Sex Affects the Relationship Between Third Party Punishment and Cooperation.

Prosocial third-party punishment (3PP) is a punitive behavior against antisocial individuals, which might explain extended cooperativeness in humans. 3PP shows sexual dimorphism, being more frequent in men than in women. We studied whether sexually dimorphic features related to sexual hormones during development (facial dimorphism and 2D:4D) influence the tendency to engage in 3PP in a sample of 511 women and 328 men. After playing a Prisoner's Dilemma, participants had to decide whether to penalize the defection of a third player who had exploited his/her counterpart's cooperation. In line with previous studies, we observe that men are more prone to engage in 3PP than women. We find that this sex difference is due to cooperative men being more likely to punish than cooperative women. In addition, men with higher facial masculinity are less likely to engage in 3PP, whereas no features influence 3PP in women. We discuss the possibility that sex differences in the motivations and fitness implications underlying 3PP might be driving the observed results.

Zebrafish aggression on the sub-second time scale: evidence for mutual motor coordination and multi-functional attack manoeuvres.

Most animals fight by repeating complex stereotypic behaviours, yet the internal structure of these behaviours has rarely been dissected in detail. We characterized the internal structure of fighting behaviours by developing a machine learning pipeline that measures and classifies the behaviour of individual unmarked animals on a sub-second time scale. This allowed us to quantify several previously hidden features of zebrafish fighting strategies. We found strong correlations between the velocity of the attacker and the defender, indicating a dynamic matching of approach and avoidance efforts. While velocity matching was ubiquitous, the spatial dynamics of attacks showed phase-specific differences. Contest-phase attacks were characterized by a paradoxical sideways attraction of the retreating animal towards the attacker, suggesting that the defender combines avoidance manoeuvres with display-like manoeuvres. Post-resolution attacks lacked display-like features and the defender was avoidance focused. From the perspective of the winner, game-theory modelling further suggested that highly energetically costly post-resolution attacks occurred because the winner was trying to increase its relative dominance over the loser. Overall, the rich structure of zebrafish motor coordination during fighting indicates a greater complexity and layering of strategies than has previously been recognized.

Facial Features: What Women Perceive as Attractive and What Men Consider Attractive.

Attractiveness plays an important role in social exchange and in the ability to attract potential mates, especially for women. Several facial traits have been described as reliable indicators of attractiveness in women, but very few studies consider the influence of several measurements simultaneously. In addition, most studies consider just one of two assessments to directly measure attractiveness: either self-evaluation or men's ratings. We explored the relationship between these two estimators of attractiveness and a set of facial traits in a sample of 266 young Spanish women. These traits are: facial fluctuating asymmetry, facial averageness, facial sexual dimorphism, and facial maturity. We made use of the advantage of having recently developed methodologies that enabled us to measure these variables in real faces. We also controlled for three other widely used variables: age, body mass index and waist-to-hip ratio. The inclusion of many different variables allowed us to detect any possible interaction between the features described that could affect attractiveness perception. Our results show that facial fluctuating asymmetry is related both to self-perceived and male-rated attractiveness. Other facial traits are related only to one direct attractiveness measurement: facial averageness and facial maturity only affect men's ratings. Unmodified faces are closer to natural stimuli than are manipulated photographs, and therefore our results support the importance of employing unmodified faces to analyse the factors affecting attractiveness. We also discuss the relatively low equivalence between self-perceived and male-rated attractiveness and how various anthropometric traits are relevant to them in different ways. Finally, we highlight the need to perform integrated-variable studies to fully understand female attractiveness.

Changes in preference for male faces during the menstrual cycle in a Spanish population / Cambios en la preferencia por rostros masculinos durante el ciclo menstrual en población española

A recent and controversial hypothesis suggests the presence of an oestrus phase in women as in other mammals. This implies that women at their optimal fertility point of the menstrual cycle exhibit behaviors focused to maximize the genetic quality of their offspring. Several studies support this hypothesis, finding that women in the fertile phase tend to prefer men with traits associated to phenotypic quality, such as greater facial masculinization and symmetry. We experimentally tested some of the observations supporting this hypothesis in a population of 810 young Spanish women. We analyzed whether the preference for masculinized male faces is affected by I) the phase of the menstrual cycle, II) having a stable partner and III) the use of birth control pills. We could not repro-duce the effect of the first two factors, but we found that women using hormonal contraceptives tend to prefer men with less masculine faces. These results indicate that some of the evidences supporting the oestrus hypothesis in humans must be reviewed, incorporating data from different socio-cultural and ethnic populations

Recientemente se ha postulado una controvertida hipótesis que propone la presencia de un periodo de estro en las mujeres, como ocurre en otros mamíferos. Ello implica que las mujeres en el óptimo de fertilidad del ciclo menstrual presenten comportamientos encaminados a maximizar la calidad genética de su descendencia. Diversas investigaciones sostienen esta hipótesis, al encontrar que las mujeres en la fase fértil prefieren hombres con rasgos que denotan mayor calidad fenotípica, como un mayor grado de masculinización o una mayor simetría. Nuestro objetivo ha sido testar experimentalmente en una población de 810 jóvenes españolas alguna de estas observaciones. Analizamos si, tal como se recoge en la bibliografía, la preferencia por rostros de hombres masculinizados se ve afectada por I) la etapa del ciclo menstrual, II) el tener pareja estable y III) el empleo anticonceptivos hormonales. No hemos podido reproducir el efecto de los dos primeros factores, pero sí encontramos que las mujeres que emplean anticonceptivos hormonales prefirieron rostros de hombre menos masculinos. Estos resultados no refutan la hipótesis del estro en humanos, pero nos indican que algunas de las pruebas que la sustentan han de ser reconsideradas, incorporando datos de poblaciones étnica y socioculturalmente diferentes