Experience-independent sex differences in newborn macaques: Females are more social than males

A common genetic variant in the Neurexin family member CNTNAP2 is related to language but not communication skills in youth with Autism Spectrum Disorder

One of the candidate genes related to language variability in individuals with Autism Spectrum Disorder (ASD) is the contactin-associated protein-like 2 gene (CNTNAP2), a member of the Neurexin family. However, due to the different assessment tools used, it is unknown whether the polymorphisms of the CNTNAP2 gene are linked to structural language skills or more general communication abilities. A total of 302 youth aged 7 to 18 years participated in the present study: 131 verbal youth with ASD (62 female), 130 typically developing (TD) youth (64 female), and 41 unaffected siblings (US) of youth with ASD (25 female). Blood samples were collected to obtain genomic DNA and processed by the Rutgers University Cell and Data Repository or using standard protocols (Gentra Puregene Blood DNA extraction kit; Qiagen). Language and verbal communication skills were screened with the Clinical Evaluation of Language Fundamental-4 (CELF-4) and Vineland-II Communication domain, subsequently. The results showed that the polymorphism of CNTNAP2 (SNP rs2710102) was related to structural language abilities, such that participants carrying the A-allele had lower language skills in comparison to the G-allele homozygotes. No relationship was found between the polymorphism of CNTNAP2 and more general communication abilities. Although the study revealed genetic mechanisms that are associated with CELF-4 measures but not Vineland-II in youth with ASD, follow-up studies are needed that will include measures of language and communication that are less correlated to each other as well as will include a group of minimally and/or non-verbal individuals with ASD.

Patterns of gender inequality perception and depressive symptoms among Chinese adults: The mediating role of marital life satisfaction

OBJECTIVES

As one of the most severe public health issues, depressive symptoms have attracted wide attention around the world. This study aims to investigate the mediating role of marital life satisfaction in the relationship between gender inequality perception and depressive symptoms.

METHODS

Data were obtained from the China Family Panel Studies (CFPS) conducted in 2020. This study incorporated a total of 13,409 married residents aged 20 and above.

RESULTS

The residents with middle (B = 0.19, 95 % CI = 0.01, 0.40) or high perception of gender inequality (B = 0.55, 95 % CI = 0.34, 0.75) were more likely to develop depressive symptoms. Marital life satisfaction plays a mediating effect in the relationship between patterns of gender inequality perception and depressive symptoms, and the mediating effect accounted for 4.89 % or 1.37 % of the total impact in the residents with middle or high patterns of gender inequality perception.

LIMITATIONS

Further studies need to understand the mechanisms of perceived patterns of gender inequality and depressive symptoms, because the cross-sectional design in this study cannot draw causal inferences.

CONCLUSION

Patterns of gender inequality perception are significantly associated with depressive symptoms. Marital life satisfaction plays a mediating role in the relationship between patterns of gender inequality perception and depressive symptoms. It is plausible that nurturing healthy marital relationships could mitigate depressive symptoms in individuals who perceive high degrees of gender disparity.

The relationship between gamma-band neural oscillations and language skills in youth with Autism Spectrum Disorder and their first-degree relatives

BACKGROUND

Most children with Autism Spectrum Disorder (ASD) have co-occurring language impairments and some of these autism-specific language difficulties are also present in their non-autistic first-degree relatives. One of the possible neural mechanisms associated with variability in language functioning is alterations in cortical gamma-band oscillations, hypothesized to be related to neural excitation and inhibition balance.

METHODS

We used a high-density 128-channel electroencephalography (EEG) to register brain response to speech stimuli in a large sex-balanced sample of participants: 125 youth with ASD, 121 typically developing (TD) youth, and 40 unaffected siblings (US) of youth with ASD. Language skills were assessed with Clinical Evaluation of Language Fundamentals.

RESULTS

First, during speech processing, we identified significantly elevated gamma power in ASD participants compared to TD controls. Second, across all youth, higher gamma power was associated with lower language skills. Finally, the US group demonstrated an intermediate profile in both language and gamma power, with nonverbal IQ mediating the relationship between gamma power and language skills.

LIMITATIONS

We only focused on one of the possible neural contributors to variability in language functioning. Also, the US group consisted of a smaller number of participants in comparison to the ASD or TD groups. Finally, due to the timing issue in EEG system we have provided only non-phase-locked analysis.

CONCLUSIONS

Autistic youth showed elevated gamma power, suggesting higher excitation in the brain in response to speech stimuli and elevated gamma power was related to lower language skills. The US group showed an intermediate pattern of gamma activity, suggesting that the broader autism phenotype extends to neural profiles.

Maximizing valid eye-tracking data in human and macaque infants by optimizing calibration and adjusting areas of interest

Remote eye tracking with automated corneal reflection provides insights into the emergence and development of cognitive, social, and emotional functions in human infants and non-human primates. However, because most eye-tracking systems were designed for use in human adults, the accuracy of eye-tracking data collected in other populations is unclear, as are potential approaches to minimize measurement error. For instance, data quality may differ across species or ages, which are necessary considerations for comparative and developmental studies. Here we examined how the calibration method and adjustments to areas of interest (AOIs) of the Tobii TX300 changed the mapping of fixations to AOIs in a cross-species longitudinal study. We tested humans (N = 119) at 2, 4, 6, 8, and 14 months of age and macaques (Macaca mulatta; N = 21) at 2 weeks, 3 weeks, and 6 months of age. In all groups, we found improvement in the proportion of AOI hits detected as the number of successful calibration points increased, suggesting calibration approaches with more points may be advantageous. Spatially enlarging and temporally prolonging AOIs increased the number of fixation-AOI mappings, suggesting improvements in capturing infants' gaze behaviors; however, these benefits varied across age groups and species, suggesting different parameters may be ideal, depending on the population studied. In sum, to maximize usable sessions and minimize measurement error, eye-tracking data collection and extraction approaches may need adjustments for the age groups and species studied. Doing so may make it easier to standardize and replicate eye-tracking research findings.

Eye-tracking as a window into primate social cognition

Over the past decade, noninvasive, restraint-free eye-tracking research with primates has transformed our understanding of primate social cognition. The use of this technology with many primate species allows for the exploration and comparison of how these species attend to and understand social agents and interactions. The ability to compare and contrast the cognitive capacities of various primate species, including humans, provides insight into the evolutionary mechanisms and selective pressures that have likely shaped social cognition in similar and divergent ways across the primate order. In this review, we begin by discussing noninvasive behavioral methods used to measure primate gaze and attention before the introduction of noninvasive, restraint-free eye-tracking methodologies. Next, we focus on findings from recent eye-tracking research on primate social cognition, beginning with simple visual and search mechanisms. We then discuss the results that have built on this basic understanding of how primates view images and videos, exploring discrimination and knowledge of social agents, following social cues, tracking perspectives and predicting behavior, and the combination of eye-tracking and other behavioral and physiological methods. Finally, we discuss some future directions of noninvasive eye-tracking research on primate social cognition and current eye-tracking work-in-progress that builds on these previous studies, investigating underexplored socio-cognitive capacities and utilizing new methodologies.

