Conspecific interactions predict social transmission of fear in female rats.

Social transmission of fear occurs in a subset of individuals, where an Observer displays a fear response to a previously neutral stimulus after witnessing or interacting with a conspecific Demonstrator during memory retrieval. The conditions under which fear can be acquired socially in rats have received attention in recent years, and suggest that social factors modulate social transmission of information. We previously found that one such factor, social rank, impacts fear conditioning by proxy in male rats. Here, we aimed to investigate whether social roles as determined by nape contacts in females, might also have an influence on social transmission of fear. In-line with previous findings in males, we found that social interactions in the home cage can provide insight into the social relationship between female rats and that these relationships predict the degree of fear acquired by-proxy. These results suggest that play behavior affects the social transfer/transmission of information in female rats.

Physiological data for affective computing in HRI with anthropomorphic service robots: the AFFECT-HRI data set.

In human-human and human-robot interaction, the counterpart influences the human's affective state. Contrary to humans, robots inherently cannot respond empathically, meaning non-beneficial affective reactions cannot be mitigated. Thus, to create a responsible and empathetic human-robot interaction (HRI), involving anthropomorphic service robots, the effect of robot behavior on human affect in HRI must be understood. To contribute to this understanding, we provide the new comprehensive data set AFFECT-HRI, including, for the first time, physiological data labeled with human affect (i.e., emotions and mood) gathered from a conducted HRI study. Within the study, 146 participants interacted with an anthropomorphic service robot in a realistic and complex retail scenario. The participants' questionnaire ratings regarding affect, demographics, and socio-technical ratings are provided in the data set. Five different conditions (i.e., neutral, transparency, liability, moral, and immoral) were considered during the study, eliciting different affective reactions and allowing interdisciplinary investigations (e.g., computer science, law, and psychology). Each condition includes three scenes: a consultation regarding products, a request for sensitive personal information, and a handover.

Reversing valproic acid-induced autism-like behaviors through a combination of low-frequency repeated transcranial magnetic stimulation and superparamagnetic iron oxide nanoparticles.

Transcranial magnetic stimulation (TMS) is a neurostimulation device used to modulate brain cortex activity. Our objective was to enhance the therapeutic effectiveness of low-frequency repeated TMS (LF-rTMS) in a rat model of autism spectrum disorder (ASD) induced by prenatal valproic acid (VPA) exposure through the injection of superparamagnetic iron oxide nanoparticles (SPIONs). For the induction of ASD, we administered prenatal VPA (600 mg/kg, I.P.) on the 12.5th day of pregnancy. At postnatal day 30, SPIONs were injected directly into the lateral ventricle of the brain. Subsequently, LF-rTMS treatment was applied for 14 consecutive days. Following the treatment period, behavioral analyses were conducted. At postnatal day 60, brain tissue was extracted, and both biochemical and histological analyses were performed. Our data revealed that prenatal VPA exposure led to behavioral alterations, including changes in social interactions, increased anxiety, and repetitive behavior, along with dysfunction in stress coping strategies. Additionally, we observed reduced levels of SYN, MAP2, and BDNF. These changes were accompanied by a decrease in dendritic spine density in the hippocampal CA1 area. However, LF-rTMS treatment combined with SPIONs successfully reversed these dysfunctions at the behavioral, biochemical, and histological levels, introducing a successful approach for the treatment of ASD.

Factors Associated with Lower Social Activity in German Older Adults at Increased Risk of Dementia: A Cross-Sectional Analysis.

Background: Studies demonstrate associations between low social activity in older adults and cognitive decline. Little has been investigated regarding which factors are associated with low social activity in older adults at increased risk of dementia. Objective: We investigate which sociodemographic, psychological, health-related, and environmental factors are associated with low social activity in older adults at increased risk of dementia. Additionally, we describe the stages of health behavior change, the types of social activities, and the duration of the current level of social activity. Methods: We used baseline data of 1,015 participants from the AgeWell.de trial. We conducted logistic and Poisson regression analyses to investigate factors associated with low social activity. We report descriptive statistics on the stages of change in the sample, the types of social activities most frequently pursued, and the duration of the current level of social activity. Results: Lower income, non-usage of public transport, depressive symptoms, cognitive, mobility, and hearing impairment were negatively associated with social activity. The majority of the sample was in the maintenance stage, followed by the precontemplation stage. The most common social activities were traveling and hobbies with others. Participants have maintained their current level of social activity for several years. Conclusions: We identified a lack of resources (income, transport), depressive symptoms and poorer health (cognitive, mobility and hearing impairment) as barriers to social activity. Interventions promoting social activity in older adults at risk of dementia may specifically target individuals with these risk factors. Low-threshold opportunities for social activity may be particularly beneficial.

