Cooperation in humans: competition between groups and proximate emotions

Understanding the ultimate and proximate mechanisms that favour cooperation remains one of the greatest challenges in the biological and social sciences. A number of theoretical studies have suggested that competition between groups may have played a key role in the evolution of cooperation within human societies, and similar ideas have been discussed for other organisms, especially cooperative breeding vertebrates. However, there is a relative lack of empirical work testing these ideas. Our experiment found, in public goods games with humans, that when groups competed with other groups for financial rewards, individuals made larger contributions within their own groups. In such situations, participants were more likely to regard their group mates as collaborators rather than competitors. Variation in contribution among individuals, either with or without intergroup competition, was positively correlated with individuals' propensity to regard group mates as collaborators. We found that the levels of both guilt and anger individuals experienced were a function of their own contributions and those of their group mates. Overall, our results are consistent with the idea that the level of cooperation can be influenced by proximate emotions, which vary with the degree of intergroup competition.     

Spite and the scale of competition

In recent years there has been a large body of theoretical work examining how local competition can reduce and even remove selection for altruism between relatives. However, it is less well appreciated that local competition favours selection for spite, the relatively neglected ugly sister of altruism. Here, we use extensions of social evolution theory that were formulated to deal with the consequences for altruism of competition between social partners, to illustrate several points on the evolution of spite. Specifically, we show that: (i) the conditions for the evolution of spite are less restrictive than previously assumed; (ii) previous models which have demonstrated selection for spite often implicitly assumed local competition; (iii) the scale of competition must be allowed for when distinguishing different forms of spite (Hamiltonian vs. Wilsonian); (iv) local competition can enhance the spread of spiteful greenbeards; and (v) the theory makes testable predictions for how the extent of spite should vary dependent upon population structure and average relatedness.     

Spite and the scale of competition in Pseudomonas aeruginosa

Scale of competition has been shown to be an important factor in shaping the evolution of social interactions. Although many theoretical and experimental studies have examined its effect on altruistic cooperation, relatively little research effort has been focused on spiteful behaviors--actions that harm both the actor and the recipient. In this study, we expand on existing theory by investigating the importance of the global frequency of spiteful alleles, and we determine experimentally how the scale of competition affects selection for spite in the bacterial pathogen Pseudomonas aeruginosa under high and intermediate spatial relatedness. Consistent with our theoretical results, we found in our experiments that spiteful genotypes are more favored under local (rather than global) competition and intermediate (rather than high) spatial relatedness, conditions that have been shown to select against indiscriminate altruism.     

Sibships: Cooperation and competition among immature vervet monkeys

The relationships between siblings were compared with those between non-sibling peers amongst immature vervet monkeys (Cercopithecus aethiops) in three free-ranging social groups. Using the frequency and context of friendly, supportive, aggressive, and competitive interactions, sibships were found to stand out as associative units characterized by high levels of grooming and support during aggression. Competition between siblings was related to contests over access to maternal care, especially grooming, which may have been important in the establishment of relative sibling dominance. Siblings who were close in age tended to interact more frequently than those who were distant in age, but few sex differences were found. The close and supportive nature of sibling relationships appeared to affect the social structure of the groups.     

The establishment of communication systems depends on the scale of competition

How communication systems emerge and remain stable is an important question in both cognitive science and evolutionary biology. For communication to arise, not only must individuals cooperate by signaling reliable information, but they must also coordinate and perpetuate signals. Most studies on the emergence of communication in humans typically consider scenarios where individuals implicitly share the same interests. Likewise, most studies on human cooperation consider scenarios where shared conventions of signals and meanings cannot be developed de novo. Here, we combined both approaches with an economic experiment where participants could develop a common language, but under different conditions fostering or hindering cooperation. Participants endeavored to acquire a resource through a learning task in a computer-based environment. After this task, participants had the option to transmit a signal (a color) to a fellow group member, who would subsequently play the same learning task. We varied the way participants competed with each other (either global scale or local scale) and the cost of transmitting a signal (either costly or noncostly) and tracked the way in which signals were used as communication among players. Under global competition, players signaled more often and more consistently, scored higher individual payoffs, and established shared associations of signals and meanings. In addition, costly signals were also more likely to be used under global competition; whereas under local competition, fewer signals were sent and no effective communication system was developed. Our results demonstrate that communication involves both a coordination and a cooperative dilemma and show the importance of studying language evolution under different conditions influencing human cooperation.     

