Calling Dunbar's Numbers

The social brain hypothesis predicts that humans have an average of about 150 relationships at any given time. Within this 150, there are layers of friends of an ego, where the number of friends in a layer increases as the emotional closeness decreases. Here we analyse a mobile phone dataset, firstly, to ascertain whether layers of friends can be identified based on call frequency. We then apply different clustering algorithms to break the call frequency of egos into clusters and compare the number of alters in each cluster with the layer size predicted by the social brain hypothesis. In this dataset we find strong evidence for the existence of a layered structure. The clustering yields results that match well with previous studies for the innermost and outermost layers, but for layers in between we observe large variability.Comment: 7 pages, 6 figure

The Social Brain Hypothesis Thirty Years On: Some Philosophical Pitfalls of Deconstructing Dunbar’s Number

The social brain hypothesis was proposed 30 years ago as an explanation for the fact that primates have much larger brains than all other animals. The claim was that primates live in unusually complex societies, and hence need a large ‘computer’ to manage the relationships involved. The core evidence subsequently provided in support of this claim was a simple statistical relationship between the social group size characteristic of a species and the size of its brain, with humans fitting into this pattern. However, testing evolutionary hypotheses raises some challenging philosophical and statistical issues that are often overlooked, and great care is needed to ensure that we test the hypothesis we think we are testing. Here, I examine some of these challenges and illustrate the traps they can create for the unwary

Male and female brain evolution is subject to contrasting selection pressures in primates

The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the "social brain" hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures

Riverology: Promoting Stewardship of Rivers Through Youth Participation in Science and Art

This project focuses on mentoring children to help reduce marine debris in their local river by implementing one of ten lessons from an inquiry-based Riverology curriculum to empower youth voice, increase geo-literacy, and spatial thinking. Eighteen participants aged seven and eight, piloted Riverology Lesson 2: What Do I Know or Imagine about the Elizabeth River? that includes six steps: inquire, visualize, draw, share, act, and reflect. The children were asked to make drawings before and after viewing an Elizabeth River Story Map presentation (Dunbar, 2021a). The drawings were then compared to see if the participants included marine debris, stewardship solutions, and a mental map of the river with branches. This study addresses four questions 1.) Why should we teach youth about rivers? 2.) How can creating art and stories serve as a communication tool for students to share their ideas? 3.) How can visualization activities be utilized to connect youth to their local rivers? 4.) What barriers do students face on their journey to act and participate in the public sphere? Scholars, such as Jürgen Habermas (1974), Sibel Ozsoy and Berat Ahi (2014), Tom Cockburn (2019), Lynda Barry (2019), and Millie Kerr (2016) have advocated for a citizen democracy fueled by youth participation in the arts. Some of these efforts have been applied to environmental conservation, but no such inquiry-based effort has been undertaken to address the stewardship of the Elizabeth River in Virginia. The scale of the marine debris issue sometimes creates the impression that local actions are futile, but research shows people using their own expertise and knowledge as stewards is a driver for change (N. Bennett, et al., 2017). To foster river stewards these young participants completed Riverology Lesson 2 and although none of their pre- drawings included marine debris or stewardship actions, 83% of the post- drawings did. In addition, only 11% drew a mental map of the river in their pre- drawings, but 44% did after viewing maps and images. An unexpected finding showed none of the drawings included people and this may relate to youth empowerment issues, the inquiry question wording, or COVID-19 isolation

Dynamics of deceptive interactions in social networks

In this paper we examine the role of lies in human social relations by implementing some salient characteristics of deceptive interactions into an opinion formation model, so as to describe the dynamical behaviour of a social network more realistically. In this model we take into account such basic properties of social networks as the dynamics of the intensity of interactions, the influence of public opinion, and the fact that in every human interaction it might be convenient to deceive or withhold information depending on the instantaneous situation of each individual in the network. We find that lies shape the topology of social networks, especially the formation of tightly linked, small communities with loose connections between them. We also find that agents with a larger proportion of deceptive interactions are the ones that connect communities of different opinion, and in this sense they have substantial centrality in the network. We then discuss the consequences of these results for the social behaviour of humans and predict the changes that could arise due to a varying tolerance for lies in society.Comment: 17 pages, 8 figures; Supplementary Information (3 pages, 1 figure

