Previous research has found that women at peak fertility show greater interest in extra-pair sex; however, recent replications have failed to detect this effect

Current Fertility Status Does Not Predict Sociosexual Attitudes and Desires in Normally Ovulating Women. Andrew G. Thomas.  Evolutionary Psychology,January 8, 2021. https://doi.org/10.1177/1474704920976318

Abstract: Previous research has found that women at peak fertility show greater interest in extra-pair sex. However, recent replications have failed to detect this effect. In this study, we add to this ongoing debate by testing whether sociosexuality (the willingness to have sex in the absence of commitment) is higher in women who are at peak fertility. A sample of normally ovulating women (N = 773) completed a measure of sociosexuality and had their current fertility status estimated using the backward counting method. Contrary to our hypothesis, current fertility was unrelated to sociosexual attitudes and desires, even when relationship status was included as a moderator. These findings raise further doubts about the association between fertility and desire for extra-pair sex.

Keywords: ovulatory shift hypothesis, sociosexuality, menstrual cycle, mate preferences, extra-pair mating

Discussion

The purpose of this study was to test the idea, derived from the ovulatory shift and dual-mating hypotheses (Gangestad & Thornhill, 1998; Penton-Voak et al., 1999), that women’s mating strategies change in accordance with fluctuations in fertility across the menstrual cycle. To do so we used a between-subjects sample of normally ovulating women to examine whether current fertility status could predict sociosexual desires and attitudes. Our hypothesis was not supported. No relationship was found between fertility status and attitude or desire subscales of the SOI-R. In fact, the β observed in the regression predicting sociosexual desire was in the opposite direction to that predicted (β = −.04). Exploratory analyses showed that the null effect of fertility persisted when relationship status was added to the models as a moderator. We did find that older women reported higher numbers of past partners and acts of uncommitted sex, but only if they were currently high in fertility. We did not predict this weak association and see no theoretical reason for it. Given that this effect also disappeared when covariates were added to the model (see Footnote 1) we are inclined to believe this to be a Type I error.

It is possible that the null results obtained in this study are due to the methodological issues outlined previously. The ‘gold standard’ in menstrual cycle research is to use within-subjects designs and to establish fertility status using hormonal measurements (Gangestad et al., 2016). Our study, in contrast, used a between-subjects design with self-reported cycle data and non-verified bleed-dates. Nonetheless, there are several reasons to be confident that our results are not due to a Type II error.

First, the sample size is large and surpasses the minimum requirement set out by both Gangestad et al. (2016) and Jones et al. (2019) for a sufficiently-powered between-subjects study. Second, as recommended by Gangestad et al. (2016), fertility status was not determined using high and low fertility windows, but instead measured along a continuous scale of conception risk (Wilcox et al., 2001). Finally, we employed a backwards-counting method to determine day of cycle. Due to the large degree of variability in the follicular phase compared to the comparatively consistent length of the luteal phase (Fehring et al., 2006), the backwards-counting method is the most reliable way to obtain self-report menstrual cycle data.

The results of this study converge with other recent well-powered between-subject investigations into the ovulatory-shift hypothesis (Dixson et al., 2018; Marcinkowska et al., 2018b) and within-subjects studies using hormonal measures (Jünger et al., 2018; Marcinkowska et al., 2018a). However, it should be noted that some studies suggest that fertility-related shifts in mating psychology depend on relationship status and on factors within a relationship, such as the attractiveness of one’s current partner (Haselton & Gangestad, 2006; Pillsworth & Haselton, 2006). We did not have data about perceived partner attractiveness for partnered women in our dataset, but we were able to include their relationship status in our models. Doing so did not qualitatively alter the role of fertility status. It is worth noting, however, that this exploratory analysis was underpowered. A full understanding of this moderation effect would have required us to examine sub-groups of single and pair-bonded women, effectively halving the sample. The two studies that report an effect of partner attractiveness were also both underpowered (see the calculations of Gangestad et al., 2016; Jones et al. (2019). Therefore, future research should investigate the role of relationship moderators on fertility effects in sufficiently large samples to test these hypotheses adequately.

