Search

The relationship between social behaviour and the microbiome is known to be reciprocal. Research in wild animal populations, particularly in primate social groups, has revealed the role that social interactions play in microbial transmission, whilst studies in laboratory animals have demonstrated that the gut microbiome can affect multiple aspects of behaviour, including social behaviour. Here we explore behavioural variation in a non-captive animal population with respect to the abundance of specific bacterial genera. Social behaviour based on grooming interactions is assessed in a population of rhesus macaques (Macaca mulatta), and combined with gut microbiome data. We focus our analyses on microbiome genera previously linked to sociability and autistic behaviours in rodents and humans. We show in this macaque population that some of these genera are also related to an individual’s propensity to engage in social interactions. Interestingly, we find that several of the genera positively related to sociability, such as Faecalibacterium, are well known for their beneficial effects on health and their anti-inflammatory properties. In contrast, the genus Streptococcus, which includes pathogenic species, is more abundant in less sociable macaques. Our results indicate that microorganisms whose abundance varies with individual social behaviour also have functional links to host immune status. Overall, these findings highlight the connections between social behaviour, microbiome composition, and health in an animal population.

Objectives Close romantic and friendship relationships are crucial for successful survival and reproduction. Both provide emotional support that can have significant effects on an individual’s health and wellbeing, and through this their longer term survival and fitness. Nonetheless, the factors that create and maintain intimacy in close relationships remain unclear. Nor is it entirely clear what differentiates romantic relationships from friendships in these terms. In this paper, we explore which factors most strongly predict intimacy in these two kinds of relationship, and how these differ between the two sexes. Results Aside from best friendships being highly gendered in both sexes, the dynamics of these two types of relationships differ between the sexes. The intimacy of female relationships was influenced by similarity (homophily) in many more factors (notably dependability, kindness, mutual support, sense of humour) than was the case for men. Some factors had opposite effects in the two sexes: gift-giving had a negative effect on women’s friendships and a positive effect on men’s, whereas shared histories had the opposite effect. Conclusion These results confirm and extend previous findings that the dynamics of male and female relationships are very different in ways that may reflect differences in their functions.

Explanations for the evolution of social monogamy in mammals typically emphasise one of two possibilities: females are overdispersed (such that males cannot defend access to more than one female at a time) or males provide a service to the female. However, the first claim has never been formally tested. I test it directly at three levels using population-level data from primates and ungulates. First, I show that the females of monogamous genera do not have territories that are significantly larger, either absolutely or relatively, than those of polygynous genera. Second, using two indices of territorial defendability, I show that, given their typical day journey lengths, males of most monogamous species could easily defend an area large enough to allow them to monopolise as many as 5–10 females if they ranged solitarily. Finally, I use a model of male mate searching strategies to show that the opportunity cost incurred by pairbonded males is typically 5–10 times the reproductive success they actually obtain by being obligately monogamous. This suggests that the selection pressure dissuading them from pursuing a roving male strategy must be very considerable. At present, the evidence is undecided as to whether mitigating predation or infanticide risk is the primary function, but estimates of their impacts suggest that both are in fact plausible.

Humans exhibit what appears to be a unique vocal property: octave equivalence whereby adult male voices are, on average, an octave lower in pitch than those of adult females and children. The evolutionary significance of this seems largely to have escaped notice. While sexual selection might explain why male voices are generally lower, it cannot explain why they should be so much lower than what would be expected for body size, nor why the average difference should be exactly one octave. Nor does a generalised dimorphism convey why precisely tuned octaves feature so commonly in human vocal interaction. The octave features strongly in the organisation of music. A consequence of this characteristic of human pitch perception and production is the capacity to share and respond to vocal pitches (and their instrumental equivalents) as if they are ‘the same’ irrespective of the difference in range, a phenomenon known as octave equivalence. We investigate the nature of octave equivalence from an adaptive perspective and propose a hypothesis for its evolution based on the importance of chorusing for social bonding and pitch-matching in inter-generational exchange.

Compared to most other mammals and birds, anthropoid primates have unusually complex societies characterised by bonded social groups. Among primates, this effect is encapsulated in the social brain hypothesis: the robust correlation between various indices of social complexity (social group size, grooming clique size, tactical behaviour, coalition formation) and brain size. Hitherto, this has always been interpreted as a simple, unitary relationship. Using data for five different indices of brain volume from four independent brain databases, we show that the distribution of group size plotted against brain size is best described as a set of four distinct, very narrowly defined grades which are unrelated to phylogeny. The allocation of genera to these grades is highly consistent across the different data sets and brain indices. We show that these grades correspond to the progressive evolution of bonded social groups. In addition, we show, for those species that live in multilevel social systems, that the typical sizes of the different grouping levels in each case coincide with different grades. This suggests that the grades correspond to demographic attractors that are especially stable. Using five different cognitive indices, we show that the grades correlate with increasing social cognitive skills, suggesting that the cognitive demands of managing group cohesion increase progressively across grades. We argue that the grades themselves represent glass ceilings on animals' capacity to maintain social and spatial coherence during foraging and that, in order to evolve more highly bonded groups, species have to be able to invest in costly forms of cognition.

