Sunday, January 24, 2021

Our findings suggest that lower male pitch and formants may be valid cues of some components of fighting ability in men

Low fundamental and formant frequencies predict fighting ability among male mixed martial arts fighters. Toe Aung, Stefan Goetz, John Adams, Clint McKenna, Catherine Hess, Stiven Roytman, Joey T. Cheng, Samuele Zilioli & David Puts. Scientific Reports volume 11, Article number: 905 (2021). Jan 13 2021. https://www.nature.com/articles/s41598-020-79408-6

h/t David Schmitt (20) David Schmitt on Twitter: ""lower male pitch and formants may be valid cues of some components of fighting ability in men" https://t.co/4dRGZT7XyH"

Abstract: Human voice pitch is highly sexually dimorphic and eminently quantifiable, making it an ideal phenotype for studying the influence of sexual selection. In both traditional and industrial populations, lower pitch in men predicts mating success, reproductive success, and social status and shapes social perceptions, especially those related to physical formidability. Due to practical and ethical constraints however, scant evidence tests the central question of whether male voice pitch and other acoustic measures indicate actual fighting ability in humans. To address this, we examined pitch, pitch variability, and formant position of 475 mixed martial arts (MMA) fighters from an elite fighting league, with each fighter’s acoustic measures assessed from multiple voice recordings extracted from audio or video interviews available online (YouTube, Google Video, podcasts), totaling 1312 voice recording samples. In four regression models each predicting a separate measure of fighting ability (win percentages, number of fights, Elo ratings, and retirement status), no acoustic measure significantly predicted fighting ability above and beyond covariates. However, after fight statistics, fight history, height, weight, and age were used to extract underlying dimensions of fighting ability via factor analysis, pitch and formant position negatively predicted “Fighting Experience” and “Size” factor scores in a multivariate regression model, explaining 3–8% of the variance. Our findings suggest that lower male pitch and formants may be valid cues of some components of fighting ability in men.

Discussion

Sexual dimorphism in fo likely arose in the common ancestor of the catarrhine primates after their divergence from the New World monkeys6 approximately 43.5mya44 and appears to have been subsequently elaborated or reduced depending on the form and degree of male mating competition6. Relatively low male fo may have evolved as a means of exaggerating the appearance of size to same-sex competitors and/or potential mates6,18, but there is considerable debate regarding whether male fo is purely deceptive20,21,45 or provides any reliable information about formidability in men11,17,33.

To shed light on this debate, we investigated whether fo is associated with fighting ability among a large sample of male MMA fighters. Results of our pre-registered analyses were generally in the direction of lower fo predicting greater fighting ability but were mixed in terms of statistical significance. When we addressed the limitations of these analyses by creating more precise measures of fighting ability and accounting for the contributions of the distinct dimensions revealed through principal axis factoring, we found that lower fo was associated with greater fighting ability in all analyses. In the statistical model that most precisely measured fighting ability by including principal axis factors related to fighting experience, fighting success, and body size, fo predicted fighting ability generally and specifically components of fighting ability related to experience and size, but not within-weight class fighting success. Overall, these results suggest that low fo is an honest cue of formidability in men (Table 3).

Table 3 Component axis analysis for measures related to fighting ability.

Effect sizes were small, however. Even when fighting ability was measured most precisely, fo explained only 1–3% of the variance (Table 4). On the one hand, the strength of these associations accords with theoretical predictions derived from the fact that signaling is multimodal and multi-component17. On the other hand, it is important to emphasize that relationships between fo and fighting success among MMA fighters may underestimate those in the general population due to range restriction on fighting ability. Among elephant seals, the body length of males who occupied the center of harems correlated with neither maximum harem size nor tenure length on the beach during the breeding season46. However, when all males were analyzed together, including those that were peripheral to or outside of the harem, male body length explained 17% of the variation in tenure length on the beach. The degree to which fo correlates with fighting ability in the general population has yet to be tested for obvious ethical reasons.

Table 4 Results of a multi-variate regression model.