Genetic Variation in Male Aggression Is Influenced by Genotype of Prior Social Partners in Drosophila melanogaster.

AbstractSocial behaviors can be influenced by the genotypes of interacting individuals through indirect genetic effects (IGEs) and can also display developmental plasticity. We investigated how developmental IGEs, which describe the effects of a prior social partner's genotype on later behavior, can influence aggression in male Drosophila melanogaster. We predicted that developmental IGEs cannot be estimated by simply extending the effects of contextual IGEs over time and instead have their own unique effects on behavior. On day 1 of the experiment, we measured aggressive behavior in 15 genotypic pairings (n=600 males). On day 2, each of the males was paired with a new opponent, and aggressive behavior was again measured. We found contextual IGEs on day 1 of the experiment and developmental IGEs on day 2 of the experiment: the influence of the day 1 partner's genotype on the focal individual's day 2 behavior depended on the genotypic identity of both the day 1 partner and the focal male. Importantly, the developmental IGEs in our system produced fundamentally different dynamics than the contextual IGEs, as the presence of IGEs was altered over time. These findings represent some of the first empirical evidence demonstrating developmental IGEs, a first step toward incorporating developmental IGEs into our understanding of behavioral evolution.

Dynamics of Information Flow and Task Allocation of Social Insect Colonies: Impacts of Spatial Interactions and Task Switching.

Models of social interaction dynamics have been powerful tools for understanding the efficiency of information spread and the robustness of task allocation in social insect colonies. How workers spatially distribute within the colony, or spatial heterogeneity degree (SHD), plays a vital role in contact dynamics, influencing information spread and task allocation. We used agent-based models to explore factors affecting spatial heterogeneity and information flow, including the number of task groups, variation in spatial arrangements, and levels of task switching, to study: (1) the impact of multiple task groups on SHD, contact dynamics, and information spread, and (2) the impact of task switching on SHD and contact dynamics. Both models show a strong linear relationship between the dynamics of SHD and contact dynamics, which exists for different initial conditions. The multiple-task-group model without task switching reveals the impacts of the number and spatial arrangements of task locations on information transmission. The task-switching model allows task-switching with a probability through contact between individuals. The model indicates that the task-switching mechanism enables a dynamical state of task-related spatial fidelity at the individual level. This spatial fidelity can assist the colony in redistributing their workforce, with consequent effects on the dynamics of spatial heterogeneity degree. The spatial fidelity of a task group is the proportion of workers who perform that task and have preferential walking styles toward their task location. Our analysis shows that the task switching rate between two tasks is an exponentially decreasing function of the spatial fidelity and contact rate. Higher spatial fidelity leads to more agents aggregating to task location, reducing contact between groups, thus making task switching more difficult. Our results provide important insights into the mechanisms that generate spatial heterogeneity and deepen our understanding of how spatial heterogeneity impacts task allocation, social interaction, and information spread.

The role of champions in the implementation of technology in healthcare services: a systematic mixed studies review.