Sexual coercion and forced in-pair copulation as sperm competition tactics in humans

Rape of women by men might be generated either by a specialized rape adaptation or as a by-product of other psychological adaptations. Although increasing number of sexual partners is a proposed benefit of rape according to the “rape as an adaptation” and the “rape as a by-product” hypotheses, neither hypothesis addresses directly why some men rape their long-term partners, to whom they already have sexual access. In two studies we tested specific hypotheses derived from the general hypothesis that sexual coercion in the context of an intimate relationship may function as a sperm competition tactic. We hypothesized that men’s sexual coercion in the context of an intimate relationship is related positively to his partner’s perceived infidelities and that men’s sexual coercion is related positively to their mate retention behaviors (behaviors designed to prevent a partner’s infidelity). The results from Study 1 (self-reports from 246 men) and Study 2 (partner-reports from 276 women) supported the hypotheses. The Discussion section addresses limitations of this research and highlights future directions for research on sexual coercion in intimate relationships.     

Large scale production of glucose oligomers and polymers for physiological studies in humans

Methods for isolating relatively large quantities of glucose oligomer and polymer subfractions from a partial corn starch hydrolysate (PCSH) are described. To ensure that the products are suitable for physiological studies in humans, potentially toxic substances were excluded from the preparative processes. For long chain glucose polymer fractions with degrees of polymerization (DP) averaging 43 glucose units, we employed molecular filtration through Amicon YM5 membranes. For fractions containing glucose oligomers with DP's 3 through 8, we employed yeast fermentation followed by ethanol fractionation.     

Cooperation,collective action,and the archeology of large‐scale societies

Archeologists investigating the emergence of large‐scale societies in the past have renewed interest in examining the dynamics of cooperation as a means of understanding societal change and organizational variability within human groups over time. Unlike earlier approaches to these issues, which used models designated voluntaristic or managerial, contemporary research articulates more explicitly with frameworks for cooperation and collective action used in other fields, thereby facilitating empirical testing through better definition of the costs, benefits, and social mechanisms associated with success or failure in coordinated group action. Current scholarship is nevertheless bifurcated along lines of epistemology and scale, which is understandable but problematic for forging a broader, more transdisciplinary field of cooperation studies. Here, we point to some areas of potential overlap by reviewing archeological research that places the dynamics of social cooperation and competition in the foreground of the emergence of large‐scale societies, which we define as those having larger populations, greater concentrations of political power, and higher degrees of social inequality. We focus on key issues involving the communal‐resource management of subsistence and other economic goods, as well as the revenue flows that undergird political institutions. Drawing on archeological cases from across the globe, with greater detail from our area of expertise in Mesoamerica, we offer suggestions for strengthening analytical methods and generating more transdisciplinary research programs that address human societies across scalar and temporal spectra.     

Switch between competition and facilitation within a seasonal scale at colony level in bryophytes

The relative importance of positive and negative interaction in species assemblages is thought to be dependent on the harshness of the physical environment. I studied the consistency of this prediction in a field experiment using growth of the target species Warnstorfia exannulata as influenced by the presence or absence of two adjacent species, Sphagnum warnstorfii and Scapania undulata. In particular, I focused on the mechanism by which colony–colony interactions occur, elucidating how the balance of positive and negative interactions changes along a water gradient. Because the natural fluctuations of the environment modify the water gradient, it was expected that the competitive hierarchies of the species would not remain consistent over time. Results indicated that the different hydrological properties of the colonies, thought to be the necessary condition for the appearance of species interactions, were not sufficient to explain the outcome of the species interactions. The switch from competition to facilitation under more stressful conditions was not confirmed along a water stress gradient. In addition, natural climatic fluctuations, by affecting the length of the water gradient, changed the competitive hierarchies of the species on a seasonal scale.     

Effects of competition outcome on testosterone concentrations in humans: An updated meta-analysis

A contribution to a special issue on Hormones and Human Competition.Since Archer's (2006) influential meta-analysis, there has been a major increase in the number of studies investigating the effect of competition outcome on testosterone reactivity patterns in humans. Despite this increased research output, there remains debate as to whether competition outcome modulates testosterone concentrations. The present paper examines this question using a meta-analytic approach including papers published over the last 35 years. