Sunday, January 9, 2022

Chess Girls Don’t Cry: Male players are substantially quicker to quit when dominated by a female than by a male; in contrast, female players’ behaviour differs little as a function of the gender of the opponent

Chess Girls Don’t Cry: Gender Composition of Games and Effort in Competitions among the Super-Elite. Maryam Dilmaghani. Journal of Economic Psychology, January 8 2022, 102482. https://doi.org/10.1016/j.joep.2022.102482

Highlights

• Using a sample of super-elite chess games, the paper examines whether the gender composition of games affects effort level.

• Male players are substantially quicker to quit when dominated by a female than by a male.

• In contrast, female players’ behaviour differs little as a function of the gender of the opponent.

Abstract: The deterministic nature of chess makes the outcome strongly predictable, especially among the elite. As a result, instead of ending in a checkmate or a forced tie, elite chess games end either in the resignation of the player in a losing position or a mutually agreed upon draw. Traits such as competitiveness, over-confidence, and risk tolerance, all more prevalent among males, likely prolong the games. In contrast, susceptibility to intimidation and stereotype threat, more relevant to females, likely accelerate the completion of games. Using a recent sample of super-elite chess games, the present paper shows that males are substantially quicker to quit when dominated by a female than by a male. In contrast, female players’ behaviour differs little as a function of the gender of opponents. The results are interpreted through the “mere effort” impact of stereotype threat and the self-handicapping concept.

Keywords: GenderChessCompetitivenessEffortStereotype threatSelf-handicapping

JEL J16Z20


Relationship-defining memories are a boon to marital happiness (marital satisfaction, intimacy, well-being, quality, etc.)

The relationship between the reminiscence of relationship-defining memories and marital outcomes: A systematic review and meta-analysis. Mohammad Reza Majzoobi, Simon Forstmeier. Journal of Family Theory & Review, January 7 2022, https://doi.org/10.1111/jftr.12442

Abstract: The current systematic review aimed to explore the interdependence of relationship-defining memories (RDMs) with positive and negative marital outcomes in order to gain a deeper insight into the nature, content, and the reminiscence of RDMs, as well as the role they may serve in the marital relationship. The studies included in the current systematic review had addressed RDMs and their impact on marital outcomes among healthy people above the age of 18 who are in a romantic relationship. After checking the studies found in our search through the scientific databases against the eligibility criteria, 16 studies were included in the systematic review, of which 14 were found to be eligible for a meta-analysis. The results of the meta-analysis indicated a relatively moderate and high correlation of RDMs with marital outcomes (r = .334) and marital satisfaction (r = .445), respectively. The review of included studies revealed that there is an inextricable link between RDMs and significant marital outcomes such as marital satisfaction, intimacy, well-being, quality, and suchlike.

DISCUSSION AND CONCLUSIONS

The present systematic review aimed to explore the interrelationship between RDMs and marital outcomes. The review of the included studies suggested that RDMs do appear to represent an effective way to predict marital outcomes. The meta-analysis of the studies scrutinized the relationship between RDMs and marital outcomes and yielded a moderate overall effect size (r = .334). The effect size for the relationship between RDMs and marital satisfaction was high (r = .445). On the other hand, the studies that had examined the impact of interior effective factors of RDMs on marital outcomes, implicitly or explicitly, indicated that there is an association between the reminiscence of RDMs and the increase of positive marital outcomes or the decrease of negative ones.

REASONS FOR THE ASSOSIATION BETWEEN RDMs AND MARITAL OUTCOMES

How RDMs are associated with positive marital outcomes has been interpreted through a diversity of approaches, such as the social bond, self-expansion, self-determining, sense-making, and self-regulation, each of which outlines some substantial explanation as to which of the change mechanisms of RDMs seems likely to be the best.

Social bond model

Drawing on ecological theories, some researchers believe that the reminiscence of RDMs may be effective because of their social function, based on which the reminiscence of RDMs leads to the development of a kind of social bond essential for the survival of the species. These researchers assume that the reminiscence of RDMs helps couples experience disclosure process and positive emotions, which in turn may lead to the increase of their marital intimacy (Alea & Bluck, 2007; Alea & Vick, 2010).

