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 Human NatureJournal Prestige (SJR): 1.092 Citation Impact (citeScore): 2Number of Followers: 20      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1936-4776 - ISSN (Online) 1045-6767 Published by Springer-Verlag  [2348 journals]
• Evidence for the Adaptive Learning Function of Work and Work-Themed Play
among Aka Forager and Ngandu Farmer Children from the Congo Basin
• Authors: Sheina Lew-Levy; Adam H. Boyette
Pages: 157 - 185
Abstract: Work-themed play may allow children to learn complex skills, and ethno-typical and gender-typical behaviors. Thus, play may have made important contributions to the evolution of childhood through the development of embodied capital. Using data from Aka foragers and Ngandu farmer children from the Central African Republic, we ask whether children perform ethno- and gender-typical play and work activities, and whether play prepares children for complex work. Focal follows of 50 Aka and 48 Ngandu children were conducted with the aim of recording children’s participation in 12 categories of work and work-themed play. Using these data, we test a set of hypotheses regarding how age, gender, ethnicity, and task complexity influence children’s activities. As hypothesized, we find performance of work-themed play is negatively correlated with age. Contrary to our hypothesis, children do not play more than they work at complex tasks, but they work more than they play at simple ones. Gender and ethnicity are associated with play and work at culturally salient activities, despite availability of other-gender and other-ethnicity social partners. Our findings show that ethnic and gender biases are apparent in the play and work behavior of Aka and Ngandu children. Moreover, our results show that play helps both forager and farmer children learn complex skills, consistent with play having an adaptive learning function.
PubDate: 2018-06-01
DOI: 10.1007/s12110-018-9314-6
Issue No: Vol. 29, No. 2 (2018)

• Tandem Androgenic and Psychological Shifts in Male Reproductive Effort

• Authors: Daniel P. Longman; Michele K. Surbey; Jay T. Stock; Jonathan C. K. Wells
Abstract: Male-male competition is involved in inter- and intrasexual selection, with both endocrine and psychological factors presumably contributing to reproductive success in human males. We examined relationships among men’s naturally occurring testosterone, their self-perceived mate value (SPMV), self-esteem, sociosexuality, and expected likelihood of approaching attractive women versus situations leading to child involvement. We then monitored changes in these measures in male rowers (N = 38) from Cambridge, UK, following a manipulated “win” or “loss” as a result of an indoor rowing contest. Baseline results revealed that men with heightened testosterone and SPMV values typically had greater inclinations toward engaging in casual sexual relationships and a higher likelihood of approaching attractive women in a hypothetical social situation. As anticipated, both testosterone and SPMV increased following a manipulated “victory” and were associated with heightened sociosexuality, and increased expectations toward approaching attractive women versus individuals who would involve them in interacting with children after the race. SPMV and self-esteem appeared to mediate some of the effects of testosterone on post-race values. These findings are considered in the broader context of individual trade-offs between mating and parental effort and a model of the concurrent and dynamic androgenic and psychological influences contributing to male reproductive effort and success.
PubDate: 2018-08-09
DOI: 10.1007/s12110-018-9323-5

• Coalitional Play Fighting and the Evolution of Coalitional Intergroup
Aggression
• Authors: Michelle Scalise Sugiyama; Marcela Mendoza; Frances White; Lawrence Sugiyama
Abstract: Dyadic play fighting occurs in many species, but only humans are known to engage in coalitional play fighting. Dyadic play fighting is hypothesized to build motor skills involved in actual dyadic fighting; thus, coalitional play fighting may build skills involved in actual coalitional fighting, operationalized as forager lethal raiding. If human psychology includes a motivational component that encourages engagement in this type of play, evidence of this play in forager societies is necessary to determine that it is not an artifact of agricultural or industrial conditions. We examine whether coalitional play fighting appears in the hunter-gatherer record and includes motor skills used in lethal raiding. Using the ethnographic record, we generated a list of motor patterns regularly used in forager warfare. Then, using Murdock’s Ethnographic Atlas, we identified 100 culture clusters containing forager societies and searched the ethnographic records of these societies for descriptions of coalitional play fighting, operationalized as contact games played in teams. Resulting games were coded for the presence of eight motor patterns regularly used in forager lethal raiding. Although play does not tend to be systematically documented in the hunter-gatherer literature, sufficiently detailed descriptions of coalitional play were found for 46 of the 100 culture clusters: all 46 exhibited coalitional play using at least one of the predicted motor patterns; 39 exhibited coalitional play using four or more of the eight predicted motor patterns. These results provide evidence that coalitional play fighting (a) occurs across a diverse range of hunter-gatherer cultures and habitats, (b) regularly recruits motor patterns used in lethal raiding, and (c) is not an artifact of agricultural or industrial life. This is a first step in a new line of research on whether human male psychology includes motivations to engage in play that develops the deployment of coordinated coalitional action involving key motor patterns used in lethal raiding.
PubDate: 2018-06-29
DOI: 10.1007/s12110-018-9319-1