Variation in the Mu-Opioid Receptor (OPRM1) and Offspring Sex Are Associated With Maternal Behavior in Rhesus Macaques (Macaca mulatta)

A μ-opioid receptor (OPRM1) single-nucleotide-polymorphism, found in both humans and rhesus macaques mediates the mother-infant attachment bond. Because mothers treat their sons and daughters differently, it is somewhat surprising that the role of infant sex has not been assessed in the context of a maternal-OPRM1-genotype-by-infant-sex interaction. The present study investigates the effect of maternal-OPRM1-genotype and infant sex on mother-infant behaviors. Over the first 6 months of offspring life, mother-infant behavioral data assessing attachment quality was collected twice weekly from a large number of rhesus monkey mother-infant pairs (N = 161 dyads; n = 64 female infants, n = 97 male infants). Mothers were genotyped for OPRM1 variation. Factor analysis of the observed behaviors showed two factors: Attachment (maternal-infant cradling, rejections, and infant approaches and leaves), and Maternal Restraints (mother restrains infant, preventing exploration). Further analyses showed a two-way, maternal-genotype-by-infant-sex interaction for both factors. For Attachment, mothers with the CC genotype cradled and restrained (Maternal Restraints) their female infants more and rejected them less, when compared to female infants of CG mothers. Perhaps as a consequence, female infants of CC genotype mothers approached and left their mothers less often, when compared to female infants of CG mothers, likely an indication that female infants from mothers with CG genotype play a greater role in maintaining the mother-infant bond than do female infants from CC genotype mothers. This finding may also indicate a more secure attachment in infants from CC genotype mothers. Unlike female infants, on average, the mother-infant relationship of dyads with a male infant was largely undifferentiated by maternal genotype. These findings suggest that, in contrast to female infants from CG mothers, CC mothers and their female infants appear to have a closer mother-infant relationship which may portend close life-long bonds, as mothers and female offspring remain together throughout life. Male offspring appear to have a more aloof mother-infant bond regardless of OPRM1-genotype. The results of this study indicate that maternal-OPRM1 variation mediates mother-infant attachment behaviors for female infants and has less effect for male infants. This suggests that offspring sex should be included in studies investigating the effect of maternal-OPRM1 genotype on the mother-infant attachment relationship.

Comparative connectomics of the primate social brain

Social interaction is thought to provide a selection pressure for human intelligence, yet little is known about its neurobiological basis and evolution throughout the primate lineage. Recent advances in neuroimaging have enabled whole brain investigation of brain structure, function, and connectivity in humans and non-human primates (NHPs), leading to a nascent field of comparative connectomics. However, linking social behavior to brain organization across the primates remains challenging. Here, we review the current understanding of the macroscale neural mechanisms of social behaviors from the viewpoint of system neuroscience. We first demonstrate an association between the number of cortical neurons and the size of social groups across primates, suggesting a link between neural information-processing capacity and social capabilities. Moreover, by capitalizing on recent advances in species-harmonized functional MRI, we demonstrate that portions of the mirror neuron system and default-mode networks, which are thought to be important for representation of the other's actions and sense of self, respectively, exhibit similarities in functional organization in macaque monkeys and humans, suggesting possible homologies. With respect to these two networks, we describe recent developments in the neurobiology of social perception, joint attention, personality and social complexity. Together, the Human Connectome Project (HCP)-style comparative neuroimaging, hyperscanning, behavioral, and other multi-modal investigations are expected to yield important insights into the evolutionary foundations of human social behavior.

Sex and gender difference in cognitive and behavioral studies in developmental age: An introduction

This paper introduces a special issue focused on sex and gender (s/g) cognitive/behavioral differences at developmental ages providing an overview of this multifaceted and debated topic. It will provide a description of the biological systems that are strongly interconnected to generate s/g differences, that is, genetic determinants, sex hormones, differences in brain structure, organization, and/or function, inherited or modifiable under environmental pressures. Developmental studies are rare. Some addressed whether s/g differences in cognitive/behavioral characteristics are evident early in life and are consistent throughout development, entailing that s/g differences can follow the evolving steps in girls and boys in different domains. The data are far from being homogeneous and consistent about s/g difference in language, social skills, and visuo/spatial abilities. The differences are small, often with overlapping performances, similar to what is seen in adulthood. Given that several variables and the interactions between them are implicated, further longitudinal studies adopting adequate assessment tools, very large size multicultural samples stratified in different, well-sized and precise age groups, considering biological and sociocultural variables, are needed. Due to the complexity of the issue, there is still the need to support and adopt an s/g difference approach also in cognitive and behavioral studies at developmental ages. Finally, these studies have not only scientific importance and relevant cultural, anthropological, and social implications, but are also useful for pedagogical programming as well as for the study of the different susceptibility to develop CNS diseases and consequently to promote different therapies and treatments.

The application of noninvasive, restraint-free eye-tracking methods for use with nonhuman primates

Over the past 50 years there has been a strong interest in applying eye-tracking techniques to study a myriad of questions related to human and nonhuman primate psychological processes. Eye movements and fixations can provide qualitative and quantitative insights into cognitive processes of nonverbal populations such as nonhuman primates, clarifying the evolutionary, physiological, and representational underpinnings of human cognition. While early attempts at nonhuman primate eye tracking were relatively crude, later, more sophisticated and sensitive techniques required invasive protocols and the use of restraint. In the past decade, technology has advanced to a point where noninvasive eye-tracking techniques, developed for use with human participants, can be applied for use with nonhuman primates in a restraint-free manner. Here we review the corpus of recent studies (N=32) that take such an approach. Despite the growing interest in eye-tracking research, there is still little consensus on "best practices," both in terms of deploying test protocols or reporting methods and results. Therefore, we look to advances made in the field of developmental psychology, as well as our own collective experiences using eye trackers with nonhuman primates, to highlight key elements that researchers should consider when designing noninvasive restraint-free eye-tracking research protocols for use with nonhuman primates. Beyond promoting best practices for research protocols, we also outline an ideal approach for reporting such research and highlight future directions for the field.