Voice pitch and other acoustic variables are modulated across social contexts, including those related to perceived fighting ability relative to a competitor13,47, relative dominance and prestige48, authority36, current aggressive intent49, emergent rank16, and volitional exaggeration50,51. On the one hand, if voice pitch is modulated in relation to self-perceived relative formidability and status, as this prior research indicates, then it is possible that any voice modulation of fighters during interviews could have strengthened relationships between acoustic parameters and measures of fighting ability in the present study. On the other hand, if voice modulation is less patterned or less dependent upon perceived relative formidability, then this would introduce noise in measuring individual differences in voices, which would tend to weaken relationships between acoustic parameters and true fighting ability. In these data based on naturalistic observations, although we cannot rule out that some fighters may have modulated their voice pitch or other vocal parameters during interviews to sound stronger, we sought to strengthen our measures of individual differences in acoustic traits by sampling across multiple interview occasions. Indeed, we found that acoustic measures were consistent across fighters, even between pre- and post-fight conditions in the subset of our sample for which this information was available (see Supplemental Procedures for details), and we attempted to capture more stable individual acoustic differences rather than measurements specific to particular recording conditions by using the unbiased linear estimates across recordings for each fighter in all analyses.

Only one previous study of which we are aware28 examined links between fighting success and fo or other acoustic measures and found that acoustic measures did not predict win percentage among male MMA fighters. Likewise, in our bivariate correlation analysis, we did not find a significant relationship between win percentage and vocal fo (Table 1), although lower fo predicted a greater number of UFC matches. Our ability in subsequent analyses to detect relationships between fo and fighting ability where a previous study did not28 may have been due in part to our examination of a larger sample of fighters (474 vs. 29), along with longer total voice samples from each fighter (approximately 85 s vs. 8 s).

Our use of unstandardized, spontaneous speech samples also offered enhanced ecological validity47, and although this approach adds noise to the measurement of individual differences in acoustic parameters, previous research shows strong correspondence across speech and/or vocalization types for both fundamental52 and formant10 frequencies. Moreover, the best linear unbiased composite estimates of acoustic measures from multiple voice recordings of each fighter, along with relatively long (> 85 s) average total speech samples from individual fighters, provided reliable estimates of individual differences in acoustic features.

Perhaps most importantly, we extracted component variables via factor analysis to produce more comprehensive measures of fighting ability than can be offered by individual measures such as Elo rating or win percentage. For example, win percentage alone is an imperfect indicator of fighting success because fighters with fewer fights and losses can achieve higher win rates53,54 and because win percentage does not account for the strength of opponents as Elo ratings do. Our factor analysis addressed such limitations and produced three unique components of fighting ability, which we termed Fighting Experience, Fighting Success, and Size. Fighting Experience reflects the component of flighting ability most strongly related to total number of fights but also strongly related to years active in the UFC and age. Given that Elo ratings also loaded positively onto this component, it may represent the component of fighting skill attributable to experience. Fighting Success reflects a component of fighting ability related to a history of winning in one’s weight class that is relatively unrelated to experience or size, perhaps tapping characteristics such as speed, agility, and strength for one’s size. The extracted Size factor reflects the component of fighting ability related to height and weight. Larger size is generally associated with lower fo across mammals55 and is a major determinant of dominance and social status across species56,57,58,59,60. Physical size is such a strong determinant of outcomes in combat sports such as wrestling, boxing, and martial arts that weight classes are needed to prevent dangerous lopsided contests, and fighters are willing to sacrifice energy and hydration by cutting weight to fight smaller opponents. Parallel to findings in previous studies32,61, fighters’ fo predicted their height and weight, as well as their Size factor scores.

Our orthogonal factor analysis extracted independent components of fighting ability, maximizing the variance among items and facilitating interpretation. A structural equation model further confirmed the structure of our proposed components of fighting ability, but allowing residual correlations between latent variables produces a better model fit. These analyses highlight the importance of considering fighting ability across related measures instead of using a single measure of fighting experience, fighting success, or size. Because fighting ability measures (e.g., win percentage and number of fights) reflect weight division-specific measures, results from analyses that do not incorporate the influence of fighter’s weight (Table 1) may be less valid than others (Table 4).