Self-expansion model

Drawing on the Aron and Aron self-expansion model (1997, as cited in Bazzini et al., 2007), another group of researchers suggested that the reason why the reminiscence of RDMs contributes to the increase of marital closeness may be that the rememberers and their partners share some overlapping viewpoints with one another, which in turn intensify the sense of connectedness between them. The other reason could be that the reminiscence of RDMs drives couples to review and reevaluate the various events of their marital life more rigorously, which then provides an opportunity for them to response to and validate each other through understanding and acceptance of one another's perspectives. Put in other words, recalling their joint RDMs, running gags, nicknames, and life experiences, couples attain a secret language that amplify their relational bond (ziv, 1997, as cited in Bazzini et al., 2007).

Self-determination theory

Another prominent approach regarding the impact of reminiscence of RDMs on marital outcomes is self-determination theory, which states that people try to satisfy three needs in their life: the need for autonomy, competence, and relatedness (Deci & Ryan, 2000). It seems likely that recalling the need-satisfying RDMs could scaffold couples' attitudes pertinent to their marital relationship and bring them to perceive their marital relationship as a need-satisfying one, which in turn leads them to experience higher rates of marital satisfaction and commitment (Guilbault & Philippe, 2017). Philippe et al. (2013) stated that the satisfaction of need in one of the spouses bring not only him or her, but also his or her partner to feel positive consequences, so that the satisfaction of needs in couples' RDMs leads the rememberers to behave in an intimate and open manner toward their partners, which in turn caused their partners to perceive more marital quality. Philippe et al. also concluded that aside from their directive function (the impact of RDMs on rememeberers and their partners' cognitions, emotions, and behaviors), RDMs appear to have a self-function (the impact of marital relationship on RDMs). That is, just as it is reasonable to assume that the quality of recalling RDMs determines the quality of couple's relationship, so too is it reasonable to suppose that couples with high level of perceived marital quality are likely to recall more satisfactory and positive RDMs. In fact, there is a reciprocal relationship between RDMs and marital outcomes that can serve to send the two on an upward or downward spiral together.

Sense-making model

In addition to positive RDMs, negative ones are likely to result in positive outcomes in couples as well, so that the recalling of RDMs may probably develop or facilitate the sense-making process regarding negative and stressful life experiences. In the course of sense-making, which is a communicational process, couples come to a new organization and understanding of their marital experiences and issues, which may then lead to the improvement of their marital well-being. As factors like involvement (the extent of engagement and interest of the parties), turn-taking (the balance between parties in terms of the share they have in the conversation), perspective-taking (the amount of verbal and non-verbal attention each person pay to his/her partner's point of view and approval or disapproval of it), and coherence (the ability of individuals to organize and integrate the narrative) increase in the reminiscence of RDMs by couples, so does the ability to find meaning and consequently the level of well-being of their relationship (Koenig Kellas et al., 2010). According to the cognitive change theory, sense-making during the reminiscence of RDMs causes some cognitive changes that help couples gain a deep insight into what has happened, which in turn leads them to put distress behind them (Frattaroli, 2006).

Self-regulation model

Self-regulation theory states that recalling RDMs regarding past difficulties provides couples with the opportunity to engage in a mastery experience, in which they find themselves expressing and controlling their emotions, which in turn results in experiencing a stronger sense of self-efficacy in emotional regulation (Frattaroli, 2006). In addition, Osgarby and Halford (2013) believed that reviewing of RDMs, even if it contributes to sadness, still has therapeutic properties, mainly because this kind of sadness, according to emotionally focused couple therapy, appears to be a vulnerable primary emotion that has its roots in the couple's attachment needs and serves a crucial role in an effective treatment. Reminiscence therapy and reviewing a couple's history can be a useful manner to elicit the mentioned primary emotions that many emotionally focused therapists seek to evoke in the treatment process (Pinquart & Forstmeier, 2012).

LIMITATIONS AND DIRECTIONS FOR FURTHER RESEARCH

In concluding the discussion about the studies included in this systematic review, it should be noted that the studies considered the quantity and quality of RDMs along with psychological and demographic characteristics of rememberers. The inclusion of studies with various designs, a comprehensive age range, as well as statistical populations consisting of both men and women enabled us to present an exhaustive description concerning the field of inquiry. However, none of the included studies considered the individual's reminiscence styles and their association with marital outcomes. The included studies do not specify whether people have a particular style of reminiscing of RDMs or whether they prefer to reminisce a specific kind of RDMs. Watt and Wong (1991 as cited in Amani et al., 2019) introduced five reminiscence styles including integrative, instrumental, transmissive, narrative, escapist, and obsessive, of which the first three styles seem to be useful and constructive, and the next two styles appear to be harmful and destructive. To our knowledge, there are no studies in which the relationship between the mentioned five styles of reminiscence and marital outcome is considered. This seems to be the biggest gap in the area of inquiry. Therefore, it is suggested that researcher take advantage of the five aforementioned reminiscence styles to draw conclusions on how couples' reminiscence styles may predict their marital outcome. For instance, will couples who are used to reminisce their RDMs in an obsessive style have the same marital outcomes as couples who reminisce their marital memories in an integrative or narrative style? Future studies filling the aforementioned gap may make a worthwhile contribution to the field of RDMs.

