Skills,division of labour and economies of scale among Amazonian hunters and South Indian honey collectors

In foraging and other productive activities, individuals make choices regarding whether and with whom to cooperate, and in what capacities. The size and composition of cooperative groups can be understood as a self-organized outcome of these choices, which are made under local ecological and social constraints. This article describes a theoretical framework for explaining the size and composition of foraging groups based on three principles: (i) the sexual division of labour; (ii) the intergenerational division of labour; and (iii) economies of scale in production. We test predictions from the theory with data from two field contexts: Tsimane'' game hunters of lowland Bolivia, and Jenu Kuruba honey collectors of South India. In each case, we estimate the impacts of group size and individual group members'' effort on group success. We characterize differences in the skill requirements of different foraging activities and show that individuals participate more frequently in activities in which they are more efficient. We evaluate returns to scale across different resource types and observe higher returns at larger group sizes in foraging activities (such as hunting large game) that benefit from coordinated and complementary roles. These results inform us that the foraging group size and composition are guided by the motivated choice of individuals on the basis of relative efficiency, benefits of cooperation, opportunity costs and other social considerations.     

The evolution of inequality

Understanding how systems of political and economic inequality evolved from relatively egalitarian origins has long been a focus of anthropological inquiry. Many hypotheses have been suggested to link socio‐ecological features with the rise and spread of inequality, and empirical tests of these hypotheses in prehistoric and extant societies are increasing. In this review, we synthesize several streams of theory relevant to understanding the evolutionary origins, spread, and adaptive significance of inequality. We argue that while inequality may be produced by a variety of localized processes, its evolution is fundamentally dependent on the economic defensibility and transmissibility of wealth. Furthermore, these properties of wealth could become persistent drivers of inequality only following a shift to a more stable climate in the Holocene. We conclude by noting several key areas for future empirical research, emphasizing the need for more analyses of contemporary shifts toward institutionalized inequality as well as prehistoric cases.     

The evolutionary history of division of labour

Functional specialization, or division of labour (DOL), of parts within organisms and colonies is common in most multi-cellular, colonial and social organisms, but it is far from ubiquitous. Several mechanisms have been proposed to explain the evolutionary origins of DOL; the basic feature common to all of them is that functional differences can arise easily. These mechanisms cannot explain the many groups of colonial and social animals that exhibit no DOL despite up to 500 million years of evolution. Here, I propose a new hypothesis, based on a multi-level selection theory, which predicts that a reproductive DOL is required to evolve prior to subsequent functional specialization. I test this hypothesis using a dataset consisting of the type of DOL for living and extinct colonial and social animals. The frequency distribution of DOL and the sequence of its acquisition confirm that reproductive specialization evolves prior to functional specialization. A corollary of this hypothesis is observed in colonial, social and also within multi-cellular organisms; those species without a reproductive DOL have a smaller range of internal variation, in terms of the number of polymorphs or cell types, than species with a reproductive DOL.     

Social intelligence, human intelligence and niche construction

This paper is about the evolution of hominin intelligence. I agree with defenders of the social intelligence hypothesis in thinking that externalist models of hominin intelligence are not plausible: such models cannot explain the unique cognition and cooperation explosion in our lineage, for changes in the external environment (e.g. increasing environmental unpredictability) affect many lineages. Both the social intelligence hypothesis and the social intelligence-ecological complexity hybrid I outline here are niche construction models. Hominin evolution is hominin response to selective environments that earlier hominins have made. In contrast to social intelligence models, I argue that hominins have both created and responded to a unique foraging mode; a mode that is both social in itself and which has further effects on hominin social environments. In contrast to some social intelligence models, on this view, hominin encounters with their ecological environments continue to have profound selective effects. However, though the ecological environment selects, it does not select on its own. Accidents and their consequences, differential success and failure, result from the combination of the ecological environment an agent faces and the social features that enhance some opportunities and suppress others and that exacerbate some dangers and lessen others. Individuals do not face the ecological filters on their environment alone, but with others, and with the technology, information and misinformation that their social world provides.     