Although not the focus of the present paper, other sexually dimorphic acoustic parameters were associated with fighting ability. In correlation analyses, lower fo-SD and Pf predicted a greater number of UFC fight matches, and lower Pf predicted higher Elo ratings (Table 1). In addition, Pf predicted overall measures of fighting ability in the multivariate regression model (Fig. 2) and independently predicted Fighting Experience and Size (Fig. S2). Our findings extend those from previous studies showing that Pf predicts objective measures of threat potential, such as size32, strength, and physical aggression10, as well as perceived fighting ability14,62, and suggest that Pf communicates size-independent information about vocalizers’ physical formidability.

A potential statistical issue concerns the use of uncorrected p-values associated with multiple tests. However, the adjustment of p-values, such as Bonferroni correction, not only decreases the rates of Type I error, but also increases the rates of Type II error and has been highly criticized63. Additional analyses used in this study, such as multi-level modeling64, multi-variate regression, and structural equation modeling, that consider dependent variables simultaneously should reduce concerns associated with multiple comparisons.

In general, our findings are consistent with the broader perspective that men’s anatomy, behavior, and psychology have been shaped by an evolutionary history of contest competition27,65, the use of force or threat of force to exclude same-sex competitors from mates59. Contest competition should favor psychological mechanisms to attend to and assess the formidability and threat potential of competitors19. People can accurately assess physical strength from body19 and face66 images. For example, sexually dimorphic facial cues predict fighting ability among MMA fighters33,67 but see68, and using these cues participants can predict fighting outcomes above chance69. The voice appears to be another aspect of the phenotype that indicates formidability10,13,19; we showed that fo was associated with both body size and fighting experience (independent of body size) among male MMA fighters. Although associations between measures of fighting ability and fo and other sexually dimorphic acoustic parameters were small, they comport with the notion that fo is but one of many components of a vocal acoustic signal, and that voices represent one of many signals of men’s formidability17. A deep, resonant voice clearly indicates status as a physically mature or maturing male. Our findings support the further possibility that attention to differences in voice pitch among men may be functional as well, as fo and other sexually dimorphic components of men’s voices appear to provide information about differences in men’s threat potential.

Group-level cooperation in chimpanzees is shaped by strong social ties

Group-level cooperation in chimpanzees is shaped by strong social ties. Liran Samuni, Catherine Crockford & Roman M. Wittig. Nature Communications volume 12, Article number: 539 (2021), January 2021. https://www.nature.com/articles/s41467-020-20709-9

h/t: (20) David Schmitt on Twitter: ""the link between strong, enduring social relationships and costly collective acts is not uniquely human" https://t.co/CedOVKTzT6"

Abstract: Humans maintain extensive social ties of varying preferences, providing a range of opportunities for beneficial cooperative exchange that may promote collective action and our unique capacity for large-scale cooperation. Similarly, non-human animals maintain differentiated social relationships that promote dyadic cooperative exchange, but their link to cooperative collective action is little known. Here, we investigate the influence of social relationship properties on male and female chimpanzee participations in a costly form of group action, intergroup encounters. We find that intergroup encounter participation increases with a greater number of other participants as well as when participants are maternal kin or social bond partners, and that these effects are independent from one another and from the likelihood to associate with certain partners. Together, strong social relationships between kin and non-kin facilitate group-level cooperation in one of our closest living relatives, suggesting that social bonds may be integral to the evolution of cooperation in our own species.

Popular version: Chimpanzee friends fight together to battle rivals: Strong social bonds increase the willingness to join others in battle. Eurekalert. https://www.eurekalert.org/pub_releases/2021-01/mpif-cff012221.php

Discussion

Within-group cohesive engagement of males and females, relatedness, and social preference each have a strong, independent influence on the participation of male and female chimpanzee in one of the costliest forms of group actions, hostile intergroup interactions. We found that participation disposition of males and females increased when more other in-group members participated, both same and opposite sex, supporting the hypothesis that ‘strength in numbers’ facilitates participation. Although cohesive engagement of many community members was influential, it was not the only participation driver. Additionally, we found that the decision to contribute to the group act heavily depended on the identity of other participants as maternal kin or social bond partners, types of relationships associated with more predictable reciprocity16,17,42,43.

