Paul L. Hooper, Kathryn Demps, Michael Gurven, Drew Gerkey, Hillard S. Kaplan. Skills, division of labour and economies of scale among Amazonian hunters and South Indian honey collectors. Philosophical Transactions B. Published 26 October 2015.DOI: 10.1098/rstb.2015.0008
Abstract: 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.
1. Introduction
Cooperation and collective action are hallmarks of human societies and major foci of research in the evolutionary sciences [1,2]. Cooperation in food acquisition and sharing of food resources are particularly critical features of foraging economies [3], whose relevance for understanding the course of hominin evolution is well acknowledged [4]. While cooperation appears to be universal and important to success in human societies that practice foraging, and perhaps in all human societies, the nature and scope of cooperation are quite variable within and among groups.
Much of the variation in the size and composition of groups that forage for wild resources appears to be patterned with respect to social and ecological environments. Examples of these patterns of variation are abundant in the ethnographic literature. For example, Steward reported that Shoshoni hunter–gatherers of the US Great Basin hunted solitarily during winter months and families were largely self-sufficient, but aggregated in larger groups and participated in communal game drives during the summer [5]. Among the Aché of Paraguay, armadillos and deer are hunted solitarily, while cooperative groups form to pursue white-lipped peccaries, monkeys, coatimundis and spotted paca [6–8]. While women are often involved in cooperative pursuits of coatimundis, they rarely participate in pursuits of other animals. In cooperative paca hunts, the role of flushing the animal is given to younger, less skilled hunters, while the role of killing the animal by hand is allocated to older, more skilled hunters. Among Lamalera whale hunters, roles within large cooperative parties and the distributions of rewards depend on age, kinship and boat ownership in complex ways [9].
The goal of this paper is to provide a theoretical framework for explaining the size and composition of groups engaged in foraging activities and to test a series of hypotheses derived from the framework. These principles build on previous work in economics and ecological anthropology, focusing attention on maximizing group efficiency when group members actively pool the spoils of labour [10–12]. We propose that three fundamental features of human foraging economies interact in generating patterns of cooperation in foraging groups, and more generally in most human societies.
The first feature derives from the differential risks and gains for women and men from engaging in different economic activities [12–17]. Productive activities that present a significant danger of injury, such as hunting mobile prey, are likely to generate particularly high gains to a sexual division of labour. Because of the intensive childcare practised by human mothers, hunting by women engaged in childcare would expose infants to substantial risks. Infants may also encumber movement and lower return rates. While women may be fully capable of developing the skills necessary to hunt successfully, the inability to build up experience while pregnant and nursing results in differences in productivity based on skill [15]. We propose, as have others, that the nutritional value of meat interacting with differential costs of hunting for the two sexes leads to a sexual division of labour with subsequent sharing of resources and biparental investment within families [11–14]. Other resources, such as honey produced by stinging bees high in trees, also generate differential risks for men versus women engaged in childcare. With this type of specialized coordination, the sexual division of labour in subsistence will be organized according to differential risks and benefits for females and males based on the skills required for production. (Other factors, such as local gender norms and expectations, may either mediate or interact with the effects of these constraints, as we discuss below).
The second feature affecting patterns of production in foraging economies is that the resources acquired demand substantial levels of accumulated skill. Studies from a variety of foraging contexts show that foragers do not reach peak economic efficiency until middle adulthood (usually in the 30s or 40s) and that peak efficiency is achieved later in life for resources requiring greater levels of skill [18–24]. We hypothesize that variation in skill and strength requirements for different resources generates an age-structured division of labour in foraging groups that complements the sexual division of labour [11]. The intergenerational division of labour is associated with a flow of resources between generations based on kinship. Net transfers (amount given minus amount received) tend to be directed downward from older to younger individuals with three generations participating: grandparents, their adult children, and grandchildren [25,26]. Children and adolescents tend not to participate in skill-intensive, strength-intensive or dangerous subsistence activities; they work less than adults and focus on learning and producing resources that are easily acquired [27–29].
A third principle organizing cooperation in foraging is economies of scale with respect to the number of individuals in a production group [10,30–34]. Foraged resources vary in terms of the relationship between the number of individuals in the foraging party and the amount acquired. For some resources, solitary individuals may be capable of achieving near-maximal return rates. Return rates from other resources may increase significantly as more individuals are added to the pursuit group. We propose that where individuals can voluntarily assort themselves, and in the absence of other external constraints, foraging parties will tend to form that maximize per capita expected returns. When these conditions hold, variation in the size of parties will reflect ecological variation in economies of scale. Economies of scale derive principally from features of the resource, the technologies used in its acquisition and the social institutions that shape the rules of joint production and/or distribution. Some mobile resources are more easily captured when several individuals cooperate, for example by blocking escape routes, herding animals, or by following specific individuals as groups disperse [8]. In general, hunting large and group-living animals often exhibits economies of scale. Collected foods, such as honey produced and defended by stinging bees, may also exhibit economies of scale involving a coordinated division of roles. Within societies, under conditions of voluntary assortment, the size of foraging parties should reflect differences in economies of scale among the specific resources or suites of resources being targeted. Variation among societies is expected to reflect the quantitative mix of resources they pursue.