The evolutionary basis of human social learning

Humans are characterized by an extreme dependence on culturally transmitted information. Such dependence requires the complex integration of social and asocial information to generate effective learning and decision making. Recent formal theory predicts that natural selection should favour adaptive learning strategies, but relevant empirical work is scarce and rarely examines multiple strategies or tasks. We tested nine hypotheses derived from theoretical models, running a series of experiments investigating factors affecting when and how humans use social information, and whether such behaviour is adaptive, across several computer-based tasks. The number of demonstrators, consensus among demonstrators, confidence of subjects, task difficulty, number of sessions, cost of asocial learning, subject performance and demonstrator performance all influenced subjects' use of social information, and did so adaptively. Our analysis provides strong support for the hypothesis that human social learning is regulated by adaptive learning rules.     

The evolutionary ecology of attachment organization

Life history theory’s principle of allocation suggests that because immature organisms cannot expend reproductive effort, the major trade-off facing juveniles will be the one between survival, on one hand, and growth and development, on the other. As a consequence, infants and children might be expected to possess psychobiological mechanisms for optimizing this trade-off. The main argument of this paper is that the attachment process serves this function and that individual differences in attachment organization (secure, insecure, and possibly others) may represent facultative adaptations to conditions of risk and uncertainty that were probably recurrent in the environment of human evolutionary adaptedness. An early version of this paper was presented in the symposium “Childhood in Life-history Perspective: Developing Views” organized by Gilda Morelli and Paula Ivey for the Annual Meeting of the Society for Cross-Cultural Research in Santa Fe, New Mexico, February 16–20, 1994. James S. Chisholm recently joined the Department of Anatomy and Human Biology at the University of Western Australia. Previously he taught in the Department of Anthropology at the University of New Mexico and in the Division of Human Development at the University of California, Davis. He is a biosocial anthropologist whose research interests lie in the fields of human behavioral biology, evolutionary ecology, and life history theory, where he focuses on infant social-emotional development and the development of reproductive strategies in adolescence and young adulthood. In addition to numerous articles he is the author ofNavajo Infancy: An Ethological Study of Child Development (Aldine de Gruyter, 1983).     

Biology of the stingless beePlebeia remota (Holmberg): observations and evolutionary implications

Summary The genusPlebeia has a special significance for the study of social evolution of stingless bees: morphologically primitive, its species display a wealth of behavioural evolution, especially with respect to the oviposition process. We comparePlebeia remota with the few other members of the genus studied so far.Related to its subtropical geographical range, brood production is seasonal (there is no brood in the colony in colder months), and adult workers occur as summer and winter bees. The nest is in tree cavities, and the involucrum is absent or restricted to the winter period. Brood cells are arranged in horizontal combs, and new cells are built completely synchronously. Each series consists of up to 50 cells, their number being mainly dependent on colony size. Construction speed is remarkably constant, allowing 4–6 batches per 24 hours. Cell building and provisioning are activities of a small group of specialized workers.The oviposition cycle follows the classical subdivisions for stingless bees. During the patrolling phase a worker may offer a trophic egg in a most remarkable way: while retreating backward from the queen she bends the abdomen under thorax and head, and lays an egg on the comb. This egg is eaten by the queen or a worker.The provisioning, oviposition and operculation of all cells occur simultaneously, each cell is provisioned by 4–9 workers. Localization of a cell by the queen may be facilitated by its characteristic guard, which defends the cell against the approaching queen. The degree of synchronization within a batch is very high: the duration per cell lasts 420–950 sec, the batch of up till 50 cells needs only 557–1160 sec. Operculation is done by a worker that was not involved in the previous steps.Males are generally produced by the queen. Several male producing cycles per year occur. In orphan colonies laying workers give rise to males, and in queenright colonies workers may occasionally reproduce as well.Division of labour follows the general pattern for stingless bees; however, cell building and provisioning are activities of a specialized group of workers.     

