Social Evolution

In consectutive rounds, each agent in a finite population chooses an action, is randomly matched, obtains a payoff and then observes the performance of another agent. An agent determines future behavior based on the information she receives from the present round. She chooses among the behavioral rules that increase expected payoffs in any specifications of the matching scenario. The rule

The social brain hypothesis was proposed as an explanation for the fact that primates have unusually large brains for body size compared to all other vertebrates: Primates evolved large brains to manage their unusually complex social systems. Although this proposal has been generalized to all vertebrate taxa as an explanation for brain evolution, recent analyses suggest that the social brain hypothesis takes a very different form in other mammals and birds than it does in anthropoid primates. In primates, there is a quantitative relationship between brain size and social group size (group size is a monotonic function of brain size), presumably because the cognitive demands of sociality place a constraint on the number of individuals that can be maintained in a coherent group. In other mammals and birds, the relationship is a qualitative one: Large brains are associated with categorical differences in mating system, with species that have pairbonded mating systems having the largest brains. It seems that anthropoid primates may have generalized the bonding processes that characterize monogamous pairbonds to other non-reproductive relationships ('friendships'), thereby giving rise to the quantitative relationship between group size and brain size that we find in this taxon. This raises issues about why bonded relationships are cognitively so demanding (and, indeed, raises questions about what a bonded relationship actually is), and when and why primates undertook this change in social style.

Recent research has revealed that horizontal gene transfer and biofilm formation are connected processes. Although published research investigating this interconnectedness is still limited, we will review this subject in order to highlight the potential of these observations because of their believed importance in the understanding of the adaptation and subsequent evolution of social traits in bacteria.

The societies of southern Central America and northern South America, a region historically occupied by Chibchan-speaking peoples, have long been acknowledged as valuable sources of information on chiefdoms and other forms of prestate social organization. Most studies, however, have focused on chiefdoms that are known ethnographically or ethnohistorically with an emphasis on the sixteenth century and the immediate precontact period. This paper reviews archaeological evidence from an earlier period in an attempt to elucidate general patterns associated with the earliest appearance of social inequality. The centuries between AD 300 and 600 are characterized by the first widespread use of prestige goods manufactured from gold and jade, special cemeteries for the interment of elites, and a rich iconography. Detailed consideration of recent research relevant to the events of this period highlights some of the problems inherent in the archaeological identification of hierarchy, chiefdoms, leadership, and other features of prestate complex societies.

Intraspecific variability in social organization is common, yet the underlying causes are rarely known 1-3 . In the fire ant Solenopsis invicta, the existence of two divergent forms of social organization is under the control of a single Mendelian genomic element marked by two variants of an odorant-binding protein gene 4-8 . Here we characterize the genomic region responsible for this important social polymorphism, and show that it is part of a pair of heteromorphic chromosomes that have many of the key properties of sex chromosomes. The two variants, hereafter referred to as the social B and social b (SB and Sb) chromosomes, are characterized by a large region of approximately 13 megabases (55% of the chromosome) in which recombination is completely suppressed between SB and Sb. Recombination seems to occur normally between the SB chromosomes but not between Sb chromosomes because Sb/Sb individuals are non-viable. Genomic comparisons revealed limited differentiation between SB and Sb, and the vast majority of the 616 genes identified in the non-recombining region are present in the two variants. The lack of recombination over more than half of the two heteromorphic social chromosomes can be explained by at least one large inversion of around 9 megabases, and this absence of recombination has led to the accumulation of deleterious mutations, including repetitive elements in the non-recombining region of Sb compared with the homologous region of SB. Importantly, most of the genes with demonstrated expression differences between individuals of the two social forms reside in the non-recombining region. These findings highlight how genomic rearrangements can maintain divergent adaptive social phenotypes involving many genes acting together by locally limiting recombination.