Further consideration should be given to the role of sociosexuality in acquiring extra-pair partners. There is an established relationship between sociosexuality and infidelity (Barta & Kiene, 2005). Thus, it is reasonable to expect that waxing interest in casual sex would facilitate acts of extra-pair infidelity and that this may form part of an ovulatory shift mechanism that functions to shift mating effort away from a primary partner and toward another. However extra-pair liaisons are not exclusively casual and may involve feelings of love and commitment, such as in cases of mate-switching (Buss et al., 2017). To the extent that uncommitted sex is not a strict prerequisite for extra-pair relationships, we cannot rule out the possibility of dual-mating mechanisms in humans based solely on an absence of relationship between within-cycle fertility and SO. Potential future research could consider forgoing sociosexuality for more implicit indicators of relationship commitment, including motivated biases favoring one’s partner (e.g., positive partner illusions) or derogating alternatives (Finkel et al., 2017).

In sum, these null results raise further doubts about the hypothesized association between fertility and desire for extra-pair sex, and more specifically the role of sociosexuality as a potential moderator of this process. Should extra-pair desire change across the menstrual cycle, then this may be context specific and/or facultative. Such changes may be difficult to detect at a general group level, emphasizing the importance of well-powered within-subject designs that both use hormonal verification to reduce measurement error and take relationship context and motivation into account.

Transgender Identity Is Associated With Bullying Involvement Among Finnish Adolescents: Both as victims and as perpetrators

Transgender Identity Is Associated With Bullying Involvement Among Finnish Adolescents. Elias Heino et al. Front. Psychol., January 8 2021. https://doi.org/10.3389/fpsyg.2020.612424

Abstract

Background: During adolescence, bullying often has a sexual content. Involvement in bullying as a bully, victim or both has been associated with a range of negative health outcomes. Transgender youth appear to face elevated rates of bullying in comparison to their mainstream peers. However, the involvement of transgender youth as perpetrators of bullying remains unclear in the recent literature.

Objective: The aim of this study was to compare involvement in bullying between transgender and mainstream youth and among middle and late adolescents in a general population sample.

Methods: Our study included 139,829 students in total, divided between a comprehensive school and an upper secondary education sample. Associations between gender identity and involvement in bullying were first studied using cross-tabulations with chi-square statistics. Logistic regression was used to study multivariate associations. Gender identity was used as the independent variable, with cisgender as the reference category. Subjection to and perpetration of bullying were entered each in turn as the dependent variable. Demographic factors, family characteristics, internalizing symptoms, externalizing behaviors, and involvement in bullying in the other role were added as confounding factors. Odds ratios (OR) with 95% confidence intervals (95% CI) are given. The limit for statistical significance was set at p < 0.001.

Results: Both experiences of being bullied and perpetrating bullying were more commonly reported by transgender youth than by cisgender youth. Among transgender youth, all involvement in bullying was more commonly reported by non-binary youth than those identifying with the opposite sex. Logistic regression revealed that non-binary identity was most strongly associated with involvement in bullying, followed by opposite sex identity and cisgender identity. Transgender identities were also more strongly associated with perpetration of bullying than subjection to bullying.

Conclusion: Transgender identity, especially non-binary identity, is associated with both being bullied and perpetrating bullying even when a range of variables including internal stress and involvement in bullying in the opposite role are taken into account. This suggests that bullying during adolescence may serve as a mechanism of maintaining heteronormativity.

Discussion

In this study we analyzed the association of gender minority identity with involvement in bullying among a large population-based sample of adolescents. We analyzed whether the association of gender identity and involvement in bullying differed among opposite sex and non-binary identifying youth or among middle and late adolescents.

We firstly found that in our large, nationally representative sample, being bullied was generally associated with transgender identity, and with non-binary identity in particular. This finding is in line with the existing literature, which indicates that experiences of being bullied are more common among gender minority than mainstream youth (Day et al., 2018; Eisenberg et al., 2019; Johns et al., 2019; Bishop et al., 2020). Various factors could explain this disparity. Transgender youth may differ from their peers in that their behavior or appearance deviates from traditional feminine and masculine roles. This could partly explain elevated rates of being bullied as bullying is often targeted at those perceived to deviate from the mainstream (Jones et al., 2018; Price-Feeney et al., 2018). More specifically, relating to sexual orientation and gender identity, bullying sexual and gender minorities could also stem from heterosexism, which refers to efforts to maintain traditional masculine and feminine roles in society (Chesir-Teran, 2003; Toomey et al., 2012). On the other hand, internal stress, as described in gender minority stress and resilience theory (Hendricks and Testa, 2012; Testa et al., 2015), could result in constant vigilance and anticipation of being victimized through the development of hostile or depressive attribution bias thus predisposing transgender youth to detect victimization by their peers where none was actually intended.

Secondly, we found that transgender identity was generally associated with perpetrating bullying and that the association was stronger than that of transgender identity and being bullied. To the best of our knowledge, past research has not examined perpetration of bullying among gender minority youth, thus rendering comparisons to prior research impossible. In a study by Dank et al. (2014), however, it was reported that the few transgender young people in their study were the ones most likely to perpetrate dating violence among their sample.

Such aggressive behavior could arise from being victimized or having witnessed victimization of other gender or sexual minorities (Eisenberg et al., 2016), as a coping mechanism or avenue through which one could release negative feelings.

On the other hand, adolescence in general is a mentally challenging time (Paus et al., 2008) during which adolescents struggle with a series of developmental tasks such as forming peer relations and coming to grips with their sexuality (Havighurst, 1948; Seiffge-Krenke and Gelhaar, 2008). The added complexity due to the emergence and further development of transgender identity could cause extra stress for adolescents. In this context, perpetrating bullying could be seen as sign of acting out, perhaps due to transgender adolescents’ own unresolved developmental issues.

Thirdly, non-binary identity was more strongly associated with involvement in bullying than opposite sex identity. Past research has found elevated rates of being subjected to bullying among youth (Lowry et al., 2020; van Beusekom et al., 2020) and transgender youth (Gower et al., 2018) who perceive themselves as more gender non-conforming (i.e., masculine females or feminine males) than youth with no such perception. Non-binary identifying youth particularly may display gender expression that does not conform to either masculine or feminine roles, and this may make them vulnerable to being bullied either due to simply being different from the mainstream, or as a result of heterosexist control. We found, however, that not only being bullied but also engaging in bullying was even more common among non-binary (perception of gender conforms to both or neither sex or it varies) than among opposite sex identifying youth.

It may be that the process of gender identity formation is a more complex process among non-binary youth than those young people identifying with the opposite sex. Such differences could stem from the nature of non-binary identity itself, as perceived gender may fluctuate, or align with both or neither traditional gender roles. This could delay the achievement of so-called transgender identity milestones, or factors associated with the formation of transgender identity, such as first living in the gender role felt within (Wilkinson et al., 2018) as young people struggle with their still unresolved gender identity. This internal turmoil due to uncertainty about one’s own identity, could, for example, impede the formation of peer relationships, a key part of adolescent development (Laursen and Hartl, 2013). This could exacerbate internal stress and predispose non-binary youth to mental health symptoms such as depression, which are known to relate to involvement in bullying (Kaltiala-Heino and Fröjd, 2011).

Finally, regarding age differences, the existing literature shows that as adolescents mature and progress toward adulthood, involvement in bullying decreases (Boulton and Underwood, 1992; Liang et al., 2007; Coulter et al., 2018). In line with this, involvement in bullying in our data was reported less commonly by the older adolescents in the upper secondary education sample across all gender identities. The association between opposite sex identification and being bullied also leveled out when confounding was controlled for in both samples. However, regardless of lower reported prevalence, the association between non-binary identity and perpetration of bullying was stronger among the older than among the younger adolescents in our study. It might be that those adolescents who still remain involved in bullying at an older age represent adolescents with the most developmental challenges. This finding could be seen to lend support to the notion that among transgender youth the possibly more complex nature of non-binary identity (in comparison to opposite sex identifying or cisgender youth) is indeed related to additional developmental challenges.

Additionally, while involvement in bullying was less prevalent among the older students of our study, the correlation between being bullied and being a bully grew stronger. This is likewise in agreement with the assumption that when involvement in bullying becomes less common as age increases, those who remain involved likely represent adolescents with the most developmental challenges. Being both a bully and a victim (bully-victim) is known to correlate with greatest amount of mental health problems and developmental difficulties (Forero et al., 1999).

Strengths and Weaknesses of the Present Study

Our study has several strengths. Our large sample was an unselected, population-based sample representative of Finnish middle and late adolescents. This enhances the generalizability of our results.

There are indications even between European countries of variation in transgender youth’s peer relationships and psychological functioning (de Graaf et al., 2018; van der Star et al., 2018). One could speculate that such differences are even greater between European and North American adolescents. As most research on gender identity and involvement in bullying originates in the United States, we feel our study in a Northern European setting is a useful addition to the existing literature on the important subject of involvement in bullying and transgender identity.

We controlled in our analyses for a wide range of confounding factors closely related to involvement in bullying and gender minority identity. This allowed us to examine more closely the relationship between transgender identity and involvement in bullying. This is a strength of our study.

As has been recommended (Reisner et al., 2014; Eisenberg et al., 2017), we identified transgender youth with two separate questions located far apart from each other in the study questionnaire (“two-step method”). Due to the large sample size, we were additionally able to separate opposite sex identifying youth from non-binary youth, rather than grouping all transgender youth as one in our analyses.