Our proposal is that the interaction of those three principles—the division of labour by sex, the division of labour by age and economies of scale—can help explain the size and composition of foraging groups. As a first step in assessing the relevance of these principles, we test a series of hypotheses in two societies, Tsimane' forager-horticulturalists of lowland Bolivia and Jenu Kuruba honey collectors of South India, focusing on two different types of foraged resources: hunted meat and collected honey. These two societies were selected given that both actively engage in foraging in addition to other economic pursuits, and extensive data on the size and composition of foraging parties permit a parallel series of statistical tests. In each case, we test hypotheses about the efficiency of individuals and groups in foraging, then test corollary hypotheses regarding the size and composition of the groups themselves.
The analysis of foraging efficiency uses an estimation strategy developed in econometrics and used with increasing frequency in quantitative anthropology [30,31,35]. This strategy estimates the effect of inputs to production—in this case, the number of individuals or hours contributed by individuals of a given age and sex—on total group production in terms of the elasticity of production with respect to each input. The elasticity represents the expected per cent change in output associated with a per cent increase in the input. Elasticity values close to 1 indicate that a 1% increase in the input results in an equal percentage increase in production (i.e. constant returns to scale), while values greater than or less than 1 indicate increasing or decreasing returns to scale, respectively. (Further details regarding this estimation strategy and its interpretation are described in electronic supplementary material, §1). The following three hypotheses will be tested regarding the efficiency of individuals of foraging groups.
(H1): The efficiency of males will be greater than that of females in skill- or strength-intensive foraging tasks that are incompatible with childcare.(P1): The elasticity of production with respect to male participation will be higher than the elasticity of production with respect to female participation.(P2): The elasticity of production with respect to male labour (in terms of time effort) will be greater than the elasticity of production with respect to female labour.(P3): The difference in the elasticities with respect to male and female inputs will be greater for larger game species and for more skill- or strength-intensive tasks.(H2): Efficiency in skill-intensive foraging activities will be greatest at middle and older ages owing to the importance of experience and learning.(P4): The elasticity of production with respect to the participation of middle-aged and older adult males will be higher than that of younger males.(P5): The elasticity of production with respect to the labour of middle-aged and older adult males will be higher than that of younger males.(P6): The difference in the elasticities with respect to the inputs of younger versus older males will be greater for larger game species and for more skill- or strength-intensive activities.(H3): Individuals will perform specific roles within foraging parties in which they are more efficient in accordance with H1 and H2.(P7): Older males will perform more dangerous, skill- and strength-intensive tasks more often than females or younger males.
The following five hypotheses will be tested regarding the size and composition of foraging parties:
(H4): Individuals will tend to participate in foraging parties in which they are relatively more efficient in accordance with H1 and H2.(P8): Females will participate in foraging parties less often than males.(P9): Middle-aged and older males will participate in foraging parties more often than younger males.(H5): Parties engaged in foraging activities that require more specialized skills will be composed more exclusively of individuals possessing those skills.(P10): Heterogeneity in the age and sex of participants will be lower for larger game and more skill- or strength-intensive activities.(H6): For activities regularly undertaken in groups, the productivity of the group will be characterized either by constant or increasing returns to scale with respect to the participation and labour of group members.(P11): Per capita returns will remain constant or increase with additional participants (particularly men) in foraging groups.1(H7): The party sizes that maximize per capita efficiency will vary according to the type of resource pursued.(P12): The impact of additional group members on per capita returns will be greater for species requiring multiple coordinated or complementary roles (particularly for larger, group-living and more dangerous species).(H8): The size of parties pursuing a given resource will reflect returns to scale in the production of that resource.(P13): The mean size of foraging parties will be greater for those species identified in P12.
This set of hypotheses is derived from the specific principles outlined above, but is not meant to account for the totality of reality on the ground. When empirical results do not conform to a framework focused on group efficiency, we are stimulated to develop alternative hypotheses. In the discussion that follows, we address the current results in light of hypotheses emphasizing other social benefits and constraints, such as learning, social norms, and failures of coordination and cooperation [10,36–38].
The rest of the paper is organized as follows. In §2, we provide an ethnographic overview and a description of the economies of the two societies from which the data are derived. We then, in §3, report the results of the analysis of the Tsimane' and Jenu Kuruba data in sequence. In §4, we conclude with a discussion of the extent to which the data support the hypotheses, and future directions for assessing the generalizability of the proposed framework.
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