BACKGROUND: Champions play a critical role in implementing technology within healthcare services. While prior studies have explored the presence and characteristics of champions, this review delves into the experiences of healthcare personnel holding champion roles, as well as the experiences of healthcare personnel interacting with them. By synthesizing existing knowledge, this review aims to inform decisions regarding the inclusion of champions as a strategy in technology implementation and guide healthcare personnel in these roles. METHODS: A systematic mixed studies review, covering qualitative, quantitative, or mixed designs, was conducted from September 2022 to March 2023. The search spanned Medline, Embase, CINAHL, and Scopus, focusing on studies published from 2012 onwards. The review centered on health personnel serving as champions in technology implementation within healthcare services. Quality assessments utilized the Mixed Methods Appraisal Tool (MMAT). RESULTS: From 1629 screened studies, 23 were included. The champion role was often examined within the broader context of technology implementation. Limited studies explicitly explored experiences related to the champion role from both champions' and health personnel's perspectives. Champions emerged as promoters of technology, supporting its adoption. Success factors included anchoring and selection processes, champions' expertise, and effective role performance. DISCUSSION: The specific tasks and responsibilities assigned to champions differed across reviewed studies, highlighting that the role of champion is a broad one, dependent on the technology being implemented and the site implementing it. Findings indicated a correlation between champion experiences and organizational characteristics. The role's firm anchoring within the organization is crucial. Limited evidence suggests that volunteering, hiring newly graduated health personnel, and having multiple champions can facilitate technology implementation. Existing studies predominantly focused on client health records and hospitals, emphasizing the need for broader research across healthcare services. CONCLUSIONS: With a clear mandate, dedicated time, and proper training, health personnel in champion roles can significantly contribute professional, technological, and personal competencies to facilitate technology adoption within healthcare services. The review finds that the concept of champions is a broad one and finds varied definitions of the champion role concept. This underscores the importance of describing organizational characteristics, and highlights areas for future research to enhance technology implementation strategies in different healthcare settings with support of a champion.

Freshwater trematodes differ from marine trematodes in patterns connected with division of labor.

Background: Prior research suggests that trematode rediae, a developmental stage of trematode parasites that reproduce clonally within a snail host, show evidence of division of labor (DOL). Single-species infections often have two morphologically distinct groups: small rediae, the 'soldiers', are active, aggressive, and do not appear to reproduce; large rediae, the 'reproductives', are larger, sluggish, and full of offspring. Most data supporting DOL come from trematodes infecting marine snails, while data from freshwater trematodes are more limited and generally do not supported DOL. The shorter lifespan typical of freshwater snails may partially explain this difference: defending a short-lived host at the expense of reproduction likely provides few advantages. Here, we present data from sixty-one colonies spanning twenty species of freshwater trematode exploring morphological and behavioral patterns commonly reported from marine trematodes believed to have DOL. Methods: Trematode rediae were obtained from sixty-one infected snails collected in central Vermont, USA. A portion of the COI gene was sequenced to make tentative species identifications ('COI species'). Samples of rediae were photographed, observed, and measured to look for DOL-associated patterns including a bimodal size distribution, absence of embryos in small rediae, and pronounced appendages and enlarged pharynges (mouthparts) in small rediae. Additional rediae were used to compare activity levels and likelihood to attack heterospecific trematodes in large vs. small rediae. Results: Many of the tests for DOL-associated patterns showed mixed results, even among colonies of the same COI species. However, we note a few consistent patterns. First, small rediae of most colonies appeared capable of reproduction, and we saw no indication (admittedly based on a small sample size and possibly insufficient attack trial methodology) that small rediae were more active or aggressive. This differs from patterns reported from most marine trematodes. Second, the small rediae of most colonies had larger pharynges relative to their body size than large rediae, consistent with marine trematodes. We also observed that colonies of three sampled COI species appear to produce a group of large rediae that have distinctly large pharynges. Conclusions: We conclude that these freshwater species likely do not have a group of specialized non-reproductive soldiers because small rediae of at least some colonies in almost every species do appear to produce embryos. We cannot rule out the possibility that small rediae act as a temporary soldier caste. We are intrigued by the presence of rediae with enlarged pharynges in some species and propose that they may serve an adaptive role, possibly similar to the defensive role of small 'soldier' rediae of marine trematodes. Large-pharynx rediae have been documented in other species previously, and we encourage future efforts to study these large-pharynx rediae.

Multi-assay approach shows species-associated personality patterns in two socially distinct gerbil species.