Both cohesive engagement of many community members and of specific preferred partners likely encompasses the range of social relationships within one’s group, from weakly to strongly bonded, facilitating coordinated contribution to intergroup competitive interactions. These effects were independent from potential energetic and reproductive costs of intergroup encounter participation observed in chimpanzees and other primates, such as old age, low dominance rank, gestation timing, and lactation22,25,26,49. Furthermore, the positive effect of relatedness and social preference on participation tendencies occurred irrespective of another social aspect which may drive interaction likelihood14, spatial proximity (association degree) between participants. This, in addition to using only active intergroup encounters, further indicates the observed pattern is not a byproduct of association tendencies and is independent of the likelihood to be present with others who are at the encounter area. Our results echo findings of studies on hunter-gatherer societies that suggest strong social ties, whether kin or non-kin relations, facilitate the emergence of cooperation14.

The degree of genetic relatedness to other community members is expected to influence individuals’ contribution to acts that are potentially costly, as participants are bound to gain higher indirect fitness benefits with more relatives in the community51. Higher numbers of maternal kin in the community likely increases the probability of acting with adult kin during the intergroup encounter making it difficult to distinguish whether it is overall relatedness or direct interactions with kin that is linked with cooperation emergence. Testing the effect of the presence of adult maternal kin in the encounter while accounting for the number of maternal kin in the community, allows us to examine the mechanisms through which genetic relatedness may operate in this context, whether directly or indirectly. We found that the total number of living maternal kin of all ages in the community had a negative significant effect on female participation tendencies. Since this number mostly comprised non-adult offspring of females, including offspring that are not carried by their mother, this negative effect may reflect increased energetic and/or injury-related participation costs for weaned young offspring, and hence for their mothers. For males, the number of living maternal kin had no significant effect on male participation tendencies, was in line with findings on male chimpanzees’ participation in territorial border patrols in Ngogo22. Conversely, the presence of adult maternal kin in the encounter increased participation of both sexes. For all males, the adult maternal kin present in intergroup encounters were females, predominantly their mothers (one male’s maternal kinship was solely his sister), whereas for females, the adult maternal kin present in the intergroup encounter were mainly their sons (two females had both adult daughter and son in the community). Congruent with studies on humans52, our results suggest that it is the coordination with adult kin, rather than the overall degree of relatedness with community members, that promotes cooperation.

Chimpanzee intergroup encounters are energetically demanding, and contact intergroup encounters are riskier and associated with elevated cortisol levels in comparison with vocal ones53. In support of potential energetic costs, time into gestation reduced female likelihood to participate in intergroup encounters. Also, although contact intergroup encounters involve higher risk of injury, we found that they were positively associated with female participation. These results are in line with a previous finding in mountain gorillas, that more aggressive intergroup encounters included a higher proportion of participating in-group members25. Across all intergroup encounters, males participated at high rates (86%). Thus, increased female participation translates to more collective engagement of the community as a whole23. As cohesive engagement is a key component of both successful intergroup encounter outcome and reduced risk of severe injury37,41, contact intergroup encounters have a higher likelihood to occur at times of heightened female involvement (indicating heightened overall community involvement) because the odds to prevail are higher and chances to suffer costs are reduced.

Due to the female-dispersal male-philopatry society of chimpanzees, mother–daughter associations at adulthood are rare, and mothers have no direct influence on their daughters’ fitness post dispersal. This is not the case for male offspring. Mother–son cohabitation during reproductive ages of sons has the potential to improve the reproductive success of sons, for instance in bonobos54 and in this population of chimpanzees55. Here, we showed that females with sons approaching reproductive age in the community were more likely to participate in intergroup encounters in comparison to females with no such sons in the community. If joint participation increases the chance of gaining improved access to mating opportunities for male community members22,35, then mothers who participate in intergroup encounters have the potential to provide future benefits to their sons. We cannot rule out that increased participation of mothers is driven by their sons’ increased motivation to participate rather than their own. Nevertheless, regardless of mothers’ motivation to participate, the potential benefits of improved future access to mating opportunities to sons remain the same.

