Online men adopting a long-term mating strategy also displayed canines more than women adopting a long-term mating strategy; men show they can provide investment to court women which is more relevant to them than it is to men

Dependents as Signals of Mate Value: Long-term Mating Strategy Predicts Displays on Online Dating Profiles for Men. Mackenzie J. Zinck, Laura K. Weir & Maryanne L. Fisher. Evolutionary Psychological Science, Oct 8 2021. https://rd.springer.com/article/10.1007/s40806-021-00294-w

Abstract: Sexual strategies theory indicates women prefer mates who show the ability and willingness to invest in a long-term mate due to asymmetries in obligate parental care of children. Consequently, women’s potential mates must show they can provide investment – especially when women are seeking a long-term mate. Investment may be exhibited through financial and social status, and the ability to care for a mate and any resulting offspring. Men who care for children and pets (hereafter “dependents”) are perceived as high-quality mates, given that dependents signal an ability to invest; however, no studies have examined how dependents are associated with short-term and long-term mating strategies. Here, online dating profiles were used to test the predictions that an interactive effect between sex and mating strategy will predict displays of dependents, with long-term mating strategy predicting for men but not women. Moreover, this pattern should hold for all dependent types and, due to relative asymmetries in required investment, differences will be strongest regarding displays of children and least in non-canine pets. As expected, men seeking long-term mates displayed dependents more than men seeking short-term mates, but both men and women seeking long-term mates displayed dependents similarly. This pattern was driven mostly by canines. These findings indicate that men adopting a long-term mating strategy display their investment capabilities more compared to those seeking short-term mates, which may be used to signal their mate value.

Discussion

To begin, it should be noted that few women in our population declared interest in a short-term mate, which is consistent with previous work (e.g., Buss & Schmitt, 1993) as, due to differences in obligate parental investment, women tend toward a long-term mating strategy while men tend to seek short-term mates. This finding suggests that men’s mating strategies may be more flexible relative to women’s strategies. Also, it points to the need for future research on relationships, given Schacht and Borgerhoff-Mulder (2015) found that men and women reported being equally interested in short-term mating.

Displays of Dependents

We supported our predictions regarding the display of dependents as influenced by mating strategies. Men who were seeking long-term mates displayed dependents on their profiles significantly more than men seeking short-term mates. Men seeking long-term relationships may show dependents as a way of advertising their parenting abilities and willingness to provide resources, which align with women’s mate preferences (e.g., Bereczkei et al., 2010; Buss & Schmitt, 1993; Li & Kenrick, 2006). These preferences are generally stronger in women when seeking long-term relationships, as compared to women adopting short-term mating strategies, who tend to place a greater importance on physical attractiveness (Li & Kenrick, 2006, see also humor and sociability: Mehmetoglu & Määttänen, 2020) rather than resource and care provisioning (Buss & Schmitt, 1993).

These results show evidence of cross-sex mind-reading. Geher (2009) posits that it is advantageous for heterosexual individuals to determine the mate preferences of potential mates and then advertise those desired features. Cross-sex mind-reading may be a form of mating intelligence, whereby one anticipates what potential mates desire, leading to more successful courtship. Geher (2009) proposes that there are different types of cross-sex mind-reading that are relevant here: men’s ability to know the short- and long-term preferences of women, and women’s ability to know the short- and long-term preferences of men. His findings largely indicate that of these four types, the most accurate form is men reading women’s long-term preferences. His reasoning is that, “given the notoriously discriminating nature of females’ choices in mate selection…coupled with strong tendencies for females to pursue long-term mating strategies…there may be particularly strong pressure on males to ‘get it right’ when it comes to long-term desires of females” (p. 344). This study’s findings align well with those of Geher (2009), as well as his explanation. That is, men may be showing dependents when seeking a long-term mate because they know that women prefer men who show these abilities in this relationship context.

Predictions regarding the between-sex comparisons were, however, not supported: men and women seeking long-term mates displayed dependents in a similar fashion. The types of investment dependents may signal regarding their carer are irrelevant to men, apart from caring abilities: qualities of a good parent are valued by men seeking long-term mates (e.g., Jackson & Kirkpatrick, 2007) to maximize return (in terms of reproductive success) of their investment (e.g., Buss & Schmitt, 1993). Consequently, women may be displaying their dependents to advertise their caring abilities to entice men into a long-term commitment (i.e., cross-sex mind-reading; Geher, 2009). This explanation is supported by Goetz (2013), who showed women seeking long-term mates were more likely to present indicators of their parenting abilities than women seeking short-term mates, and compared to men seeking any mate, in their online personal advertisements.

Displays of Dependent Types

How daters displayed their dependents varied by type (e.g., canine, feline), though our prediction was unsupported: not only did the pattern in which children, canines, and other pets were displayed differ, but the magnitude of between-group differences was similar. However, the results do paint an informative picture; different dependents have specific qualities about them that may explain our findings.

Children were among the most frequently displayed dependents by men seeking long-term mates. Such findings are logical as Kemkes (2008) showed men pictured with children are perceived as having elevated financial and social status, as well as parenting abilities. Men enjoy this elevation of perceived status as children in Canada take, on average, roughly $250,000 to raise to adulthood (Brown, 2015), and financial status is linked with social standing, thus making them an indicator of their parent’s ability to accrue and provide financial resources (on top of caring abilities). Moreover, such investment is strongly desired by women seeking long-term mates (e.g., Buss & Schmitt, 1993), which could explain these men’s propensity to display them so frequently. Children were also the most frequently displayed dependent on the profiles of women seeking long-term mates. Children require considerable care, which mothers typically provide more than fathers (e.g., while their partners performed childcare on non-workdays, fathers engaged in leisure activities 47% of this time: Kamp Dush et al., 2017), making them strong signals of a woman’s caring abilities (Kemkes, 2008). Furthermore, women are presumably most likely to display a child given 80% of separated Canadian women have primary custody of their children (Government of Canada, 2015). Therefore, women may be using children to showcase their caring abilities (as men seek qualities of a good parent in long-term mates: Buss & Schmitt, 1993), to honestly inform a prospective mate of her current familial situation, or even to signal fecundity if said dater was in her reproductive prime.