Use of artificial arenas to predict the social organisation of halictine bees: Data for fourteen species from Chile

I studied the behavioural profiles of fourteen species of Chilean halictine bee using the circle tube apparatus. Interactions were classified as aggressive, avoidance or cooperative. One species, Corynura chloris, is believed to be semisocial and its behaviour was largely aggressive, Ruizantheda mutabilis is known to be communal and its behaviour was predominantly cooperative whereas Penapis toroi is a member of a subfamily from which only solitary behaviour is known and it primarily exhibited avoidance behaviours. As a result, I suggest that the relative frequency of these different behaviours may be useful in establishing the social organisation of species. Based upon comparisons of behavioural profiles, I predict the social organizations of the remaining species and suggest that at least some of the bees in the populations of Ruizantheda proxima, Caenohalictus dolator, Ca. species A and Pseudagapostemon pississi investigated exhibit communal behaviour; those of Co. patagonica and Co. herbsti likely have a reproductive division of labour, probably within semisocial societies, and that the populations of Co. corinogaster, Co. melanocladius, Ca. pygosinuatum, Ca. cuprellus and Lasioglossum aricense studied are probably solitary. Phylogenies suggest that solitary behaviour in Ca. pygosinuatum and Ca. cuprellus is reversed from communal behaviour and solitary behaviour in L. aricense may be a reversal from eusociality. The response “back and follow” is not indicative of dominance or cooperation as it correlated only with the frequency of avoidance interactions among the taxa studied. I discuss the utility of the circle tube apparatus in the identification of populations worthy of more detailed sociobiological investigation. Received 10 August 2005; revised 8 March 2006; accepted 21 March 2006.     

The evolution of altruistic social preferences in human groups

In this paper, we consider three hypotheses to account for the evolution of the extraordinary capacity for large-scale cooperation and altruistic social preferences within human societies. One hypothesis is that human cooperation is built on the same evolutionary foundations as cooperation in other animal societies, and that fundamental elements of the social preferences that shape our species'' cooperative behaviour are also shared with other closely related primates. Another hypothesis is that selective pressures favouring cooperative breeding have shaped the capacity for cooperation and the development of social preferences, and produced a common set of behavioural dispositions and social preferences in cooperatively breeding primates and humans. The third hypothesis is that humans have evolved derived capacities for collaboration, group-level cooperation and altruistic social preferences that are linked to our capacity for culture. We draw on naturalistic data to assess differences in the form, scope and scale of cooperation between humans and other primates, experimental data to evaluate the nature of social preferences across primate species, and comparative analyses to evaluate the evolutionary origins of cooperative breeding and related forms of behaviour.     

Methoprene accelerates age polyethism in workers of a social wasp (Polybia occidentalis)

Abstract. Topical applications of the Juvenile Hormone (JH) analogue methoprene to 1-day-old adult workers of the highly eusocial wasp Polybia occidentalis (Olivier) (Hymenoptera: Vespidae) accelerate the rate of age polyethism. Longevity of laboratory-reared wasps is negatively correlated with dose of topically applied methoprene. Doses of 25 μg methoprene or greater are lethal. Untreated wasps show marked age polyethism in the field. Age of first performance of acts in seven behavioural categories (in-nest, transition to outside, non-task on nest envelope, nest maintenance, foraged material handling, defence, and foraging) is negatively correlated with methoprene dose. Topical applications of methoprene accelerate age polyethism of highly eusocial bee and wasp workers, but do not have this effect on primitively eusocial bees and wasps, suggesting that JH control of age polyethism evolved independently in advanced species of Apidae and Vespidae.     

The evolutionary roots of creativity: mechanisms and motivations

We consider the evolution of cognition and the emergence of creative behaviour, in relation to vocal communication. We address two key questions: (i) what cognitive and/or social mechanisms have evolved that afford aspects of creativity?; (ii) has natural and/or sexual selection favoured human behaviours considered ‘creative’? This entails analysis of ‘creativity’, an imprecise construct: comparable properties in non-humans differ in magnitude and teleology from generally agreed human creativity. We then address two apparent problems: (i) the difference between merely novel productions and ‘creative’ ones; (ii) the emergence of creative behaviour in spite of high cost: does it fit the idea that females choose a male who succeeds in spite of a handicap (costly ornament); or that creative males capable of producing a large and complex song repertoire grew up under favourable conditions; or a demonstration of generally beneficial heightened reasoning capacity; or an opportunity to continually reinforce social bonding through changing communication tropes; or something else? We illustrate and support our argument by reference to whale and bird song; these independently evolved biological signal mechanisms objectively share surface properties with human behaviours generally called ‘creative’. Studying them may elucidate mechanisms underlying human creativity; we outline a research programme to do so.     