Sexual Dimorphism in Language, and the Gender Shift Hypothesis of Homosexuality

Psychological sex differences have been studied scientifically for more than a century, yet linguists still debate about the existence, magnitude, and causes of such differences in language use. Advances in psychology and cognitive neuroscience have shown the importance of sex and sexual orientation for various psychobehavioural traits, but the extent to which such differences manifest in language use is largely unexplored. Using computerised text analysis (Linguistic Inquiry and Word Count: LIWC 2015), this study found substantial psycholinguistic sexual dimorphism in a large corpus of English-language novels (n = 304) by heterosexual authors. The psycholinguistic sex differences largely aligned with known psychological sex differences, such as empathising–systemising, people–things orientation, and men’s more pronounced spatial cognitive styles and abilities. Furthermore, consistent with predictions from cognitive neuroscience, novels (n = 158) by lesbian authors showed minor signs of psycholinguistic masculinisation, while novels (n = 167) by homosexual men had a female-typical psycholinguistic pattern, supporting the gender shift hypothesis of homosexuality. The findings on this large corpus of 66.9 million words indicate how psychological group differences based on sex and sexual orientation manifest in language use in two centuries of literary art.

The Developing Human Connectome Project: typical and disrupted perinatal functional connectivity

The Developing Human Connectome Project is an Open Science project that provides the first large sample of neonatal functional MRI data with high temporal and spatial resolution. These data enable mapping of intrinsic functional connectivity between spatially distributed brain regions under normal and adverse perinatal circumstances, offering a framework to study the ontogeny of large-scale brain organization in humans. Here, we characterize in unprecedented detail the maturation and integrity of resting state networks (RSNs) at term-equivalent age in 337 infants (including 65 born preterm). First, we applied group independent component analysis to define 11 RSNs in term-born infants scanned at 43.5–44.5 weeks postmenstrual age (PMA). Adult-like topography was observed in RSNs encompassing primary sensorimotor, visual and auditory cortices. Among six higher-order, association RSNs, analogues of the adult networks for language and ocular control were identified, but a complete default mode network precursor was not. Next, we regressed the subject-level datasets from an independent cohort of infants scanned at 37–43.5 weeks PMA against the group-level RSNs to test for the effects of age, sex and preterm birth. Brain mapping in term-born infants revealed areas of positive association with age across four of six association RSNs, indicating active maturation in functional connectivity from 37 to 43.5 weeks PMA. Female infants showed increased connectivity in inferotemporal regions of the visual association network. Preterm birth was associated with striking impairments of functional connectivity across all RSNs in a dose-dependent manner; conversely, connectivity of the superior parietal lobules within the lateral motor network was abnormally increased in preterm infants, suggesting a possible mechanism for specific difficulties such as developmental coordination disorder, which occur frequently in preterm children. Overall, we found a robust, modular, symmetrical functional brain organization at normal term age. A complete set of adult-equivalent primary RSNs is already instated, alongside emerging connectivity in immature association RSNs, consistent with a primary-to-higher order ontogenetic sequence of brain development. The early developmental disruption imposed by preterm birth is associated with extensive alterations in functional connectivity.

Pandemic Leadership: Sex Differences and Their Evolutionary-Developmental Origins

The COVID-19 pandemic has caused a global societal, economic, and social upheaval unseen in living memory. There have been substantial cross-national differences in the kinds of policies implemented by political decision-makers to prevent the spread of the virus, to test the population, and to manage infected patients. Among other factors, these policies vary with politicians' sex: early findings indicate that, on average, female leaders seem more focused on minimizing direct human suffering caused by the SARS-CoV-2 virus, while male leaders implement riskier short-term decisions, possibly aiming to minimize economic disruptions. These sex differences are consistent with broader findings in psychology, reflecting women's stronger empathy, higher pathogen disgust, health concern, care-taking orientation, and dislike for the suffering of other people-as well as men's higher risk-taking, Machiavellianism, psychopathy, narcissism, and focus on financial indicators of success and status. This review article contextualizes sex differences in pandemic leadership in an evolutionary framework. Evolution by natural selection is the only known process in nature that organizes organisms into higher degrees of functional order, or counteracts the unavoidable disorder that would otherwise ensue, and is therefore essential for explaining the origins of human sex differences. Differential sexual selection and parental investment between males and females, together with the sexual differentiation of the mammalian brain, drive sex differences in cognition and behavioral dispositions, underlying men's and women's leadership styles and decision-making during a global pandemic. According to the sexually dimorphic leadership specialization hypothesis, general psychobehavioral sex differences have been exapted during human evolution to create sexually dimorphic leadership styles. They may be facultatively co-opted by societies and/or followers when facing different kinds of ecological and/or sociopolitical threats, such as disease outbreaks or intergroup aggression. Early evidence indicates that against the invisible viral foe that can bring nations to their knees, the strategic circumspection of empathic feminine health "worriers" may bring more effective and humanitarian outcomes than the devil-may-care incaution of masculine risk-taking "warriors".

Superior Detection of Faces in Male Infants at 2 Months

Females generally attend more to social information than males; however, little is known about the early development of these sex differences. With eye tracking, 2-month olds' (N = 101; 44 females) social orienting to faces was measured within four-item image arrays. Infants were more likely to detect human faces compared to objects, suggesting a functional face detection system. Unexpectedly, males looked longer at human faces than females, and only males looked faster and longer at human faces compared to objects. Females, in contrast, looked less at human faces relative to animal faces and objects, appearing socially disinterested. Notably, this is the first report of a male face detection advantage at any age. These findings suggest a unique stage in early infant social development.

Causal evidence for the adaptive benefits of social foraging in the wild

Sociality is a fundamental organizing principle across taxa, thought to come with a suite of adaptive benefits. However, making causal inferences about these adaptive benefits requires experimental manipulation of the social environment, which is rarely feasible in the field. Here we manipulated the number of conspecifics in Trinidadian guppies (Poecilia reticulata) in the wild, and quantified how this affected a key benefit of sociality, social foraging, by investigating several components of foraging success. As adaptive benefits of social foraging may differ between sexes, we studied males and females separately, expecting females, the more social and risk-averse sex in guppies, to benefit more from conspecifics. Conducting over 1600 foraging trials, we found that in both sexes, increasing the number of conspecifics led to faster detection of novel food patches and a higher probability of feeding following detection of the patch, resulting in greater individual resource consumption. The extent of the latter relationship differed between the sexes, with males unexpectedly exhibiting a stronger social benefit. Our study provides rare causal evidence for the adaptive benefits of social foraging in the wild, and highlights that sex differences in sociality do not necessarily imply an unequal ability to profit from the presence of others.

Men, women and STEM: Why the differences and what should be done?

It is a well-known and widely lamented fact that men outnumber women in a number of fields in STEM (science, technology, engineering and maths). The most commonly discussed explanations for the gender gaps are discrimination and socialization, and the most common policy prescriptions target those ostensible causes. However, a great deal of evidence in the behavioural sciences suggests that discrimination and socialization are only part of the story. The purpose of this paper is to highlight other aspects of the story: aspects that are commonly overlooked or downplayed. More precisely, the paper has two main aims. The first is to examine the evidence that factors other than workplace discrimination contribute to the gender gaps in STEM. These include relatively large average sex differences in career and lifestyle preferences, and relatively small average differences in cognitive aptitudes – some favouring males, others favouring females – which are associated with progressively larger differences the further above the average one looks. The second aim is to examine the evidence suggesting that these sex differences are not purely a product of social factors but also have a substantial biological (i.e. inherited) component. A more complete picture of the causes of the unequal sex ratios in STEM may productively inform policy discussions.

New approaches to quantify social development in rhesus macaques (Macaca mulatta): Integrating eye tracking with traditional assessments of social behavior

The nonhuman primate provides a sophisticated animal model system both to explore neurobiological mechanisms underlying complex behaviors and to facilitate preclinical research for neurodevelopmental and neuropsychiatric disease. A better understanding of evolutionarily conserved behaviors and brain processes between humans and nonhuman primates will be needed to successfully apply recently released NIMH guidelines (NOT-MH-19-053) for conducting rigorous nonhuman primate neurobehavioral research. Here, we explore the relationship between two measures of social behavior that can be used in both humans and nonhuman primates-traditional observations of social interactions with conspecifics and eye gaze detection in response to social stimuli. Infant male rhesus macaques (Macaca mulatta) serving as controls (N = 14) for an ongoing study were observed in their social rearing groups and participated in a noninvasive, longitudinal eye-tracking study. We found significant positive relationships between time spent viewing eyes of faces in an eye tracker and number of initiations made for social interactions with peers that is consistent with similar observations in human populations. Although future studies are needed to determine if this relationship represents species-typical social developmental processes, these preliminary results provide a novel framework to explore the relationship between social interactions and social attention in nonhuman primate models for neurobehavioral development.

Do young rhesus macaques know what others see?: A comparative developmental perspective

Humans undergo robust ontogenetic shifts in the theory of mind capabilities. Are these developmental changes unique to human development or are they shared with other closely related non-human species? To explore this issue, we tested the development of the theory of mind capacities in a population of 236 infant and juvenile rhesus macaques (Macaca mulatta). Using a looking-time method, we examined what developing monkeys know about others' perceptions. Specifically, we tested whether younger monkeys predict that a person will reach for an object where she last saw it. Overall, we found a significant interaction between a monkey's age and performance on this task (p = .014). Juvenile monkeys (between two and 5 years of age) show a nonsignificant trend towards human infant-like patterns of performance, looking longer during the unexpected condition as compared to the expected condition, though this difference is nonsignificant (p = .09). However, contrary to findings in human infants, infant rhesus macaques show a different trend. Infant monkeys on average look slightly longer on average during the expected condition than the unexpected condition, though this pattern was not significant (p = .06). Our developmental results in monkeys provide some hints about the development of the theory of mind capacities in non-humans. First, young rhesus macaques appear to show some interest in the perception of other agents. Second, young rhesus seems able to make predictions based on the visual perspective of another agent, though the developmental pattern of this ability is not as clear nor as robust as in humans. As such, though an understanding of others' perceptions is early-emerging in human infants, it may require more experience interacting with other social agents in our non-human relatives.

Damage to Orbitofrontal Areas 12 and 13, but Not Area 14, Results in Blunted Attention and Arousal to Socioemotional Stimuli in Rhesus Macaques

An earlier study in monkeys indicated that lesions to the mid-portion of the ventral orbitofrontal cortex (OFC), including Walker’s areas 11 and 13 (OFC11/13), altered the spontaneous scanning of still pictures of primate faces (neutral and emotional) and the modulation of arousal. Yet, these conclusions were limited by several shortcomings, including the lesion approach, use of static rather than dynamic stimuli, and manual data analyses. To confirm and extend these earlier findings, we compared attention and arousal to social and nonsocial scenes in three groups of rhesus macaques with restricted lesions to one of three OFC areas (OFC12, OFC13, or OFC14) and a sham-operated control group using eye-tracking to capture scanning patterns, focal attention and pupil size. Animals with damage to the lateral OFC areas (OFC12 and OFC13) showed decreased attention specifically to the eyes of negative (threatening) social stimuli and increased arousal (increased pupil diameter) to positive social scenes. In contrast, animals with damage to the ventromedial OFC area (OFC14) displayed no differences in attention or arousal in the presence of social stimuli compared to controls. These findings support the notion that areas of the lateral OFC are critical for directing attention and modulating arousal to emotional social cues. Together with the existence of face-selective neurons in these lateral OFC areas, the data suggest that the lateral OFC may set the stage for multidimensional information processing related to faces and emotion and may be involved in social judgments.

Sex Differences in Neural Responses to the Perception of Social Interactions

Social interaction is critical to emotional well-being. Previous studies have suggested sex differences in the perception of social interaction. However, the findings depend on the nature of interactions and whether it involves facial emotions. Here, we explored sex differences in neural responses to the perception of social interaction using the Human Connectome Project data. Participants (n = 969, 505 women) were engaged in a social cognition task with geometric objects moving and colliding to simulate social interaction. Behaviorally, men relative to women demonstrated higher accuracy in perceiving social vs. random interactions. Men vs. women showed higher activation in the right superior temporal gyrus, bilateral occipital and posterior cingulate cortex and precuneus, and women vs. men showed higher activation in the right inferior frontal cortex, during exposure to social vs. random interactions. In whole-brain regressions, the differences in accuracy rate in identifying social vs. random interactions (AR SOC - AR RAN ) were associated with higher activation in the paracentral lobule (PCL) and lower activation in bilateral anterior insula (AI), pre-supplementary motor area (preSMA), and left middle frontal gyrus (MFG) in men and women combined, lower activation in bilateral AI, preSMA and left MFG in men alone, and higher activation in the PCL and the medial orbitofrontal cortex in women alone. The latter sex differences were confirmed by slope tests. Further, the PCL activity mediated the correlation between an internalizing syndromal score, as assessed by the Achenbach Self-Report, and (AR SOC - AR RAN ) across all subjects. These findings highlighted sex differences in the behavioral and neural processes underlying the perception of social interaction, as well as the influence of internalizing traits on these processes.