Following male biased predisposition for intergroup conflict participation in some primate species, including chimpanzees and humans23,24,25,44,56, we observed clear sex-specific differences in participation frequencies. In comparison with males, females showed lower participation rates with larger variation. Further, in accord with homophily predictions for cooperation appearance (i.e., similarity of individuals’ attributes, such as sex, increases the likelihood of tie formation14), the number of other female or male participants more strongly affected same sex participation. Despite differences in participation rates, similar mechanisms appear to regulate participation of both sexes in territorial defense.

The importance of maintaining strong social networks that encompass a range of relationships for the emergence of cooperation is evident in humans14,15. Intergroup competition is known to shape human social group dynamics and cooperative capacities34,57. This relationship likely stems from the high stakes associated with participation in intergroup encounters, together with the benefits that one may gain in case of success, where success rests upon the number and value of cooperators. Here we demonstrated the link between intergroup competition, group social dynamics and cooperation in male and female chimpanzees. It may be that the access to and maintenance of differentiated social relationships between kin and non-kin also supports other group-level activities or even energetic demands, as suggested for humans15,58. For instance, the maintenance of a range of social ties in humans is thought to support our costly life history and demanding foraging niche15,58. Therefore, future research into the effect of differentiated social relationships on chimpanzee capacity for coordinated hunting59,60 or support of life history trajectories could have an immense potential in revealing the evolutionary processes leading to distinctively human large-scale cooperation that extends beyond borders.

To conclude, cohesive group engagement, interactions with kin, spatial proximity, and social preference all independently contributed to chimpanzee intergroup encounter participation, a risky group act. By choosing to act with maternal kin and social bond partners, and when more in-group members are present, individuals are likely to minimize the costs and maximize the benefits associated with intergroup encounter participation. This emphasizes the importance of chimpanzee social relationship properties and partner choice in driving not only dyadic cooperation, but as well cooperation on the group-level. Our results suggest that the link between strong and enduring social relationships and costly collective acts is not uniquely human.

Most people do not have accurate knowledge about the concept of heritability: Fewer than 25% of the participants selected the correct description of the heritability of insomnia

What Do People Know About the Heritability of Sleep? Juan J. Madrid-Valero, Robert Chapman, Evangelina Bailo, Juan R. Ordoñana, Fatos Selita, Yulia Kovas & Alice M. Gregory. Behavior Genetics, Jan 23 2021. https://rd.springer.com/article/10.1007/s10519-021-10041-3

Abstract

Study Objectives: Twin studies have provided data about the relative weight of genetic and environmental factors on sleep variables over the last few decades. However, heritability is a non-intuitive concept and it is often misunderstood even amongst the scientific community. This study aimed to analyze: (1) understanding of the meaning of heritability of insomnia; (2) the accuracy of estimations of heritability in the general population regarding three sleep traits (sleep duration, sleep quality and insomnia); (3) perceptions of the effectiveness of different treatments for insomnia depending on how the disorder is presented (i.e. having an environmental or genetic etiology) and whether the subject’s estimate of genetic influence on sleep traits impacted beliefs about the effectiveness of different treatments.

Methods: Participants (N = 3658) completed a survey which included: questions about general genetic knowledge; a specific question about the meaning of heritability; estimates of heritability of three different sleep traits; and the effectiveness of different treatments for insomnia depending on how the etiology of this condition was presented.

Results: Fewer than 25% of the participants selected the correct description of the heritability of insomnia. Almost half of the sample incorrectly believed that heritability refers to the chance of passing a disorder onto their children. We also found that participants provided different estimates for the effectiveness of different treatments depending on the presumed etiology of the disorder.

Conclusion: Most people do not have accurate knowledge about the concept of heritability. People’s assumptions about the etiology of a disorder may influence which treatments they consider most effective.