Next, on the profiles of long-term oriented men, canines (alongside children) were the most frequently displayed dependent, significantly more than men seeking short- and women seeking long-term mates. This pattern follows our between-strategy and between-sex predictions and was likely the main driver of the results for dependents in general. Some studies have suggested canines are a strong signal for a male’s investment capacity and masculinity (Gray et al., 2015; Kogan & Volsche, 2020; Mitchell & Ellis, 2013; Tifferet et al., 2013), as well as dominance-related qualities (Alba & Haslam, 2015, which is also sought by women: Buss & Schmitt, 1993). The types of investment that canines signal in a male carer (i.e., social and financial status, caring abilities) are sought more by women under long-term mating contexts than short-term ones, which could explain the inclination for long-term oriented males to display them over short-term ones. This conjecture is largely supported by Tifferet et al., (2013) who found perceived dog ownership improves men’s value as long-term mates in the eyes of women. Men adopting a long-term mating strategy also displayed canines more than women adopting a long-term mating strategy. Again, this can be interpreted as men showing they can provide investment to court women which is more relevant to them than it is to men (e.g., Buss & Schmitt, 1993).

Finally, other pets—this variable mainly comprised of cats—were displayed infrequently. Men’s hesitancy to display them may in part be explained through the findings of Mitchell and Ellis (2013): men show awareness of Western perceptions of feline-ownership being more feminine, which has negative social connotations for men and may not be a trait that women seek in a potential mate (Kogan & Volsche, 2020). Moreover, if non-canine pets are weak signals of their carer’s investment capacity (as they require minimal investment), neither sex would be inclined to display them to attract a mate, which could also explain the lack of difference regarding the between-sex comparison.

Future Work and Limitations

Future work could continue to use SST to predict human behavior in naturalistic settings such as online dating profiles. Such contexts are important as they allow researchers to examine behavior that is difficult to manipulate in the laboratory and findings are more generalizable to the public (Leichsenring, 2004). Because mating motivates human behavior and cognition (Jones et al., 2013; Miller & Maner, 2011), which develop through evolutionary forces (Buss & Schmitt, 1993), understanding how humans show that they are a valuable mate can further our understanding of the underlying drives for these processes.

As an immediate next step, future research could explore whether daters who show dependents are more successful in attracting a mate. This could be done by analyzing the number of profile-clicks or time spent observing a profile by prospective mates. Such findings could support the idea that dependents are honest signals of their carer’s investment capacity if sex- and mating strategy-specific differences are found. Additionally, to support (or weaken) the argument regarding pets as signals of caring abilities, whether people with pets make better parents should be examined.

This study was also conducted during the COVID-19 pandemic. Though one would think this level of environmental danger could influence human mating strategies (e.g., mate selection criteria become relaxed during times of increased species mortality; Reeve et al., 2016), we do not think this played a role in our findings as sampling occurred after a sharp decrease in viral presence, resulting in restrictions on social movements being relaxed (Nova Scotia’s weekly percent positivity per 100,000 population was between 0.0 and 0.2, rest of Canada between 0.8 and 1.1; see Public Health Agency of Canada, 2021). However, we procured two other samples in the late fall of 2020 which saw a resurgence of cases and intend to collect more samples as the pandemic continues. We hope to use these data to analyze whether a global pandemic influences how men (and women) display their investment capacity (i.e., via dependents) in an online mating context.

There are two main limitations of this study. First, daters were assumed to adopt a certain mating strategy according to their intent for online dating. Though online presences permit an opportunity for deceitful self-representation, dishonest advertisement decreases as the probability of meeting increases in mating contexts (Finkel et al., 2012; Gibbs et al., 2006; Guadagno et al., 2012). Overall, it was assumed daters were relatively honest in their profile construction as their indicated reasons for being on the platform implied a future meeting with a prospective mate. Haselton et al., (2005) showed that women, more than men, report previous long-term mates misconstrued their mating intentions to coerce a sexual encounter. If this was the case in this study, we would have incorrectly categorized men adopting a short-term mating strategy as adopting a long-term mating strategy which could have produced artificial (or hidden) differences between groups if these men were or were not displaying dependents. For a more accurate understanding of a dater’s true intentions, daters could be assessed using the Sociosexual Orientation Inventory (for example, see Jackson & Kirkpatrick, 2007) to determine whether daters leaned toward short-term or long-term mating, before recording their profile’s content. Overall, using SST to predict how people display their mate value on dating profiles is a valuable avenue of exploration, given individuals are seeking mating arrangements which reflect the need for physical encounters.

Second, the age of daters was left unrestricted. Age influences mating behaviour as it correlates with fertility (Conroy-Beam & Buss, 2019): with an increase in age, women’s fecundity decreases more sharply than men’s reproductive potential (Hill & Hurtado, 1991). Consequently, motives for mating change with age as well (McWilliams & Barrett, 2012): older women report seeking younger companions who can provide an active social life—rather than resources—and feel obliged to be a caretaker in later life. Men also seek out younger mates with caregiving abilities. Therefore, how these motives influence how middle- and later-aged individuals present their mate value in mating arenas deserves future consideration. For example, an extension of the current work may entail examining how daters in their reproductive prime, as well as those pre- and post-reproductive prime, display their dependents on an online dating platform.

