators, who spent years of their life chasing the perpetrators; such detailed police work entitles to estimates about the deeds of offenders.

5. Documentation effort in internet-data sets. A lot of our searches and results rely on pages like murderpedia.org and lists of cannibalistic incidents. Many of these data sets do not comply with strict scientific standards of referencing; nevertheless, it would be a mistake to underestimate the effort and expertise that went into aggregating these data sets.

6. Access to rare cases. Cannibalistic homicides are rare and if one wants to investigate subclasses of such cases (i.e., very rare cases) the comprehensive search strategy is indispensable.

7. Informal cross validation. Whenever possible we informally cross-validated data sets against each other.

Our results indicate that cannibalistic homicide is a distinctive offense with a special pattern of murder methods, a strong relation to sexual acts, distinctive patterns of victims and offenders, and unique victim-offender relationships. There is a seemingly high amount of kin-avoidance in such crimes, in particular, if offenders do not suffer from serious mental health problems. We suggest that kin-avoidance and spitting out of conspecifics might be triggered by internally generated disgust against kin-ingestion.

Social status is a universal and consequential dimension of variation within human groups; multiple prominent theories have been proposed to explain how status is allocated

Psychological foundations of human status allocation. Patrick K. Durkee, Aaron W. Lukaszewski, and David M. Buss. Proceedings of the National Academy of Sciences, August 18, 2020. https://doi.org/10.1073/pnas.2006148117

Significance: Social status is a universal and consequential dimension of variation within human groups. Multiple prominent theories have been proposed to explain how status is allocated, but extant evidence is insufficient to adjudicate between their conflicting predictions. Here we show that distinctions between each theory hinge on the relative importance of four key affordance dimensions: benefit-generation ability, benefit-generation willingness, cost-infliction ability, and cost-infliction willingness. Each theory makes a different prediction about the role of each affordance in status allocation. We test these competing predictions to explain status allocations across 14 nations. We found that benefit-generation affordances uniquely predicted status allocations across nations, whereas cost-infliction affordances were weak or null competing predictors.

Abstract: Competing theories of status allocation posit divergent conceptual foundations upon which human status hierarchies are built. We argue that the three prominent theories of status allocation—competence-based models, conflict-based models, and dual-pathway models—can be distinguished by the importance that they place on four key affordance dimensions: benefit-generation ability, benefit-generation willingness, cost-infliction ability, and cost-infliction willingness. In the current study, we test competing theoretical predictions about the relative centrality of each affordance dimension to clarify the foundations of human status allocation. We examined the extent to which American raters’ (n = 515) perceptions of the benefit-generation and cost-infliction affordances of 240 personal characteristics predict the status impacts of those same personal characteristics as determined by separate groups of raters (n = 2,751) across 14 nations. Benefit-generation and cost-infliction affordances were both positively associated with status allocation at the zero-order level. However, the unique effects of benefit-generation affordances explained most of the variance in status allocation when competing with cost-infliction affordances, whereas cost-infliction affordances were weak or null predictors. This finding suggests that inflicting costs without generating benefits does not reliably increase status in the minds of others among established human groups around the world. Overall, the findings bolster competence-based theories of status allocation but offer little support for conflict-based and dual-pathway models.

Keywords: statushierarchyaffordancesdominanceprestige