The ecological and evolutionary energetics of hunter‐gatherer residential mobility

Residential mobility is a key aspect of hunter‐gatherer foraging economies and therefore is an issue of central importance in hunter‐gatherer studies. 1 - 7 Hunter‐gatherers vary widely in annual rates of residential mobility. Understanding the sources of this variation has long been of interest to anthropologists and archeologists. The vast majority of hunter‐gatherers who are dependent on terrestrial plants and animals move camp multiple times a year because local foraging patches become depleted and food, material, and social resources are heterogeneously distributed through time and space. In some environments, particularly along coasts, where resources are abundant and predictable, hunter‐gatherers often become effectively sedentary. But even in these special cases, a central question is how these societies have maintained viable foraging economies while reducing residential mobility to near zero.     

Interindividual variability in social insects – proximate causes and ultimate consequences

Individuals within social groups often show consistent differences in behaviour across time and context. Such interindividual differences and the evolutionary challenge they present have recently generated considerable interest. Social insects provide some of the most familiar and spectacular examples of social groups with large interindividual differences. Investigating these within‐group differences has a long research tradition, and behavioural variability among the workers of a colony is increasingly regarded as fundamental for a key feature of social insects: division of labour. The goal of this review is to illustrate what we know about both the proximate mechanisms underlying behavioural variability among the workers of a colony and its ultimate consequences; and to highlight the many open questions in this research field. We begin by reviewing the literature on mechanisms that potentially introduce, maintain, and adjust the behavioural differentiation among workers. We highlight the fact that so far, most studies have focused on behavioural variability based on genetic variability, provided by e.g. multiple mating of the queen, while other mechanisms that may be responsible for the behavioural differentiation among workers have been largely neglected. These include maturational, nutritional and environmental influences. We further discuss how feedback provided by the social environment and learning and experience of adult workers provides potent and little‐explored sources of differentiation. In a second part, we address what is known about the potential benefits and costs of increased behavioural variability within the workers of a colony. We argue that all studies documenting a benefit of variability so far have done so by manipulating genetic variability, and that a direct test of the effect of behavioural variability on colony productivity has yet to be provided. We emphasize that the costs associated with interindividual variability have been largely overlooked, and that a better knowledge of the cost/benefit balance of behavioural variability is crucial for our understanding of the evolution of the mechanisms underlying the social organization of insect societies. We conclude by highlighting what we believe to be promising but little‐explored avenues for future research on how within‐colony variability has evolved and is maintained. We emphasize the need for comparative studies and point out that, so far, most studies on interindividual variability have focused on variability in individual response thresholds, while the significance of variability in other parameters of individual response, such as probability and intensity of the response, has been largely overlooked. We propose that these parameters have important consequences for the colony response. Much more research is needed to understand if and how interindividual variability is modulated in order to benefit division of labour, homeostasis and ultimately colony fitness in social insects.     

Effects of a juvenile hormone analogue on honey bee foraging behaviour and alarm pheromone production

Worker honey bees treated with 250 μg of the juvenile hormone analogue methoprene shifted from the broodnest to the food storage region prematurely and displayed precocious foraging behaviour. Treatments with 25 and 2.5 μg caused slight but non-significant effects. Methoprene did not influence individual foraging performance as measured by mean number of foraging trips/h, mean amount of time spent foraging/h or mean duration of the total foraging period. Methoprene also induced premature production of two alarm pheromones, 2-heptanone and isopentyl acetate. These results support the hypothesis that juvenile hormone regulates temporal division of labour in the honey bee colony.