The COVID-19 vaccination primes positive emotions which are known in the literature to promote cheating by increasing cognitive flexibility and lowering self-control

Tobol, Y., Siniver, E., & Yaniv, G. (2021). COVID-19 vaccination and subsequent dishonest behavior: Experimental evidence. Journal of Neuroscience, Psychology, and Economics, 14(3), 131–137. Oct 2021. https://doi.org/10.1037/npe0000146

Abstract: As of the beginning of 2021, the State of Israel, with a population of 9.3 million, had administered more coronavirus disease 2019 (COVID-19) vaccine doses than all countries aside from China, the United States, and the United Kingdom. The vaccine is administered in two doses, 21–28 days apart from each other, which are necessary to confer adequate immunity. The present paper reports the results of a field experiment designed to examine the hypothesis that the COVID-19 vaccination stimulates subsequent dishonest behavior. Specifically, people relaxing after receiving the first and second vaccine doses as well as people waiting to receive the first dose were invited to perform a money-rewarding simple task which involves an opportunity to cheat with no possible detection. Before performing the task, subjects filled out a questionnaire regarding the emotions they were experiencing at that moment. We hypothesized that the COVID-19 vaccination primes positive emotions which are known in the literature to promote cheating by increasing cognitive flexibility and lowering self-control. Therefore, we predicted that (a) people vaccinated with the first dose are more likely to subsequently lie than people who have not yet taken the vaccine and (b) people vaccinated with the second dose are more likely to lie than people vaccinated with the first dose or people who have not yet taken the vaccine. The experiment’s results weakly support the first hypothesis but strongly support the second.

Depression: Households spend less overall, visit grocery stores less & convenience stores more frequently; spend a smaller share of their baskets on fresh produce & alcohol but a larger share on tobacco, no changes in cakes, candy & salty snacks

Meckel, Katherine and Shapiro, Bradley, Depression and Shopping Behavior (September 30, 2021). SSRN: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3934028

Abstract: Using a large survey panel that connects household shopping behavior with individual health information, this paper documents correlations between self reported depression and the size and composition of shopping baskets. First, we find that roughly 16% of individuals report suffering from depression and over 30% of households have at least one member who reports suffering from depression. Households with a member suffering from depression exhibit striking differences in shopping behavior: they spend less overall, visit grocery stores less and convenience stores more frequently and spend a smaller share of their baskets on fresh produce and alcohol but a larger share on tobacco. They spend similar shares on unhealthy foods like cakes, candy, and salty snacks. These cross-sectional correlations hold within counties, suggesting that they are not driven by region specific demographics or preferences that are incidentally correlated with depression status. They also hold when considering only single-member households. However, we rule out large differences in shopping behavior within households as they change depression status throughout the sample. Further, using the take-up of antidepressant drugs as an event, we document little change in shopping in response to treatment. With our results, we discuss the takeaways for health policy, decision modeling and targeted marketing.

Keywords: Mental Health, Economic Burden of Depression, Depression, Shopping, Household Panel Data

JEL Classification: I1, I10, I12, M31,

Paper retraction: Fraud and plagiarism accounted for 28.6 and 59.2% of women and men-authored retractions, respectively

Retraction according to gender: a descriptive study. Evelyne Decullier & Hervé Maisonneuve. Accountability in Research, Oct 7 2021. https://doi.org/10.1080/08989621.2021.1988576

Abstract: Although the underrepresentation of women in publication is a proven fact, there is no information on its counterpart: retractions. Using a previously studied cohort of retractions, the gender of the first author was checked manually to see if there was a similar pattern in the reasons for retraction for women and men authors. Out of 120 retractions, gender was identified for 113 (94.2%). A total of 42 (37.2%) retractions concerned publications authored by women and the reasons for retraction were significantly different between men and women authors. Overall, fraud and plagiarism accounted for 28.6 and 59.2% of women and men-authored retractions, respectively. These findings may have implications as regards training in responsible conduct in research; however, without further investigating larger cohorts and a better understanding of underlying mechanisms, it would be premature to draw any firm conclusions at this stage.

Keywords: Misconduct – retraction- gender

Child access prevention, minimum age requirements for gun purchases, and mandatory gun safety training laws exhibited weak and inconsistent relationships with school firearm incidents

Are gun ownership rates and regulations associated with firearm incidents in American schools? A forty-year analysis (1980–2019). Daniel Hamlin. Journal of Criminal Justice, Volume 76, September–October 2021, 101847. https://doi.org/10.1016/j.jcrimjus.2021.101847

Abstract

Purpose: This study examines the relationship between state gun ownership rates and school firearm incidents (n = 1275) and injured/killed victims (n = 2026) of these incidents over a forty-year period (1980–2019). It also investigates whether child access prevention, minimum age requirements for gun purchases, and mandatory gun safety training laws are associated with fewer school firearm incidents and injured/killed victims.

Methods: Data were linked together from the School Shootings Database, State Firearm Law Database, the National Center for Education Statistics, and the US Census Bureau. State fixed effects and interrupted time series analyses were performed.

Results: State gun ownership rates declined between 1980 and 2019 while school firearm incidents generally ranged between 20 and 40 incidents before skyrocketing to 102 incidents in 2018 and 110 incidents in 2019. Findings were mixed on the relationship between state gun ownership rates and school firearm incidents and injured/killed victims. Additionally, child access prevention, minimum age requirements for gun purchases, and mandatory gun safety training laws exhibited weak and inconsistent relationships with school firearm incidents.

Discussion: Although access to firearms plays an undeniable role in school shootings, it remains unclear what policies are needed to reduce these incidents. Future research may be needed to explore holistic approaches to addressing this problem.

Introduction

School shootings have become a pressing concern for the American public education system. In the United States, the number of shootings on school grounds is consistently higher than that of any other country in the world (Hahn et al., 2005). While many gun incidents in US schools do not lead to injury or death, a non-trivial number of devastating mass shootings occurring in the past decade have resulted in substantial numbers of victims and ignited intense gun control debates. One of these highly distressing incidents was in 2012 when a 20-year old with a history of mental health problems murdered six adults and twenty children between the ages of six and seven in a mass shooting at an elementary school in Connecticut (Langman, 2015). More recently in 2018, national attention became refocused on gun control after a 19-year old assailant killed fourteen students and four school staff at a high school in Florida where he had been previously expelled (Aslett, Webb Williams, Casas, Zuidema, & Wilkerson, 2020). Loss of life and psychological trauma are directly observable ramifications for schools and communities that experience a school shooting. The traumatic effects of these incidents also appear to extend beyond the location of the shooting itself, inflicting damage on the psyche, confidence, and wellbeing of the broader public (Collins, 2014; Newman, Fox, Harding, Mehta, & Roth, 2005).

