scholarly journals Social complexity and the fractal structure of group size in primate social evolution

2021 ◽  
Author(s):  
Robin I. M. Dunbar ◽  
Susanne Shultz
Keyword(s):  
Group Size ◽  
Social Evolution ◽  
Social Complexity ◽  
Fractal Structure

New research frameworks in the study of chimpanzee and gorilla sociality and communication

2019 ◽  
Author(s):  
Sam G. B. Roberts ◽  
Anna Roberts
Keyword(s):  
Social Evolution ◽  
Social Complexity ◽  
Brain Size ◽  
Social Systems ◽  
Strongly Correlated ◽  
The Social ◽  
Human Social Evolution ◽  
Research Frameworks ◽  
New Research ◽  
Large Groups

Group size in primates is strongly correlated with brain size, but exactly what makes larger groups more ‘socially complex’ than smaller groups is still poorly understood. Chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) are among our closest living relatives and are excellent model species to investigate patterns of sociality and social complexity in primates, and to inform models of human social evolution. The aim of this paper is to propose new research frameworks, particularly the use of social network analysis, to examine how social structure differs in small, medium and large groups of chimpanzees and gorillas, to explore what makes larger groups more socially complex than smaller groups. Given a fission-fusion system is likely to have characterised hominins, a comparison of the social complexity involved in fission-fusion and more stable social systems is likely to provide important new insights into human social evolution

scholarly journals Group size effects in social evolution

2018 ◽  
Vol 457 ◽  
pp. 211-220 ◽  
Author(s):  
Jorge Peña ◽  
Georg Nöldeke
Keyword(s):  
Group Size ◽  
Size Effects ◽  
Social Evolution

scholarly journals The multinomial index: a robust measure of reproductive skew

2020 ◽  
Vol 287 (1936) ◽  
pp. 20202025
Author(s):  
Cody T. Ross ◽  
Adrian V. Jaeggi ◽  
Monique Borgerhoff Mulder ◽  
Jennifer E. Smith ◽  
Eric Alden Smith ◽  
...  
Keyword(s):  
Group Size ◽  
Social Evolution ◽  
Natural Populations ◽  
R Package ◽  
Reproductive Skew ◽  
Primate Species ◽  
Highly Sensitive ◽  
Highly Nonlinear ◽  
Population Comparisons ◽  
Negative Effect

Inequality or skew in reproductive success (RS) is common across many animal species and is of long-standing interest to the study of social evolution. However, the measurement of inequality in RS in natural populations has been challenging because existing quantitative measures are highly sensitive to variation in group/sample size, mean RS, and age-structure. This makes comparisons across multiple groups and/or species vulnerable to statistical artefacts and hinders empirical and theoretical progress. Here, we present a new measure of reproductive skew, the multinomial index, M , that is unaffected by many of the structural biases affecting existing indices. M is analytically related to Nonacs’ binomial index, B , and comparably accounts for heterogeneity in age across individuals; in addition, M allows for the possibility of diminishing or even highly nonlinear RS returns to age. Unlike B , however, M is not biased by differences in sample/group size. To demonstrate the value of our index for cross-population comparisons, we conduct a reanalysis of male reproductive skew in 31 primate species. We show that a previously reported negative effect of group size on mating skew was an artefact of structural biases in existing skew measures, which inevitably decline with group size; this bias disappears when using M . Applying phylogenetically controlled, mixed-effects models to the same dataset, we identify key similarities and differences in the inferred within- and between-species predictors of reproductive skew across metrics. Finally, we provide an R package, SkewCalc , to estimate M from empirical data.

scholarly journals The Infertility Trap: The Fertility Costs of Group-Living in Mammalian Social Evolution

2021 ◽  
Vol 9 ◽  
Author(s):  
Robin I. M. Dunbar ◽  
Susanne Shultz
Keyword(s):  
Group Size ◽  
Social Evolution ◽  
Low Cost ◽  
Social Groups ◽  
Group Living ◽  
The Other ◽  
Risk Averse ◽  
Limit Group ◽  
Grouping Patterns ◽  
Environmental Demands