We aimed to investigate whether two closely related but socially distinct species of gerbils differ in personality patterns. Using a suit of multivariate repeated assays (docility test, dark-light emergence test, startle test, novel object test, elevated platform test, and stranger test), we assessed contextual and temporal consistency of docility, boldness, exploration, anxiety, and sociability in the solitary midday gerbil, Meriones meridianus, and social Mongolian gerbil, M. unguiculatus. We revealed contextually consistent and highly repeatable sex-independent but species-specific personality traits. Species differed in temporal repeatability of different behaviours, and contextual consistency was more pronounced in solitary M. meridianus than in social M. unguiculatus. This finding contradicts the social niche specialization hypothesis, which suggests that personality traits should be more consistent in more social species. Instead, we hypothesize that social complexity should favour more flexible and less consistent behavioural traits. The habituation effect indicative of learning abilities was weak in both species yet stronger in social M. unguiculatus, supporting the relationship between the sociality level and cognitive skills. In both species, only a few different behavioural traits covaried, and the sets of correlated behaviours were species-specific such that the two species did not share any pair of correlated traits. Between-species differences in personality traits, habituation, and behavioural syndromes may be linked to differences in sociality. The lack of prominent behavioural syndromes is consistent with the idea that context-specific individual behavioural traits might be favoured to allow more flexible and adequate responses to changing environments than syndromes of correlated functionally different behaviours.

Social and genetic connectivity despite ecological variation in a killer whale network.

Philopatric kin-based societies encourage a narrow breadth of conservative behaviours owing to individuals primarily learning from close kin, promoting behavioural homogeneity. However, weaker social ties beyond kin, and across a behaviourally diverse social landscape, could be sufficient to induce variation and a greater ecological niche breadth. We investigated a network of 457 photo-identified killer whales from Norway (548 encounters in 2008-2021) with diet data available (46 mixed-diet individuals feeding on both fish and mammals, and 411 exclusive fish-eaters) to quantify patterns of association within and between diet groups, and to identify underlying correlates. We genotyped a subset of 106 whales to assess patterns of genetic differentiation. Our results suggested kinship as main driver of social bonds within and among cohesive social units, while diet was most likely a consequence reflective of cultural diffusion, rather than a driver. Flexible associations within and between ecologically diverse social units led to a highly connected network, reducing social and genetic differentiation between diet groups. Our study points to a role of social connectivity, in combination with individual behavioural variation, in influencing population ecology in killer whales.

Collective behavior from surprise minimization.

Collective motion is ubiquitous in nature; groups of animals, such as fish, birds, and ungulates appear to move as a whole, exhibiting a rich behavioral repertoire that ranges from directed movement to milling to disordered swarming. Typically, such macroscopic patterns arise from decentralized, local interactions among constituent components (e.g., individual fish in a school). Preeminent models of this process describe individuals as self-propelled particles, subject to self-generated motion and "social forces" such as short-range repulsion and long-range attraction or alignment. However, organisms are not particles; they are probabilistic decision-makers. Here, we introduce an approach to modeling collective behavior based on active inference. This cognitive framework casts behavior as the consequence of a single imperative: to minimize surprise. We demonstrate that many empirically observed collective phenomena, including cohesion, milling, and directed motion, emerge naturally when considering behavior as driven by active Bayesian inference-without explicitly building behavioral rules or goals into individual agents. Furthermore, we show that active inference can recover and generalize the classical notion of social forces as agents attempt to suppress prediction errors that conflict with their expectations. By exploring the parameter space of the belief-based model, we reveal nontrivial relationships between the individual beliefs and group properties like polarization and the tendency to visit different collective states. We also explore how individual beliefs about uncertainty determine collective decision-making accuracy. Finally, we show how agents can update their generative model over time, resulting in groups that are collectively more sensitive to external fluctuations and encode information more robustly.

A Delphi Panel of People With Parkinson's Disease Regarding Responsibility: Toward a Preliminary Taxonomy.

IMPORTANCE: A sense of agency is associated with complex occupation-related responsibilities. A taxonomy can guide clinicians in enhancing responsibility in patients with Parkinson's disease (PwPD). OBJECTIVE: To (1) discover levels of responsibility in occupations for PwPD and (2) propose a taxonomy for occupations. DESIGN: A two-round Delphi study with PwPD and a one-round Delphi study with international experts. SETTING: Electronic survey. PARTICIPANTS: PwPD (N = 75) and international experts (N = 8). OUTCOMES AND MEASURES: PwPD expressed their levels of an inherent sense of responsibility for each occupation (1 = very low responsibility, 5 = very high responsibility). International experts rated their level of agreement (5 = strongly agree, 1 = strongly disagree) with each dimension of the taxonomy. A consensus was determined to have been reached if the interquartile range was ≤1 and 70% agreement in two adjacent categories was achieved. RESULTS: Thirty-three occupation categories were deemed as having very high to moderate responsibility for PwPD. Consequences of actions and the presence of others made up the two-dimensional responsibility taxonomy. Occupations have more challenging responsibility characteristics when they are performed with free choice, a level of high physical effort, alone, and with moral consequences. CONCLUSIONS AND RELEVANCE: This study yielded the first consensus among PwPD regarding responsibility in occupations as well as a classification system for charting the complexity of responsibility in occupations. The occupation list we have created can be beneficial to health care professionals when providing interventions or conducting outcome assessments. Plain-Language Summary: When planning interventions for patients with Parkinson's disease, it can be helpful for clinicians to be aware of patients' perspectives regarding their sense of responsibility to perform occupations. The use of a systematic sequence of challenging occupations with responsibility attributes ranging from less complex to more complex can help enhance patient occupational participation.