Public outcry after major school shootings has spurred varying proposals for action from federal, state, and local officials (Schildkraut & Hernandez, 2014). While policy recommendations have ranged from arming teachers to strengthening mental health supports for troubled youth, gun control has been at the forefront of disputes over how to prevent school shootings (Rajan & Branas, 2018). Many states have enacted gun safety legislation following rampage-style school shootings (Schell, Cefalu, Griffin, Smart, & Morral, 2020). The main rationale for enhanced gun control is straightforward. The United States has both the highest rate of gun ownership and the greatest number of school shooting incidents in the developed world. Proponents of strong legal restrictions on firearms argue that these patterns demonstrate that guns are too accessible to those with mental health issues and a history of violence, making school shootings an inevitable consequence. Yet, opponents claim that gun prevalence is a response to existing crime and violence, and that restrictive gun laws violate the right to bear arms enshrined in the US Constitution by preventing law abiding citizens from owning guns (Stolzenberg & D'alessio, 2000).

In the empirical literature, many researchers have estimated correlational associations between gun ownership rates and general crime and violence, but this work is inconclusive (Kleck, 2015; Shetgiri, Boots, Lin, & Cheng, 2016; Siegel, Ross, & King III, 2013). Investigations of gun control regulations have exhibited more consistent associations with lower crime and violence (Andres & Hempstead, 2011; Fleegler et al., 2013; Hurka & Knill, 2020; Schell et al., 2020; Smith & Spiegler, 2020). For school-based incidents with firearms, empirical analyses are lacking. Nevertheless, there are compelling reasons to expect that high rates of gun ownership increase the likelihood of school firearm incidents as school shootings often involve weapons stolen by minors from family members, friends, and neighbors (Jeynes, 2020; Shetgiri et al., 2016). Some evidence on regulation is suggestive, indicating that laws holding gun owners criminally liable for negligent storage of firearms (e.g. child access prevention laws) are linked to lower prevalence of gun carrying in school (Anderson & Sabia, 2018; Fla. Stat. Ann. § 790.174, 2011; Hawaii Rev. Stat. § 134-10.5, 2011). Other scholarship on preventative measures is predominantly theoretical, drawing from threat assessment models (Cornell, 2020) or in-depth analyses of a subset of school shootings (Langman, 2009a). Broader empirical analysis is needed to launch a line of inquiry that can shed light on policy responses that might hold promise for reducing school shootings.

This study investigates the relationship between state gun ownership rates and school firearm incidents (n = 1275) and injured/killed victims (n = 2026) of these incidents from 1980 to 2019 in the United States. Over this forty-year period, it also examines whether child access prevention, minimum age requirements for gun purchases, and mandatory gun safety training laws are associated with decreases in school firearm incidents and injured/killed victims. For the analyses, data from the School Shootings Database were linked to data from the State Firearm Law Database, the National Center for Education Statistics, and US Census. State-level fixed effects models are performed to explore whether state-level gun ownership rates are related to the number of school firearm incidents and injured/killed victims. Interrupted time series analyses are then used to examine whether child access prevention, minimum age requirements for gun purchases, and mandatory gun safety training laws are associated with declines in school firearm incidents and injured/killed victims. This study provides a quantitative analysis of school firearm incidents over a forty-year period that has the potential to contribute to an underdeveloped literature. It may also raise important questions for gun policy and regulation.

Some evidence suggests that people behave more cooperatively and generously when observed or in the presence of images of eyes (termed the ‘watching eyes’ effect); replication failed

Rotella A, Sparks AM, Mishra S, Barclay P (2021) No effect of ‘watching eyes’: An attempted replication and extension investigating individual differences. PLoS ONE 16(10): e0255531. Oct 6 2021. https://doi.org/10.1371/journal.pone.0255531

Abstract: Some evidence suggests that people behave more cooperatively and generously when observed or in the presence of images of eyes (termed the ‘watching eyes’ effect). Eye images are thought to trigger feelings of observation, which in turn motivate people to behave more cooperatively to earn a good reputation. However, several recent studies have failed to find evidence of the eyes effect. One possibility is that inconsistent evidence in support of the eyes effect is a product of individual differences in sensitivity or susceptibility to the cue. In fact, some evidence suggests that people who are generally more prosocial are less susceptible to situation-specific reputation-based cues of observation. In this paper, we sought to (1) replicate the eyes effect, (2) replicate the past finding that people who are dispositionally less prosocial are more responsive to observation than people who are more dispositionally more prosocial, and (3) determine if this effect extends to the watching eyes effect. Results from a pre-registered study showed that people did not give more money in a dictator game when decisions were made public or in the presence of eye images, even though participants felt more observed when decisions were public. That is, we failed to replicate the eyes effect and observation effect. An initial, but underpowered, interaction model suggests that egoists give less than prosocials in private, but not public, conditions. This suggests a direction for future research investigating if and how individual differences in prosociality influence observation effects.

Check also Stylized and photographic eye images do not increase charitable donations in a field experiment. Paul Lennon, Rachel Grant, and V. Tamara Montrose. Letters on Evolutionary Behavioral Science, Vol 8, No 2 (2017). https://www.bipartisanalliance.com/2017/09/stylized-and-photographic-eye-images-do.html

Discussion

This study examined if people were more prosocial in public, under “watching eyes”, or in a control condition with no-eyes. We failed to replicate the previously reported eyes and observation effects. Our results suggest that prosocial disposition (as measured by social value orientation) relates to responses to reputational incentives, where SVO prosocials gave similar amounts in both public and private conditions, but SVO egoists give less than prosocials in private conditions. Only SVO was a consistent predictor of dictator game donations, with prosocials giving more than egoists. Below we discuss each of these results and study limitations.