Involvement in bullying was elicited using questions derived from WHO’s Youth Study (King et al., 1996). The WHO questions have since then been used in numerous studies across countries (for review see Kaltiala-Heino and Fröjd, 2011) which makes data elicited with them comparable with earlier research. This is a strength of our study.

Our study also has several weaknesses. In spite of our large sample, the number of transgender youth reporting perpetrating bullying was on the smaller side, although we still feel we reached adequate cell sizes for statistical validity.

In the present study, a secondary data was used. The data was not planned nor collected by us, and we were therefore unable to influence the way certain topics of interest were elicited. As a result, the way experiences of bullying were elicited in the study questionnaire made it impossible to distinguish between different types of bullying behavior in which adolescents had been involved, such as traditional school bullying or cyberbullying, or physical and verbal bullying and exclusion.

Additionally, whether respondents were living in their desired gender roles was not elicited in the questionnaire. This inhibited additional comparisons regarding involvement in bullying among those who conceal their gender identity vs. those who do not. The GMSR theory suggests concealment of one’s experienced gender identity (for example not living in the desired gender role) is a stressor that could possibly negatively affect mental health of gender minority people. One could thus speculate that living in the desired gender role could in fact reduce mental health symptoms such as depression, thus decreasing bullying involvement, a behavior associated with mental health issues. On the other hand, living in the desired gender role could manifest as behavior or appearance deviating from traditional masculine and feminine roles (such as natal girls using boys’ restrooms or natal boys having a more feminine appearance) thus predisposing youths to bullying, a behavior commonly directed to those who deviate from the mainstream. Lastly, as the study was a cross-sectional one, caution must be exercised when interpreting the results as causality cannot be determined from such data.

The Stock Market as a Casino: Associations Between Costly Excessive Stock Market Trading and Problem Gambling

Mosenhauer, Moritz, Philip W. S. Newall, and Lukasz Walasek. 2021. “The Stock Market as a Casino: Associations Between Costly Excessive Stock Market Trading and Problem Gambling.” PsyArXiv. January 8. doi:10.31234/osf.io/zqe9s

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347401853458329600

Abstract: The stock market should be a unique kind of casino, where the average person wins money over time. However, previous research shows that excessive stock market trading can contribute to financial losses --- just like in any other casino. While gambling research has documented the adverse consequences of problem gambling, there has been comparatively less behavioral finance research on the correlates of excessive stock market trading. This study aimed to document whether excessive stock trading was positively associated with problem gambling, and whether this hypothesized association was robust to controlling for demographics, and objective measures of overconfidence and financial literacy in a convenience sample of 798 US investors. We found that self-reported relative stock portfolio turnover was positively associated with problem gambling, that this association was robust to controls, and occurred equally over investors of all self-reported portfolio sizes. This study showed that problem gamblers may also make suboptimal risky choices more generally, and that a behavioral dependence explanation for suboptimal investment decisions should be subject to further investigation in the behavioral finance literature.

The Psychology, Geography, and Architecture of Horror: How Places Creep Us Out

The Psychology, Geography, and Architecture of Horror: How Places Creep Us Out. Francis T. McAndrew. Evolutionary Studies in Imaginative Culture, Vol. 4, No. 2 (Fall 2020), pp. 47-62 (15 pages). https://www.jstor.org/stable/10.26613/esic.4.2.189

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347223531902431239

Abstract: Why do some types of settings and some combinations of sensory information induce a sense of dread in humans? This article brings empirical evidence from psychological research to bear on the experience of horror, and explains why the tried-and-true horror devices intuitively employed by writers and filmmakers work so well. Natural selection has favored individuals who gravitated toward environments containing the “right” physical and psychological features and avoided those which posed a threat. Places that contain a bad mix of these features induce unpleasant feelings of dread and fear, and therefore have become important ingredients of the settings for horror fiction and films. This article applies McAndrew and Koehnke's (2016) theory of creepiness to the study of classic horror settings and explores the role played by architecture, isolation, association with death, and other environmental qualities in the experience of creepiness and dread.

Keywords: horror, architecture, ghosts, haunted houses, paranormal experiences, environmental psychology, evolutionary psychology

We are Programmed to Respond Emotionally to Our Physical Surroundings

It is well established that the environmental preferences of animals are under genetic control (Alcock 1993), and to some extent this appears to be true for humans as well. Research by environmental psychologists has confirmed that the most attractive natural environments contain things such as running water and open meadows surrounded by woods, the very features that would have been beneficial for the survival of early humans (Kaplan 1987). In other words, people who were drawn to the “right” places did better than those who were not, and over time their genes were favored over those of individuals who spent too much time in sparser, more barren landscapes.

But places exhibit more abstract evolutionarily relevant features as well, and it turns out that being drawn to the “right” abstract features of places may have been just as important for our ancestors’ survival. McAndrew (1993) has referred to such environmental features as psychological features, and places that lack the right psychological features set off our creep detectors.

British geographer Jay Appleton (1975) was the first to describe two qualities of physical space that determine whether a place is attractive or frightening to humans: “Prospect” and “Refuge.” Refuge means having a secure, protected place to hide where one can be sheltered from danger, while prospect refers to one’s clear, unobstructed view of the landscape. Attractive places offer us a lot of prospect and a lot of refuge, or what landscape architect Randolph Hester (1979) refers to as a “Womb with a View.”  

Our love of such spaces shows up everywhere. Universally, children love playing in enclosed spaces such as cardboard boxes, tree houses, and in bushes or other dense vegetation where they feel hidden; the concepts of prospect and refuge may help explain the almost magical quality of the feelings evoked by memories of favorite childhood hiding places and the richness of detail that can often be recalled about them decades later. Similarly, diners in restaurants usually prefer to occupy tables in corners or nooks, especially when these locations allow them to sit with their backs against a wall, and they will usually only settle for tables in the center of the room when all of the more desirable seats have been taken (McAndrew 1993).

In the words of Appleton, we love the feel of these spaces because they are, evolutionarily speaking, places where “you can see without being seen, and eat without being eaten” (Greenbie, 1982, 2).

The optimal environment for human comfort is one that offers a lot of prospect and refuge for the individual; the worst combination is very little prospect or refuge for the individual. Research has confirmed that places that offer bad combinations of prospect and refuge for us are perceived as unsafe and dangerous (Fisher and Nasar 1992), also because they may offer a lot of hiding places for people or things that may intend to do us harm.

Scary places may also lack what environmental psychologists refer to as “legibility.” Legibility reflects the ease with which a place can be recognized, organized into a pattern and recalled—in other words, a place that we can wander around in without getting lost (McAndrew 1993).

More legible places are usually preferred over less legible ones, but if we feel assured that a place is not dangerous, a dose of illegibility can actually enhance the attractiveness of a place to us; this property has been referred to as “Mystery.” Mystery implies that the place contains more information than can be seen at the moment, and that one could learn much about it by walking through it and exploring. The strategic use of mystery has been used to great effect by landscape architects in settings such as Japanese gardens (Eliovson 1978). Many studies have confirmed that people do in fact perceive mystery as a distinct quality of landscapes and that a sense of mystery can increase the attractiveness of natural environments (Kaplan and Kaplan 1989). However, when a heightened sense of mystery is accompanied by a sense of potential danger, as it is in deep narrow canyons, dark urban alleys, and houses thought to be haunted, mystery decreases the attractiveness of the place (Herzog 1987; Herzog and Smith 1988).

It is not only the psychological features of places that can make them good settings for horror. Physical features that posed a threat to our ancestors can easily become creepy, even if they have other qualities that make them beneficial to us; water is a perfect example of an indispensable and usually attractive element of a natural setting that is frequently associated with horror. Rivers, lakes, and ponds often provide the setting for horror stories about ghosts. This makes sense in that deep water has always posed a hazard to humans and drowning is a common cause of human death, both accidental and intentional. It is therefore not very surprising to find that bodies of water are frequently linked with paranormal experiences, as in the stories of haunted highways, ponds, wells, ships, and bridges detailed by Davies (2007) and Nickell (2012).

The kinds of places described above can evoke feelings of fear, horror, and being creeped out. It may be useful to think of these three related emotions as different stages of the same experience. Getting creeped out is an unpleasant state of heightened vigilance in which we grapple with ambiguity in our immediate situation. We are not sure if there is an actual danger or threat to be wary of, but the lack of clarity focuses our attention as we deal with the felt urgency of resolving the ambiguity so that we know how to proceed. Horror, on the other hand, is the growing awareness that we are indeed facing some sort of danger, although we may not yet exactly understand the nature of the threat or how best to deal with it. Fear is the clearest of the three emotions. It occurs when we clearly recognize the nature of the danger that we face and we concoct a strategy for dealing with it.

Throughout this paper, the focus will remain firmly fixed on the frightening, negative experience of horror, but it must be acknowledged that under some circumstances creepiness and horror can be seductive (Clasen, 2017), as evidenced by the sums of money we spend each year on horror movies and commercial haunted houses. Clearly, for many people, the creepy can have a peculiar “allure.”

How could such things possibly be entertaining to us?

I propose that our enjoyment of haunted houses and horror movies taps into the same evolved psychological mechanisms that exist to help us learn from the experiences of others (De Backer, Nelissen, Vyncke, Braeckman and McAndrew 2007). In the safety of a movie theater or amusement park, watching other individuals deal with serial killers, zombies, or other paranormal threats gives us the chance to mentally rehearse strategies that we might use if we would ever find ourselves in a similar situation (Clasen, Kjeldgaard-Christiansen and Johnson 2018). 

So yes, horror can be fun if it is not the real thing. Having said this, the rest of this article will concern itself with the less fun stuff.

Women: Of factors like sexual orientation/shame/pride/assertiveness/& attitudes (permissiveness, birth control &c), and endorsement of traditional gender roles & of the double standard, assertiveness better predicts more orgasms

The Big “O”: Sociocultural Influences on Orgasm Frequency and Sexual Satisfaction in Women. Anna Maree Lentz & Yuliana Zaikman. Sexuality & Culture, Jan 6 2021. https://rd.springer.com/article/10.1007/s12119-020-09811-8

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347070227088089090

Abstract: Previous research revealed a gap in orgasm frequency between men and women, with women orgasming less frequently than men. Because female orgasms are rooted partially in psychological origins, this gap may be partly explained by sociocultural factors. Utilizing sexual satisfaction as an outcome measure and orgasm frequency as a mediator, we surveyed 1043 women about a multitude of factors to determine the relationship between sociocultural factors, orgasm frequency and sexual satisfaction. Because women may orgasm in different frequencies depending on context, we measured four different orgasm variables: orgasm with self (masturbation), orgasm with a familiar partner, orgasm with a new partner, and multiple orgasm frequency. Factors such as sexual orientation, sexual shame, sexual pride, sexual assertiveness, sexual attitudes (related to permissiveness, birth control and communion), endorsement of traditional gender roles, and endorsement of the sexual double standard were correlated with female orgasm frequency within different contexts. The only orgasm variable that predicted sexual satisfaction was orgasm with a familiar partner, indicating that not all orgasms can predict sexual satisfaction. Overall, sexual assertiveness was the variable that positively correlated with and predicted orgasm frequency in almost all contexts as well as sexual satisfaction. This indicates that socializing women to be more sexually assertive could potentially lead to more frequent orgasms and greater sexual satisfaction. The findings of this study can be used to bridge the orgasm gap between men and women, and in general help women in curating better and more positive sexual encounters.

Drosophila brain: The systems that mediate the pleasure component of reward in mammals, including those involving the endogenous opioid & endocannabinoid systems, are unlikely to be present in insects

Drosophila reward system - A summary of current knowledge. Jiri Dvoracek, Dalibor KodrIk. Neuroscience & Biobehavioral Reviews, January 6 2021. https://doi.org/10.1016/j.neubiorev.2020.12.032

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347063544802635778

Highlights

• Drosophila has a very well-developed brain enabling the associative learning.

• Reward functions of Drosophila represent a complex network system.

• Drosophila has activity-enhancing systems associated with wanting component of reward.

• Hedonic component of reward system is unlikely to be present in Drosophila.

Abstract: The fruit fly Drosophila melanogaster brain is the most extensively investigated model of a reward system in insects. Drosophila can discriminate between rewarding and punishing environmental stimuli and consequently undergo associative learning. Functional models, especially those modelling mushroom bodies, are constantly being developed using newly discovered information, adding to the complexity of creating a simple model of the reward system. This review aims to clarify whether its reward system also includes a hedonic component. Neurochemical systems that mediate the ´wanting´ component of reward in the Drosophila brain are well documented, however, the systems that mediate the pleasure component of reward in mammals, including those involving the endogenous opioid and endocannabinoid systems, are unlikely to be present in insects. The mushroom body components exhibit differential developmental age and different functional processes. We propose a hypothetical hierarchy of the levels of reinforcement processing in response to particular stimuli, and the parallel processes that take place concurrently. The possible presence of activity-silencing and meta-satiety inducing levels in Drosophila should be further investigated.