Family Meals and Social Eating Behavior and Their Association with Disordered Eating among Spanish Adolescents: The EHDLA Study.

PURPOSE: The aim of this study was to examine the association of family meals and social eating behavior with disordered eating behavior in Spanish adolescents. METHODS: This was a cross-sectional study that included 706 adolescents (43.9% boys) from the Eating Habits and Daily Life Activities (EHDLA) study (aged 12 to 17) from Valle de Ricote, Region of Murcia, Spain. The frequency of family meals was assessed by asking participants to report how often their family, or most household members, had shared meals in the past week. Social eating behavior was evaluated using three statements: "I enjoy sitting down with family or friends for a meal", "Having at least one meal a day with others (family or friends) is important to me", and "I usually have dinner with others". To evaluate disordered eating, two psychologists administered the Sick, Control, One, Fat and Food (SCOFF) questionnaire. RESULTS: After adjusting for several covariates, for each additional family meal, the likelihood of having disordered eating behavior was lower (odds ratio (OR) = 0.96; 95% confidence interval (CI) 0.93 to 0.9997, p = 0.049). On the other hand, a lower likelihood of having disordered eating behavior was observed for each additional point in the social eating behavior scale (OR = 0.85; 95% CI 0.77 to 0.93, p = 0.001). The likelihood of having disordered eating behavior was 0.7% lower for each additional family meal (95% CI 0.01% to 1.4%, p = 0.046). Furthermore, for each additional point in the social eating behavior scale, a lower probability of having disordered eating behavior was observed (3.2%; 95% CI 1.4% to 5.0%, p < 0.001). CONCLUSIONS: While disordered eating behavior is complex and can be shaped by various factors, both family meals and social eating behavior emerge as significant factors inversely associated with this condition among adolescents. Promoting regular engagement in family meals and fostering positive social eating experiences could serve as effective strategies in public health initiatives aimed at mitigating the incidence of disordered eating behavior among the young population.

The prenatal use of agmatine prevents social behavior deficits in VPA-exposed mice by activating the ERK/CREB/BDNF signaling pathway.

BACKGROUND: According to reports, prenatal exposure to valproic acid can induce autism spectrum disorder (ASD)-like symptoms in both humans and rodents. However, the exact cause and therapeutic method of ASD is not fully understood. Agmatine (AGM) is known for its neuroprotective effects, and this study aims to explore whether giving agmatine hydrochloride before birth can prevent autism-like behaviors in mouse offspring exposed prenatally to valproic acid. METHODS: In this study, we investigated the effects of AGM prenatally on valproate (VPA)-exposed mice. We established a mouse model of ASD by prenatally administering VPA. From birth to weaning, we evaluated mouse behavior using the marble burying test, open-field test, and three-chamber social interaction test on male offspring. RESULTS: The results showed prenatal use of AGM relieved anxiety and hyperactivity behaviors as well as ameliorated sociability of VPA-exposed mice in the marble burying test, open-field test, and three-chamber social interaction test, and this protective effect might be attributed to the activation of the ERK/CREB/BDNF signaling pathway. CONCLUSION: Therefore, AGM can effectively reduce the likelihood of offspring developing autism to a certain extent when exposed to VPA during pregnancy, serving as a potential therapeutic drug.

Social Defeat Stress Model for Adolescent C57BL/6 Male and Female Mice.