Failed replications: Observation and ‘watching eyes’ effects

Our manipulation check found that participants felt more observed in the public condition compared to both the eyes and no eyes conditions, suggesting that our public manipulation worked. Despite this, participants did not give more in the dictator game in the public condition compared to the eyes and control conditions. That is, we did not find an observation effect. This result was surprising, given that many prior studies suggests that people are more generous when they are being watched [6–9,11–16,39].

Based on the effect size for watching eyes in a prior study using similar methodology (i.e., short exposure to eyespots; Cohen’s f of .21 [23]), our sample of 355 participants would have given us 95% power to detect the eyes effect and observation effect. Despite this, we did not replicate the canonical “watching eyes” effect. Thus, our first prediction was not supported.

Our result is consistent with several recent failed replications [33–39]. Notably, a recent meta-analysis argues that eyes effects are effective at reducing antisocial behavior, with the speculation that images of eyes may be more effective at reducing bad behaviours than increasing good ones [32]. Watching eyes may not be particularly effective at increasing prosocial behaviours.

Reputation and social value orientation

In our pre-registered analysis, egoists did not give less than prosocials across all three conditions. However, we conducted an exploratory analysis where we combined the no eyes control condition and eyes condition into a single private condition to replicate the analyses in a prior study [39]. Although the overall analysis did not reach statistical significance, egoists gave less than prosocials in private conditions, but not in public conditions. This finding is consistent with the prior study [39], where proselfs (egoists and competitors combined) contributed less in private conditions, whereas prosocials did not. This result suggests that egoists give less than prosocials in a dictator game when anonymous. When comparing dictator game allocations among egoists in public and private conditions we did not find any differences. Given that egoists give less than prosocials in anonymous conditions, this suggests that the strategic motives of egoists are different than that of prosocials. Notably, this analysis was underpowered and we cannot draw definitive conclusions whether SVO relates to responses to observation.

Although we had a larger sample in this study compared to Simpson and Willer (2008; [39]), they used a decision with consequences as their primary dependent measure (i.e., participants were informed that a third party could see their decision and use it to inform a subsequent decision). Their manipulation was likely stronger than a decision without consequences, as employed in the present study. It is worth noting, however, that our study was underpowered to find this effect; we could not match the SVOs of approximately 44% of participants due to an error in survey administration. Nevertheless, this is the third study suggesting that SVO may relate to responses to reputation-relevant stimuli and emotions; future studies should continue to investigate the role of individual differences in reputation-based responses.

Notably, our results are suggestive of gender effects in response to reputation-based cues. Researchers have previously proposed gender differences in prosociality [57,58], though see meta-analysis in [59], and recent research finds that people expect women to be more prosocial than men [58]. These findings suggest that there may be gender differences in reputational costs/benefits for acting prosocial in public contexts, which should be further investigated.

Limitations

The most notable limitation in this study is our sample size. Although our sample was sufficient to replicate the observation and eyes effects, given prior samples (we had 95% power), we could not match the SVOs to their in-lab data of for a large proportion of participants, limiting our ability to draw conclusions about how SVO influences participants responses to reputation-based cues. These results should therefore be interpreted with caution. Despite this limitation, our sample size is much larger than those included in the original study (189 participants, compared to 89 and 70 in two studies [39]). This larger sample can provide a more accurate effect size to estimate power and sample sizes for future studies.

Another possible limitation to our study is that participants gave close to ceiling in the dictator game (i.e., $5) in all conditions (overall M = 4.06, SD = 2.00; all medians = 5), which may have limited our ability to find an observation effect. In fact, 62.4% of participants gave at ceiling in the public condition, and 53.6% in the private condition. However, prior research on eyes effects with a dictator game also found high allocations in the control condition (i.e., $4 out of $10) and found that images of watching eyes increased dictator game allocations beyond $4 [23]. Given that our study used similar methodology as Sparks and Barclay (2013) [23], we can conclude that we failed to replicate the eyes effect in this study. Participants did not report feeling more observed in the presence of eyes and did not give more money in a dictator game when images of eyes were present compared to the control condition. We also failed to replicate an observation effect, despite people feeling more observed in the public condition compared to the control condition, which suggests that people may not always increase cooperation when there are reputational incentives. Notably, many studies investigating observation and eyes effects do not include manipulation checks to confirm if participants feel observed. Future research could investigate when and why we would expect observation effects to occur and should include manipulation checks to confirm the experimental manipulation.

Additionally, people in our anonymous control condition (i.e., no eyes control) reported feeling somewhat observed, likely because they were in a lab environment, where there are some cues of observation such as the presence of other participants and the experimenter [59,60]. Although participants in the public condition reported feeling more observed than those in the control and eyes conditions, their scores were close to the midpoint of the scale, which suggests that participants in the public condition didn’t feel particularly observed. Notably, perceptions of observability were not correlated with dictator game allocations (see supplementary material).

A recent meta-analysis found that decisions with consequences—where participants expected their behaviours to influence how others will respond to them within the experimental protocol—produced larger observation effects on economic game allocations than decisions without consequence (rs of 0.25 and 0.12 respectively; [14]). The dictator game decision in this experiment was a decision without consequence, which may have limited the strength of our manipulation. However, studies using similar methodologies in small group sessions (as in this study) have reported eyes effects [20,23]. We also note that the ‘revelation moment’ differed between the eyes condition and public condition. In the eyes condition, reputational cues (eyes) were revealed right before the dictator game decision, whereas in the public condition participants were told more in advance that others would see their decisions, but the decisions were only made known to others after all decisions were made. Although both of these conditions are comparable to our control condition, these methodological differences may alter participants’ response patterns and should be considered when designing future studies.