Human and monkey infant attention to dynamic social and nonsocial stimuli

The present study explored behavioral norms for infant social attention in typically developing human and nonhuman primate infants. We examined the normative development of attention to dynamic social and nonsocial stimuli longitudinally in macaques (Macaca mulatta) at 1, 3, and 5 months of age (N = 75) and humans at 2, 4, 6, 8, and 13 months of age (N = 69) using eye tracking. All infants viewed concurrently played silent videos-one social video and one nonsocial video. Both macaque and human infants were faster to look to the social than the nonsocial stimulus, and both species grew faster to orient to the social stimulus with age. Further, macaque infants' social attention increased linearly from 1 to 5 months. In contrast, human infants displayed a nonlinear pattern of social interest, with initially greater attention to the social stimulus, followed by a period of greater interest in the nonsocial stimulus, and then a rise in social interest from 6 to 13 months. Overall, human infants looked longer than macaque infants, suggesting humans have more sustained attention in the first year of life. These findings highlight potential species similarities and differences, and reflect a first step in establishing baseline patterns of early social attention development.

Macaque Gaze Responses to the Primatar: A Virtual Macaque Head for Social Cognition Research

Following the expanding use and applications of virtual reality in everyday life, realistic virtual stimuli are of increasing interest in cognitive studies. They allow for control of features such as gaze, expression, appearance, and movement, which may help to overcome limitations of using photographs or video recordings to study social responses. In using virtual stimuli however, one must be careful to avoid the uncanny valley effect, where realistic stimuli can be perceived as eerie, and induce an aversion response. At the same time, it is important to establish whether responses to virtual stimuli mirror responses to depictions of a real conspecific. In the current study, we describe the development of a new virtual monkey head with realistic facial features for experiments with nonhuman primates, the "Primatar." As a first step toward validation, we assessed how monkeys respond to facial images of a prototype of this Primatar compared to images of real monkeys (RMs), and an unrealistic model. We also compared gaze responses between original images and scrambled as well as obfuscated versions of these images. We measured looking time to images in six freely moving long-tailed macaques (Macaca fascicularis) and gaze exploration behavior in three rhesus macaques (Macaca mulatta). Both groups showed more signs of overt attention to original images than scrambled or obfuscated images. In addition, we found no evidence for an uncanny valley effect; since for both groups, looking times did not differ between real, realistic, or unrealistic images. These results provide important data for further development of our Primatar for use in social cognition studies and more generally for cognitive research with virtual stimuli in nonhuman primates. Future research on the absence of an uncanny valley effect in macaques is needed, to elucidate the roots of this mechanism in humans.

The evolutionary origins of natural pedagogy: Rhesus monkeys show sustained attention following nonsocial cues versus social communicative signals

The natural pedagogy hypothesis proposes that human infants preferentially attend to communicative signals from others, facilitating rapid cultural learning. In this view, sensitivity to such signals is a uniquely human adaptation and as such nonhuman animals should not produce or utilize these communicative signals. We test these evolutionary predictions by examining sensitivity to communicative cues in 206 rhesus monkeys (Macaca mulatta) using an expectancy looking time task modeled on prior work with infants. Monkeys observed a human actor who either made eye contact and vocalized to the monkey (social cue), or waved a fruit in front of her face and produced a tapping sound (nonsocial cue). The actor then either looked at an object (referential look) or looked toward empty space (look away). We found that, unlike human infants in analogous situations, rhesus monkeys looked longer at events following nonsocial cues, regardless of the demonstrator's subsequent looking behavior. Moreover younger and older monkeys showed similar patterns of responses across development. These results provide support for the natural pedagogy hypothesis, while also highlighting evolutionary changes in human sensitivity to communicative signals.

Infant rhesus macaque (Macaca mulatta) personality and subjective well-being

Infant temperament is theorized to lay the foundation for adult personality; however, many questions remain regarding personality in infancy, including the number of dimensions, extent to which they are adult-like, and their relation to other outcomes, such as mental and physical health. Here we tested whether adult-like personality dimensions are already present in infancy in a nonhuman primate species. We measured personality and subjective well-being in 7-month-old rhesus macaques (N = 55) using the Hominoid Personality Questionnaire and Subjective Well-Being Questionnaire, both of which were developed for adult primates based on human measures. Multiple human raters, who provided infants with daily care since birth, independently rated each infant. We found high interrater reliability. Results from a parallel analysis and scree plot indicated a five component structure, which, using principal components analysis, we found to be comprised of dimensions relating to Openness (e.g., curiosity, inquisitive, playfulness), Assertiveness (e.g., dominance, bullying, aggressive), Anxiety (e.g., vigilance, fearful), Friendliness (e.g., sociable, affectionate, sympathetic), and Intellect (e.g., organized, not erratic). These components are largely analogous to those in adult macaques, suggesting remarkably stable structural personality components across the lifespan. Infant macaques' subjective well-being positively correlates with Openness and Assertiveness and negatively correlated with Anxiety, similar to findings in adult macaques and other primates. Together, these findings suggest that, in macaques, infant personality dimensions may be conceptually related to adult personality and challenge the view that infant temperament may be disorganized and not as meaningful as adult personality. Further research is necessary to explore the antecedents, predictive validity, and stability of these personality components across situations and with development.

Social touch alters newborn monkey behavior

In humans, infants respond positively to slow, gentle stroking-processed by C-tactile (CT) nerve fibers-by showing reductions in stress and increases in eye contact, smiling, and positive vocalizations. More frequent maternal touch is linked to greater activity and connectivity strength in social brain regions, and increases children's attention to and learning of faces. It has been theorized that touch may prime children for social interactions and set them on a path towards healthy social cognitive development. However, less is known about the effects of touch on young infants' psychological development, especially in the newborn period, a highly sensitive period of transition with rapid growth in sensory and social processing. It remains untested whether newborns can distinguish CT-targeted touch from other types of touch, or whether there are benefits of touch for newborns' social, emotional, or cognitive development. In the present study, we experimentally investigated the acute effects of touch in newborn monkeys, a common model for human social development. Rhesus macaques (Macaca mulatta), like humans, are highly social, have complex mother-infant interactions with frequent body contact for the first weeks of life, making them an excellent model of infant sociality. Infant monkeys in the present study were reared in a neonatal nursery, enabling control over their early environment, including all caregiver interactions. One-week-old macaque infants (N = 27) participated in three 5-minute counter-balanced caregiver interactions, all with mutual gaze: stroking head and shoulders (CT-targeted touch), stroking palms of hands and soles of feet (Non-CT touch), or no stroking (No-touch). Immediately following the interaction, infants watched social and nonsocial videos and picture arrays including faces and objects, while we tracked their visual attention with remote eye tracking. We found that, during the caregiver interactions, infants behaved differently while being touched compared to the no-touch condition, irrespective of the body part touched. Most notably, in both touch conditions, infants exhibited fewer stress-related behaviors-self-scratching, locomotion, and contact time with a comfort object-compared to when they were not touched. Following CT-targeted touch, infants were faster to orient to the picture arrays compared to the other interaction conditions, suggesting CT-targeted touch may activate or prime infants' attentional orienting system. In the No-touch condition infants attended longer to the nonsocial compared to the social video, possibly reflecting a baseline preference for nonsocial stimuli. In contrast, in both touch conditions, infants' looked equally to the social and nonsocial videos, suggesting that touch may influence the types of visual stimuli that hold infants' attention. Collectively, our results reveal that newborn macaques responded positively to touch, and touch appeared to influence some aspects of their subsequent attention, although we found limited evidence that these effects are mediated by CT fibers. These findings suggest that newborn touch may broadly support infants' psychological development, and may have early evolutionary roots, shared across primates. This study illustrates the unique insight offered by nonhuman primates for exploring early infant social touch, revealing that touch may positively affect emotional and attentional development as early as the newborn period.

A parameterized digital 3D model of the Rhesus macaque face for investigating the visual processing of social cues

BACKGROUND

Rhesus macaques are the most popular model species for studying the neural basis of visual face processing and social interaction using intracranial methods. However, the challenge of creating realistic, dynamic, and parametric macaque face stimuli has limited the experimental control and ethological validity of existing approaches.

NEW METHOD

We performed statistical analyses of in vivo computed tomography data to generate an anatomically accurate, three-dimensional representation of Rhesus macaque cranio-facial morphology. The surface structures were further edited, rigged and textured by a professional digital artist with careful reference to photographs of macaque facial expression, colouration and pelage.

RESULTS

The model offers precise, continuous, parametric control of craniofacial shape, emotional expression, head orientation, eye gaze direction, and many other parameters that can be adjusted to render either static or dynamic high-resolution faces. Example single-unit responses to such stimuli in macaque inferotemporal cortex demonstrate the value of parametric control over facial appearance and behaviours.

COMPARISON WITH EXISTING METHOD(S)

The generation of such a high-dimensionality and systematically controlled stimulus set of conspecific faces, with accurate craniofacial modelling and professional finalization of facial details, is currently not achievable using existing methods.

CONCLUSIONS

The results herald a new set of possibilities in adaptive sampling of a high-dimensional and socially meaningful feature space, thus opening the door to systematic testing of hypotheses about the abundant neural specialization for faces found in the primate.

Sex differences in early communication development: behavioral and neurobiological indicators of more vulnerable communication system development in boys

Perhaps due to different roles they have had in social groups during evolution, men and women differ in their verbal abilities. These differences are also (if not even more) present in children, both in the course of typical and pathological development. Beside the fact that girls have a well-documented advantage in early language development, almost all developmental disorders primarily affecting communication, speech, and language skills are more frequent in boys. The sex-related difference in the prevalence of these disorders is especially pronounced in autism spectrum disorder (1 girl for each 4-5 boys is affected). The aim of this review is to present the sex differences in typical communication and language development and in the prevalence of communication-related neurodevelopmental disorders. Also, a special focus is put on data from the field of neuroscience that might provide insight into the neurobiological mechanisms that can add to the understanding of this phenomenon. We argue that the functional organization of the female brain gives women an inherent advantage in the acquisition of communication and language system over men.

Sex differences in early communication development: behavioral and neurobiological indicators of more vulnerable communication system development in boys

Perhaps due to different roles they have had in social groups during evolution, men and women differ in their verbal abilities. These differences are also (if not even more) present in children, both in the course of typical and pathological development. Beside the fact that girls have a well-documented advantage in early language development, almost all developmental disorders primarily affecting communication, speech, and language skills are more frequent in boys. The sex-related difference in the prevalence of these disorders is especially pronounced in autism spectrum disorder (1 girl for each 4-5 boys is affected). The aim of this review is to present the sex differences in typical communication and language development and in the prevalence of communication-related neurodevelopmental disorders. Also, a special focus is put on data from the field of neuroscience that might provide insight into the neurobiological mechanisms that can add to the understanding of this phenomenon. We argue that the functional organization of the female brain gives women an inherent advantage in the acquisition of communication and language system over men.

Maternal pre- and postnatal anxiety symptoms and infant attention disengagement from emotional faces

BACKGROUND

Biases in socio-emotional attention may be early markers of risk for self-regulation difficulties and mental illness. We examined the associations between maternal pre- and postnatal anxiety symptoms and infant attention patterns to faces, with particular focus on attentional biases to threat, across male and female infants.

METHODS

A general population, Caucasian sample of eight-month old infants (N = 362) were tested using eye-tracking and an attention disengagement (overlap) paradigm, with happy, fearful, neutral, and phase-scrambled faces and distractors. Maternal self-reported anxiety symptoms were assessed with the Symptom Checklist-90/anxiety subscale at five time points between gestational week 14 and 6 months postpartum.

RESULTS

Probability of disengagement was lowest for fearful faces in the whole sample. Maternal pre- but not postnatal anxiety symptoms associated with higher threat bias in infants, and the relation between maternal anxiety symptoms in early pregnancy and higher threat bias in infants remained significant after controlling for maternal postnatal symptoms. Maternal postnatal anxiety symptoms, in turn, associated with higher overall probability of disengagement from faces to distractors, but the effects varied by child sex.

LIMITATIONS

The small number of mothers suffering from very severe symptoms. No control for the comorbidity of depressive symptoms.

CONCLUSIONS

Maternal prenatal anxiety symptoms associate with infant's heightened attention bias for threat. Maternal postnatal anxiety symptoms, in turn, associate with infant's overall disengagement probability differently for boys and girls. Boys may show enhanced vigilance for distractors, except when viewing fearful faces, and girls enhanced vigilance for all socio-emotional stimuli. Long-term implications of these findings remain to be explored.

