Cooperation in organisms, whether bacteria or primates, has been a difficulty for evolutionary theory since Darwin. On the assumption that interactions between pairs of individuals occur on a probabilistic basis, a model is developed based on the concept of an evolutionarily stable strategy in the context of the Prisoner's Dilemma game. Deductions from the model, and the results of a computer tournament show how cooperation based on reciprocity can get started in an asocial world, can thrive while interacting with a wide range of other strategies, and can resist invasion once fully established. Potential applications include specific aspects of territoriality, mating, and disease.

The Evolution of Cooperation

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world's top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) societies. Researchers - often implicitly - assume that either there is little variation across human populations, or that these "standard subjects" are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species - frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior - hence, there are no obvious a priori grounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re-organize the behavioral sciences to best tackle these challenges.

/pdf/the-weirdest-people-in-the-world-480wr4m3kb.pdf

The WEIRDest People in the World

The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

General guidelines for use of wild mammal species are updated from the 1998 version approved by the American Society of Mammalogists (ASM) and expanded to include additional resources. Included are details on marking, housing, trapping, and collecting mammals. These guidelines cover current professional techniques and regulations involving mammals used in research. Institutional animal care and use committees, regulatory agencies, and investigators should review and approve procedures concerning use of vertebrates at any particular institution. These guidelines were prepared and approved by the ASM, whose collective expertise provides a broad and comprehensive understanding of the biology of nondomesticated mammals in their natural environments.

/pdf/guidelines-of-the-american-society-of-mammalogists-for-the-2g7v778e1f.pdf

Guidelines of the american society of mammalogists for the use of wild mammals in research

Part I. From There to Here - Theoretical Background: 1. From visiousness to viciousness: theories of intergroup relations 2. Social dominance theory as a new synthesis Part II. Oppression and its Psycho-Ideological Elements: 3. The psychology of group dominance: social dominance orientation 4. Let's both agree that you're really stupid: the power of consensual ideology Part III. The Circle of Oppression - The Myriad Expressions of Institutional Discrimination: 5. You stay in your part of town and I'll stay in mine: discrimination in the housing and retail markets 6. They're just too lazy to work: discrimination in the labor market 7. They're just mentally and physically unfit: discrimination in education and health care 8. The more of 'them' in prison, the better: institutional terror, social control and the dynamics of the criminal justice system Part IV. Oppression as a Cooperative Game: 9. Social hierarchy and asymmetrical group behavior: social hierarchy and group difference in behavior 10. Sex and power: the intersecting political psychologies of patriarchy and empty-set hierarchy 11. Epilogue.

http://catdir.loc.gov/catdir/samples/cam032/98044356.pdf

Social Dominance: An Intergroup Theory of Social Hierarchy and Oppression

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation1,2,3,4,5,6,7. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans8,9,10,11. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds12,13. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures14 but previously unrecognised in non-human species.

Cultures in chimpanzees

1. Multi-female groups of primates fall into two main classes, (a) female-bonded (FB) and (b) non-female-bonded (non-FB). A model is presented to account for the evolution of FB groups in terms of ecological pressures on female relationships. 2. The model suggests that FB groups have evolved as a result of competition for high-quality food patches containing a limited number of feeding sites. Groups are viewed as being based on cooperative relationships among females. These relationships are beneficial because cooperators act together to supplant others from preferred food patches. 3. Ecological data support the model for most FB species, but not for Theropithecus gelada or Colobus guereza, whose foods are not found in high-quality patches with limited feeding sites. Non-FB species conform to expectation, either because they do not use high-quality patches, or because feeding competition has disruptive effects during periods of food scarcity. 4. The behaviour of females differs as expected between FB and non-FB species in group movements and in inter-group interactions; in both contexts females are more involved in FB species. 5. Multi-male groups tend to be found in non-territorial FB species. The presence of several males per group is suggested to benefit females by raising the competitive ability of the group in inter-group interactions. 6. Competitive relationships among females are more strongly marked in FB groups than in non-FB groups. The model suggests that relationships in most FB groups are ultimately related to feeding competition.

An Ecological Model of Female-Bonded Primate Groups

Demonic Males: Apes and the Origins of Human Violence.@@@War Before Civilization: The Myth of the Peaceful Savage.@@@A History of Warfare.

This study is an analysis of the roots of human savagery, dealing with the fundamental questions of why the majority of violence is perpetrated by men, whether this is a matter of nature or nurture and whether anything can be done about it. The book provides some surprising answers, based on comparison of male violence among human and among man's closest relatives, the great apes. In three or four species, male violence is common, but the form of violence differs: male orangutangs tend to rape, male chimps wage war and male gorillas kill the offspring of other males. Only in the fourth species, the little-known bonobo, are males (as well as females) non-violent - females are co-dominant, there is no observable aggression between groups, and there is a high level and diversity of sexual activity. The findings are based on 30 years of field research on the behaviour and ecology of chimpanzees and other mammals in Africa.

Demonic Males: Apes and the Origins of Human Violence

The social organization of spider monkeys (Ateles geoffroyi) and chimpanzees (Pan troglodytes) appear remarkably similar. In this paper, field studies of these two species were used to (1) test a model of ecological constraints on animal group size which suggests that group size is a function of travel costs and (2) assess ecological and social factors underlying the social organization of these two species. Spider monkeys were studied over a 6-year period in Santa Rosa National Park, Costa Rica, and chimpanzees were studied for 6 years in Kibale National Park, Uganda. Adults of both species spent their time in small subgroups that frequently changed size and composition. Thus, unlike most primate species, spider monkeys and chimpanzees were not always in a spatially cohesive social group; each individual had the option of associating in subgroups of a different size or composition. Both species relied on ripe fruit from trees that could be depleted through their feeding activity. However, spider monkey food resources tended to occur at higher densities, were more common, less temporally variable, and did not reach the low levels experienced by chimpanzees. Analyses of the relationship between subgroup size and the density and distribution of their food resources suggested that travel costs limit subgroup size. However, these ecological factors did not influence all age/sex classes equally. For example, the number of adult males in a subgroup was a function of food density and travel costs. However, this was not the case for female chimpanzees, suggesting that the benefits of being in a subgroup for females did not exceed the costs, even when ecological conditions appeared to minimize subgroup foraging costs. Therefore, it seems likely that social strategies influenced the relationship between food resource variables and subgroup size.

Richard W. Wrangham

Papers

Cultures in chimpanzees

An Ecological Model of Female-Bonded Primate Groups

Demonic Males: Apes and the Origins of Human Violence.@@@War Before Civilization: The Myth of the Peaceful Savage.@@@A History of Warfare.

Demonic Males: Apes and the Origins of Human Violence

Ecological constraints on group size : an analysis of spider monkey and chimpanzee subgroups