Food-Sharing Networks in Lamalera,Indonesia

Exponential random graph modeling (ERGM) is used here to test hypotheses derived from human behavioral ecology about the adaptive nature of human food sharing. Respondents in all (n = 317) households in the fishing and sea-hunting village of Lamalera, Indonesia, were asked to name those households to whom they had more frequently given (and from whom they had more frequently received) food during the preceding sea-hunting season. The responses were used to construct a social network of between-household food-sharing relationships in the village. The results show that kinship, proximity, and reciprocal sharing all strongly increase the probability of giving food to a household. The effects of kinship and distance are relatively independent of each other, although reciprocity is more common among residentially and genealogically close households. The results show support for reciprocal altruism as a motivation for food sharing, while kinship and distance appear to be important partner-choice criteria.     

Kin-selection,reciprocal altruism,and information sharing among Maine lobstermen

In this paper, the sharing of information about the location of lobsters among lobstermen in two Maine harbors is described. First, why the sharing of such information is likely to entail an economic loss for the transmitters is explained. Then, the extent to which the principles of kin-selection and reciprocal altruism can account for the sharing of information is determined. Many cases of information sharing in one of the harbors do not appear to be the type of kin-directed or reciprocal acts expected to be produced by kin-selection or reciprocal altruism as they are usually conceived. The behavior of these lobstermen may be the result of the advantages of maintaining a complex web of social relationships among them. Failure to appreciate the complexity of such relationships in some fishing communities is suggested to be a major shortcoming in the economic models previously used to explain information management among commercial fishermen. I conclude that a more complex model of reciprocal altruism is needed to account for the information sharing among this group of Maine lobstermen, and perhaps many other human social groups.     

Interhousehold Meat Sharing among Mayangna and Miskito Horticulturalists in Nicaragua

Recent analyses of food sharing in small-scale societies indicate that reciprocal altruism maintains interhousehold food transfers, even among close kin. In this study, matrix-based regression methods are used to test the explanatory power of reciprocal altruism, kin selection, and tolerated scrounging. In a network of 35 households in Nicaragua’s Bosawas Reserve, the significant predictors of food sharing include kinship, interhousehold distance, and reciprocity. In particular, resources tend to flow from households with relatively more meat to closely related households with little, as predicted by kin selection. This generalization is especially true of household dyads with mother-offspring relationships, which suggests that studies of food sharing may benefit from distinctions between lineal and collateral kin. Overall, this analysis suggests that exchanges among kin are primarily associated with differences in need, not reciprocity. Finally, although large game is distributed widely, qualitative observations indicate that hunters typically do not relinquish control of the distribution in ways predicted by costly signaling theory.     

Reciprocal altruism in bats and other mammals

In this paper five conditions are specified which must be met before reciprocal altruism, rather than kin selection, should be invoked. Four purported mammalian examples— social grooming in coati, cluster position in roosting pallid bats, information exchange among greater spear-nosed bats, and blood regurgitation among vampire bats—are examined to determine if reciprocal altruism is necessary to plausibly explain each situation. Results from a computer simulation which apportions the relative selective advantage of vampire bat food sharing to kin selection and reciprocal altruism are then presented. The results demonstrate that the increase in individual survivorship due to reciprocal food sharing events in this species provides a greater increase in inclusive fitness than can be attributed to aiding relatives. This analysis suggests that reciprocal altruism can be selectively more important than kin selection when altruistic behaviors in a relatively large social group occur frequently and provide a major fitness benefit to the recipient even when that recipient is related to the donor.     

Evolution of cooperative cross-feeding could be less challenging than originally thought

The act of cross-feeding whereby unrelated species exchange nutrients is a common feature of microbial interactions and could be considered a form of reciprocal altruism or reciprocal cooperation. Past theoretical work suggests that the evolution of cooperative cross-feeding in nature may be more challenging than for other types of cooperation. Here we re-evaluate a mathematical model used previously to study persistence of cross-feeding and conclude that the maintenance of cross-feeding interactions could be favoured for a larger parameter ranges than formerly observed. Strikingly, we also find that large populations of cross-feeders are not necessarily vulnerable to extinction from an initially small number of cheats who receive the benefit of cross-feeding but do not reciprocate in this cooperative interaction. This could explain the widespread cooperative cross-feeding observed in natural populations.     