Visual preferences for direct-gaze faces in infant macaques (Macaca mulatta) with limited face exposure

From birth, human and nonhuman primates attend more to faces with direct gaze compared with averted gaze, and previous studies report that attention to the eyes is linked to the emergence of later social skills. Here, we explored whether early experiences influence attraction to eye contact in infant macaques by examining their attention to face pairs varying in their gaze direction across the first 13 weeks of life. Infants raised by human caretakers had limited conspecific interactions (nursery-reared; N = 16) and were compared to infants raised in rich social environments (mother-reared; N = 20). Both groups looked longer to faces and the eyes of direct compared to averted-gaze faces. Looking to all faces and eyes also increased with age. Nursery-reared infants did not display age-associated increases in attention to direct-gaze faces specifically, suggesting that, while there may be an initial preference for direct-gaze faces from birth, social experiences may support its early development.

Infant perception of sex differences in biological motion displays

We examined mechanisms underlying infants' ability to categorize human biological motion stimuli from sex-typed walk motions, focusing on how visual attention to dynamic information in point-light displays (PLDs) contributes to infants' social category formation. We tested for categorization of PLDs produced by women and men by habituating infants to a series of female or male walk motions and then recording posthabituation preferences for new PLDs from the familiar or novel category (Experiment 1). We also tested for intrinsic preferences for female or male walk motions (Experiment 2). We found that infant boys were better able to categorize PLDs than were girls and that male PLDs were preferred overall. Neither of these effects was found to change with development across the observed age range (∼4-18 months). We conclude that infants' categorization of walk motions in PLDs is constrained by intrinsic preferences for higher motion speeds and higher spans of motion and, relatedly, by differences in walk motions produced by men and women.

Sex and rank affect how infant rhesus macaques look at faces

We investigated how differences in infant sex and mothers' dominance status affect infant rhesus macaques' (Macaca mulatta) interest in visually exploring emotional facial expressions. Thirty-eight infants were presented with animated avatars of macaque facial expressions during the first month of life. Sons of high-ranking mothers looked more at faces, especially the eye region, than sons of low-ranking mothers, but no difference in looking duration was found for daughters. Males looked significantly more at eyes than females, but this effect was reversed in infants who were reared without mothers in a primate nursery facility. In addition, in mother-infant interactions, mothers of sons were more likely to gaze at their infant's face compared to mothers of daughters. Combined with previous research indicating that rhesus macaque mothers interact differently with infants based on their own rank and infant's sex, these results support the view that social experiences shape early face preferences in rhesus macaques.

Sex differences in nonhuman primate behavioral development

Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields, and a persistent topic of discussion and debate is the relative contribution of biological vs. social influences to such differences. Given the potentially large effects of cultural and social influences on human child development, nonhuman primates are important model species for investigating the biological and evolutionary roots of sex differences in human development. This Mini-Review briefly summarizes the existing literature on sex-biased behavior toward infant nonhuman primates by mothers and other social partners, followed by a review of findings on sex differences (or lack thereof) in primate behavioral development from a variety of species in wild and naturalistic settings. These include differences in physical and social development, including play, grooming, and object manipulation patterns, as well as nursing and the development of foraging behavior. The Mini-Review concludes by providing potential avenues for future research. © 2016 Wiley Periodicals, Inc.

Preference for novel faces in male infant monkeys predicts cerebrospinal fluid oxytocin concentrations later in life

The ability to recognize individuals is a critical skill acquired early in life for group living species. In primates, individual recognition occurs predominantly through face discrimination. Despite the essential adaptive value of this ability, robust individual differences in conspecific face recognition exist, yet its associated biology remains unknown. Although pharmacological administration of oxytocin has implicated this neuropeptide in face perception and social memory, no prior research has tested the relationship between individual differences in face recognition and endogenous oxytocin concentrations. Here we show in a male rhesus monkey cohort (N = 60) that infant performance in a task used to determine face recognition ability (specifically, the ability of animals to show a preference for a novel face) robustly predicts cerebrospinal fluid, but not blood, oxytocin concentrations up to five years after behavioural assessment. These results argue that central oxytocin biology may be related to individual face perceptual abilities necessary for group living, and that these differences are stable traits.

Handling newborn monkeys alters later exploratory, cognitive, and social behaviors

Touch is one of the first senses to develop and one of the earliest modalities for infant-caregiver communication. While studies have explored the benefits of infant touch in terms of physical health and growth, the effects of social touch on infant behavior are relatively unexplored. Here, we investigated the influence of neonatal handling on a variety of domains, including memory, novelty seeking, and social interest, in infant monkeys (Macaca mulatta; n=48) from 2 to 12 weeks of age. Neonates were randomly assigned to receive extra holding, with or without accompanying face-to-face interactions. Extra-handled infants, compared to standard-reared infants, exhibited less stress-related behavior and more locomotion around a novel environment, faster approach of novel objects, better working memory, and less fear towards a novel social partner. In sum, infants who received more tactile stimulation in the neonatal period subsequently demonstrated more advanced motor, social, and cognitive skills-particularly in contexts involving exploration of novelty-in the first three months of life. These data suggest that social touch may support behavioral development, offering promising possibilities for designing future early interventions, particularly for infants who are at heightened risk for social disorders.

Tolerant Barbary macaques maintain juvenile levels of social attention in old age, but despotic rhesus macaques do not

Complex social life is thought to be a major driver of complex cognition in primates, but few studies have directly tested the relationship between a given primate species' social system and their social cognitive skills. We experimentally compared life span patterns of a foundational social cognitive skill (following another's gaze) in tolerant Barbary macaques, Macaca sylvanus, and despotic rhesus macaques, Macaca mulatta. Semi-free-ranging monkeys (N = 80 individuals from each species) followed gaze more in test trials where an actor looked up compared to control trials. However, species differed in ontogenetic trajectories: both exhibited high rates of gaze following as juveniles, but rhesus monkeys exhibited declines in social attention with age, whereas Barbary macaques did not. This pattern indicates that developmental patterns of social attention vary with social tolerance, and that diversity in social behaviour can lead to differences in social cognition across primates.

Rhesus monkeys show human-like changes in gaze following across the lifespan

Gaze following, or co-orienting with others, is a foundational skill for human social behaviour. The emergence of this capacity scaffolds critical human-specific abilities such as theory of mind and language. Non-human primates also follow others' gaze, but less is known about how the cognitive mechanisms supporting this behaviour develop over the lifespan. Here we experimentally tested gaze following in 481 semi-free-ranging rhesus macaques (Macaca mulatta) ranging from infancy to old age. We found that monkeys began to follow gaze in infancy and this response peaked in the juvenile period-suggesting that younger monkeys were especially attuned to gaze information, like humans. After sexual maturity, monkeys exhibited human-like sex differences in gaze following, with adult females showing more gaze following than males. Finally, older monkeys showed reduced propensity to follow gaze, just as older humans do. In a second study (n = 80), we confirmed that macaques exhibit similar baseline rates of looking upwards in a control condition, regardless of age. Our findings indicate that-despite important differences in human and non-human primate life-history characteristics and typical social experiences-monkeys undergo robust ontogenetic shifts in gaze following across early development, adulthood and ageing that are strikingly similar to those of humans.

