bioRxiv (Cold Spring Harbor Laboratory), Jun 25, 2024
Although feral goats are an invasive species renowned for their ability to survive in degraded ha... more Although feral goats are an invasive species renowned for their ability to survive in degraded habitats, their capacity to occupy high latitude habitats is severely restricted. I analyse long term data on the lifehistory and demography of a feral goat population on the Isle of Rùm, NW Scotland, in relation to both longterm variation in climatic variables and within-population variation in environmental variables. While exhibiting many features characteristic of ungulate lifehistory, goats are especially sensitive to variations in thermal conditions, especially during winter. This is compounded by the fact that, at the latitude of Rùm, goats give birth in mid-winter, even though this imposes significant stress on both mother and kid. Longterm patterns in population growth rates are correlated with winter temperature and the NAO index, with little evidence for density-dependent effects (except in respect of fertility). In addition, there was evidence that the presence of a large sympatric red deer population was limiting the goats' capacity to increase by denying them access to preferred foraging habitat. Nonetheless, their unusual sensitivity to the thermal environment implies that the goat population will increase significantly with progressive climate warming.
Adaptive human behavior and physiology, Mar 26, 2024
Objective In a UK national census sample, women from the upper and lower socioeconomic (SES) clas... more Objective In a UK national census sample, women from the upper and lower socioeconomic (SES) classes achieve parity in completed family size, despite marked differences in both birth rates and offspring survival rates. We test the hypothesis that women adopt reproductive strategies that manipulate age at first reproduction to achieve this. Methods We use a Monte-Carlo modeling approach parameterized with current UK lifehistory data to simulate the reproductive lifehistories of 64,000 individuals from different SES classes, with parameter values at each successive time step drawn from a statistical distribution defined by the census data. We show that, if they are to achieve parity with women in the higher socioeconomic classes, women in lower socioeconomic classes must begin reproducing 5.65 years earlier on average than women in the higher SES classes in order to offset the higher class-specific mortality and infertility rates that they experience. The model predicts very closely the observed differences in age at first reproduction in the census data. Conclusions Opting to delay reproduction in order to purse an education-based professional career may be a high risk strategy that many lower SES women are unwilling and unable to pursue. As a result, reproducing as early as possible may be the best strategy available to them.
Communities of practice (COP) are informal (sometimes formal) groupings of professionals with sha... more Communities of practice (COP) are informal (sometimes formal) groupings of professionals with shared interests that form to facilitate the exchange of expertise and shared learning or to function as professional support networks. We analyse a dataset on the size of COPs and show that their distribution has a fractal structure similar to that found in huntergatherer social organisation and the structure of human personal social networks. Small communities up to about 40 in size can be managed democratically, but all larger communities require a leadership team structure. We show that frequency of interaction declines as size increases, as is the case in personal social networks. This suggests that professional work-oriented organisations may be subject to the same kinds of constraint imposed on human social organisation by the social brain. We discuss the implications for business management structure.
The spotted hyaena lives in unusually large social groups for a carnivore. Since the infertility ... more The spotted hyaena lives in unusually large social groups for a carnivore. Since the infertility trap normally limits the size of social groups in mammals, it seems likely that this species has evolved some way of mitigating the stresses involved. In primates, this usually takes the form of female-female alliances, often embedded in multilevel social systems. I show (1) that the distribution of hyaena clan sizes is multimodal, with a fractal scaling close to 3 and a base unit of 12-15 individuals (3-5 reproductive females) and (2) that fertility is a trade off between the benefits of having more males in the group and the costs incurred by having more females, with 4-5 as the limit on the number of females that can live together without their reproductive rates falling below the demographic replacement rate. I present evidence that females buffer themselves against the infertility trap by forming matrilineal alliances that in turn create a multilevel structure. In this respect, hyae...
Relationships are central to human life strategies and have crucial fitness consequences. Yet, at... more Relationships are central to human life strategies and have crucial fitness consequences. Yet, at the same time, they incur significant maintenance costs that are rarely considered in either social psychological or evolutionary studies. Although many social psychological studies have explored their dynamics, these studies have typically focused on a small number of emotionally intense ties, whereas social networks in fact consist of a large number of ties that serve a variety of different functions. In this study, we examined how entire active personal networks changed over 18 months across a major life transition. Family relationships and friendships differed strikingly in this respect. The decline in friendship quality was mitigated by increased effort invested in the relationship, but with a striking gender difference: relationship decline was prevented most by increased contact frequency (talking together) for females but by doing more activities together in the case of males.
Primates use social grooming to create and maintain coalitions. Because of this, individuals focu... more Primates use social grooming to create and maintain coalitions. Because of this, individuals focus their time on a small number of individuals, and this means that in many cases group networks are not fully connected. I use data on primate grooming networks to show that three different social grades can be differentiated in terms of network structuring. These grades seem to arise from a glass ceiling imposed on group size by limits on the time available for social grooming. It seems that certain genera have managed to circumvent this constraint by a phase shift in the behavioural and cognitive mechanisms that underpin social relationships in a way that allows a form of multilevel sociality based on weak and strong ties not unlike those found in human social networks.
Transportation, the experience of feeling “transported” into a fictional world, differs widely ac... more Transportation, the experience of feeling “transported” into a fictional world, differs widely across individuals. We examined transportation in 3 studies. Study 1 investigated links between individual differences in various measures of audience response, whereas the latter 2 studies examined links between trait measures (independent variables) and audience response (dependent variables). Study 1 found that individual differences in self-reported transportation to a film explained variation in virtually all other dependent measures, such as identification with characters, emotion, and attribution of blame for the protagonist's struggles. Group bonding after watching the film was nonlinearly related to endorphin response (as measured by pain threshold), and transportation related to these variables as well (although more weakly). Study 2 found that individual differences in celebrity worship predicted transportation, as well as tendency to identify with the characters and approve...
Primate and human social groups exhibit a fractal structure that has a very limited range of pref... more Primate and human social groups exhibit a fractal structure that has a very limited range of preferred layer sizes, with groups of 5, 15, 50 and (in humans) 150 and 500 predominating. This same fractal distribution is also observed in the distribution of species mean group sizes in primates. Here we demonstrate that this preferential numbering arises because of the critical nature of dynamic self-organization within complex social networks. We calculate the size dependence of the scaling properties of complex social network models and argue that this aggregate behaviour exhibits a form of collective intelligence. Direct calculation establishes that the complexity of social networks as measured by their scaling behaviour is non-monotonic, peaking globally around 150 with a secondary peak at 500 and tertiary peaks centred on 15 and 50, thereby providing a theory-based rationale for the fractal layering of primate and human social groups.
bioRxiv (Cold Spring Harbor Laboratory), Feb 5, 2024
Although brain size and body size co-evolves in primates, the correlation is far from perfect. Th... more Although brain size and body size co-evolves in primates, the correlation is far from perfect. This was originally interpreted as implying that evolutionary changes in brain size lag behind evolutionary changes in body size. Subsequent tests of the hypothesis, however, concluded that there is no meaningful lag. I reanalyse the original data taking socio-cognitive grades into account and show that there is, in fact, a very strong lag effect, but that the original "catch-up" hypothesis is not the explanation. Rather, the "lag" is part of an adaptive response to predation risk in which species initially respond by increasing body size, but later switch to increasing group size (with the latter made possible by a correlated increase in brain size). This adaptive response takes between 2 and 8 million years to fully implement, and is dependent on a switch to a more energyrich diet. This trajectory can be clearly documented in the evolutionary history of fossil hominins over the past 5 My.
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Papers by robin dunbar