On the other hand, one of the major limitations of the studies included in this systematic review is that their subjects were predominantly couples with above-average marital quality. None of the studies, except for one (viz., Osgarby & Halford, 2013), provided information related to couples with low levels of marital satisfaction and how they process their RDMs. In addition, the included studies only examined heterosexual couples, and the resultant findings were based on samples from Western societies such as the United States, Canada, and Australia. Hence, caution should be exercised when attempting to generalize the findings to homosexual couples and couples from societies not belonging to the Western cultural context. Moreover, although RDMs were assessed using highly precise methods like coding in most studies, only self-assessment questionnaires were used to measure marital outcomes.

To address these shortcomings, reminiscence styles in couples with high and low rates of marital satisfaction should be assessed through creating a number of measures. At the same time, it is also necessary to study the relationship between RDMs and marital outcomes in couples with sexual orientations other than heterosexual, and to study the mentioned relationship in non-Western societies in order to provide a truly exhaustive picture of this relationship. It is suggested as well that researchers take advantages of interviews as well as questionnaires to measure the extent of marital outcomes in their future studies in order to obtain more robust findings.

Despite such gaps, recalling RDMs remains a field with great potential for becoming a major wave approach in couple therapy. As Gottman (1999) argues, if couples share many pleasant memories of their marital relationship, this could be a sign that couples are still experiencing high marital satisfaction, and the therapist can take advantages of this information to highlight the strengths of their relationship. On the other hand, although the couple's history as told by the couple may contain issues that have brought them to treatment, this approach does remain beneficial, because the therapists can draw their attention to the positive memories they have shared with each other and apply them to achieve therapeutic goals.

The Origins and Psychology of Human Cooperation: The authors synthesize experimental and observational evidence from studies of children and adults from diverse societies with research among nonhuman primates

The Origins and Psychology of Human Cooperation. Joseph Henrich and Michael Muthukrishna. Annual Review of Psychology, Volume 72, 2021, pp 207-240. https://doi.org/10.1146/annurev-psych-081920-042106

Abstract: Humans are an ultrasocial species. This sociality, however, cannot be fully explained by the canonical approaches found in evolutionary biology, psychology, or economics. Understanding our unique social psychology requires accounting not only for the breadth and intensity of human cooperation but also for the variation found across societies, over history, and among behavioral domains. Here, we introduce an expanded evolutionary approach that considers how genetic and cultural evolution, and their interaction, may have shaped both the reliably developing features of our minds and the well-documented differences in cultural psychologies around the globe. We review the major evolutionary mechanisms that have been proposed to explain human cooperation, including kinship, reciprocity, reputation, signaling, and punishment; we discuss key culture–gene coevolutionary hypotheses, such as those surrounding self-domestication and norm psychology; and we consider the role of religions and marriage systems. Empirically, we synthesize experimental and observational evidence from studies of children and adults from diverse societies with research among nonhuman primates.

Keywords: cooperation, ultrasociality, evolutionary psychology, cultural evolution, culture-gene coevolution, social behavior


Saturday, January 8, 2022

Most White respondents felt safe, but most Black respondents lived in fear of the police killing them & hurting their family members; approximately half of Black respondents preferred to be robbed or burglarized than to have unprovoked contact with officers

The American racial divide in fear of the police. Justin T. Pickett, Amanda Graham, Francis T. Cullen. Criminology, January 8 2022. https://doi.org/10.1111/1745-9125.12298

Abstract: The mission of policing is “to protect and serve,” but recent events suggest that many Americans, and especially Black Americans, do not feel protected from the police. Understanding police-related fear is important because it may impact civilians’ health, daily lives, and policy attitudes. To examine the prevalence, sources, and consequences of both personal and altruistic fear of the police, we surveyed a nationwide sample (N = 1,150), which included comparable numbers of Black (N = 517) and White (N = 492) respondents. Most White respondents felt safe, but most Black respondents lived in fear of the police killing them and hurting their family members. Approximately half of Black respondents preferred to be robbed or burglarized than to have unprovoked contact with officers. The racial divide in fear was mediated by past experiences with police mistreatment. In turn, fear mediated the effects of race and past mistreatment on support for defunding the police and intentions to have “the talk” with family youths about the need to distrust and avoid officers. The deep American racial divide in police-related fear represents a racially disparate health crisis and a primary obstacle to law enforcement's capacity to serve all communities equitably.