Keywords: Reward systemDopamineEndogenous opioidsMushroom bodyDrosophila

Comparison of the Hadza hunter-gatherers & non-human primates: The sexual division of labour likely co-evolved with increased sex differences in spatial behaviour and landscape use

Gendered movement ecology and landscape use in Hadza hunter-gatherers. Brian M. Wood, Jacob A. Harris, David A. Raichlen, Herman Pontzer, Katherine Sayre, Amelia Sancilio, Colette Berbesque, Alyssa N. Crittenden, Audax Mabulla, Richard McElreath, Elizabeth Cashdan & James Holland Jones. Nature Human Behaviour, Jan 4 2021. https://www.nature.com/articles/s41562-020-01002-7

Abstract: Understanding how gendered economic roles structure space use is critical to evolutionary models of foraging behaviour, social organization and cognition. Here, we examine hunter-gatherer spatial behaviour on a very large scale, using GPS devices worn by Hadza foragers to record 2,078 person-days of movement. Theory in movement ecology suggests that the density and mobility of targeted foods should predict spatial behaviour and that strong gender differences should arise in a hunter-gatherer context. As predicted, we find that men walked further per day, explored more land, followed more sinuous paths and were more likely to be alone. These data are consistent with the ecology of male- and female-targeted foods and suggest that male landscape use is more navigationally challenging in this hunter-gatherer context. Comparisons of Hadza space use with space use data available for non-human primates suggest that the sexual division of labour likely co-evolved with increased sex differences in spatial behaviour and landscape use.

Discussion

Our study demonstrates that substantial gender differences in spatial behaviour were present across the life course in this hunter-gatherer society. Among the Hadza, men travelled further, visited more areas of the landscape, followed more sinuous routes and were more solitary while foraging. These patterns are consistent with the gendered ecology of hunting and gathering, in which men search for rarer, more energy-dense and more mobile resources than women23,26,27,46. These metrics of spatial behaviour also suggest that male-typical travel is more navigationally challenging. An earlier study3 showed that Hadza men scored higher on average than Hadza women in measures of spatial cognition and performance, a result that is consistent with the gender difference in spatial behaviour seen here. Gender differences in Hadza spatial behaviour emerge early; by the age of 6 years, boys are travelling slightly further on a daily basis (Cohen’s d = 0.1, 95% CI = 0.02–0.18; Supplementary Table 5). This means that the developmental environments that boys and girls experience are spatially distinct from an early age, and they continue to be so across the life course. It is important to note the following limitation of this study: as with most studies of gender differences, there is no way for our study to disentangle whether gender differences in spatial cognition or performance emerge solely from differences in developmental environments or are also impacted by innate physiological differences. Future work that examines changes in Hadza spatial behaviour and cognition in those areas where the traditional hunting and gathering economy has declined may provide useful insights into the consequences of different developmental environments.

The emergence of a gender difference in Hadza spatial behaviour around 6 years of age is broadly similar in timing to meta-analysis results7 showing that gender differences in spatial cognition emerge in the years 7–14 in Western samples. A study of children in the UK reported that gender differences in both exploratory behaviour and spatial cognition are detectable in the age range of 6 to 11 years47.

The Hadza’s highly mobile lifestyle is readily apparent in our data. Adult Hadza women walked an average of 7.6 km per day and logged 10,888 steps, while men walked 12.9 km and logged 18,476 steps. For comparison, a GPS study in Pretoria, South Africa48 found that urban women and men walked much less (2.9 and 3.9 km per day, respectively). Mbendjele women in the Republic of Congo, who practise a mixed farming and foraging lifestyle, also appear to have walked less than Hadza women (median of 4.35 km per day), but the Mbendjele study18 differed from ours in recording only travel out of camp, for 5.2 hours per day on average, while our study records all travel, for an average of 11.49 hours per day. Hadza women’s step counts were about twice as high as average smartphone-using subjects enrolled in a 111-nation study45, and Hadza men’s about three times higher than men in this global sample from middle- and high-income countries. Other rural, non-industrial societies may walk even more than the Hadza: a study of an Old Order Amish49 community in Ontario, Canada reported that adult women and men logged 14,196 and 18,425 steps per day, respectively.

It is interesting that we did not find clear statistical evidence that young children limited how far their mothers walked each day. Perhaps because Hadza plant foods are so abundant, there was little foraging incentive for a woman without young children to travel faster or further than another woman in her party carrying a small child. It seems equally plausible that women with small children are incentivized to keep up with the group. A recent study among the Twe of Namibia also found no difference in daily distances travelled between nursing and non-nursing reproductively aged women19. A limitation of this study is that subadults were not sampled as frequently as adults, for reasons discussed in Methods. In a future study, we hope to examine more fully the coupled patterns of movement by women and their children.