INTRODUCTION: Previous studies have shown that engaging in formal social participation may protect against declining mental health, but social network size (the number of close social ties a person has) may moderate the relationship. We assessed the potential moderating role of social network size using longitudinal data. METHODS: Nationally representative data from two consecutive waves (2011, 2013) of the SHARE survey were analyzed. The data consisted of 38,300 adults from 13 European countries aged 50 years and older in 2011. Measures pertaining to formal social participation, social network size, quality of life, and depression symptoms were used. Multivariable linear regression models were conducted. RESULTS: The majority of participants (over 70% of the sample) had a social network size of four or less close social ties. We identified significant moderations in both models. Individuals with relatively few close social ties may have benefitted from formal social participation both in terms of reductions in depression symptoms and increases in quality of life, while formal social participation among those with many social ties did not appear to be beneficial, and may even to some extent have been detrimental. CONCLUSIONS: Declines in mental health specifically among those with relatively few close social ties could potentially be prevented through the promotion of formal social participation. It is possible that such strategies could have a greater impact by specifically targeting individuals that are otherwise socially isolated. High levels of formal participation among those with relatively many close social ties may not be pragmatically beneficial.

Communal eating, whether in feasts or everyday meals with family or friends, is a human universal, yet it has attracted surprisingly little evolutionary attention. I use data from a UK national stratified survey to test the hypothesis that eating with others provides both social and individual benefits. I show that those who eat socially more often feel happier and are more satisfied with life, are more trusting of others, are more engaged with their local communities, and have more friends they can depend on for support. Evening meals that result in respondents feeling closer to those with whom they eat involve more people, more laughter and reminiscing, as well as alcohol. A path analysis suggests that the causal direction runs from eating together to bondedness rather than the other way around. I suggest that social eating may have evolved as a mechanism for facilitating social bonding.

Aim: In this study we use a modelling approach to identify: (1) the factors responsible for the differences in ape biogeography, (2) the effects that global warming might have on distribution patterns of African apes, (3) the underlying mechanisms for these effects, and (4) the implications that behavioural flexibility might be expected to have for ape survival. All African apes are highly endangered, and the need for efficient conservation methods is a top priority. The expected changes in world climate are likely to further exacerbate the difficulties they face. Our study aims to further understand the mechanisms that link climatic conditions to the behaviour and biogeography of ape species. Location: Africa. Method: We use an existing validated time budgets model, derived from data on 20 natural populations of gorillas (Gorilla beringei and Goriglla gorilla) and chimpanzees (Pan troglodytes and Pan paniscus), which specifies the relationship between climate, group size, body weight and time available for various activities, to predict ape distribution across Africa under a uniform worst-case climate change scenario. Results: We demonstrate that a worst-case global warming scenario is likely to alter the delicate balance between different time budget components. Our model points to the importance of annual temperature variation, which was found to have the strongest impact on ape biogeography. Our simulation indicates that rising temperatures and changes in rainfall patterns are likely to have strong effects on ape survival and distribution, particularly for gorillas. Even if they behaved with maximum flexibility, gorillas may not be able to survive in most of their present habitats if the climate was to undergo extreme changes. The survival of chimpanzees was found to be strongly dependent on the minimum viable group size required. Main conclusions: Our model allows us to explore how climatic conditions, individual behaviour and morphological traits may interact to limit the biogeographical distributions of these species, thereby allowing us to predict the effects of climate change on African ape distributions under different climate change regimes. The model suggests that climate variability (i.e. seasonality) plays a more important role that the absolute magnitude of the change, but these data are not normally provided by climate models.

We are somewhat concerned by the number of errors and misconceptions in Traynor et al.’s (2015) comment on our paper (Pearce et al. 2013) in which we argue that Neanderthal brain structure must have been sufficiently different to that of anatomically modern humans to have had significant consequences for the sizes of their communities and key social cognitive abilities.