Testing the arousal hypothesis of neonatal imitation in infant rhesus macaques

Neonatal imitation is the matching of (often facial) gestures by newborn infants. Some studies suggest that performance of facial gestures is due to general arousal, which may produce false positives on neonatal imitation assessments. Here we examine whether arousal is linked to facial gesturing in newborn infant rhesus macaques (Macaca mulatta). We tested 163 infants in a neonatal imitation paradigm in their first postnatal week and analyzed their lipsmacking gestures (a rapid opening and closing of the mouth), tongue protrusion gestures, and yawn responses (a measure of arousal). Arousal increased during dynamic stimulus presentation compared to the static baseline across all conditions, and arousal was higher in the facial gestures conditions than the nonsocial control condition. However, even after controlling for arousal, we found a condition-specific increase in facial gestures in infants who matched lipsmacking and tongue protrusion gestures. Thus, we found no support for the arousal hypothesis. Consistent with reports in human newborns, imitators’ propensity to match facial gestures is based on abilities that go beyond mere arousal. We discuss optimal testing conditions to minimize potentially confounding effects of arousal on measurements of neonatal imitation.

Modeling Rett Syndrome Using TALEN-Edited MECP2 Mutant Cynomolgus Monkeys

Gene-editing technologies have made it feasible to create nonhuman primate models for human genetic disorders. Here, we report detailed genotypes and phenotypes of TALEN-edited MECP2 mutant cynomolgus monkeys serving as a model for a neurodevelopmental disorder, Rett syndrome (RTT), which is caused by loss-of-function mutations in the human MECP2 gene. Male mutant monkeys were embryonic lethal, reiterating that RTT is a disease of females. Through a battery of behavioral analyses, including primate-unique eye-tracking tests, in combination with brain imaging via MRI, we found a series of physiological, behavioral, and structural abnormalities resembling clinical manifestations of RTT. Moreover, blood transcriptome profiling revealed that mutant monkeys resembled RTT patients in immune gene dysregulation. Taken together, the stark similarity in phenotype and/or endophenotype between monkeys and patients suggested that gene-edited RTT founder monkeys would be of value for disease mechanistic studies as well as development of potential therapeutic interventions for RTT.

Acute oxytocin improves memory and gaze following in male but not female nursery-reared infant macaques

RATIONALE

Exogenous oxytocin administration is widely reported to improve social cognition in human and nonhuman primate adults. Risk factors of impaired social cognition, however, emerge in infancy. Early interventions-when plasticity is greatest-are critical to reverse negative outcomes.

OBJECTIVE

We tested the hypothesis that oxytocin may exert similar positive effects on infant social cognition, as in adults. To test this idea, we assessed the effectiveness of acute, aerosolized oxytocin on two foundational social cognitive skills: working memory (i.e., ability to briefly hold and process information) and social gaze (i.e., tracking the direction of others' gaze) in 1-month-old nursery-reared macaque monkeys (Macaca mulatta). We did not predict sex differences, but we included sex as a factor in our analyses to test whether our effects would be generalizable across both males and females.

RESULTS

In a double-blind, placebo-controlled design, we found that females were more socially skilled at baseline compared to males, and that oxytocin improved working memory and gaze following, but only in males.

CONCLUSIONS

These sex differences, while unexpected, may be due to interactions with gonadal steroids and may be relevant to sexually dimorphic disorders of social cognition, such as male-biased autism spectrum disorder, for which oxytocin has been proposed as a potential treatment. In sum, we report the first evidence that oxytocin may influence primate infant cognitive abilities. Moreover, these behavioral effects appear sexually dimorphic, highlighting the importance of considering sex differences. Oxytocin effects observed in one sex may not be generalizable to the other sex.

Sex Differences in Androgen Regulation of Metabolism in Nonhuman Primates

The in-depth characterization of sex differences relevant to human physiology requires the judicious use of a variety of animal models and human clinical data. Nonhuman primates (NHPs) represent an important experimental system that bridges rodent studies and clinical investigations. NHP studies have been especially useful in understanding the role of sex hormones in development and metabolism and also allow the elucidation of the effects of pertinent dietary influences on physiology pertinent to disease states such as obesity and diabetes. This chapter summarizes the current state of our understanding of androgen effects on male and female NHP metabolism relevant to hypogonadism in human males and polycystic ovary syndrome in human females. This review will also focus on the interaction between altered androgen levels and dietary restriction and excess, in particular the Western-style diet that underlies significant human pathophysiology.

Neonatal imitation predicts infant rhesus macaque (Macaca mulatta) social and anxiety-related behaviours at one year

The identification of early markers that predict the development of specific social trajectories is critical to understand the developmental and neurobiological underpinnings of healthy social development. We investigated, in infant rhesus macaques (Macaca mulatta), whether newborns’ capacity to imitate facial gestures is a valid predictive marker for the emergence of social competencies later in development, at one year of age. Here we first assessed whether infant macaques (N = 126) imitate lipsmacking gestures (a macaque affiliative expression) performed by a human experimenter in their first week of life. We then collected data on infants’ social interactions (aggression, grooming, and play) and self-scratching (a proxy indicator of anxiety) at 11–14 months when infants were transferred into a new enclosure with a large social group. Our results show that neonatal imitators exhibit more dominant behaviours, are less anxious, and, for males only, spend more time in play at one year old. These findings suggest that neonatal imitation may be an early predictor of infant sociality and may help identify infants at risk of neurodevelopmental social deficits.

Personality and gender differences in global perspective

Men's and women's personalities appear to differ in several respects. Social role theories of development assume gender differences result primarily from perceived gender roles, gender socialization and sociostructural power differentials. As a consequence, social role theorists expect gender differences in personality to be smaller in cultures with more gender egalitarianism. Several large cross-cultural studies have generated sufficient data for evaluating these global personality predictions. Empirically, evidence suggests gender differences in most aspects of personality-Big Five traits, Dark Triad traits, self-esteem, subjective well-being, depression and values-are conspicuously larger in cultures with more egalitarian gender roles, gender socialization and sociopolitical gender equity. Similar patterns are evident when examining objectively measured attributes such as tested cognitive abilities and physical traits such as height and blood pressure. Social role theory appears inadequate for explaining some of the observed cultural variations in men's and women's personalities. Evolutionary theories regarding ecologically-evoked gender differences are described that may prove more useful in explaining global variation in human personality.