A consideration of ethnographic data, computational model results, and archaeological data suggest that changes in family-level economics coincident with subsistence intensification contributed to the emergence of social complexity among prehistoric hunter–gatherers in eastern North America by creating the conditions for a “rich get richer” scenario. Ethnographic data are used to construct a general computational model representing key person- and family-level behaviors, constraints, and decisions affecting the size and composition of hunter–gatherer families. Results from model experiments suggest that lowering the age at which children make a significant contribution to subsistence (e.g., through the broadening of the diet to include the kinds of mass-harvested, “low quality” foods that were increasingly exploited during the Archaic and Woodland periods) relaxes constraints on family size and makes large, polygynous families economically viable. Positive feedbacks between the productive and reproductive potentials of larger families produce right-tailed distributions of family size and “wealth” when the productive age of children is low and polygyny is incentivized. Size data from over 800 prehistoric residential structures suggest right-tailed distributions of family size were present during the Late Archaic through Middle Woodland periods. These distributions would have provided variability in family-based status that permitted the emergence of hereditary social distinctions.

The African mole-rats (family Bathyergidae) are subterranean hystricomorph rodents occurring in a variety of habitats and displaying levels of sociality which range from solitary to eusocial, making them a unique mammalian taxonomic group to test ecological in£uences on sociality. Here, we use an extensive DNA-based phylogeny and comparative analysis to investigate the relationship between ecology, sociality and evolution within the family. Mitochondrial cytochrome-b and 12s rRNA trees reveal that the solitary species are monophyletic when compared to the social species. The naked mole-rat (Heterocephalus glaber) is ancestral and divergent from the Damaraland mole-rat (Cryptomys damarensis), supporting previous ¢ndings that have suggested the multiple evolution of eusociality within the family. The Cryptomys genus is speciesrich and contains taxa exhibiting di¡erent levels of sociality, which can be divided into two distinct clades. A total of seven independent comparisons were generated within the phylogeny, and three ecological variables were signi¢cantly correlated with social group size: geophyte density (p50.05), mean months per year of rainfall greater than 25 mm (p50.001), and the coe¤cient of rainfall variation (p 0.001). These results support the food^aridity hypothesis for the evolution of highly social cooperative behaviour in the Bathyergidae, and are consistent with the current theoretical framework for skew theory.

Although it is commonly believed that women are kinder and more cooperative than men, there is conflicting evidence for this assertion. Current theories of sex differences in social behavior suggest that it may be useful to examine in what situations men and women are likely to differ in cooperation. Here we derive predictions from both sociocultural and evolutionary perspectives on context-specific sex differences in cooperation and conduct a unique meta-analytic study of 272 effect sizes -- sampled across 50 years of research -- on social dilemmas to examine several potential moderators. The overall average effect size is not statistically different from zero (d = -.05), suggesting that men and women do not differ in their overall amounts of cooperation. However, the association between sex and cooperation is moderated by several key features of the social context: Male-male interactions are more cooperative than female-female interactions (d = .16) yet women cooperate more than men in mixed-sex interactions (d = -.22). In repeated interactions men are more cooperative than women. Women were more cooperative than men in larger groups and in more recent studies, but these differences dissappeared after statistically controlling for several study characteristics. We discuss these results in the context of both sociocultural and evolutionary theories of sex differences, stress the need for an integrated biosocial approach, and outline directions for future research.

Kin and levels-of-selection models are common approaches for modelling social evolution. Indirect genetic effect (IGE) models represent a different approach, specifying social effects on trait values rather than fitness. We investigate the joint effect of relatedness, multilevel selection and IGEs on response to selection. We present a measure for the degree of multilevel selection, which is the natural partner of relatedness in expressions for response. Response depends on both relatedness and the degree of multilevel selection, rather than only one or the other factor. Moreover, response is symmetric in relatedness and the degree of multilevel selection, indicating that both factors have exactly the same effect. Without IGEs, the key parameter is the product of relatedness and the degree of multilevel selection. With IGEs, however, multilevel selection without relatedness can explain evolution of social traits. Thus, next to relatedness and multilevel selection, IGEs are a key element in the genetical theory of social evolution.

Multilevel societies are unique in their ability to facilitate the maintenance of strong and consistent social bonds among some individuals while allowing separation among others, which may be especially important when social and sexual bonds carry significant and reliable benefits to individuals within social groups. Here we examine the importance of social and sexual bonds in the multilevel society of hamadryas baboons (Papio hamadryas) and apply these principles to social evolution in Plio-Pleistocene hominins. The behavior, adaptations, and socioecology of baboons (Papio spp.) have long been recognized as providing an important comparative sample to elucidate the processes of human evolution, and the social system of hamadryas baboons in particular shares even more similarities with humans than that of other baboons. Here we draw parallels between processes during the evolution of hamadryas social organization and those characterizing late Pliocene or early Pleistocene hominins, most likely Homo erectus. The higher costs of reproduction faced by female Homo erectus, exacerbated by an increased reliance on difficult to acquire, nutrient-dense foods, are commonly thought to have been alleviated by a strengthening of male–female bonds (via male provisioning and the evolution of monogamy) or by the assistance of older, postreproductive females (via grandmothering). We suggest that both of these social arrangements could have been present in Plio-Pleistocene hominins if we assume the development of a multilevel society such as that in hamadryas baboons. The evolution of a multilevel society thus underlies the adaptive potential for the complexity that we see in modern human social organization.

We discuss the evolutionary origin and elaboration of sociality using an indirect genetic effects perspective. Indirect genetic effects models simultaneously consider zygotic genes, genes expressed in social partners (especially mothers and siblings), and the interactions between them. Incorporation of these diverse genetic effects should lead to more realistic models of social evolution. We first review
haplodiploidy as a factor that promotes the evolution of eusociality. Social insect biologists have doubted the importance of relatedness asymmetry caused by haplodiploidy and focused on other predisposing factors such as maternal care. However, indirect effects theory shows that maternal care evolves more readily in haplodiploids, especially with inbreeding and despite multiple mating. Because extended maternal care is believed to be a precondition for the evolution of eusociality, the evolutionary bias towards maternal care in haplodiploids may result in a further bias towards eusociality in these groups. Next, we compare kin selection and parental manipulation and then briefly review additional hypotheses for the evolutionary origin of eusociality. We present a verbal model for the evolutionary origin and elaboration of sib-social care from maternal care based on the modification of the timing of expression of maternal care behaviors. Specifically, heterochrony genes cause maternal care behaviors to be expressed prereproductively towards siblings instead of postreproductively towards offspring. Our review demonstrates that both maternal effect genes (expressed in a parental manipulation manner) and direct effect zygotic genes (expressed in an offspring control manner) are likely involved in the evolution of eusociality. We conclude by describing theoretical and empirical advances with indirect genetic effects and sociogenomics, and we provide specific quantitative genetic and genomic predictions from our heterochrony model for the evolutionary origin and elaboration of eusociality.

The idea that in the near future we should expect “the Singularity” has become quite popular recently, primarily thanks to the activities of Google technical director in the field of machine training Raymond Kurzweil and his book The Singularity Is Near (2005). It is shown that the mathematical analysis of the series of events (described by Kurzweil in his famous book), which starts with the emergence of our galaxy and ends with the decoding of the DNA code, is indeed ideally described by an extremely simple mathematical function (not known to Kurzweil himself) with a singularity in the region of 2029. It is also shown that a similar time series (beginning with the onset of life on Earth and ending with the information revolution—composed by the Russian physicist Alexander Panov completely independently of Kurzweil) is also practically perfectly described by a mathematical function (very similar to the above and not used by Panov) with a singularity in the region of 2027. It is shown that this function is also extremely similar to the equation discovered in 1960 by Heinz von Foerster and published in his famous article in the journal “Science”—this function almost perfectly describes the dynamics of the world population up to the early 1970s and is characterized by a mathematical singularity in the region of 2027. All this indicates the existence of sufficiently rigorous global macroevolutionary regularities (describing the evolution of complexity on our planet for a few billions of years), which can be surprisingly accurately described by extremely simple mathematical functions. At the same time, it is demonstrated that in the region of the Singularity point there is no reason, after Kurzweil, to expect an unprecedented (many orders of magnitude) acceleration of the rates of technological development. There are more grounds for interpreting this point as an indication of an inflection point, after which the pace of global evolution will begin to slow down systematically in the long term.

