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Humans display a remarkable tendency to cooperate with strangers; however, identifying prospective cooperation partners accurately before entering any new relationship is essential to mitigate the risk of being exploited. Visual appearance, as inferrable, for example, from facial images on job portals and dating sites, may serve as a potential signal of cooperativeness. This experimental study examines whether static images enable the correct detection of an individual’s propensity to cooperate. Participants first played the Prisoner’s Dilemma (PD) game, a standard cooperation task. Subsequently, they were asked to predict the cooperativeness of participants from a prior PD study relying solely on their static facial photographs. While our main results indicate only marginal accuracy improvements over random guessing, a more detailed analysis reveals that participants were more successful at identifying cooperative tendencies similar to their own. Despite no detectable main effect in our primary treatment variations (time pressure versus time delay), participants exhibited increased accuracy in identifying male cooperators under time pressure. These findings point towards a limited yet nuanced role of static facial images in predicting cooperativeness, advancing our understanding of non-behavioral cues in cooperative interactions.

Long-term memory (LTM) requires transcription and translation of new proteins, yet the transcriptional control of memory remains poorly understood. Here, we performed a transcriptome time-course during LTM formation in Drosophila melanogaster exposed to courtship conditioning. We identified a mushroom body-specific transcriptional memory trace that becomes activated during memory consolidation. Using scRNAseq of CREB-activated cells we were able to detect a persistent transcriptional response in MB neurons after LTM consolidation and retrieval. As a proof of causality, we conducted a loss-of-function screen for genes comprising the transcriptional memory trace, finding 16 positive hits whose disruption impaired LTM. Among them, we identified two neuron activity-regulated genes, Hr38 and sr , which encode transcription factors that are activated by courtship LTM training, required for LTM, and bind to many genes comprising the transcriptional memory trace. Overall, we further define the transcriptional response to LTM and identify transcription factors that may help shape it. Gene expression programs underlying memory are not well understood in Drosophila. Here, authors use mushroom body-specific RNA sequencing to characterize the transcriptional trace of long-term memory and key TFs that may regulate it.

In the last few years, several studies have questioned the value of the second-to-fourth digit ratio (2D:4D) as a measure of exposure to sex hormones before birth. Controversy has also extended to the 2D:4D association with individual features previously related to this exposure such as handedness and sexual orientation. Given that it has been argued that sex differences in 2D:4D could be a consequence of body-size differences, we have tested in a large sample the allometric relationship between finger lengths and body size. Our results show that the association is either allometric or isometric, depending on the analyses performed. In any case, the deviation from isometry is not large enough to explain the typically observed sex difference in this trait. We have also tested the association between sexual orientation and 2D:4D, finding a relationship between 2D:4D and sexual orientation in men but not in women. We attribute this discordance with previously published meta-analysis to differences in genetic background, a variable that has gained relevance in recent years in studies involving 2D:4D. Finally, we did not find any relationship between 2D:4D and handedness, evaluated through self-reported preference and hand performance. Our main conclusion is that 2D:4D shows differences between sexes beyond their disparity in body size. In our opinion, 2D:4D can be used cautiously as an indicator of intrauterine exposure to sex hormones taking into account some considerations, such as analysing a very large sample and taking careful measurements of the ethnicity of the sample.

In modern human societies, social isolation acts as a negative factor for health and life quality. On the other hand, social interaction also has profound effects on animal and human, impacting aggressiveness, feeding and sleep, among many other behaviors. Here, we observe that in the fly Drosophila melanogaster these behavioral changes long-last even after social interaction has ceased, suggesting that the socialization experience triggers behavioral plasticity. These modified behaviors maintain similar levels for 24 h and persist up to 72 h, although showing a progressive decay. We also find that impairing long-term memory mechanisms either genetically or by anesthesia abolishes the expected behavioral changes in response to social interaction. Furthermore, we show that socialization increases CREB-dependent neuronal activity and synaptic plasticity in the mushroom body, the main insect memory center analogous to mammalian hippocampus. We propose that social interaction triggers socialization awareness, understood as long-lasting changes in behavior caused by experience with mechanistic similarities to long-term memory formation.