The evolution of extraordinary self-sacrifice

The evolution of extraordinary self-sacrifice. D. B. Krupp & Wes Maciejewski. Scientific Reports volume 12, Article number: 90. Jan 7 2022. https://www.nature.com/articles/s41598-021-04192-w

Abstract: From a theoretical perspective, individuals are expected to sacrifice their welfare only when the benefits outweigh the costs. In nature, however, the costs of altruism and spite can be extreme, as in cases of irreversible sterility and self-destructive weaponry. Here we show that “extraordinary” self-sacrifice—in which actors pay costs that exceed the benefits they give or the costs they impose on recipients—can evolve in structured populations, where social actions bring secondary benefits to neighboring kin. When given information about dispersal, sedentary actors evolve extraordinary altruism towards dispersing kin. Likewise, when given information about dispersal and kinship, sedentary actors evolve extraordinary spite towards sedentary nonkin. Our results can thus be summed up by a simple rule: extraordinary self-sacrifice evolves when the actor’s neighbors are close kin and the recipient’s neighbors are not.

Discussion

We find that individuals can evolve to value others’ fitness more than their own. Specifically, selection favors extraordinary altruism when sedentary actors interact with dispersing kin (Fig. 3f,l), and it favors extraordinary spite when sedentary actors interact with sedentary nonkin (Fig. 3o). Because extraordinary self-sacrifice entails C>|B|, the sum of the effects on the actor and recipient is always negative (BC<0), leading overall to a secondary decrease in competition that can benefit kin. Under limited dispersal, the actor’s neighboring kin benefit secondarily when the actor remains on the natal island. Likewise, the actor’s neighboring kin benefit secondarily from spite when the recipient remains on the actor’s natal island. Finally, in the case of altruism, it is nonkin that pay the price when the recipient arrives on their island. Taken together, we arrive at a simple rule: extraordinary self-sacrifice evolves when an actor’s neighbors are close kin and the recipient’s neighbors are not.

The effects of dispersal and kinship among actors, recipients, and neighbors also become apparent when we consider the conditions of our model that fail to favor the evolution of extraordinary self-sacrifice, even when dispersal is limited (d0) and neighborhood consanguinity is high (q1). First, extraordinary self-sacrifice in general does not evolve with a dispersing actor (Fig. 3b,d,e,h–k), because, by dispersing to a new island, the actor gives the secondary benefit of its sacrifice (in the form of reduced competition) to neighbors who are not kin and who therefore bear rival alleles. Second, extraordinary altruism does not evolve with a recipient that is not kin (Fig. 3i,k,m), because this provides a primary benefit to a recipient bearing a rival allele. Third, extraordinary altruism does not evolve with a sedentary recipient (Fig. 3a,c,e,g,j,k,n), because, by remaining on the natal island, the recipient imposes a secondary cost (in the form of increased competition) on neighbors who are the actor’s kin and who therefore bear copies of the focal allele. Fourth, extraordinary spite does not evolve with a recipient that is likely or known to be kin (Fig. 3a–e,g,h,j,n), because this imposes a primary cost on a recipient bearing a copy of the focal allele. Finally, extraordinary spite does not evolve with a dispersing recipient (Fig. 3d,h,i,m), for the same reason that it does not evolve with a dispersing actor: because, by dispersing to a new island, the recipient gives the secondary benefit of the spiteful action (in the form of reduced competition) to neighbors who are not the actor’s kin and who therefore bear rival alleles.

We are aware of two other models that report conditions under which extraordinary self-sacrifice can evolve. The first, by Krupp and Taylor23, was briefly discussed above. It also used an inclusive fitness approach set in an island structure, wherein actors could use a signal matching mechanism to distinguish between “native” individuals, whose parents were born on the focal island, and “migrant” individuals, whose parents were born elsewhere. Although actors had no information about dispersal status in their model, dispersal was generally assumed to be rare (d0), causing native actors to be close kin with their neighbors and causing both actors and recipients to be sedentary. Given the close parallels between these conditions and our own (represented in Fig. 3o), it is no surprise that they found that extraordinary spite can evolve among native actors interacting with migrant recipients. Our model extends their analysis, separating the effects of actor and recipient dispersal and making them explicit.