This paper maps a coevolutionary research agenda for ecological economics. At an epistemological level coevolution offers a powerful logic for transcending environmental and social determinisms and developing a cross-disciplinary approach in the study of socio-ecological systems. We identify four consistent stories emerging out of coevolutionary studies in ecological economics, concerning: environmental degradation and development failure in peripheral regions; the lock-in of unsustainable production–consumption patterns; the vicious cycle between human efforts to control undesirable microorganisms and the evolution of these organisms; and the adaptive advantages of other-regarding, cooperative behaviors and institutions. We identify challenges in the conceptualization of coevolutionary relationships in relation to: the interaction between different hierarchical levels of evolution; the role of space and social power; uneven rates of change and crises. We conclude with the political implications of a coevolutionary perspective based on the premises of pragmatism.

Summary: this paper develops the idea of finite social space – that there are only a limited number of possible social systems, and uses this model cladistically to reconstruct early hominin social behaviour and evolutionary pathways.
Original abstract: Changes in social behaviour were a key aspect of human evolution, and yet it is notoriously difficult for palaeobiologists to determine patterns of social evolution. By defining the limited number of distributional strategies available to members of each sex of any species and investigating the conditions under which they may occur and change, the social behaviour of different hominid taxa may be reconstructed.

This chapter offers an analysis of the conditions in the MENA countries on the eve of the Arab Spring in the World System perspective, as well as causes (internal and external, general and specific) and certain consequences of the Arab revolutions in certain countries, the MENA region and in the World System. We will discuss Arab revolutions in a wide historical and theoretical context. It is very useful to compare the causes of revolutions in modern and previous epochs, in Arab and others countries; to find similarities and specificity. For example, in Arab revolutions, a very important role was played by new information technologies. The revolutionary sentiments are especially fueled by the diffusion of radical ideas and ideologies in a society, as well as by a rapid urbanization, growing youth share in the demographic composition and rapidly increasing education level of a part of population in combination with poor education of the other part. Thus, the rapid unregulated changes, and increasing structural disproportions may bring a society to a modernization trap which often causes revolutions and other political upheavals. All these phenomena were present in the Arab countries on the eve of the Arab Spring, especially in Egypt and Tunisia.

Numerous theoretical studies have investigated how limited dispersal may provide an explanation for the evolution of cooperation, by leading to interactions between relatives. However, despite considerable theoretical attention, there has been a lack of empirical tests. In this article, we test how patterns of dispersal influence the evolution of cooperation, using iron-scavenging in the bacterium Pseudomonas aeruginosa as our cooperative trait. We found that relatively limited dispersal does not favor cooperation. The reason for this is that although limited dispersal increases the relatedness between interacting individuals, it also leads to increased local competition for resources between relatives. This result supports Taylor's prediction that in the simplest possible scenario, the effects of increased relatedness and local competition exactly cancel out. In contrast, we show that one way for cooperation to be favored is if individuals disperse in groups (budding dispersal), because this maintains high relatedness while reducing local competition between relatives (relatively global competition).

Eusociality in mammals is defined in the present paper by the following criteria: reproductive altruism (which involves reproductive division of labor and cooperative alloparental brood care), overlap of adult generations, and permanent (lifelong) philopatry. We argue that additional criteria such as the existence of castes, colony size, reproductive skew, and social cohesion are not pertinent to the definition of eusociality in mammals. According to our definition of mammalian eusociality, several rodent species of the African family Bathyergidae can be considered eusocial, including the naked mole-rat (Heterocephalus glaber), Damaraland mole-rat (Cryptomys damarensis), and several additional, if not all, species in the genus Cryptomys. Furthermore, some species of social voles (like Microtus ochrogaster) may also fulfill criteria of mammalian eusociality. Understanding the evolution of eusociality in mole-rats requires answers to two primary questions: (1) What are the preconditions for the development of their eusocial systems? (2) Why do offspring remain in the natal group rather than dispersing and reproducing? Eusociality in mammals is by definition a special case of monogamy (more specifically: monogyny one female breeding), involving prolonged pair bonding for more than one breeding period. We argue that eusociality in mole-rats evolved from a monogamous mating system where cooperative brood care was already established. A tendency for group living is considered to be an ancestral (plesiomorph) trait among African bathyergid mole-rats, linking them to other hystricognath rodents. A solitary lifestyle seen in some genera, such as Bathyergus, Georychus, and Heliophobius, is assumed to be a derived trait that arose independently in different lineages of bathyergids, possibly as a consequence of selective constraints associated with the subterranean environment. In proximate terms, in eusocial mole-rats either puberty is assumed to be developmentally delayed so that under natural conditions most animals die before dispersal is triggered (e.g., in the case of Heterocephalus) or dispersal is induced only by an incidental encounter with an unfamiliar, yet adequate sexual partner (e.g., in the case of Cryptomys). Ultimately, a combination of strategies involving either dispersal and/or philopatry can be beneficial, especially in a highly unpredictable environment. If genetic relatedness among siblings is high (e.g., a coefficient of relatedness of 0.5 or more), then philopatry would not invoke an appreciable loss of fitness, especially if the cost of dispersing is higher than staying within the natal group. High genetic relatedness is more likely in a monogamous mating system or a highly inbred population. In this paper, we argue that the preconditions for eusociality in bathyergid mole-rats were a monogamous mating system and high genetic relatedness among individuals. We argue against the aridity food-distribution hypothesis (AFDH) that suggests a causal relationship between cooperative foraging for patchily distributed resources and the origin of eusociality. The AFDH may explain group size dynamics of social mole-rats as a function of the distribution and availability of resources but it is inadequate to explain the formation of eusocial societies of mole-rats, especially with respect to providing preconditions conducive for the emergence of eusociality.