Moreover, there are methodological similarities between SVO measures and the dictator game, where both measures ask participants to divide resources. In the present experiment, a key difference is that the dictator game is incentivized and continuous, while the SVO task is a series of hypothetical forced-choice scenarios. A conceptual replication with another measure of prosocial (or antisocial) behavior is needed to determine the generalizability of how SVO relates to prosocial behaviors.

Given the limitations outlined above, future research should investigate individual differences in observation and ‘watching eyes’ effects using dependent measures with greater reputational benefits or costs (see [32]). Moreover, future studies could use the SVO slider measure [47], as opposed to the triple-dominance measure employed in the present study. The SVO slider measure is a continuous measure as opposed to categorical, allowing a more precise classification of participants’ level of SVO [47]. However, SVO is a narrow personality construct, which may limit the ability to detect individual differences in reputation-based effects. Future studies could also examine if broader personality constructs, such as HEXACO Honesty-Humility or Agreeableness [58] are associated with differential response to reputation-based cues.

Contributions

This study adds to the literature in several ways. Using established methodology, our aggregate data provide a well-powered attempted replication of the eyes effect (which excludes individual difference data based on SVO). Additionally, our results are suggestive that individual differences may influence how people respond to reputation-based cues. These findings are in the same direction as Simpson and Willer’s (2008; [39]) finding that people who are less prosocial (i.e., SVO egoists) are more likely to calibrate their decisions according to reputation-based cues, whereas SVO prosocials are consistently prosocial. Although our study was underpowered to detect individual differences, our sample size is much larger than the original study [39]. These results can inform future research methodologies; future studies should use observation manipulation with consequences, broader personality variables, and a dependent measure with higher reputational benefits or costs to participants to investigate reputation-based effects.

Compared to vegans, meat consumers experienced both lower depression & anxiety; the more rigorous the study, the more positive and consistent the relation between meat consumption and better mental health

Meat and mental health: A meta-analysis of meat consumption, depression, and anxiety. Urska Dobersek et al. Critical Reviews in Food Science and Nutrition, Oct 6 2021. https://www.tandfonline.com/doi/full/10.1080/10408398.2021.1974336

Abstract: In this meta-analysis, we examined the quantitative relation between meat consumption or avoidance, depression, and anxiety. In June 2020, we searched five online databases for primary studies examining differences in depression and anxiety between meat abstainers and meat consumers that offered a clear (dichotomous) distinction between these groups. Twenty studies met the selection criteria representing 171,802 participants with 157,778 meat consumers and 13,259 meat abstainers. We calculated the magnitude of the effect between meat consumers and meat abstainers with bias correction (Hedges’s g effect size) where higher and positive scores reflect better outcomes for meat consumers. Meat consumption was associated with lower depression (Hedges’s g = 0.216, 95% CI [0.14 to 0.30], p < .001) and lower anxiety (g = 0.17, 95% CI [0.03 to 0.31], p = .02) compared to meat abstention. Compared to vegans, meat consumers experienced both lower depression (g = 0.26, 95% CI [0.01 to 0.51], p = .041) and anxiety (g = 0.15, 95% CI [-0.40 to 0.69], p = .598). Sex did not modify these relations. Study quality explained 58% and 76% of between-studies heterogeneity in depression and anxiety, respectively. The analysis also showed that the more rigorous the study, the more positive and consistent the relation between meat consumption and better mental health. The current body of evidence precludes causal and temporal inferences.

Keywords: anxietydepressionmeatmental healthveganvegetarianismsex

Discussion

This meta-analysis extends the findings of our prior systematic review (Dobersek et al. 2020) by presenting a quantitative evaluation of the relation between meat consumption/abstention and mental health. It included 171,802 participants aged 11 to 105 years, from varied geographic regions, including Europe, Asia, North America, and Oceania. The findings show a significant association between meat consumption/abstention and depression and anxiety. Specifically, individuals who consumed meat had lower average depression and anxiety levels than meat abstainers. We also showed that vegans experienced greater levels of depression than meat consumers. Sex did not modify these relations. Study quality explained a significant proportion of between-studies heterogeneity and a cumulative meta-analysis confirmed these findings. Specifically, the higher the study quality, the more positive the benefit of meat consumption.

Our results may explain the equivocal nature of prior research. In contrast to our clear findings (both past (Dobersek et al. 2020 and present), other systematic reviews and meta-analytic results were inconsistent or contradictory. These equivocal results suggested that vegetarians, and in some cases vegans had lower levels of depression or anxiety (Askari et al. 2020; Iguacel et al. 2020; Lai et al. 2014; Li et al. 2017; Liu et al. 2016; Nucci et al. 2020; Zhang et al. 2017). As detailed in our systematic review (Dobersek et al. 2020), numerous factors explain these inconsistent conclusions. Briefly, most prior studies employed invalid or unreliable assessment protocols to measure exposures and outcomes (i.e., diet and mental health, respectively). For example, it is well established that dietary recalls and FFQs produce physiologically implausible and non-falsifiable (pseudo-scientific) data (Archer, Pavela, and Lavie 2015; Archer, Hand, and Blair 2013; Archer, Lavie, and Hill 2018a; Archer, Marlow, and Lavie 2018b, 2018c). Thus, the disparity between self-reported and actual dietary intake may render definitive conclusions impossible when analyzing meat consumption as a continuous rather than dichotomous variable (Archer, Pavela, and Lavie 2015; Archer, Hand, and Blair 2013; Archer, Lavie, and Hill 2018a; Archer, Marlow, and Lavie 2018b, 2018c).

With respect to mental health, the most rigorous research relied on physician-diagnosed disorders using the Diagnostic and Statistical Manual of Mental Disorders (DSM) (Michalak, Zhang, and Jacobi 2012) (APA 2013) rather than self-reported (subjective) assessments with untested validity. The use of tools with questionable validity can lead to ambiguous findings and limited cross-study analyses.

