Group size is a function of relative neocortical volume in nonhuman primates. Extrapolation from this regression equation yields a predicted group size for modern humans very similar to that of certain hunter-gatherer and traditional horticulturalist societies. Groups of similar size are also found in other large-scale forms of contemporary and historical society. Among primates, the cohesion of groups is maintained by social grooming; the time devoted to social grooming is linearly related to group size among the Old World monkeys and (...) apes. To maintain the stability of the large groups characteristic of humans by grooming alone would place intolerable demands on time budgets. It is suggested that (1) the evolution of large groups in the human lineage depended on the development of a more efficient method for time-sharing the processes of social bonding and that (2) language uniquely fulfills this requirement. Data on the size of conversational and other small interacting groups of humans are in line with the predictions for the relative efficiency of conversation compared to grooming as a bonding process. Analysis of a sample of human conversations shows that about 60% of time is spent gossiping about relationships and personal experiences. It is suggested that language evolved to allow individuals to learn about the behavioural characteristics of other group members more rapidly than is possible by direct observation alone. (shrink)

This paper examines social network size in contemporary Western society based on the exchange of Christmas cards. Maximum network size averaged 153.5 individuals, with a mean network size of 124.9 for those individuals explicitly contacted; these values are remarkably close to the group size of 150 predicted for humans on the basis of the size of their neocortex. Age, household type, and the relationship to the individual influence network structure, although the proportion of kin remained relatively constant at around 21%. (...) Frequency of contact between network members was primarily determined by two classes of variable: passive factors (distance, work colleague, overseas) and active factors (emotional closeness, genetic relatedness). Controlling for the influence of passive factors on contact rates allowed the hierarchical structure of human social groups to be delimited. These findings suggest that there may be cognitive constraints on network size. (shrink)

Data from various settings suggest that there is an upper limit of about four on the number of individuals who can interact in spontaneous conversation. This limit appears to be a consequence of the mechanisms of speech production and detection. There appear to be no differences between men and women in this respect, other than those introduced by women’s lighter voices.

Data on the number of adults that an individual contacts at least once a month in a set of British populations yield estimates of network sizes that correspond closely to those of the typical “sympathy group” size in humans. Men and women do not differ in their total network size, but women have more females and more kin in their networks than men do. Kin account for a significantly higher proportion of network members than would be expected by chance. The (...) number of kin in the network increases in proportion to the size of the family; as a result, people from large families have proportionately fewer non-kin in their networks, suggesting that there is either a time constraint or a cognitive constraint on network size. A small inner clique of the network functions as a support group from whom an individual is particularly likely to seek advice or assistance in time of need. Kin do not account for a significantly higher proportion of the support clique than they do for the wider network of regular social contacts for either men or women, but each sex exhibits a strong preference for members of their own sex. (shrink)

A family reconstitution study of the Krummhörn population (Ostfriesland, Germany, 1720–1874) reveals that infant mortality and children’s probabilities of marrying or emigrating unmarried are affected by the number of living same-sexed sibs in farmers’ families but not in the families of landless laborers. We interpret these results in terms of a “local resource competition” model in which resource-holding families are obliged to manipulate the reproductive future of their offspring. In contrast, families that lack resources have no need to manipulate their (...) offspring and are more likely to benefit from allowing their offspring to capitalize on whatever opportunities to reproduce present themselves. (shrink)

Heroism is apparently nonadaptive in Darwinian terms, so why does it exist at all? Risk-taking and heroic behavior are predominantly male tendencies, and literature and legend reflect this. This study explores the possibility that heroism persists in many human cultures owing to a female preference for risk-prone rather than risk-averse males as sexual partners, and it suggests that such a preference may be exploited as a male mating strategy. It also attempts to quantify the relative influences of altruism and bravery (...) in the evolution of heroism. Our study found that females do prefer risk-prone brave males to risk-averse non-brave males, and that men are aware of this preference. Bravery in a male was shown to be the stronger factor influencing female choice of short-term partners, long-term partners, and male friends, with altruism playing a lesser part in their choice. Altruism was deemed important in long-term relationships and friendships, but for short-term liaisons, non-altruists were preferred to altruists. Heroism may therefore have evolved owing to a female preference for brave, risk-prone males because risk-taking acts as an honest cue for "good genes." Altruism was judged to be a less influential factor in the evolution of heroism than bravery and a demonstrated willingness to take risks. (shrink)

Hyperlink cinema is an emergent film genre that seeks to push the boundaries of the medium in order to mirror contemporary life in the globalized community. Films in the genre thus create an interacting network across space and time in such a way as to suggest that people’s lives can intersect on scales that would not have been possible without modern technologies of travel and communication. This allows us to test the hypothesis that new kinds of media might permit us (...) to break through the natural cognitive constraints that limit the number and quality of social relationships we can manage in the conventional face-to-face world. We used network analysis to test this hypothesis with data from 12 hyperlink films, using 10 motion pictures from a more conventional film genre as a control. We found few differences between hyperlink cinema films and the control genre, and few differences between hyperlink cinema films and either the real world or classical drama (e.g., Shakespeare’s plays). Conversation group size seems to be especially resilient to alteration. It seems that, despite many efficiency advantages, modern media are unable to circumvent the constraints imposed by our evolved psychology. (shrink)