A limitation of our study is that we identified two features of socioecology that are likely to limit Hadza women’s travel relative to men’s: the fact that plant foods are immobile and found in much greater abundance than men’s foods, and the fact that women appear more fearful of encountering Datoga pastoralists while foraging out of camp. Our sense, based on many years of ethnographic research, is that the Datoga threat is kept in check by armed Hadza men and older boys who accompany parties of foraging women, and that the gender differences in spatial behaviour we identify here are by and large owing to the foraging ecology. A future study that examines movement patterns in areas with more or less Datoga presence should shed light on this issue.

The strong gender differences in space use observed here have implications for disease ecology and health measures. Our data show that men travelled more expansively (Fig. 3, Table 1 and Fig. 5), so one could reasonably assume that they were exposed to more diverse pathogens. Men are also more likely to be exposed to zoonotic pathogens because of interacting with and butchering animals. Sex differences in host immune responses are reported for many species, including humans50. Spatial data like those presented here should factor into causal modelling of such differences.

As evolutionary anthropologists, we are compelled to ask how these data can inform reconstructions of the past. Patterns of behaviour observed in diverse samples of contemporary hunter-gatherers are more likely to have been a part of our species’ evolutionary history than are patterns of daily life observed among university students or citizens of rich nation-states, who today make up most research subjects in social science51. The broad gender differences in spatial behaviour that we observed among the Hadza are likely to have been a regular feature of hunter-gatherer societies in the past and to also be present today where gendered foraging persists. Cross-cultural analyses show that hunting is a male-typical activity, and that when women do hunt, they tend to focus on smaller and less mobile prey46,52,53. The male hunting specialization is not a function of contemporary gender roles per se, as it is also consistent with signs of lower limb morphology and wear seen in prehistoric skeletal samples54. Interestingly, among non-human primates that occasionally hunt vertebrates, including chimpanzees, baboons and capuchins, males hunt more frequently than females55,56,57.

Over the last 2.5 million years, diets in the genus Homo shifted to include more hunting and pursuit of mobile foods53,55,56,58. These shifts undoubtedly increased home range sizes and are likely to have increased sex differences in spatial behaviour. Among living apes, sex differences in ranging are comparatively modest and reflect sex differences in reproductive ecology and territory defence. Male orangutans maintain larger home ranges than females despite similar diets, as males apparently seek increased access to females59. In chimpanzees, males travel an average of ~20% farther than females each day (3.6 versus 3.0 km per day), reflecting males’ larger foraging group sizes and territory defence60. Mountain gorilla males, whether solitary or in groups, have similar daily travel distances to females61. Studies of non-human primate ranging using GPS devices are rare, but GPS data from a recent study of olive baboons62 show little to no evidence for a sex difference. By contrast, the day ranges of Hazda men are 14.3 km per day at age 25 years and are 62% higher than those of Hazda women (Supplementary Table 3). An increase in gender-differentiated foraging over the last 2.5 million years may have increased sex differences in spatial cognition. More studies of spatial behaviour and cognition among non-human primates—especially apes—would be very helpful for constructing maximally plausible models of hominin cognitive evolution. At present, this interspecies analysis is limited to only a few studies in which precise spatial measures have been collected.

Our study has demonstrated a high degree of gender segregation in Hadza landscape use. It is worth remembering that this segregation out of camp is bookended with intense sociality and co-operation in camp among all co-residents24. Like other hunter-gatherer societies, the Hadza practise central place foraging, which anchors people’s movements to a camp and socially embeds them into a co-operative network of neighbours. Over evolutionary time, central place foraging and language would have fundamentally changed our genus’s spatial strategies. Among much else, it would have permitted early humans to form much vaster and dynamic mental models of landscapes by incorporating others’ spatial knowledge and their own experiences. It is routine for Hadza to exchange information at the end of the day, detailing their daily travels and experiences, and men and women often relay to one another any promising signs of plant or animal life they encounter. These derived features of human sociality mean that our spatial strategies are likely to differ strongly from those of other primates, above and beyond the role played by gender-differentiated foraging.

Research in movement ecology is examining space use with sophisticated methods and theory from diverse fields18,62,63,64,65,66, and these tools are increasingly being used to examine human behaviour. Such studies, carried out across diverse cultural contexts, will allow researchers to identify regular features of human spatial behaviour and shed light on spatial adaptations to varying climatic, economic and epidemiological conditions.