Another major design error was the use of biased and selective sampling strategies. Several of the included studies recruited samples from vegan and vegetarian websites, social-networking groups, communities, and restaurants. We surmise this may have substantially biased data collection and may skew self-reported variables and findings if participants with a high degree of emotional or ideological commitment to their dietary behaviors intentionally or unconsciously misreport. An antecedent of this error may be a form of confirmation bias in which the flawed sampling confirms the investigators’ ideology or expectations rather than providing dispassionate data and results.

Finally, statistical and communication errors were ubiquitous. These included the failure to correct for multiple comparisons and the inappropriate use of causal language which can lead to invalid results, interpretations, and conclusions. In summary, given that these errors are widespread in the literature, valid conclusions from previous reviews that failed to examine study quality are not possible.

In the present meta-analysis, these errors taken together are related to significant between-studies variation in effect sizes. Study quality explained 58% and 76% of between-studies heterogeneity in the differences in depression and anxiety, respectively. Furthermore, our analyses (see Figures 2, 4, 6, 7, 10, and 11) demonstrated that higher quality studies showed a more positive and consistent relation between meat consumption and mental health. Higher quality studies had much larger sample sizes.

Finally, limited reporting of participant characteristics prevented an examination of several covariates (e.g., BMI, age of diet adoption/length of diet, clinical history, socioeconomic status, culture) that could potentially contribute to between-studies heterogeneity.

Strengths and limitations

Strengths

This meta-analysis had several strengths. First, our a priori decision to select only studies that provided a clear dichotomy between meat consumers and meat abstainers allowed for a clear and rigorous assessment. While myriad studies have examined vegetarianism along a continuum, these were excluded because the lack of a clear distinction between groups rendered inferences equivocal. This distinction is necessary because self-reported (memory-based) dietary assessments (FFQ) should not be used for quantitative analyses because of their invalidity. Any study that attempts to use FFQs as continuous variables are invalid due to nonquantifiable measurement error (Archer, Lavie, and Hill 2018a; Archer, Marlow, and Lavie 2018b; Archer, Pavela, and Lavie 2015).

Second, we limited our psychological outcomes to the most prevalent and debilitative disorders: depression and anxiety. This allowed a focused yet rigorous analysis and ameliorated the effects of poorly operationalized psychological phenomena such as disordered eating, dietary restraint, orthorexia, and neuroticism. This exclusion helps to avoid potential misclassification and concomitant pathologizing of those who simply wish to avoid specific foods or food groups (e.g., vegans). Finally, with over 170,000 participants from several geographic regions, our meta-analysis allowed for more generalizable and definitive conclusions.

Limitations

Our meta-analysis also had limitations. First, we excluded non-English-language studies. This potentially biased our results in favor of ‘Western’ norms which include meat consumption. For example, we excluded papers published in languages other than English (e.g., Japanese, Hindi). Thus, we may have omitted studies from geographic regions that follow predominantly vegetarian or plant-based dietary patterns.

Second, while our search was clearly defined and comprehensive, our inclusion criteria excluded many publications that provided data on this topic (e.g., see (Anderson et al. 2019; Barthels, Meyer, and Pietrowsky 2018; Burkert et al. 2014; Cooper, Wise, and Mann 1985; Jacka et al. 2012; Larsson et al. 2002; Li et al. 2019; Northstone, Joinson, and Emmett 2018)). Specifically, these papers were excluded because they examined constructs other than depression or anxiety (e.g., orthorexia, restrained eating behavior) or assessed meat consumption as a continuous rather than dichotomous variable. As previously stated, self-reported dietary status and FFQs lead to nonquantifiable measurement error. Nevertheless, we think that our rigorous and highly focused meta-analysis has the potential to provide stronger evidence for the medical, research, and lay communities.

Third, despite the high confidence we place in our finding that meat abstention is linked to a greater prevalence of psychological disorders, study designs precluded inferences of temporality and causality. Specifically, only two of the included studies (Lavallee et al. 2019; Velten et al. 2018) provided information on temporality. Therefore, we were unable to conclusively examine this effect. Given that there are many reasons why people abstain from meat (e.g., ethical, environmental, animal rights-related reasons), this empirical question has not been adequately addressed. However, our previous systematic review (Dobersek et al. 2020) showed conflicting evidence on the temporal relations between meat abstention and depression and anxiety. Also, conclusions on causality require evidence from rigorous RCTs. Since only one low-quality RCT met our inclusion criteria (Beezhold and Johnston 2012), no conclusions regarding causality are supported.

Finally, the results of our meta-analysis are only as valid as the data collected in the included primary studies. Given that most studies used FFQs and self-reported questionnaires, participants may have been misclassified. Merely reporting that one avoids meat is not the equivalent of actual meat abstention (Archer, Pavela, and Lavie 2015; Archer, Hand, and Blair 2013; Archer, Lavie, and Hill 2018a; Archer, Marlow, and Lavie 2018b, 2018c). In fact, self-defined vegetarians and meat abstainers may consume meat (Haddad and Tanzman 2003).

Recommendations for future directions

Future investigators should avoid the most common flaws exhibited in the included studies. First, investigators must acknowledge and address the effects of both researcher and participant biases (e.g., confirmation bias, cognitive dissonance, observer-expectancy effects/reactivity) when employing highly selective or biased samples. Individuals who are highly invested in their dietary behaviors may be predisposed to intentional and non-intentional misreporting.

Second, the use of physician-diagnosed disorders based on criteria from the DSM-V (APA 2013; Michalak, Zhang, and Jacobi 2012) is preferable to self-reported symptoms, and assists in producing more definitive results. Additionally, the severe limitations and pseudo-scientific nature of self-reported dietary data and FFQs (Archer, Pavela, and Lavie 2015; Archer, Hand, and Blair 2013; Archer, Lavie, and Hill 2018a; Archer, Marlow, and Lavie 2018b, 2018c) could be overcome in part with point-of-purchase (barcode) data (Ng and Popkin 2012). However, while these data may be less biased, they are not necessarily an accurate proxy for actual dietary consumption.

