Family counts: deciding when to murder among the Icelandic Vikings

In small scale societies, lethal attacks on another individual usually invite revenge by the victim's family. We might expect those who perpetrate such attacks to do so only when their own support network (mainly family) is larger than that of the potential victim so as to minimise the risk of retaliation. Using data from Icelandic family sagas, we show that this prediction holds whether we consider biological kin or affinal kin (in-laws): on average, killers had twice as many relatives as their victims. These findings reinforce the importance of kin as a source of implicit protection even when they are not physically present. The results also support Hughes' (1988) claim that affines are biological kin because of the shared genetic interests they have in the offspring generation.     

Contingent movement and cooperation evolve under generalized reciprocity

How cooperation and altruism among non-relatives can persist in the face of cheating remains a key puzzle in evolutionary biology. Although mechanisms such as direct and indirect reciprocity and limited movement have been put forward to explain such cooperation, they cannot explain cooperation among unfamiliar, highly mobile individuals. Here we show that cooperation may be evolutionarily stable if decisions taken to cooperate and to change group membership are both dependent on anonymous social experience (generalized reciprocity). We find that a win-stay, lose-shift rule (where shifting is either moving away from the group or changing tactics within the group after receiving defection) evolves in evolutionary simulations when group leaving is moderately costly (i.e. the current payoff to being alone is low, but still higher than that in a mutually defecting group, and new groups are rarely encountered). This leads to the establishment of widespread cooperation in the population. If the costs of group leaving are reduced, a similar group-leaving rule evolves in association with cooperation in pairs and exploitation of larger anonymous groups. We emphasize that mechanisms of assortment within populations are often behavioural decisions and should not be considered independently of the evolution of cooperation.     

Trust and cooperation among economic agents

The units that are subject to selection pressure in evolutionary biology are ‘strategies’, which are conditional actions (‘Do P if X occurs, otherwise do Q’). In contrast, the units in economics select strategies from available menus so as to further their projects and purposes. As economic agents do not live in isolation, each agent''s optimum choice, in general, depends on the choices made by others. Because their projects and purposes involve the future, not just the present, each agent reasons about the likely present and future consequences of their respective choices. That is why beliefs, about what others may do and what the consequences of those choices could be, are at the basis of strategy selection. A catalogue of social environments is constructed in which agents not only promise each other''s cooperation, but also rationally believe that the promises will be kept. Unfortunately, non-cooperation arising from mistrust can be the outcome in those same environments: societies harbour multiple ‘equilibria’ and can skid from cooperation to non-cooperation. Moreover, a pre-occupation among analysts with the Prisoners'' Dilemma game has obscured the fact that cooperative arrangements can harbour not only inequality, but also exploitation. The analysis is used to discuss why international cooperation over the use of global public goods has proved to be so elusive.     

Avoiding the bullies: The resilience of cooperation among unequals

Can egalitarian norms or conventions survive the presence of dominant individuals who are ensured of victory in conflicts? We investigate the interaction of power asymmetry and partner choice in games of conflict over a contested resource. Previous models of cooperation do not include both power inequality and partner choice. Furthermore, models that do include power inequalities assume a static game where a bully’s advantage does not change. They have therefore not attempted to model complex and realistic properties of social interaction. Here, we introduce three models to study the emergence and resilience of cooperation among unequals when interaction is random, when individuals can choose their partners, and where power asymmetries dynamically depend on accumulated payoffs. We find that the ability to avoid bullies with higher competitive ability afforded by partner choice mostly restores cooperative conventions and that the competitive hierarchy never forms. Partner choice counteracts the hyper dominance of bullies who are isolated in the network and eliminates the need for others to coordinate in a coalition. When competitive ability dynamically depends on cumulative payoffs, complex cycles of coupled network-strategy-rank changes emerge. Effective collaborators gain popularity (and thus power), adopt aggressive behavior, get isolated, and ultimately lose power. Neither the network nor behavior converge to a stable equilibrium. Despite the instability of power dynamics, the cooperative convention in the population remains stable overall and long-term inequality is completely eliminated. The interaction between partner choice and dynamic power asymmetry is crucial for these results: without partner choice, bullies cannot be isolated, and without dynamic power asymmetry, bullies do not lose their power even when isolated. We analytically identify a single critical point that marks a phase transition in all three iterations of our models. This critical point is where the first individual breaks from the convention and cycles start to emerge.     