We studied foraging ecology of feral goats (Capra hircus) on the Isle of Rum, Scotland, from June to November 2000. Grazing bout length varied greatly from 1 min to 460 min with mean duration being 103. 1 ± 15. 0 (SD) min. Adult males and females differed marginally significantly in feeding bout length with females having relatively longer feeding bouts (P=0.077). The average bite rate for feral goats was 46. 3 ± 0. 6 bites/min with significant variations between sexes (P=0.023) and among months ( P < 0.001). Adult males had faster bite rates during pre- (June-July) and post-rutting (October-November) periods than during rutting period ( August-September) ( P < 0.008) , but the bite rate of adult females during pre-rutting period was not different from that during rutting period (P=0.327). Adult males also spent significantly less daytime feeding during rutting period. The differences in bite rates and feeding time between the two sexes might result in sexual differences in forage intake by feral goats : females had relatively stable intake, but males fluctuated greatly in their forage intake. The estimated forage intake decreased from June to November (although a slight increase from September to November) , which means that feral goats on Rum may be in negative energy balance during autumn/winter period when the quality of forage is lower and the weather is beginning to deteriorate. There was no significant difference in step rate while feeding between sexes or among months.

Past research suggests that various courtship rituals, such as romantic kissing, may convey useful mate quality information. Two studies were carried out to examine how purported romantic kissing abilities, as a potential cue to some form of mate information, affect appraisals of potential mating partners. In Experiment 1, 724 participants were presented with vignette descriptions of potential mating partners and were asked to rate partner desirability for various mating-related situations. The primary result of this experiment was that purported kissing ability increased mate desirability in “casual sex” mating situations for women to a greater extent than for men. Experiment 2 repeated the same procedure with another 178 participants, this time including visual information alongside vignette descriptions containing kissing-related information to examine the relative effects of these two modalities. It was found that the presence of a picture alongside a descriptive vignette negated the effect of kissing-related information only when rating potential partners on attractiveness or desirability for further courtship, though not when evaluating partners for casual sex or long-term relationship scenarios. Visual information containing “attractive” photos of potential partners was also found to have a greater effect on men’s ratings of partner desirability than on women’s ratings of partner desirability. The results are discussed in light of romantic kissing’s potential function of conveying important mate quality and desirability information, and its relative role in the presence of additional visual mate cues.

This chapter focuses on the evolution of intelligence and Richard D. Alexander's 1989 paper that explains how the human psyche has evolved. Alexander's prescient paper was one of the first studies to comprehensively seek to explain the “why” question of human consciousness and other core facets of the human mind. Alexander proposes a new hypothesis that human mental capacities evolved in the context of selection for ability to “play” in the mind—to build and permute, consciously and unconsciously, alternative social strategies and tactics in a world where evolutionary success is strongly contingent on skills for social navigation. Language, brain size, the “social” components of the brain, complex cognition and affect, social-network structures, the neurological “default mode” system of functional brain activation—all follow naturally from Alexander's model for the evolution of the human psyche.

In this paper we present a new approach to modelling group coordination, based on dyadic synchronisation in a non-panmictic, structured network (a problem that applies widely to all species that live in medium to large groups). Using this approach, we present three models with three new theoretical results. (1) Multi-layered networks are optimal for groups that face costs associated with maintaining relationships among the members, combined with costs associated with information flows. (2) The presence of a social hierarchy can be an adaptive feature of the community: the steeper the optimal social hierarchy is, the fewer relationships group members need to have. (3) Falling communication costs lead to a less steep optimal social hierarchy in communities in which socially useful information is evenly distributed, but to an even steeper social hierarchy in groups in which socially useful information is uneven. Thus we show how, when communication is costly, cooperation can give rise to communities that are socially highly structured.

Gelada faecal samples were analyzed for nutritional content and for particle size, and compared with similar data forPapio baboons, cattle, and zebra. Particle size in gelada is similar to that for zebra, larger than that for cattle and smaller than that for baboons. Gelada and baboons are less efficient than ungulates at extracting protein from their diet. The data on energy extraction are less easy to interpret and appear to be confounded by dietary and seasonal factors. It is suggested that gelada may be too large to compete effectively with ruminants in low altitude grassland habitats under the climatic conditions that have prevailed in eastern Africa since the late Pleistocene.

Striedter's account of human brain evolution fails on two key counts. First, he confuses developmental constraints with selection explanations in the initial jump in hominid brain size around two MYA. Second, he misunderstands the Machiavellian Intelligence explanation. © 2006 Cambridge University Press.

I argue that, while Finlay et al, are correct to suggest that there are developmental regularities (or constraints) acting on brain component evolution, they are incorrect to infer from this that a developmental explanation necessarily implies that structural changes preceded functional use. Developmental and functional (adaptationist) explanations are complementary, not alternatives.