Numerous studies have examined how morphological features showing sex differences relate to prosocial behaviors, often yielding contradictory results. However, these studies have never simultaneously considered the affinity of sex hormone receptors alongside variables such as sex-related facial morphology. In this study, we analyze their combined effect on behavior in three economic games: the prisoner’s dilemma, the dictator game, and the ultimatum game, as well as participants’ considerations regarding these games. Our results indicate that facial morphology and genetic polymorphisms in sex hormone receptors associated with hormone-binding affinity have an effect on prosocial behavior. These effects are often significant in women but not in men. When polymorphisms are included in the models, facial shape difference emerges as a relevant variable. Regarding hormone receptors, polymorphisms in the androgen receptor and β estrogen receptor genes, but not in the α estrogen receptor, show behavioral effects. Short androgen receptor alleles are associated with making larger offers and expecting less generosity. In women, greater facial differentiation shows similar effects, while larger β estrogen receptor alleles are linked to requiring higher offers. Overall, our findings point to the value of jointly considering receptor affinity and proxies for hormone exposure when exploring their relationship with prosocial behavior.

Recent research has explored the relationship between facial masculinity, human male behaviour and males' perceived features (i.e. attractiveness). The methods of measurement of facial masculinity employed in the literature are quite diverse. In the present paper, we use several methods of measuring facial masculinity to study the effect of this feature on risk attitudes and trustworthiness. We employ two strategic interactions to measure these two traits, a first-price auction and a trust game. We find that facial width-to-height ratio is the best predictor of trustworthiness, and that measures of masculinity which use Geometric Morphometrics are the best suited to link masculinity and bidding behaviour. However, we observe that the link between masculinity and bidding in the first-price auction might be driven by competitiveness and not by risk aversion only. Finally, we test the relationship between facial measures of masculinity and perceived masculinity. As a conclusion, we suggest that researchers in the field should measure masculinity using one of these methods in order to obtain comparable results. We also encourage researchers to revise the existing literature on this topic following these measurement methods.

Bodily attractiveness is an important component of mate value. Musculature—a crucial component of men’s bodily attractiveness—provides women with probabilistic information regarding a potential mate’s quality. Overall musculature is comprised of several muscle groups, each of which varies in information value; different muscles should be weighted differently by attractiveness-assessment adaptations as a result. In the current study, women and men (N = 1,742) reported size preferences for 14 major muscle groups. Women’s reported preferences provided only partial support for our hypotheses that women will prefer muscles that most reliably differentiate between potential mates to be larger; men tended to prefer larger upper-body muscles. We discuss possible interpretations of these mixed findings. Ultimately, our findings suggest that attractiveness-assessment adaptations are sensitive to the information contained within specific muscle groups and they highlight the potential for additional research on the nuances of bodily attractiveness assessment.

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.

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.

HCN channels are becoming pharmacological targets mainly in cardiac diseases. But apart from their well-known role in heart pacemaking, these channels are widely expressed in the nervous system where they contribute to the neuron firing pattern. Consequently, abolishing Ih current might have detrimental consequences in a big repertoire of behavioral traits. Several studies in mammals have identified the Ih current as an important determinant of the firing activity of dopaminergic neurons, and recent evidences link alterations in this current to various dopamine-related disorders. We used the model organism Drosophila melanogaster to investigate how lack of Ih current affects dopamine levels and the behavioral consequences in the sleep:activity pattern. Unlike mammals, in Drosophila there is only one gene encoding HCN channels. We generated a deficiency of the DmIh core gene region and measured, by HPLC, levels of dopamine. Our data demonstrate daily variations of dopamine in wild-type fly heads. Lack of Ih current dramatically alters dopamine pattern, but different mechanisms seem to operate during light and dark conditions. Behaviorally, DmIh mutant flies display alterations in the rest:activity pattern, and altered circadian rhythms. Our data strongly suggest that Ih current is necessary to prevent dopamine overproduction at dark, while light input allows cycling of dopamine in an Ih current dependent manner. Moreover, lack of Ih current results in behavioral defects that are consistent with altered dopamine levels.