Mobility and cooperation among nomadic shepherds: The case of theRaikas

This paper describes and then analyzes the decision-making arrangements that prevail among the Raikas—nomadic shepherds from Western India. The paper suggests, using a simple analytical framework, that the existing distribution of decision-making during migration helps the Raikasto utilize available economies of scale, represent the different interest groups in their collectives, and control their decision-makers. At the same time, the ordinary shepherds in the camp are able to extract a comfortable subsistence from a complex and harsh environment by delegating much of their decision-making responsibilities to the leaders in the camp. To the extent shepherds in other parts of the world migrate over long distances and must confront similar issues of delegation of responsibilities and control over decision-makers, the analysis holds general relevance.     

Apoptotic DNase network: Mutual induction and cooperation among apoptotic endonucleases

DNA fragmentation produced by apoptotic DNases (endonucleases) leads to irreversible cell death. Although apoptotic DNases are simultaneously induced following toxic/oxidative cell injury and/or failed DNA repair, the study of DNases in apoptosis has generally been reductionist in approach, focusing on individual DNases rather than their possible cooperativity. Coordinated induction of DNases would require a mechanism of communication; however, mutual DNase induction or activation of DNases by enzymatic or non-enzymatic mechanisms is not currently recognized. The evidence presented in this review suggests apoptotic DNases operate in a network in which members induce each other through the DNA breaks they produce. With DNA breaks being a common communicator among DNases, it would be logical to propose that DNA breaks from other sources such as oxidative DNA damage or actions of DNA repair endonucleases and DNA topoisomerases may also serve as triggers for a cooperative DNase feedback loop leading to elevated DNA fragmentation and subsequent cell death. Therefore, mutual induction of apoptotic DNases has serious implications for studies focused on activation or inhibition of specific DNases as a strategy for therapeutic intervention aimed at modulation of cell death.     

Evidence for competition and cooperation among climbing plants

A plant's best strategy for acquiring resources may often depend on the identity of neighbours. Here, I ask whether plants adjust their strategy to local relatedness: individuals may cooperate (reduce competitiveness) with kin but compete relatively intensely with non-kin. In a greenhouse experiment with Ipomoea hederacea, neighbouring siblings from the same inbred line were relatively uniform in height; groups of mixed lines, however, were increasingly variable as their mean height increased. The reproductive yield of mixed and sibling groups was similar overall, but when adjusted to a common mean height and height inequality, the yield of mixed groups was significantly less. Where this difference in yield was most pronounced (among groups that varied most in height), mixed groups tended to allocate more mass to roots than comparable sibling groups, and overall, mixed groups produced significantly fewer seeds per unit mass of roots. These results suggest that, from the group perspective, non-kin may have wasted resources in below-ground competition at the expense of reproduction; kin groups, on the other hand, displayed the relative efficiency that is expected of reduced competitiveness.     

The Fly Agaric,Soma,Father Christmas and the Vikings

1　ThemushroomTheFlyAgaric (Amanitamuscaria (L :Fr.)Hooker)belongstothegenusAmanitaPers .,agroupwhichhasplayedmajorrolesinhumanaffairsthrough outhistory .Itincludesboththemostlydeadlypoi sonousspeciesandpossiblythemostdeliciousspeciesofalloftheediblewildmushrooms.TheFlyAgaricrepresentsthebestknownofallthewildmushroomsandhadthegreatesteffectuponmankindandworldhistory .Itistobeseeninmanychildren′sbooksasthelarge ,brightredmushroomwiththewhitespots,invariablyassociatedwithfairiesandelves.It…     

Resource use,energetic profitability,and behavioral decisions in migrant rufous hummingbirds