SUMMARY SUMMARY (1) Gelada baboon (Theropithecus gelada) populations living in three habitats that differed markedly in vegetation and climate are compared in order to assess the influence of temperature and habitat quality on their behavioural ecology. (2) Habitat and seasonal differences in diet are attributed to the local availability of preferred food types (in particular, grass). (3) Time spent feeding increased with altitude due to a combination of increasing temperature-dependent energy requirements and declining habitat quality. Resting time was used as a reserve store from which additional feeding time could be drawn; social time was conserved. (4) Day journey length increased as a linear function of band size because the increase in food requirement with altitude was exactly offset by a corresponding increase in food density. (5) Although range size was also a linear function of band size, the amount of graze required to support one animal increased with declining ambient temperatures. SUMMARY SUMMARY

Peer reviewed: True, Funder: NIHR Cambridge Biomedical Research Centre; FundRef: https://doi.org/10.13039/501100018956, Funder: Autism Research Trust, Funder: Autistica; FundRef: https://doi.org/10.13039/501100008161, Funder: Templeton World Charity Foundation; FundRef: https://doi.org/10.13039/501100011730, Funder: NIHR Collaboration for Leadership in Applied Health Research and Care East of England at Cambridgeshire and Peterborough NHS Foundation Trust, Funder: Medical Research Council; FundRef: https://doi.org/10.13039/501100000265, Assortative mating is a phenomenon in which romantic partners typically resemble each other at a level greater than chance. There is converging evidence that social behaviours are subject to assortative mating, though less is known regarding social cognition. Social functioning requires the ability to identify and understand the mental states of others, i.e., theory of mind. The present study recruited a sample of 102 heterosexual couples via an online survey to test if theory of mind as measured using facial expressions (Reading the Mind in the Eyes Test) or language (Stiller-Dunbar Stories Task) is associated with assortative mating. Results provide evidence of assortative mating for theory of mind via facial expressions, though there was no such effect for theory of mind via language. Assortative mating for theory of mind via facial expressions was not moderated by length of relationship nor by partner similarity in age, educational attainment, or religiosity, all variables relevant to social stratification. This suggests assortative mating for theory of mind via facial expressions is better explained by partners being alike at the start of their relationship (initial assortment) rather than becoming similar through sustained social interaction (convergence), and by people seeking out partners that are like themselves (active assortment) rather than simply pairing with those from similar demographic backgrounds (social homogamy).

UNLABELLED: The claim that nonverbal cues provide more information than the linguistic content of a conversational exchange (the Mehrabian Conjecture) has been widely cited and equally widely disputed, mainly on methodological grounds. Most studies that have tested the Conjecture have used individual words or short phrases spoken by actors imitating emotions. While cue recognition is certainly important, speech evolved to manage interactions and relationships rather than simple information exchange. In a cross-cultural design, we tested participants' ability to identify the quality of the interaction (rapport) in naturalistic third party conversations in their own and a less familiar language, using full auditory content versus audio clips whose verbal content has been digitally altered to differing extents. We found that, using nonverbal content alone, people are 75-90% as accurate as they are with full audio cues in identifying positive vs negative relationships, and 45-53% as accurate in identifying eight different relationship types. The results broadly support Mehrabian's claim that a significant amount of information about others' social relationships is conveyed in the nonverbal component of speech. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10919-021-00386-y.

First paragraph: Multi-level and fission-fusion social systems are relatively uncommon across the animal kingdom: most group-living species live in at least temporarily stable social groups, where all members of the group form a relatively cohesive group. However, there are two major deviations from this scheme. In some species, small cohesive (usually reproductive) units, such as families or one-male units with attached females and offspring, aggregate regularly with other small cohesive units, thereby forming higher level groupings. This type of multi-layered sociality has e.g. been shown for African and Asian elephants (Moss &Poole 1983, Wittemyer et al. 2005; de Silva et al., 2011), zebras (Rubenstein & Hack 2004), whales (Baird 2000, Whitehead et al. 1991), prairie dogs (Hoogland 1995), horses (Linklater 2000), parrots (Wanker et al., 1998) and several primate taxa, including the African papionins Papio hamadryas and Theropithecus and some Asian colobines (notably Rhinopithecus, Nasalis and Pygathrix). In all these cases, the small unit is the stable social unit with higher level groupings being built out of these smaller units; multi-level sociality is thus achieved via a bottom-up mechanism with small stable groups flexibly aggregating into larger, more fluid groupings (of which several layers can exist).