In this paper, I investigate the relevance of recent work in reproductive skew theory to explanations of the evolution of social stratification in human societies. I briefly review human social evolution and corresponding increases in stratification, as well as recent developments in skew theory. I then attempt to integrate basic factors that have been a focus of interest by skew theorists to previous work on human social stratification from an evolutionary ecological perspective. I also discuss factors peculiar to human social systems that could profitably be incorporated into future models of reproductive skew.

Theories of social evolution have predicted that early permanent population concentrations will frequently be unstable,
with fissioning the predominant mechanism for resolving intravillage conflict. It has further been suggested that village fissioning will
cease with the emergence of higher-level integrative institutions. These processes have remained archaeologically undocumented. In this
article I attempt to identify the village fissioning process in the Formative Period of Bolivia’s Titicaca Basin. I conclude that village fissioning
took place in the Early Formative, and that it ceased with the emergence of a regional religious tradition in the Middle Formative. These
results confirm the utility and applicability of the evolutionary model. [Keywords: village fissioning, social evolution, scalar stress, Lake
Titicaca, Bolivia]

The evolution in animals of a first possession convention, in which individuals retain what they are the first to acquire, has often been taken as a foundation for the evolution of human ownership institutions. However, among humans, individuals actually only seldom retain an item they have acquired from the environment, instead typically transferring what they possess to other members of the community, to those in command, or to those who hold a contractual title. This paper presents a novel game-theoretic model of the evolution of ownership institutions as rules governing resource transfers. Integrating existing findings, the model contributes a new perspective on the emergence of communal transfers among hominin large game hunters around 200,000 years ago, of command ownership among sedentary humans in the millennia prior to the transition to agriculture, and of titled property ownership around 5,500 years ago. Since today’s property institutions motivate transfers through the promise of future returns, the analysis presented here suggests that these institutions may be placed under considerable pressure should resources become significantly constrained.

Punishment promotes contributions to public goods, but recent evidence suggests that its effectiveness varies across societies. Prior theorizing suggests that cross-societal differences in trust play a key role in determining the effectiveness of punishment, as a form of social norm enforcement, to promote cooperation. One line of reasoning is that punishment promotes cooperation in low-trust societies, primarily because people in such societies expect their fellow members to contribute only if there are strong incentives to do so. Yet another line of reasoning is that high trust makes punishment work, presumably because in high-trust societies people may count on each other to make contributions to public goods and also enforce norm violations by punishing free riders. This poses a puzzle of punishment: Is punishment more effective in promoting cooperation in high- or low-trust societies? In the present article, we examine this puzzle of punishment in a quantitative review of 83 studies involving 7,361 participants across 18 societies that examine the impact of punishment on cooperation in a public goods dilemma. The findings provide a clear answer: Punishment more strongly promotes cooperation in societies with high trust rather than low trust.

In this paper, the problem of social order posed by infosocieties is illustrated and solutions are discussed. Two main solutions are currently implemented in the fields of Artificial Societies and Multiagent Systems, i.e. Evolutionary Algorithms, on one hand, and Designed Institutions, on the other. Both proceed from controversial assumptions. Evolutionary Algorithms are based upon the idea that reproduction and imitation of fit individuals yield social evolution. However, this idea has been efficaciously [Journal of Artificial Societies and Social Simulation 1 (1998) 3] questioned. The complementary solution, i.e. Designed Institutions, is based upon systems of incentives and sanctions. In this paper, these are argued to be unreliable and even counterproductive, especially when natural agents are involved. Emergent social Institutions and distributed control are thus discussed as an alternate solution to the problem of social order. Hypotheses about the co-evolutionary process, including mental and social structures, leading to Emergent Institutions are discussed, and advantages over the preceding solutions are illustrated. Unlike Evolutionary Algorithms, Emergent Institutions are based upon (implicit) social norms and reputation. Unlike Designed Institutions, Emergent Institutions give rise to spontaneous social control, which is more efficient and less costly than centralised control. Finally, the role of Emergent Institutions in infosocieties is examined.

Social insects (ants, bees, wasps and termites) as a group are species rich and ecologically dominant. Many are outstanding``ecological engineers'', or providers of``ecosystem services'', or potential bioindicator species. Few social insects are currently formally classi®ed as Threatened, but this is almost certainly due to a lack of information on population sizes and trends in scarce species. The main in¯uence that sociality has on threats faced by social insects is in reducing effective population sizes, increasing population genetic subdivision and possibly reducing levels of genetic variation relative to solitary species. The main in¯uence that sociality has on threats from social insects is via its role in the ecological success of invasive species, which frequently pose a major hazard to native biotas. In some cases, social features underpinning ecological success in the original range almost certainly contribute to the success of invasive social insects. However, recent studies show or strongly suggest that, in some of the most notoriously invasive populations of ants, bees and wasps, novel social traits have arisen that greatly enhance the rate of spread and ecological competitiveness of these populations. Sociality can therefore represent either a liability or an asset in its contribution to the persistence of social insect populations.

Homo sapiens is the only species in which we observe extensive cooperation among large numbers of genetically unrelated individuals. Incompatible approaches to explaining cooperation among humans have been offered by sociologists, biologists, and economists. None is wholly successful. Each discipline, moreover, has ignored basic insights of the others. This paper explains cooperation by combining central contributions of these disciplines, developing a model of cultural evolution in which we use (a) the sociological concept of the internalization of norms to explain cultural transmission; (b) the biological concepts of vertical and oblique transmission to model the interaction of cultural and biological adaptation; and (c) the economic concepts of rational action and the replicator dynamic to model the interaction between self-interested and altruistic behavior. * Forthcoming, Rationality and Society.

Medical science is typically pitted against the evolutionary forces acting upon infective populations of bacteria. As an alternative strategy, we could exploit our growing understanding of population dynamics of social traits in bacteria to help treat bacterial disease. In particular, population dynamics of social traits could be exploited to introduce less virulent strains of bacteria, or medically beneficial alleles into infective populations. We discuss how bacterial strains adopting different social strategies can invade a population of cooperative wild-type, considering public good cheats, cheats carrying medically beneficial alleles (Trojan horses) and cheats carrying allelopathic traits (anti-competitor chemical bacteriocins or temperate bacteriophage viruses). We suggest that exploitation of the ability of cheats to invade cooperative, wild-type populations is a potential new strategy for treating bacterial disease.

Observation of leadership in small-scale societies offers unique insights into the evolution of human collective action and the origins of sociopolitical complexity. Using behavioural data from the Tsimane forager-horticulturalists of Bolivia and Nyangatom nomadic pastoralists of Ethiopia, we evaluate the
traits of leaders and the contexts in which leadership becomes more institutional. We find that leaders tend to have more capital, in the form of age-related knowledge, body size or social connections. These attributes can reduce the costs leaders incur and increase the efficacy of leadership. Leadership becomes more institutional in domains of collective action, such as resolution of intragroup conflict, where collective action failure threatens group integrity. Together these data support the hypothesis that leadership is an important means by which collective action problems are overcome in small-scale societies.