Inference or enaction?:the impact of genre on the narrative processing of other minds

Do narratives shape how humans process other minds or do they presuppose an existing theory of mind? This study experimentally investigated this problem by assessing subject responses to systematic alterations in the genre, levels of intentionality, and linguistic complexity of narratives. It showed that the interaction of genre and intentionality level are crucial in determining how narratives are cognitively processed. Specifically, genres that deployed evolutionarily familiar scenarios (relationship stories) were rated as being higher in quality when levels of intentionality were increased; conversely, stories that lacked evolutionary familiarity (espionage stories) were rated as being lower in quality with increases in intentionality level. Overall, the study showed that narrative is not solely either the origin or the product of our intuitions about other minds; instead, different genres will have different-even opposite-effects on how we understand the mind states of others

Sex differences in intimate relationships

Social networks have turned out to be of fundamental importance both for our understanding human sociality and for the design of digital communication technology. However, social networks are themselves based on dyadic relationships and we have little understanding of the dynamics of close relationships and how these change over time. Evolutionary theory suggests that, even in monogamous mating systems, the pattern of investment in close relationships should vary across the lifespan when post-weaning investment plays an important role in maximising fitness. Mobile phone data sets provide us with a unique window into the structure of relationships and the way these change across the lifespan. We here use data from a large national mobile phone dataset to demonstrate striking sex differences in the pattern in the gender-bias of preferred relationships that reflect the way the reproductive investment strategies of the two sexes change across the lifespan: these differences mainly reflect women's shifting patterns of investment in reproduction and parental care. These results suggest that human social strategies may have more complex dynamics than we have tended to assume and a life-history perspective may be crucial for understanding them.Comment: 5 pages, 3 figures, contains electronic supplementary materia

Impact of users inter-contact times on information dissemination in pervasive social networks

It is commonly perceived that the design principles of the future Internet might be drastically different from today. It is natural to ask what will be the impact of such evolution on the design of future Online Social Networks (OSNs). There is evidence that human social networks may be invariant with respect to the underlying online technology supporting them. Furthermore, the increasing pervasiveness of communication technologies is likely to enable any two users to communicate anytime and anywhere. Thus, a possible evolution of OSN design could map directly the structure of human social networks, and build future OSN services on top of a network whose edges represent "communication channels" between users sharing social relationships, and activated when they interact because of their social ties. In this paper we look, in the perspective of future OSN designed according to this concept, at how the patterns of interactions between people in human social networks impact on information dissemination properties. Based on well-established theories from the anthropology field, we study the properties of inter-contact times between users, i.e. the time between successive communication opportunities. This is a crucial feature for information dissemination, as previous results obtained in a conceptually similar environment have shown that the distribution of inter-contact times determines the convergence properties of information diffusion protocols. In the paper we investigate, by analysis, simulation and experimental results, the impact of different users interaction patterns on the properties of inter-contact times and, thus, on the convergence properties of information dissemination protocols

Modelling inter-contact times in human social pervasive networks

Thanks to the diffusion of mobile user devices (e.g. smart- phones) with rich computation and networking capabilities, we are witnessing an increasing integration between the cy- ber world of devices and the physical world of users. In this perspective, a possible evolution of pervasive networking (throughout referred to as social pervasive networks, SPNs) might consist in closely mapping human social structures in the network of the devices. Links between devices would cor- respond to social relationships between users, and communi- cation events between devices would correspond to commu- nications between users. It can be shown that fundamental convergence properties of PSN forwarding protocols are de- termined by the distributions of inter-contact times between the individual nodes (i.e. the time elapsed between two suc- cessive communication events between the nodes). Individ- ual pairs inter-contact times are hard to completely chara- terise, while the distribution of the aggregate inter-contact times is often a much more convenient figure. However, the aggregate distribution is not always representative of the individual pairs distributions, such that using it to charac- terise the properties of PSN forwarding protocols might not be correct. In this paper we provide an analytical model showing the exact dependence between the two in heteroge- neous SPNs. Moreover, we use the model to i) study cases in which studying the aggregate distribution is not enough, and ii) find sufficient conditions that guarantee that study- ing the aggregate distribution is enough to characterise the properties of PSN forwarding protocols