• May God Guide Our Guns
• Authors: Jeremy Pollack; Colin Holbrook; Daniel M. T. Fessler; Adam Maxwell Sparks; James G. Zerbe
Abstract: The perceived support of supernatural agents has been historically, ethnographically, and theoretically linked with confidence in engaging in violent intergroup conflict. However, scant experimental investigations of such links have been reported to date, and the extant evidence derives largely from indirect laboratory methods of limited ecological validity. Here, we experimentally tested the hypothesis that perceived supernatural aid would heighten inclinations toward coalitional aggression using a realistic simulated coalitional combat paradigm: competitive team paintball. In a between-subjects design, US paintball players recruited for the study were experimentally primed with thoughts of supernatural support using a guided visualization exercise analogous to prayer, or with a control visualization of a nature scene. The participants then competed in a team paintball battle game modeled after “Capture the Flag.” Immediately before and after the battle, participants completed surveys assessing confidence in their coalitional and personal battle performance. Participants assessed their coalition’s prospects of victory and performance more positively after visualizing supernatural aid. Participants primed with supernatural support also reported inflated assessments of their own performance. Importantly, however, covarying increases in assessments of their overall coalition’s performance accounted for the latter effect. This study provided support for the hypothesis that perceived supernatural support can heighten both prospective confidence in coalitional victory and retrospective confidence in the combat performance of one’s team, while highlighting the role of competitive play in evoking the coalitional psychology of intergroup conflict. These results accord with and extend convergent prior findings derived from laboratory paradigms far removed from the experience of combat. Accordingly, the field study approach utilized here shows promise as a method for investigating coalitional battle dynamics in a realistic, experientially immersive manner.
PubDate: 2018-06-18
DOI: 10.1007/s12110-018-9320-8

• Toward a Natural History of Team Sports
• Authors: Kevin M. Kniffin; Michelle Scalise Sugiyama
PubDate: 2018-06-16
DOI: 10.1007/s12110-018-9322-6

• Coalitional Physical Competition
• Authors: Timothy S. McHale; Wai-chi Chee; Ka-chun Chan; David T. Zava; Peter B. Gray
Abstract: A large body of research links testosterone and cortisol to male-male competition. Yet, little work has explored acute steroid hormone responses to coalitional, physical competition during middle childhood. Here, we investigate testosterone, dehydroepiandrosterone (DHEA), androstenedione, and cortisol release among ethnically Chinese boys in Hong Kong (N = 102), aged 8–11 years, during a soccer match (n = 84) and an intrasquad soccer scrimmage (n = 81), with 63 participants competing in both treatments. The soccer match and intrasquad soccer scrimmage represented out-group and in-group treatments, respectively. Results revealed that testosterone showed no measurable change. DHEA increased during both treatments in the majority of participants and the degree of change had no relation to independent variables (e.g., performance, age, treatment, outcome) or covariate measures (Body Mass Index, Pubertal Development Scale). Most boys experienced androstenedione increases during match play, but no significant differences during the intrasquad soccer scrimmage competitions. The magnitude of change differed significantly between treatments and was positively associated with age. These latter findings suggest boys’ androstenedione responses may be sensitive to competitor type (i.e., unknown competitors vs. peers). For most subjects, cortisol significantly increased during match play, decreased during the intrasquad soccer scrimmage, and differed significantly between treatments, suggesting each treatment promoted a different psychological state among competitors. Cortisol/DHEA molar ratio decreased during the intrasquad scrimmage, suggestive of a more relaxed mental state. These data shed new light on potential proximate mechanisms associated with coalitional competition among prepubescent boys, with relevance to adrenarche and life history theory.
PubDate: 2018-06-16
DOI: 10.1007/s12110-018-9321-7