Genomic tools are allowing us to dissect the roles of genes and genetic architecture in social evolution, and eusocial insects are excellent models. Numerous hypotheses for molecular evolution of eusociality have been proposed, ranging from regulatory shifts in ‘old’ genes to rapid evolution of ‘new’ genes. A broad model to explain this major transition in evolution has been lacking. We provide a synthetic framework centered on the idea that different evolutionary processes dominate during different transitional stages, beginning with changes in gene regulation and culminating in novel genes later on. By considering multiple mechanisms as we ‘climb the social ladder’, we can test whether the transitions from solitary to simple sociality to complex sociality represent incremental changes or genetic revolutions.

Although the variability and complexity of chimpanzee behaviour frustrates generalization, it is widely believed that social evolution in this species occurs in the context of the recognizable social group or community. We used a combination of field observations and noninvasive genotyping to study the genetic structure of a habituated community of 55 wild chimpanzees, Pan troglodytes verus, in the Tai } Forest, Côte d'Ivoire. Pedigree relationships in that community show that female mate choice strategies are more variable than previously supposed and that the observed social groups are not the exclusive reproductive units. Genetic evidence based on nuclear microsatellite markers and behavioural observations reveal that females in the Tai } forest actively seek mating partners outside their social unit; noncommunity males accounted for half the paternities over 5 years. This female mating strategy increases male gene flow between communities despite male philopatry, and negates the predicted higher relatedness among community males. Kin selection seems unlikely to explain the frequent cooperation and sharing observed among group males in this population. Similarly, inbreeding avoidance is probably not the sole cause of permanent adolescent female dispersal as a combination of extragroup mating and avoidance of incest with home group males would allow females to avoid inbreeding without the hazards associated with immigration into a new community. Extragroup mating as part of chimpanzee females' reproductive strategy may allow them to choose from a wider variety and number of males, without losing the resources and support provided by their male social group partners.

Organizational ecology is a theoretical perspective on organizations that attempts to explain long-term social evolution, especially the rise and fall of orgar~izational populations. This article reviews the most successful research program of the perspective, one based on the density-dependent model of legitimation and competition. It discusses the model and evidence that has been offered in its support as well as criticisms that have been registered. Unsolved research problems of the program are identified and models-in-progress attempting to address these open questions are discussed and compared.

The authors quantitatively analyse the long-term dynamics of technological progress from 40,000 BCE and offer projections through the 22nd century. We provide one method to measure technological progress over that time period, using a simple hyperbolic equation, yt = C/(t0 – t), as our model. We define yt as the
technological growth rate, measured as number of technological phase transitions per unit of time. Our method measures the worldwide technology dynamic growth
with an accuracy of R2 = 0.99. We find the singularity date occurs in the early 21st century and expect a new powerful acceleration of technological development
after the 2030s followed by a slow-down in the late 21st and early 22nd centuries. The authors discuss the role of global ageing as one of the main factors in both the technological acceleration and the subsequent deceleration.

We investigated higher-level phylogenetic relationships within the genus Halictus based on parsimony and maximum likelihood (ML) analysis of elongation factor-1␣ DNA sequence data. Our data set includes 41 OTUs representing 35 species of halictine bees from a diverse sample of outgroup genera and from the three widely recognized subgenera of Halictus (Halictus s.s., Seladonia, and Vestitohalictus). We analyzed 1513 total aligned nucleotide sites spanning three exons and two introns. Equal-weights parsimony analysis of the overall data set yielded 144 equally parsimonious trees.

The relationship between organizational complexity and demographic scale is an enduring research problem at the intersection of the natural and social sciences and has far reaching implications for the study of social evolution, particularly the emergence and collapse of complex social organizations such as chiefdoms, states and empires. Anthropological models of social evolution universally assume that population growth plays a critical role in the development of organizational complexity; however, the relationship between organizational complexity and demographic scale has not been formalized and cross-culturally validated. There is a rich yet unsystematized body of diachronic organizational and demographic data describing the evolution of organizational complexity in 10 archaeologically known cases of primary state formation. Using this dataset, this essay proposes and tests a complex network model that describes state societies as discrete, self-similar, hierarchical social networks. The model accurately describes how organizational complexity and population scale in all cases. The complex network architecture of state societies suggests that further advances in our understanding of modern social organization may be found by a deeper investigation of the role of human nature in the evolution of human societies.