Mammal social groups vary considerably in size from single individuals to very large herds. In some taxa, these groups are extremely stable, with at least some individuals being members of the same group throughout their lives; in other taxa, groups are unstable, with membership changing by the day. We argue that this variability in grouping patterns reflects a tradeoff between group size as a solution to environmental demands and the costs created by stress-induced infertility (creating an infertility trap). These costs are so steep that, all else equal, they will limit group size in mammals to ∼15 individuals. A species will only be able to live in larger groups if it evolves strategies that mitigate these costs. We suggest that mammals have opted for one of two solutions. One option (fission-fusion herding) is low cost but high risk; the other (bonded social groups) is risk-averse, but costly in terms of cognitive requirements.

scholarly journals Group Size as a Trade Off Between Fertility and Predation Risk: Implications for Social Evolution

2018 ◽  
Author(s):  
R.I.M. Dunbar ◽  
Padraig Mac Carron
Keyword(s):  
Cluster Analysis ◽  
Predation Risk ◽  
Group Size ◽  
Social Evolution ◽  
Female Fertility ◽  
Fertility Rates ◽  
Trade Off ◽  
Lower Pair ◽  
Increase Group Size ◽  
Do So

AbstractCluster analysis reveals a fractal pattern in the sizes of baboon groups, with peaks at ∼20, ∼40, ∼80 and ∼160. Although all baboon species individually exhibit this pattern, the two largest are mainly characteristic of the hamadryas and gelada. We suggest that these constitute three pairs of linear oscillators (20/40, 40/80 and 80/160), where in each case the higher value is set by limits on female fertility and the lower by predation risk. The lower pair of oscillators form an ESS in woodland baboons, with choice of oscillator being determined by local predation risk. Female fertility rates would naturally prevent baboons from achieving the highest oscillator with any regularity; nonetheless, hamadryas and gelada have been able to break through this fertility ‘glass ceiling’ and we suggest that they have been able to do so by using substructuring (based partly on using males as ‘hired guns’). This seems to have allowed them to increase group size significantly so as to occupy higher predation risk habitats (thereby creating the upper oscillator).

scholarly journals Neocortex evolution in primates: the ‘social brain’ is for females

2005 ◽  
Vol 1 (4) ◽  
pp. 407-410 ◽  
Author(s):  
Patrik Lindenfors
Keyword(s):  
Group Size ◽  
Social Intelligence ◽  
Social Evolution ◽  
Female Group ◽  
Male And Female ◽  
Social Intelligence Hypothesis ◽  
Male Group ◽  
The Social ◽  
Size Limits ◽  
The Relationship

According to the social intelligence hypothesis, relative neocortex size should be directly related to the degree of social complexity. This hypothesis has found support in a number of comparative studies of group size. The relationship between neocortex and sociality is thought to exist either because relative neocortex size limits group size or because a larger group size selects for a larger neocortex. However, research on primate social evolution has indicated that male and female group sizes evolve in relation to different demands. While females mostly group according to conditions set by the environment, males instead simply go where the females are. Thus, any hypothesis relating to primate social evolution has to analyse its relationship with male and female group sizes separately. Since sex-specific neocortex sizes in primates are unavailable in sufficient quantity, I here instead present results from phylogenetic comparative analyses of unsexed relative neocortex sizes and female and male group sizes. These analyses show that while relative neocortex size is positively correlated with female group size, it is negatively, or not at all correlated with male group size. This indicates that the social intelligence hypothesis only applies to female sociality.

Biology of a weakly social bee, Exoneura (Exoneurella) setosa (Hymenoptera : Apidae) and implications for social evolution in Australian allodapine bees

1998 ◽  
Vol 46 (3) ◽  
pp. 221 ◽  
Author(s):  
Tania Neville ◽  
Michael P. Schwarz ◽  
Simon M. Tierney
Keyword(s):  
Group Size ◽  
Social Evolution ◽  
Sensu Stricto ◽  
Brood Production ◽  
Brood Rearing ◽  
Large Group ◽  
Basal Position ◽  
Social Bee

Australian allodapine bees provide excellent material for comparative approaches to understanding social evolution. The subgenus Exoneurella occupies a cladistically basal position in the Australian Exoneura group and comprises only four species. We describe sociality in one Exoneurella species, E. setosa, and combine this with other data to infer some patterns of social evolution in allodapines. E. setosa rears a first brood solitarily, although staggered brood production and the production of a second brood in some nests leads to a situation where older, recently emerged brood have the ability to help rear their younger siblings and this overlaps with opportunities to lay eggs. This is similar to the situation for two other phylogenetically distal species of Exoneurella, as well as for members of the genus Braunsapis, which is used as an outgroup for Exoneura. When combined with other studies, our results suggest that the opportunity for sib-rearing is a plesiomorphic trait for Australian allodapines and this has been largely lost in a distal subgenus, Exoneura sensu stricto. Instead, multifemale brood-rearing colonies in this latter group mostly comprise individuals of the same generation, and species exhibit large group size, univoltinism and kin cofounding. This suggests that evolution can favour semisociality and quasisociality, even when eusociality has already arisen.