• Steroid Hormone Reactivity in Fathers Watching Their Children Compete
• Authors: Louis Calistro Alvarado; Martin N. Muller; Melissa A. Eaton; Melissa Emery Thompson
Abstract: This study examines steroid production in fathers watching their children compete, extending previous research of vicarious success or failure on men’s hormone levels. Salivary testosterone and cortisol levels were measured in 18 fathers watching their children play in a soccer tournament. Participants completed a survey about the game and provided demographic information. Fathers with higher pregame testosterone levels were more likely to report that referees were biased against their children’s teams, and pre- to postgame testosterone elevation was predicted by watching sons compete rather than daughters as well as perceptions of unfair officiating. Pregame cortisol was not associated with pregame testosterone or with perceived officiating bias, but cortisol did fluctuate synergistically with testosterone during spectator competition. Although fathers showed no consistent testosterone change in response to winning or losing, pregame testosterone may mediate steroid hormone reactivity to other aspects of their children’s competition.
PubDate: 2018-06-08
DOI: 10.1007/s12110-018-9318-2

• Trash-Talking and Trolling
• Authors: Kevin M. Kniffin; Dylan Palacio
Abstract: Among the extra-physical aspects of team sports, the ways in which players talk to each other are among the more colorful but understudied dimensions of competition. To contribute an empirical basis for examining the nature of “trash talk,” we present the results of a study of 291 varsity athletes who compete in the top division among US universities. Based on a preliminary review of trash-talk topics among student-athletes, we asked participants to indicate the frequency with which they have communicated or heard others talk about opposing players’ athleticism, playing ability, physical appearance, boyfriends, girlfriends, sexual behavior, parents, and home institution during competitions. Our three main findings are: (1) Trash-talking is most commonly about the proximately important topic of playing ability while ultimately relevant topics such as physical appearance also appear to be common; (2) Men appear to trash-talk significantly more than women, and consistently across topics; and (3) contact sports such as football, hockey, lacrosse, and wrestling are associated with trash talk significantly more than other sports. We also examined whether the anonymity provided by face-masked helmets in “combat sports” was associated with more trash talk than contact sports played without a helmet (e.g., wrestling) and found no consistent association with face masks. Our findings highlight the ways in which competitors in physical sporting contests attempt to use language—often in ways that focus on players’ kin or reproductive interests—in pursuit of victory while establishing a baseline for future research into trash-talking.
PubDate: 2018-05-26
DOI: 10.1007/s12110-018-9317-3

• University Sports Rivalries Provide Insights on Coalitional Psychology
• Authors: Daniel J. Kruger; Michael Falbo; Sophie Blanchard; Ethan Cole; Camille Gazoul; Noreen Nader; Shannon Murphy
Abstract: Sports are an excellent venue for demonstrating evolutionary principles to audiences not familiar with academic research. Team sports and sports fandom feature dynamics of in-group loyalty and intergroup competition, influenced by our evolved coalitional psychology. We predicted that reactions to expressions signaling mutual team/group allegiance would vary as a function of the territorial context. Reactions should become more prevalent, positive, and enthusiastic as one moves from the home territory to a contested area, and from a contested area to a rival’s territory during active rival engagement. We also predicted that men would be more responsive than women based on sex differences in evolved coalitional psychology. The research team visited public places immediately prior to 2016–2017 collegiate football and basketball games. A male research confederate wore a sweatshirt displaying the logo of one of the competing university teams and vocalized the team’s most popular slogan when he saw a fan displaying similar logos. Observers followed 5 m behind, recording reactions (N = 597) and response positivity/enthusiasm. Reaction tone was most positive in the rival territory, least positive in the home territory, and intermediate in the periphery and contested territory. Rates of “no reaction” were lowest in the rival territory but were highest in the periphery. Men had higher reaction rates and more positive and enthusiastic reaction tones than women. Reactions generally followed predictions based on expected signal value. This project provides evidence that coalitional psychology influences dynamics related to university sports team rivalries and that context matters for expressions of alliance.
PubDate: 2018-05-11
DOI: 10.1007/s12110-018-9316-4