Summary Migrant Rufous Hummingbirds (Selasphorus rufus) defend nectar resources at stopover sites while replenishing fat reserves needed for migratory flights. During late summer in the Sandia Mountains, central New Mexico, they defend the wasp- and bee-pollinated Scrophularia montana from other hummingbirds. Both hummingbirds and hymenopterans exploit Scrophularia nectar during the early part of its flowering period. As summer colony growth increases the densities of the eusocial hymenopterans by 100–150%, their exploitation of Scrophularia nectar lowers its mean standing crop in flowers by 200–300%. Sometime during the summer, Rufous Hummingbirds abandon and do not further use this resource for the remaining 3–4 weeks of its flowering period. The abandonment always occurs when the mean standing crop of nectar is approximately 0.2–0.3 L/ flower. This paper describes a model of Rufous Hummingbird energetics, that shows abandonment occurred 1–3 days after they passed the threshold at which the resource could have provided their minimum daily energy requirements. I suggest that constraints imposed by a highly competitive social environment severely reduced the options available to the hummingbirds, and caused them to continue to defend a resource that could no longer meet their energetic requirements.     

Competition Coalitions and Conflict Interventions among Captive Female Gorillas

Like mountain gorillas (Gorilla gorilla beringei), western gorillas (Gorilla gorilla gorilla) at Howletts Wild Animal Park in Kent, England, intervene in conflicts on behalf of kin. However, in each of the 3 study groups, the female gorillas also appeared to form political alliances: all members of the group almost exclusively supported familiar adult females, i.e., the ones with the greatest group tenure, and their offspring in conflicts involving adult females, the silverback, and immatures. The long-term resident high-status females (HSFs) appeared to form a supportive clique, providing effective competition against low-status females (LSFs). The former maintained dominance status over younger, less familiar adult females that were more recent to the group. Such a pattern is not typical of mountain gorillas in the wild—the subspecies for which data on female relationships are available— except perhaps when groups are unusually large, possibly because mountain gorillas experience little competition over food resources that are widely distributed and relatively freely available. In contrast, the Howletts gorillas had periodic and irregular access to high-energy/-nutrient food resources, for which dominant individuals were able to monopolize the limited available feeding spots. The pattern of agonistic alliances of Howletts females show some similarities with that of some female-philopatric cercopithecines, which also compete over defendable food resources. In female-transfer species, such as gorillas, long-term resident female cliques may be equivalent to matrilines in cercopithecines when resources are patchily distributed, highly nutritious, and defendable.     

Foraging across a variable landscape: behavioral decisions made by woodland caribou at multiple spatial scales

We examined the foraging behavior of woodland caribou (Rangifer tarandus caribou) relative to the spatial and temporal heterogeneity of their environment. We assessed (1) whether caribou altered their behavior over time while making trade-offs between forage abundance and accessibility; and (2) whether foraging decisions were consistent across spatial scales (i.e., as scale increased, similar decision criteria were used at each scale). We discuss whether caribou adjusted their behavior to take advantage of changing forage availability through time and space. At the scale of the feeding site (as revealed by discriminant function analyses), caribou in both forested and alpine (above tree-line) environments selected sites where the biomass of particular lichen species was greatest and snow the least deep. Caribou did not select those species with the highest nutritional value (i.e., digestible protein and energy) in either area. Where snow depth, density, and hardness limited access to terrestrial lichens in the forest, caribou foraged instead at those trees with the greatest amount of arboreal lichen. Selection of lichen species and the influence of snow differed across time, indicating that in this system the abundance or accessibility of forage temporally influenced foraging behavior. A path analysis of forest data and multiple regression analysis of alpine data were used to test the hypothesis that variables important at the scale of the feeding site explained foraging effort at the scale of the patch. For forest patches, our hypothesized model reliably explained foraging effort, but not all variables that were statistically important at the scale of the feeding site were significant predictors at the scale of the patch. For alpine patches, our hypothesized model did not explain a statistically significant portion of the variation in the number of feeding sites within the patch, and none of the individual variables from the feeding site remained statistically significant at the patch scale. The incongruity between those variables important at the scale of the feeding site and those important at the patch showed that spatial scale affects the foraging decisions of woodland caribou. At the scale of the landscape, there was a trade-off between forage abundance and accessibility. Relative to the alpine environment, caribou in the forest foraged at feeding sites and patches with greater amounts of less variably distributed lichen, but deeper less variable snow depths. Considering the behavioral plasticity of woodland caribou, there may be no distinct advantage to foraging in one landscape over the other.     