Third, the use of more rigorous study designs (e.g., RCTs) is desirable over mere observational investigations. However, it would be extremely difficult to conduct a randomized study of diets with a long enough duration to impact fundamental affective outcomes such as anxiety and depression. Furthermore, detailed participant information regarding behavioral and health-related histories and current lifestyles is essential to valid interpretation and conclusions. Finally, studies should provide complete statistical information that allow for the calculations of effect sizes. More complete reporting would enable meta-analysts to extract both effect measures and study characteristics thus allowing for exploration of potentially important but unanswered questions (e.g., how is time of diet adoption related to mental health?).

Heterozygosity of the major histocompatibility complex predicts later self-reported pubertal maturation in men, suggesting a genetic trade-off between immunocompetence and sexual maturation in human males

Heterozygosity of the major histocompatibility complex predicts later self-reported pubertal maturation in men. Steven Arnocky, Carolyn Hodges-Simeon, Adam C. Davis, Riley Desmarais, Anna Greenshields, Robert Liwski, Ellen E. Quillen, Rodrigo Cardenas, S. Marc Breedlove & David Puts. Scientific Reports volume 11, Article number: 19862. Oct 6 2021. https://www.nature.com/articles/s41598-021-99334-5

Abstract: Individual variation in the age of pubertal onset is linked to physical and mental health, yet the factors underlying this variation are poorly understood. Life history theory predicts that individuals at higher risk of mortality due to extrinsic causes such as infectious disease should sexually mature and reproduce earlier, whereas those at lower risk can delay puberty and continue to invest resources in somatic growth. We examined relationships between a genetic predictor of infectious disease resistance, heterozygosity of the major histocompatibility complex (MHC), referred to as the human leukocyte antigen (HLA) gene in humans, and self-reported pubertal timing. In a combined sample of men from Canada (n = 137) and the United States (n = 43), MHC heterozygosity predicted later self-reported pubertal development. These findings suggest a genetic trade-off between immunocompetence and sexual maturation in human males.

Discussion

Our results support the prediction that greater MHC heterozygosity, a genetic contributor to pathogen resistance33,34, predicts later pubertal timing. In a combined data set derived from two independent samples, MHC heterozygosity predicted relative, but not absolute, recalled puberty. Because males lack a salient, singular pubertal event like menarche, when considering retrospective reports relative pubertal timing may be more accurate because men may be better able to recall whether they matured earlier or later than their peers rather than the precise ages of pubertal events48,49.

Correlations between immunocompetence and pubertal timing could reflect the linked heritability of both traits, common developmental underpinnings50, or pleiotropic effects of MHC genes, which could influence both immunocompetence and sexual maturation. Indeed, some research has shown that MHC class II expression occurs alongside maturation of the adrenal cortex51. Interestingly, dehydroepiandrosterone (DHEA), which is produced by the adrenal cortex and affects aspects of reproductive development, has been implicated in immune function in humans and other species52,53.

LHT offers a framework to explain why immunocompetence and pubertal timing may be related at a functional level: Individuals with reduced extrinsic mortality risk due to lower vulnerability to pathogens may be able to continue growth and delay sexual maturation and reproduction. If so, then selection should favor mechanisms, potentially including pleiotropy and genetic linkage, that couple immunocompetence and the timing of sexual maturation. This possibility aligns with some research on intra-species differences in LH. For example, Tasmanian devil populations affected by an infectious facial tumor disease had a 16-fold higher chance of reaching sexual maturity at an earlier age than usual26. In a study of 22 small-scale human societies, populations with higher extrinsic mortality risk displayed earlier puberty and reproduction—as well as shorter adult height and life expectancy5.

Future work must reconcile research showing opposing patterns, such as among perinatal HIV infection and slower pubertal maturation54. Perhaps the distinction lies in genetic versus acquired factors affecting immunocompetence, or environmental factors (e.g., food energy availability of safety/survival rates), which might also influence luteinizing hormone (LH) release in diverse human populations55. For example, malnutrition has been linked to delayed pubertal maturation in humans44. Accordingly, future research should consider the role of energy availability in the environment as a potentially important moderator of the potential link between MHC and pubertal development. For instance, perhaps the influence of infectious burden on energy availability may be lower in populations with energy abundance and substantial health infrastructure, such as in Western industrialized nations.

Our findings also help explain why MHC heterozygous men have been found to be taller in adulthood56. Height is driven by long bone growth via chondrogenesis at the growth plate57, and epiphyseal fusion at puberty terminates growth. Later pubertal maturation allows more long bone growth before epiphyseal fusion, resulting in taller adult height18; therefore, heterozygous individuals may be taller because they begin puberty later. Future research could test whether pubertal timing mediates the relationship between MHC heterozygosity and adult height. It may be useful to examine the potential moderating role of early stressors in the environment to the MHC-pubertal timing link. From this perspective, developmental plasticity gives rise to an array of phenotypes that emerge in response to specific local social and ecological conditions58. These genetic variants are putatively adaptive insofar as they contribute to greater fitness in the environments in which they manifest. Accordingly, an interaction between HLA homozygosity and early life stressors may be a stronger predictor of pubertal timing than either variable alone.

Within the context of LHT, some researchers have predicted that greater investment in immunocompetence should correspond with later sexual maturation. Although previous research linking early pubertal maturation to a diverse range of health problems supports this notion, this is the first research to demonstrate a correlation between MHC heterozygosity and later recalled pubertal development. Such a link has important implications for understanding the development of puberty-linked physical and mental health outcomes. These results suggest that variation in genetic influences on pubertal timing may reflect a trade-off between somatic growth and maintenance and reproduction, at least in energy-rich environments. However, within the broader context of well-established positive links between environmental condition and earlier (rather than later) pubertal timing, these findings imply that understanding variability in reproductive effort will likely rely upon examining more complex interactions between genetics and local ecological condition.