Previous empirical studies have suggested that language is primarily used to exchange social information, but our evidence on this derives mainly from English speakers. We present data from a study of natural conversations among Farsi speakers in Iran and show that not only are conversation groups the same size as those observed in Europe and North America, but people also talk predominantly about social topics. We argue that these results reinforce the suggestion that language most likely evolved for the transmission (...) of information about the social world. We also explore sex differences in conversational behavior: while the pattern is broadly similar between the sexes, men may be more sensitive than women are to discussing some topics in the presence of many other people. (shrink)

The study of church growth has historically been divided into two strands of research: the Church Growth Movement and the Social Science approach. This article argues that Dunbar’s Social Brain Hypothesis represents a legitimate and fruitful third strand in the study of church growth, sharing features of both previous strands but identical with neither. We argue that five predictions derived from the Social Brain Hypothesis are accurately borne out in the empirical and practical church growth literature: that larger congregations lead (...) to lower active engagement from members; that single-leader congregations are limited to around 150 members; that congregations of 150 are further stratified into smaller functioning groups; that congregations expanding beyond 150 members undergo internal tensions and are forced to reorganise; and that congregations larger than 150 will require structural sub-divisions to retain active member involvement. While these assertions are reflected in the church growth literature and articulate the common sense assumptions of church growth experts, the Social Brain Hypothesis offers a coherent theoretical framework which unifies these observations and thereby represents a distinctive contribution to church growth studies. (shrink)

This study examines the socioeconomic and familial background of Irish Catholic priests born between 1867 and 1911. Previous research has hypothesized that lack of marriage opportunities may influence adoption of celibacy as part of a religious institution. The present study traced data from Irish seminary registries for 46 Catholic priests born in County Limerick, Ireland, using 1901 Irish Census returns and Land Valuation records. Priests were more likely to originate from landholding backgrounds, and with landholdings greater in size and wealth (...) than the local average. Priests were found to originate from families with more sons than the national average, but with similar numbers of daughters. These findings are discussed in relation to competition for resources and lineage survival strategies. (shrink)

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.

In my target article, I argued (1) that the relationship between neocortical size and group size in primates implies that there is a cognitive limit on the size of human groups, and (2) that time constraints forced the evolution of language as a more efficient means of bonding the large groups that humans evolved. The doubts about these claims raised by these additional commentaries largely reflect misinterpretation of my original claims.

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.

While the evidence that cetaceans exhibit behaviours that are every bit as cultural as those recognised in chimpanzees is unequivocal, I argue that it is unlikely that either taxon has the social cognitive mechanisms required to underpin the more advanced forms of culture characteristic of humans (namely those that depend on shared meaning).

This study investigated the use of mobile telephones by males and females in a public bar frequented by professional people. We found that, unlike women, men who possess mobile telephones more often publicly display them, and that these displays were related to the number of men in a social group, but not the number of women. This result was not due simply to a greater number of males who have telephones: we found an increase with male social group size in (...) the proportion of available telephones that were on display. Similarly, there was a positive relationship between the number of visible telephones and the ratio of males to females. Our results further show that the increased display of telephones in groups with more males is not due to the ostensive function of these devices (i.e., the making and receiving of calls), although single males tended to use their phones more. We interpret these results within the framework of male-male competition, with males in larger group sizes functioning in an increasingly competitive environment. This competitive environment is suggested to be akin to a lek mating system in which males aggregate and actively display their qualities to females who assess males on a number of dimensions. We suggest that mobile telephones might be used by males as an indicator of their status and wealth (sensu “cultural ornaments”). (shrink)

Introduction, W G Runciman Social Evolution in Primates: The Role of Ecological Factors and Male Behaviour, Carel P van Schaik Determinants of Group Size in Primates: A General Model, R I M Dunbar Function and Intention in the Calls of Non-Human Primates, Dorothy L Cheney & Robert M Seyfarth Why Culture is Common, but Cultural Evolution is Rare, Robert Boyd & Peter J Richerson An Evolutionary and Chronological Framework for Human Social Behaviour, Robert A Foley Friendship and the Banker?s Paradox: (...) Other Pathways to the Evolution of Adaptations for Altruism, John Tooby & Leda Cosmides The Early Prehistory of Human Social Behaviour: Issues of Archaeological Inference and Cognitive Evolution, Steven Mithen The Emergence of Biologically Modern Populations in Europe: A Social and Cognitive ?Revolution??, Paul Mellars Responses to Environmental Novelty: Changes in Men?s Marriage Strategies in a Rural Kenyan Community, Monique Borgerhoff Mulder Genetic Language Impairment: Unruly Grammars, M Gopnik, J Dalalakis, S E Fukuda, S Fukuda & E Kehayia The Emergence of Cultures among Wild Chimpanzees, Christophe Boesch Terrestriality, Bipedalism and the Origin of Language, Leslie C Aiello Conclusions, John Maynard Smith. (shrink)