scholarly journals Group size effects in social evolution

2018 ◽  
Author(s):  
Jorge Peña ◽  
Georg Nöldeke
Keyword(s):  
Group Size ◽  
Size Effects ◽  
Evolutionary Biology ◽  
Social Evolution ◽  
Evolutionary Dynamics ◽  
Replicator Dynamics ◽  
Basin Of Attraction ◽  
Evolution Of Cooperation ◽  
Positive Effects ◽  
Public Goods Games

AbstractHow the size of social groups affects the evolution of cooperative behaviors is a classic question in evolutionary biology. Here we investigate group size effects in the evolutionary dynamics of games in which individuals choose whether to cooperate or defect and payoffs do not depend directly on the size of the group. We find that increasing the group size decreases the proportion of cooperators at both stable and unstable rest points of the replicator dynamics. This implies that larger group sizes can have negative effects (by reducing the amount of cooperation at stable polymorphisms) and positive effects (by enlarging the basin of attraction of more cooperative outcomes) on the evolution of cooperation. These two effects can be simultaneously present in games whose evolutionary dynamics feature both stable and unstable rest points, such as public goods games with participation thresholds. Our theory recovers and generalizes previous results and is applicable to a broad variety of social interactions that have been studied in the literature.

scholarly journals Optimal response to quorum-sensing signals varies in different host environments with different pathogen group size

2019 ◽  
Author(s):  
Liqin Zhou ◽  
Leyla Slamti ◽  
Didier Lereclus ◽  
Ben Raymond
Keyword(s):  
Bacillus Thuringiensis ◽  
Quorum Sensing ◽  
Social Interactions ◽  
Group Size ◽  
Social Evolution ◽  
Local Population ◽  
Gram Positive ◽  
Competitive Fitness ◽  
Oral Infections ◽  
Gram Positive Bacteria

AbstractThe persistence of genetic variation in master regulators of gene expression, such as quorum-sensing systems, is hard to explain. Here, we investigated two alternative hypotheses for the prevalence of polymorphic quorum-sensing in Gram-positive bacteria, i.e. the use of different signal / receptor pairs (‘pherotypes’) to regulate the same functions. First, social interactions between pherotypes or ‘facultative cheating’ may favour rare variants that exploit the signals of others. Second, different pherotypes may increase fitness in different environments. We evaluated these hypotheses in the invertebrate pathogen Bacillus thuringiensis, using three pherotypes expressed in a common genetic background. Facultative cheating occurred in homogenized hosts, in contrast, rare pherotypes had reduced fitness in naturalistic infections. There was clear support for environment-dependent fitness: pherotypes varied in responsiveness to signals and in mean competitive fitness. Notably, competitive fitness varied with group size: the pherotype with highest responsiveness to signals performed best in smaller hosts where infections have a lower pathogen group size. Less responsive pherotypes performed best in larger hosts. Results using homogenized insect media fit with the expectation of facultative cheating and social evolution theory, but results from naturalist oral infections do not fit many of the predictions from this body of theory. In this system, low signal abundance appears to limit fitness in hosts while the optimal level of response to signals varies in different host environments.ImportanceQuorum sensing describes the ability of microbes to alter gene regulation according to their local population size. Some successful theory suggests that this is a form of cooperation: investment in shared products is only worthwhile if there are sufficient bacteria making the same product. This theory can explain the genetic diversity in these signaling systems in Gram-positive bacteria such as Bacillus and Staphylococcus. The possible advantages gained by rare genotypes (which can exploit the products of their more common neighbours) could explain why different genotypes can coexist. We show that while these social interactions can occur in simple laboratory experiments they do not occur in naturalistic infections using an invertabrate pathogen, Bacillus thuringiensis. Instead our results suggest that different genotypes are adapted to different-sized hosts. Overall, social models are not easily applied to this system implying that a new explanation for this form of quorum sensing is required.

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