When the Tutelary Spirit Objected: Conflict and Possession among the Using of East Java,Indonesia

This article discusses a case of possession in East Java that took place in the context of an important customary ritual, the seblang dance. In the course of this ritual, villagers meet their obligations to the spirits of fertility that allowed them to use the land on which their village and fields are located. Considerable stress was caused by a potential dancer who, perhaps for religious reasons, declined to dance although she had been specifically chosen by the spirits. This was an unheard of situation, and was feared to put the welfare of the community at risk. Further stress was caused by perceived interference by government officials whose rejection of an alternate dancer for aesthetic reasons caused the village’s tutelary spirit to become angry, jeopardising the presentation of the ritual and thereby the welfare of the community. After two and a half hours of negotiation, during which narratives reflecting both tradition and the current situation were constructed and reconstructed, the village head resolved the immediate problem by appealing to the spirit’s civic position, though leaving the door open for further problems in the future.     

Conflict of interest between sexes over cooperation: a supergame on egg carrying and mating in a coreid bug

In the golden egg bug (Phyllomorpha laciniata Vill. Heteroptera: Coreidae) females lay eggs on the backs of conspecifics, oftenon courting males. Although the bugs do not provide care tothe eggs, this decreases the risk of egg predation. As an effectmales carry many eggs which are not their own. The male andfemale interests are in conflict; females need to find an ovipositionsite, and male fitness depends on the obtained number of matings. By using a very rare modeling approach, a supergame where theindividuals actions change payoffs over time, we show thatcombinations of reciprocating strategies where males obtaina mating in return for a carried egg can be stable. The valueof the mating, to males, is more important than the relatednessto the eggs in gaining their cooperation in carrying eggs. Females may also take advantage of the males without reciprocating.This is especially likely if the probability of future meetingis high and the value of a mating is high for the male. Werelate our results to our own data from empirical studies andexperiments on the species. In the light of the results we discuss the behavior of the bugs in relation to nuptial gifts. We alsodiscuss the general applicability of the supergame approach.     

Coalitions,cooperation and reproductive tactics among adult male baboons

Male savanna baboons, Papio cynocephalus, form coalitions with each other as a technique for gaining access to a female in consort with another male. Reciprocal altruism has been invoked as the primary mechanism which underlies this reproductive tactic, but a 19-month field study of the reproductive behaviour of olive baboons, P. c. anubis, in Kenya contradicted this interpretation. Males who solicited others for coalition formation were not more likely to gain access to consort females than were their fellow coalition members. Males who refused to participate in a coalition at one time were still sought as coalition partners at other times by the same male. Coalitions were generally formed by older, middle- to lower-ranking males and targeted at younger, higher-ranking males. Coalitions are a low risk reproductive tactic and the benefits are not partitioned according to initiator/joiner status. Coalitions are likely to be an outcome of cooperation between males which results from the pursuit of self-interest.     

Beyond the prisoner's dilemma: Toward models to discriminate among mechanisms of cooperation in nature

The iterated prisoner's dilemma game, or IPD, has now established itself as the orthodox paradigm for theoretical investigations of the evolution of cooperation; but its scope is restricted to reciprocity, which is only one of three categories of cooperation among unrelated individuals. Even within that category, a cooperative encounter has in general three phases, and the IPD has nothing to say about two of them. To distinguish among mechanisms of cooperation in nature, future theoretical work on the evolution of cooperation must distance itself from economics and develop games as a refinement of ethology's comparative approach.