The second model, by McAvoy et al.33, used a game theoretic approach set in a heterogeneous social network of N individuals, each of whom plays either a “producer” strategy that pays a cost to give a benefit or a “non-producer” strategy that pays no cost and gives no benefit. (Because their approach differs significantly from our own, we have changed their notation and description to better correspond to ours.) One set of games entailed proportional benefits but fixed costs (“pf goods”), wherein a new benefit is given to each connected recipient without additional cost to the actor. Thus, if actor i is connnected to ni recipients, then in games with pf goods, i pays ci>0 only once to give a benefit bi>0 to each of the ni recipients. McAvoy et al. found that ci>bi can evolve in games with pf goods when there are more connections among individuals in the network than there are individuals themselves. However, this implies that C<B, because the net benefit B=bini grows with the number of connections whereas the net cost C=ci does not. Consequently, these results do not meet the definition of extraordinary self-sacrifice.

Another set of games in the McAvoy et al. model entailed fixed benefits and fixed costs (“ff goods”), wherein the benefit is divided equally among all connected recipients. Thus, in games with ff goods, the actor pays ci only once to give a benefit bi/ni to each of the ni recipients. McAvoy et al. found that ci>bi can evolve in games with ff goods within “rich-club” networks consisting of a central group of m individuals who are connected to each other as well as to a peripheral group of l individuals who are connected only to the members of the central group. Under these circumstances, the producer strategy works well for the central group but poorly for the peripheral group; nevertheless, the peripheral group evolves to play the producer strategy. We suspect, however, that this exploitative state of affairs is maintained by a peculiarity of the updating mechanisms of the model, which require individuals to imitate the strategy of better-performing connections, even if it is to their detriment. By playing the producer strategy, the central group causes the peripheral group to play the producer strategy as well: central producers have higher payoffs than peripheral non-producers, so peripheral non-producers must update their strategy to produce—despite the fact that it leaves them worse off—because they are connected strictly to better-performing central producers. As the authors show, the central group benefits greatly from this arrangement, particularly as the size of the peripheral group increases, while the peripheral group suffers losses. On the one hand, this implies that C<B for the central group, because the initial cost ci of the producer strategy to central individuals is more than repaid by the benefits bil/m it receives in return for causing peripheral individuals to produce as well; that is, the net cost C=cibil/m to a central producer is negative, meaning that it is actually a benefit. On the other hand, this also implies that C>B for the peripheral group, because the net cost to a peripheral producer is C=ci and the net benefit it gives is B=bi. Thus, production at the periphery would seem to meet the definition of extraordinary self-sacrifice. We wonder, then, if selection would still favor extraordinary self-sacrifice under these conditions if individuals were not powerless to play the strategy that worked best for them, irrespective of the strategy played by their connections.

Hamilton4 initially proposed that limited dispersal (in the form of “viscous” populations) would foster the evolution of altruism, because it would give kin the opportunity to interact. Conversely, he suggested that spite would most likely evolve in “dwindling panmictic species”5. With the benefit of hindsight, however, we can see that both claims are in need of refinement. From an inclusive fitness perspective, a cost to the actor must be compensated by a benefit to kin, being either the recipient or a neighbor. But limited dispersal also puts these parties in competition with one another, turning altruistic benefits to the former into costs to the latter9,11,13,34. As we find here, however, the dilemma of limited dispersal is resolved if the recipient—but not the actor or neighboring kin—can be expected to disperse after the interaction, providing a primary benefit to a consanguineous recipient and imposing a secondary cost on nonkin elsewhere (much as predicted by [9]). Indeed, the high degree of kinship that limited dispersal brings to a neighborhood is essential to the evolution of extraordinary altruism.

Likewise, spite profits not from panmixia but from population structure, because the primary costs to both the actor and the recipient are returned as secondary benefits to the actor’s neighboring kin. However, since limited dispersal increases the chances that individuals interact with kin, actors cannot simply be spiteful to anyone3. Rather, actors should discriminate along genealogical lines and, although they may not be strictly necessary, kin recognition mechanisms can be helpful in this regard.