• Men’s Interest in Allying with a Previous Combatant for Future Group
Combat
• Authors: Nicole Barbaro; Justin K. Mogilski; Todd K. Shackelford; Michael N. Pham
Abstract: Intra- and intergroup conflict are likely to have been recurrent features of human evolutionary history; however, little research has investigated the factors that affect men’s combat alliance decisions. The current study investigated whether features of previous one-on-one combat with an opponent affect men’s interest in allying with that opponent for future group combat. Fifty-eight undergraduate men recruited from a psychology department subject pool participated in a one-on-one laboratory fight simulation. We manipulated fight outcome (between-subjects), perceived fighter health asymmetry (within-subjects), and the presence of a witness (within-subjects) over six sets of five rounds of fighting. Following each set, we asked men how interested they would be in allying with their opponent for future group combat. We found that men were more interested in allying with their opponent for future group combat if their opponent won the fight or if a witness was present, but perceived fighter-health asymmetry did not affect men’s decision to ally with their opponent. Exploratory analyses revealed a two-way interaction between fight outcome and the presence of a witness, such that winners without a witness present expressed less interest in allying with their opponent for future group combat. Our findings suggest that men attend to the benefits of allying with a man who has demonstrated relatively superior fighting ability. Alliance with a previous opponent for group combat may vary with the relationship value of the opponent and the utility of demonstrating cooperativeness to third-party observers. These findings inform our understanding of coalition formation.
PubDate: 2018-05-08
DOI: 10.1007/s12110-018-9315-5

• Food Sharing across Borders
• Authors: Barbara Fruth; Gottfried Hohmann
Abstract: Evolutionary models consider hunting and food sharing to be milestones that paved the way from primate to human societies. Because fossil evidence is scarce, hominoid primates serve as referential models to assess our common ancestors’ capacity in terms of communal use of resources, food sharing, and other forms of cooperation. Whereas chimpanzees form male-male bonds exhibiting resource-defense polygyny with intolerance and aggression toward nonresidents, bonobos form male-female and female-female bonds resulting in relaxed relations with neighboring groups. Here we report the first known case of meat sharing between members of two bonobo communities, revealing a new dimension of social tolerance in this species. This observation testifies to the behavioral plasticity that exists in the two Pan species and contributes to scenarios concerning the traits of the last common ancestor of Pan and Homo. It also contributes to the discussion of physiological triggers of in-group/out-group behavior and allows reconsideration of the emergence of social norms in prehuman societies.
PubDate: 2018-04-05
DOI: 10.1007/s12110-018-9311-9

• Why Only Humans Shed Emotional Tears
• Authors: Asmir Gračanin; Lauren M. Bylsma; Ad J. J. M. Vingerhoets
Abstract: Producing emotional tears is a universal and uniquely human behavior. Until recently, tears have received little serious attention from scientists. Here, we summarize recent theoretical developments and research findings. The evolutionary approach offers a solid ground for the analysis of the functions of tears. This is especially the case for infant crying, which we address in the first part of this contribution. We further elaborate on the antecedents and (intra- and interpersonal) functions of emotional tears in adults. The main hypothesis that emerges from this overview is that crying evolved as an emotional expression that signals distress and promotes prosocial behaviors in conspecifics. Further, shedding tears may influence the mood of the crier and his/her outlook on life primarily as a consequence of fulfillment of the proposed signaling function of tears. We also describe how cultural phenomena such as ritual weeping nicely fit within this framework, as they often aim to support a request for help to a powerful person or deity and promote social bonding.
PubDate: 2018-03-20
DOI: 10.1007/s12110-018-9312-8

• Judaism as a Group Evolutionary Strategy
• Authors: Nathan Cofnas
Abstract: MacDonald argues that a suite of genetic and cultural adaptations among Jews constitutes a “group evolutionary strategy.” Their supposed genetic adaptations include, most notably, high intelligence, conscientiousness, and ethnocentrism. According to this thesis, several major intellectual and political movements, such as Boasian anthropology, Freudian psychoanalysis, and multiculturalism, were consciously or unconsciously designed by Jews to (a) promote collectivism and group continuity among themselves in Israel and the diaspora and (b) undermine the cohesion of gentile populations, thus increasing the competitive advantage of Jews and weakening organized gentile resistance (i.e., anti-Semitism). By developing and promoting these movements, Jews supposedly played a necessary role in the ascendancy of liberalism and multiculturalism in the West. While not achieving widespread acceptance among evolutionary scientists, this theory has been enormously influential in the burgeoning political movement known as the “alt-right.” Examination of MacDonald’s argument suggests that he relies on systematically misrepresented sources and cherry-picked facts. It is argued here that the evidence favors what is termed the “default hypothesis”: Because of their above-average intelligence and concentration in influential urban areas, Jews in recent history have been overrepresented in all major intellectual and political movements, including conservative movements, that were not overtly anti-Semitic.
PubDate: 2018-03-10
DOI: 10.1007/s12110-018-9310-x