Cheirogaleids are one of the most primitive extant primate taxa in the world. Their lifestyle and mating system, therefore, have been considered to be representative for social systems in primate ancestors. Accepted models of social evolution in primates state that pair-bonding has evolved secondarily from diurnal group-living taxa and should therefore be constrained primarily to diurnal species. In contrast to these assumptions, the nocturnal fat-tailed dwarf lemur (Cheirogaleus medius) lives in permanent pairs, with obligate paternal care probably representing the evolutionary basis of pairliving. In this sociobiological field study, we analyzed the reproduction strategy of C. medius in the tropical forest of western Madagascar. In the rainy seasons from 1995 to 1999, 173 individuals of C. medius were captured and individually marked and 131 were genetically characterized through seven microsatellite loci. Additionally, 36 of these individuals were radio-tracked and observed. For 53 genotyped individuals, including 16 offspring, information about pair-bonding and family structure was known from field observations. Genetic analyses revealed that yearlings and infants living with an adult pair were in all cases sibs of the social mother. However, C. medius does not restrain from extra-pair copulations (EPCs) and a high rate of extra-pair paterni-ty (44%) was detected. Males sired offspring with their female partners as well as with extra-pair females within the same year, indicating that males may increase their reproductive success by EPCs without necessarily running the risk of cuckoldry. Females on the other hand do not seem to run the risk of reduced paternal care, either because males cannot detect relatedness of young, or because they might even increase their inclusive fitness by raising offspring of closely related males. Since females reproduce preferentially with territory holders and no paternity could be assigned to floating males, superior genetic quality of the males might be crucial for female choice.

is facilitated by dissecting it into simpler behavioral components. Using this approach, we present evidence implicating increased manganese transport by the malvolio (mvl) gene into brain cells as one factor that influences age-related division of labor in honey bee colonies. We studied mvl because manganese affects sucrose responsiveness in Drosophila melanogaster, and sucrose responsiveness is related to division of labor in honey bee colonies. Honey bee foragers are more responsive to sucrose in the laboratory than are younger nurse bees, and pollen foragers are more responsive to sucrose than nectar foragers. Levels of mvl mRNA in the brain and manganese in the head were higher in pollen foragers compared with nurses, with nectar foragers intermediate. Manganese treatment increased honey bee sucrose responsiveness and caused precocious foraging. Manganese levels showed a similar pattern to mvl mRNA but manganese treatment did not increase pollen foraging. These results suggest that, while there are molecular pathways common to sucrose responsiveness and division of labor, linkages between a complex behavior and some of its simpler behavioral components are not obligatory. Together with previous findings, these results support the idea that some feeding-related genes in Drosophila have been used in social evolution to regulate division of labor.

The evolution of parent-offspring interactions for the provisioning of care is usually explained as the phenotypic outcome of resolved conflicting selection pressures. However, parental care and offspring solicitation are expected to have complex patterns of inheritance. Here we present a quantitative genetic model of parentoffspring interactions that allows us to investigate the evolutionary maintenance of a state of resolved conflict. We show that offspring solicitation and parental provisioning are expected to become genetically correlated through coadaptation and that their genetic architecture is dictated by an interaction between patterns of selection and the proximate mechanisms regulating supply and demand. When selection is predominately on offspring solicitation, our model suggests that the genetic correlations between provisioning and solicitation are usually positive if provisioning reduces solicitation. Conversely, when selection is predominately on parental provisioning, the correlations are mostly negative as long as parents show a positive response to offspring demand. Empirical estimates of the genetic architecture of traits involved in family interactions fit these predictions. Our model demonstrates how the evolutionary maintenance of parent-offspring interactions can result in variable patterns of coadaptation, and it provides an explanation for the diversity of family interactions within and among species.

Implications for carcinogenesis of radiation-induced bystander effects are both mechanistic and practical. They include induction of second cancers, perturbations to tissue social control and induction of genomic instability and delayed or immediate mutations in areas not receiving a direct deposition of energy. Bystander effects have consequences for DNA damage-mutation-cancer initiation paradigms of radiation carcinogenesis that provide the mechanistic justification for