Our model makes use of learned kin recognition systems, which are widespread in nature35,36,37,38,39. To the extent that kin recognition can operate via other routes, however, our results are not limited to organisms capable of cognition. While there are known theoretical obstacles to the evolution of genetic kin recognition40,41, for example, systems such as this have been identified and characterized in several species (e.g.42,43,44). Indeed, allorecognition is common, predates multicellularity, and has independently evolved numerous times45.

Notably, our study departs from previous theoretical work on the evolution of self-sacrifice under dispersal and kinship, largely because we ask not only whether individuals might discriminate as a function of kinship but also as a function of both actor and recipient dispersal (see also [22]). Plausibly, sedentary and dispersing types can evolve different degrees of self-interest, such that sedentary individuals generally give more than their dispersing counterparts. This should occur when the actions of sedentary individuals are systematically “funnelled” towards dispersing individuals as a function of organismal physiology or species ecology. In some cases, actors may even cause recipients to develop a dispersing phenotype—for example, by influencing caste determination46.

However, our findings also suggest the possibility that, alongside mechanisms of kin recognition, species may have evolved adaptations to estimate the spatial scale of competition47,48,49, such as mechanisms of dispersal recognition. That is, organisms might identify cues of their probability of future competition with social partners or neighboring kin and discriminate accordingly. Certainly, the eusocial insects already provide ample evidence that sedentary and dispersing individuals behave differently. For example, workers of most such species act altruistically (or, in some cases, spitefully) and are sedentary whereas reproductives act selfishly and disperse to found new colonies19. Yet, it is unclear whether some mechanism of competition estimation is the cause of such differences. If so, we might expect that individuals can predict the probability of partner dispersal by cues of future dispersal status, such as by chemical signal (e.g.50), location within the colony, presence of wings, or body size.

Though this is a knottier problem than we can address here, our results also suggest that aspects of multicellular and colony evolution, such as the division of labor between cell lines and self/nonself discrimination, are a consequence of dispersal patterns and their attendant secondary effects. Sedentary cells may sacrifice themselves to assist dispersing cells in reproducing elsewhere, as can be seen in the social amoeba Dictyostelium discoideum which, when starved, aggregates with kin to form a sterile stalk and a reproductive fruiting body51. Interestingly, individuals that starve earlier are more likely than those that starve later to become spores52. This presents the possibility that signals produced by early starvers to aggregate are attended to because they predict that these same individuals will disperse and compete elsewhere—signals that may be kept honest by virtue of the fact that starvation itself imposes pressure to disperse to find new food sources.

Moreover, sedentary individuals may serve as soldiers or enforcers, ensuring the integrity of the body or colony. For instance, the ascidian Botryllus schlosseri operates under limited dispersal, fusing with kin to create a colony with a shared vasculature53. However, when individuals encounter nonkin, they produce an immune response that causes damage at the interaction site42,54 which, arguably, is a spiteful response to a foreign competitor. Likewise, clones of the polyembryonic parasitoid wasp Copidosoma floridanum develop into two distinct castes: soldiers and reproductives. Soldiers grow quickly, spitefully attacking unrelated competitors with specialized mandibles and dying in the host body, whereas reproductives grow more slowly, eventually dispersing to parasitize new hosts55,56.

Of course, extraordinary self-sacrifice may evolve more or less easily in the wild than our model suggests. For instance, beyond the assumptions that actors use information about kinship and dispersal, we also assumed diminishing returns of the actor’s behavior, which can make the evolution of extraordinary self-sacrifice more difficult than might some other kinds of cost-benefit relationship. While there are many cases of social systems with diminishing returns32, it is possible that some interactions yield linear or even accelerating returns, improving the conditions for extraordinary self-sacrifice. Likewise, whether social goods entail proportional or fixed costs and benefits33 may also affect the ease with which extraordinary self-sacrifice evolves.

Even if each of the assumptions made here is met, other factors (such as sexual reproduction) may reduce consanguinity within the neighborhood, working against the evolution of extraordinary self-sacrifice. More generally, extraordinary self-sacrifice may cause significant but rare evolutionary events. This is because the conditions required to support it are themselves likely to be rare, as evidenced by the many scenarios of our model (represented in Fig. 3a–e,g–k,m,n) in which extraordinary self-sacrifice is not evolutionarily stable. Thus, while our model has been productive in demonstrating when and where extraordinary self-sacrifice might arise, further work establishing its prevalence, both theoretical and empirical, is certainly needed. In particular, complementary approaches, such as direct fitness and evolutionary game theoretic methods, may reveal further insights and applications.