• Living Slow and Being Moral
• Authors: Nan Zhu; Skyler T. Hawk; Lei Chang
Abstract: Drawing from the dual process model of morality and life history theory, the present research examined the role of cognitive and emotional processes as bridges between basic environmental challenges (i.e., unpredictability and competition) and other-centered moral orientation (i.e., prioritizing the welfare of others). In two survey studies, cognitive and emotional processes represented by future-oriented planning and emotional attachment, respectively (Study 1, N = 405), or by perspective taking and empathic concern, respectively (Study 2, N = 424), positively predicted other-centeredness in prosocial moral reasoning (Study 1) and moral judgment dilemmas based on rationality or intuition (Study 2). Cognitive processes were more closely related to rational aspects of other-centeredness, whereas the emotional processes were more closely related to the intuitive aspects of other-centeredness (Study 2). Finally, the cognitive and emotional processes also mediated negative effects of unpredictability (i.e., negative life events and childhood financial insecurity), as well as positive effects of individual-level, contest competition (i.e., educational and occupational competition) on other-centeredness. Overall, these findings support the view that cognitive and emotional processes do not necessarily contradict each other. Rather, they might work in concert to promote other-centeredness in various circumstances and might be attributed to humans’ developmental flexibility in the face of environmental challenges.
PubDate: 2018-03-08
DOI: 10.1007/s12110-018-9313-7

• Grandmothers and Children’s Schooling in Sub-Saharan Africa
• Authors: Sandor Schrijner; Jeroen Smits
Abstract: Under poor circumstances, co-residence of a grandmother is generally considered to be beneficial for (grand)children. Empirical evidence does not unequivocally support this expectation and suggests that the grandmother’s importance depends on the family’s circumstances. We study the relationship between grandmother’s co-residence and children’s schooling in sub-Saharan Africa under a broad range of circumstances. Results make clear that the effect of a co-residing grandmother varies but is almost always positive. Grandmothers over age 60 are most effective in helping their (grand)children. They are particularly important for girls, and when the mother is deceased or not living in the household. Grandmothers are less effective in situations with few opportunities, as in very poor regions or in communities with few schooling opportunities. Our findings indicate that providing support to grandmothers should not be overlooked when designing policies aimed at strengthening the position of women and children in the sub-Saharan African context.
PubDate: 2017-12-09
DOI: 10.1007/s12110-017-9306-y

• Possible Balancing Selection in Human Female Homosexuality
• Authors: Andrea Camperio Ciani; Umberto Battaglia; Linda Cesare; Giorgia Camperio Ciani; Claudio Capiluppi
Abstract: A growing number of researchers suggest that female homosexuality is at least in part influenced by genetic factors. Unlike for male homosexuality, few familial studies have attempted to explore maintenance of this apparently fitness-detrimental trait in the population. Using multiple recruitment methods, we explored fecundity and sexual orientation within the pedigrees of 1,458 adult female respondents. We compared 487 homosexual and 163 bisexual with 808 heterosexual females and 30,203 of their relatives. Our data suggest that the direct fitness of homosexual females is four times lower than the direct fitness of heterosexual females of corresponding ages. The prevalence of nonheterosexuality within the homosexual female respondents’ families (2.83%) appear to be more than four times higher than the basal prevalence in the Italian population (0.63%). Pedigree size and relative fecundity in both the paternal and maternal sides of the homosexual women’s families were significantly higher than in the heterosexuals’ families. If confirmed, the relative average fecundity increase within the family seems to offset the loss in fitness due to the low direct fitness of homosexual females. Therefore, the balanced fecundity in the homosexual females’ families may allow the trait to be maintained at a low-frequency equilibrium in the population.
PubDate: 2017-12-04
DOI: 10.1007/s12110-017-9309-8

• Correction to: Altruistic Behavior among Twins
• Authors: Encarnación Tornero; Juan F. Sánchez-Romera; José J. Morosoli; Alexandra Vázquez; Ángel Gómez; Juan R. Ordoñana
Abstract: The original version of this article unfortunately contained a mistake. The presentation of the article title and subtitle was incorrect.
PubDate: 2017-11-22
DOI: 10.1007/s12110-017-9308-9