Distinctions among reciprocal altruism,kin selection,and cooperation and a model for the initial evolution of beneficent behavior

Reciprocal altruism is usually regarded as distinct from kin selection. However, because reciprocators are likely to establish long-term relations and to deliver most of their aid to other individuals genetically predisposed to reciprocation, most acts of reciprocal altruism should involve indirect increments to inclusive fitness, at least as regards alleles for reciprocation. Thus, as usually defined, reciprocal altruism is not clearly distinct from kin selection because both involve indirect increments to inclusive fitness. We propose a new definition for reciprocal altruism that makes the phenomenon distinct from kin selection and allows for reciprocation between nonrelatives in which current costs exceed future benefits returned to the reciprocal altruist. Cooperation and reciprocal altruism are often considered synonymous or different only in the timing of donating and receiving aid. We show, however, that there are other critical differences between reciprocal altruism and other forms of cooperation, most importantly, the latter often involve no clearly identifiable aid. We propose a four-category system to encompass the range of cooperative and beneficent behaviors that occur in nature (reciprocal altruism, pseudoreciprocity, simultaneous cooperation and by-product beneficence). Reciprocal altruism must involve aid that is returned to an original donor as a result of behavior that has a net cost to an original recipient. Our simplest category of cooperative/beneficent behavior, “by-product beneficence,” occurs when a selfish act also benefits another individual and requires no prior or subsequent interactions between the individuals involved. By-product beneficence may be the primitive state from which more complicated types of cooperative/beneficent behavior evolved. We show via simple models that by-product beneficence can allow for the initial increase of helping behavior in a completely unstructured population although the individuals showing such behavior pay all the costs while sharing the benefits with other individuals. Previous models that attempted to explain the initial increase of cooperative/beneficent behavior were much more complex and were based on the prisoner's dilemma, which does not accurately reflect most forms of cooperation and beneficence that occur in nature.     

Strong reciprocity, human cooperation, and the enforcement of social norms

This paper provides strong evidence challenging the self-interest assumption that dominates the behavioral sciences and much evolutionary thinking. The evidence indicates that many people have a tendency to voluntarily cooperate, if treated fairly, and to punish noncooperators. We call this behavioral propensity “strong reciprocity” and show empirically that it can lead to almost universal cooperation in circumstances in which purely self-interested behavior would cause a complete breakdown of cooperation. In addition, we show that people are willing to punish those who behaved unfairly towards a third person or who defected in a Prisoner’s Dilemma game with a third person. This suggests that strong reciprocity is a powerful device for the enforcement of social norms involving, for example, food sharing or collective action. Strong reciprocity cannot be rationalized as an adaptive trait by the leading evolutionary theories of human cooperation (in other words, kin selection, reciprocal altruism, indirect reciprocity, and costly signaling theory). However, multilevel selection theories of cultural evolution are consistent with strong reciprocity.     

Altruism and reciprocity among friends and kin in a Tibetan village

To explain the high level of altruism among unrelated friends, some people propose that friends may apply the feeling and emotions that underlie kin-selected nepotism to each other. Alternatively, altruism among friends may be sustained by an evolved psychology that is sensitive to the dynamic of contingent reciprocity. A recent study (Stewart-Williams, S., 2007. Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28, 193–198) with North American students showed that the amount of help given and received was less likely to be balanced among friends (as among relatives) than among acquaintances, suggesting that exchange among friends and relatives may rely on similar psychological mechanisms. To assess whether the similar pattern in exchange reflects the similar psychology in exchange, I tested how different types of relationship regulated the amount of help given and received, and people’s emotional reaction to non-reciprocation. I asked 45 participants from a Tibetan village in China to imagine how unhappy they would feel if the target person (sibling, cousin, friend or acquaintance) failed to reciprocate their help in various contexts. I found that overall, friends and relatives were more tolerant to non-reciprocation than acquaintances were. For emotional help, friends were more likely to feel unhappy about non-reciprocation than relatives were, but were similar to relatives in responses to other types of help (aid during crisis, labor, and financial help). The study suggests that people may evaluate the importance of reciprocity differently in various situations, and exhibit different levels of sensitivity to the dynamic of reciprocity. Thus it calls for careful distinctions between friends and kin in the everyday lives of individuals.     

A neural basis for social cooperation

Cooperation based on reciprocal altruism has evolved in only a small number of species, yet it constitutes the core behavioral principle of human social life. The iterated Prisoner's Dilemma Game has been used to model this form of cooperation. We used fMRI to scan 36 women as they played an iterated Prisoner's Dilemma Game with another woman to investigate the neurobiological basis of cooperative social behavior. Mutual cooperation was associated with consistent activation in brain areas that have been linked with reward processing: nucleus accumbens, the caudate nucleus, ventromedial frontal/orbitofrontal cortex, and rostral anterior cingulate cortex. We propose that activation of this neural network positively reinforces reciprocal altruism, thereby motivating subjects to resist the temptation to selfishly accept but not reciprocate favors.     