Social adversity in adolescence is prevalent and can negatively impact mental health trajectories. Modeling social stress in adolescent male and female rodents is needed to understand its effects on ongoing brain development and behavioral outcomes. The chronic social defeat stress paradigm (CSDS) has been widely used to model social stress in adult C57BL/6 male mice by leveraging on the aggressive behavior displayed by an adult male rodent to an intruder invading its territory. An advantage of this paradigm is that it allows to categorize defeated mice into resilient and susceptible groups based on their individual differences in social behavior 24 h after the last defeat session. Implementing this model in adolescent C57BL/6 mice has been challenging because adult or adolescent mice do not typically attack early adolescent male or female mice and because adolescence is a short period of life, encompassing discreet temporal windows of vulnerability. This limitation was overcome by adapting an accelerated version of the CSDS to be used for adolescent male and female mice. This 4-day stress paradigm with 2 physical attack sessions per day uses a C57BL/6 male adult to prime the CD-1 mouse for aggressiveness such that it readily attacks the male or female adolescent mouse. This model was termed accelerated social defeat stress (AcSD) for adolescent mice. Adolescent exposure to AcSD induces social avoidance 24 h later in both males and females, but only in a subset of defeated mice. This vulnerability occurs despite the number of attacks being consistent across sessions between resilient and susceptible groups. The AcSD model is short enough to allow exposure during discrete periods within adolescence, allows the segregation of mice according to the presence or absence of social avoidance behavior, and is the first model available to study social defeat stress in adolescent C57BL/6 female mice.

Social Behavior in Animal Models of Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by social deficits and stereotyped, repetitive patterns of behaviors, limited interests, and cognitive impairment. Especially, social deficit has been considered a core feature of ASD. Because of the limitations of the experimental approach in humans, valid animal models are essential in an effort to identify novel therapeutics for social deficits in ASD. The genetic and environmental factors are clinically relevant to the pathophysiology of ASD. Epidemiological studies demonstrate environmental interventions such as prenatal exposure to valproic acid (VPA). Prenatal exposure to VPA represents a robust model of ASD exhibiting face, construct, and predictive validity. Here, we introduce protocols of the social interaction test and the three-chamber test for evaluating social deficits in mice prenatally exposed to VPA.

Modeling children's moral development in postwar Taiwan through naturalistic observations preserved in historical texts.

A core issue in the interdisciplinary study of human morality is its ontogeny in diverse cultures, but systematic, naturalistic data in specific cultural contexts are rare to find. This study conducts a novel analysis of 213 children's socio-moral behavior in a historical, non-Western, rural setting, based on a unique dataset of naturalistic observations from the first field research on Han Chinese children. Using multilevel multinomial modeling, we examined a range of proactive behaviors in 0-to-12-year-old children's peer cooperation and conflict in an entire community in postwar Taiwan. We modeled the effects of age, sex, kinship, and behavioral roles, and revealed complex interactions between these four variables in shaping children's moral development. We discovered linkages between coercive and non-coercive behaviors as children strategically negotiated leadership dynamics. We identified connections between prosocial and aggressive behaviors, illuminating the nuances of morality in real life. Our analysis also revealed gendered patterns and age-related trends that deviated from cultural norms and contradicted popular assumptions about Chinese family values. These findings highlight the importance of naturalistic observations in cultural contexts for understanding how we become moral persons. This re-analysis of historically significant fieldnotes also enriches the interdisciplinary study of child development across societies.

Hierarchically embedded scales of movement shape the social networks of vampire bats.

Social structure can emerge from hierarchically embedded scales of movement, where movement at one scale is constrained within a larger scale (e.g. among branches, trees, forests). In most studies of animal social networks, some scales of movement are not observed, and the relative importance of the observed scales of movement is unclear. Here, we asked: how does individual variation in movement, at multiple nested spatial scales, influence each individual's social connectedness? Using existing data from common vampire bats (Desmodus rotundus), we created an agent-based model of how three nested scales of movement-among roosts, clusters and grooming partners-each influence a bat's grooming network centrality. In each of 10 simulations, virtual bats lacking social and spatial preferences moved at each scale at empirically derived rates that were either fixed or individually variable and either independent or correlated across scales. We found that numbers of partners groomed per bat were driven more by within-roost movements than by roost switching, highlighting that co-roosting networks do not fully capture bat social structure. Simulations revealed how individual variation in movement at nested spatial scales can cause false discovery and misidentification of preferred social relationships. Our model provides several insights into how nonsocial factors shape social networks.