• Inbreeding in Southeastern Spain
• Authors: R. Calderón; C. L. Hernández; G. García-Varela; D. Masciarelli; P. Cuesta
Abstract: In this paper, the structure of a southeastern Spanish population was studied for the first time with respect to its inbreeding patterns and its relationship with demographic and geographic factors. Data on consanguineous marriages (up to second cousins) from 1900 to 1969 were taken from ecclesiastic dispensations. Our results confirm that the patterns and trends of inbreeding in the study area are consistent with those previously observed in most non-Cantabrian Spanish populations. The rate of consanguineous marriages was apparently stable between 1900 and 1935 and then sharply decreased since 1940, which coincides with industrialization in Spain. A marked departure from Hardy-Weinberg expectations (0.25) in the ratio of first cousin (M22) to second cousin (M33) marriages in the study population (0.88) was observed. The high levels of endogamy (>80%) and its significant steadiness throughout the twentieth century is noteworthy. Accordingly, our results show that exogamous marriages were not only poorly represented but also that this reduced mobility (<6 km) suggests that the choice of a mate was preferentially local. We found higher mobility in M22 with respect to M33 cousin mating. The relationships between population size and consanguinity rates and inbreeding fit power-law distributions. A significant positive correlation was observed between inbreeding and elevation. Many Spanish populations have experienced a prolonged and considerable isolation across generations, which has led to high proportions of historical and local endogamy that is associated, in general, with high $$\overline{F}$$ values. Thus, assessing genomic inbreeding using runs of homozygosity (ROH) in current Spanish populations could be an additional pertinent strategy for obtaining a more refined perspective regarding the population history inferred from the extent and frequency of ROH regions.
PubDate: 2017-11-20
DOI: 10.1007/s12110-017-9305-z

• Measuring the Unmeasurable
• Authors: Stefan L. K. Gruijters; Bram P. I. Fleuren
Abstract: Within evolutionary biology, life-history theory is used to explain cross-species differences in allocation strategies regarding reproduction, maturation, and survival. Behavioral scientists have recently begun to conceptualize such strategies as a within-species individual characteristic that is predictive of behavior. Although life history theory provides an important framework for behavioral scientists, the psychometric approach to life-history strategy measurement—as operationalized by K-factors—involves conceptual entanglements. We argue that current psychometric approaches attempting to identify K-factors are based on an unwarranted conflation of functional descriptions and proximate mechanisms—a conceptual mix-up that may generate unviable hypotheses and invites misinterpretation of empirical findings. The assumptions underlying generic psychometric methodology do not allow measurement of functionally defined variables; rather these methods are confined to Mayr’s proximate causal realm. We therefore conclude that K-factor scales lack validity, and that life history strategy cannot be identified with psychometrics as usual. To align theory with methodology, suggestions for alternative methods and new avenues are proposed.
PubDate: 2017-11-15
DOI: 10.1007/s12110-017-9307-x

• Altruistic Behavior among Twins Willingness to Fight and Self-Sacrifice
for their Closest Relatives
• Authors: Encarnación Tornero; Juan F. Sánchez-Romera; José J. Morosoli; Alexandra Vázquez; Ángel Gómez; Juan R. Ordoñana
Abstract: According to kin selection theory, indirect reproductive advantages may induce individuals to care for others with whom they share genes by common descent, and the amount of care, including self-sacrifice, will increase with the proportion of genes shared. Twins represent a natural situation in which this hypothesis can be tested. Twin pairs experience the same early environment because they were born and raised at the same time and in the same family but their genetic relatedness differs depending on zygosity. We compared the degree of willingness to fight and sacrifice for the co-twin among monozygotic (MZ) and dizygotic (DZ) pairs in a sample of 1443 same-sex and opposite-sex twins. We also analyzed the effect of the subject’s gender and that of the co-twin on those altruistic behaviors. Results partly supported the postulated explanation. MZ twins (who share nearly their entire genome) were significantly more likely than DZ twins (who on average share half of their segregating genes) to self-sacrifice for their co-twins, but zygosity did not affect willingness to fight for him/her. The genders of the subject and of the co-twin, not genetic relatedness, were the best predictors of aggressive altruistic intentions.
PubDate: 2017-10-28
DOI: 10.1007/s12110-017-9304-0

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