Meal sharing among the Ye’kwana

In this study meal sharing is used as a way of quantifying food transfers between households. Traditional food-sharing studies measure the flow of resources between households. Meal sharing, in contrast, measures food consumption acts according to whether one is a host or a guest in the household as well as the movement of people between households in the context of food consumption. Our goal is to test a number of evolutionary models of food transfers, but first we argue that before one tests models of who should receive food one must understand the adaptiveness of food transfers. For the Ye’kwana, economies of scale in food processing and preparation appear to set the stage for the utility of meal sharing. Evolutionary models of meal sharing, such as kin selection and reciprocal altruism, are evaluated along with non-evolutionary models, such as egalitarian exchange and residential propinquity. In addition, a modified measure of exchange balance—proportional balance—is developed. Reciprocal altruism is shown to be the strongest predictor of exchange intensity and balance.     

Alarm calls of wintering great tits Parus major: warning of mate,reciprocal altruism or a message to the predator?

When a predator is not an immediate threat, a prey may produce relatively loud alarm calls because the risk is low. Since such calls could nevertheless attract acoustically oriented predators, the cost of predator attraction must be outweighed by factors beneficial to the caller. In this field study we elicited low-risk alarm calls by temporarily catching wintering adult male great tits Parus major at feeders both within and outside their territories. We tested whether the alarm calls of dominant males can be explained in terms of mate warning, reciprocal altruism or notifying the predator of detection. If alarms are intended to warn mates, males accompanied by their mates should give alarm calls both within and outside home range, even if other permanent flock members are absent. If alarms are to be explained by reciprocal altruism, male great tits should give low-risk alarm calls when accompanied by permanent flock members other than mate within and not outside of the home-range. If alarm calling is a message to a predator, males should call when foraging alone. We found that male great tits gave low-risk alarm calls when accompanied by their mates, independent of feeder location. They also gave low-risk alarm calls within home ranges in the presence of other permanent flock members when mates were absent. In contrast, only a few males gave calls when foraging alone within their home ranges, or when in the company of unfamiliar great tits outside their usual home-range. The results suggest that the utterance of alarm calls may be explained as mate protection and reciprocal altruism among familiar individuals.     

Kin Preference and Partner Choice

This paper presents a comparison of social kinship (patrilineage) and biological kinship (genetic relatedness) in predicting cooperative relationships in two different economic contexts in the fishing and whaling village of Lamalera, Indonesia. A previous analysis (Alvard, Human Nature 14:129-163, 2003) of boat crew affiliation data collected in the village in 1999 found that social kinship (patrilineage) was a better predictor of crew affiliation than was genetic kinship. A replication of this analysis using similar data collected in 2006 finds the same pattern: lineage is a better predictor than genetic kinship of crew affiliation, and the two together explain little additional variance over that explained by lineage alone. However, an analogous test on food-sharing relationships finds the opposite pattern: biological kinship is a better predictor of food-sharing relationships than is social kinship. The difference between these two cooperative contexts is interpreted in terms of kin preferences that shape partner choice, and the relative autonomy with which individuals can seek to satisfy those preferences. Drawing on stable matching theory, it is suggested that unilineal descent may serve as a stable compromise among multiple individuals' incongruent partner preferences, with patriliny favored over matriliny in the crew-formation context because it leads to higher mean degrees of relatedness among male cooperators. In the context of food-sharing, kin preferences can be pursued relatively autonomously, without the necessity of coordinating preferences with those of other households through the institution of lineage.     

The Time Frame of Partner Choice in the Grooming Reciprocation of Cebus apella

Recent theoretical and experimental studies argued that reciprocity is constrained by the cognitive limitations of most animals and that, when reciprocation occurs, it should necessarily be short term. In this study, we examined the time frame of partner choice in the reciprocal grooming of captive female tufted capuchin monkeys ( Cebus apella ). Female capuchins groomed preferentially those individuals that overall groomed them most. Tufted capuchins did sometimes reciprocate grooming immediately. We quantified the time course and probability of immediate reciprocation, and excluded from the analysis cases of immediate reciprocation. We then showed that, even excluding immediate reciprocation, female capuchins still preferred to groom those individuals that groom them most. Our results show that partner choice is not necessarily based on immediate reciprocation and suggest that capuchins are able to reciprocate over longer time frames. These findings argue against the hypothesis that long-term reciprocation is absent in species lacking sophisticated cognitive abilities. We suggest that reciprocal altruism over long time frames relies on a system of emotional bookkeeping.     

Altruism and mental disorders

Data suggest that the theories of kin selection and reciprocal altruism are viable working models to explain altruistic behavior. It remains to be demonstrated if these models can explain the behavior of persons with mentaL disorders for whom altruistic behavior is reported to be reduced. This paper addresses this issue. Part I reviews proximate factors that are thought to influence both altruistic decision making and interindividual variation in altruistic behavior. The focus is on trait signaling by potential beneficiaries and the evaluation of signals and altruistic decision making by potential altruists. In Part II, points developed in Part I are combined with clinical and empirical findings to analyze data on personality disorders and dysthymic disorder. The analysis leads to three causal hypotheses: Reduced altruistic behavior may be an evolved strategy, a consequence of dysfunctional recognition systems or algorithms, and/or a secondary response to an increase in symptoms. Different disorders and features of disorders are explained by each hypothesis.     

A Prisoner's Dilemma model of the evolution of paternal care

The heavy energetic demands of gestation, lactation and rearing of offspring mean that studies of paternal care in primates usually focus on female reproductive effort. Here it is shown that both male and female reproductive effort must be considered in order to understand how paternal care evolved. This is done using the Prisoner's Dilemma, best known as a model of reciprocal altruism. It is found that the relative cost of reproduction for males and females is crucially important in determining co-operative and competitive strategies. In particular, when male reproductive costs are less than female reproductive costs, males co-operate with females even when females do not reciprocate. This surprising behaviour, termed non-reciprocal altruism, is comparable with male investment in a female and her offspring.     

Food sharing: a model of manipulation by harassment

Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is in their own self-interest—they avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic.     

Is the repeated prisoner's dilemma a good model of reciprocal altruism?

Axelrod and Hamilton (1981) used the repeated prisoner's dilemma game as a basis for their widely cited analysis of the evolution of reciprocal altruism. Recently, it has been argued that the repeated prisoner's dilemma is not a good model for this task. Some critics have argued that the single period prisoner's dilemma represents mutualistic rather than altruistic social interactions. Others have argued that reciprocal altruism requires that the opportunities for altruism occur sequentially, first one individual and then after some delay the other. Here I begin by arguing that the single period prisoner's dilemma game is consistent with the definition of altruism that is widely accepted in evolutionary biology. Then I present two modified versions of the repeated prisoner's dilemma, one in which behavior is sequential, and a second in which behavior occurs in continuous time. Each of these models shares the essential qualitative properties with the version used by Axelrod and Hamilton.     

Altruism among non-relatives: alternatives to the 'Prisoner's Dilemma'

Triver's model of reciprocal altruism, and its descendants based on the Prisoner's Dilemma model, have dominated thinking about cooperation and altruism between non-relatives. However, there are three alternative models of altruism directed to non-relatives. These models, which are not based on the Prisoner's Dilemma, may explain a variety of phenomena, from allogrooming among impala to helping by non-relatives in cooperatively breeding birds and mammals.     

Mobbing behaviour: reciprocity-based co-operation in breeding Pied Flycatchers Ficedula hypoleuca

Recent non-experimental evidence suggests that reciprocal altruism may be more common in nature than was previously thought. Here we present experimental evidence for mobbing behaviour as reciprocal altruism in breeding Pied Flycatchers Ficedula hypoleuca , a small migratory passerine. Pied Flycatchers attended mobs initiated by their co-operating neighbours. However, they did not join in mobbing initiated by their conspecific neighbours when not assisted in the test an hour before. The results suggest that birds followed a 'tit-for-tat-like' strategy and that responses of neighbouring Flycatchers may be related to reciprocal altruism.     

Food sharing at meals

The presence of a kinship link between nuclear families is the strongest predictor of interhousehold sharing in an indigenous, predominantly Dolgan food-sharing network in northern Russia. Attributes such as the summed number of hunters in paired households also account for much of the variation in sharing between nuclear families. Differences in the number of hunters in partner households, as well as proximity and producer/consumer ratios of households, were investigated with regard to cost-benefit models. The subset of households involved in reciprocal meal sharing is 26 of 84 household host-guest pairs. The frequency of reciprocal meal sharing between families in this subset is positively correlated with average household relatedness. The evolution of cooperation through clustering may illuminate the relationship between kinship and reciprocity at this most intimate level of food sharing.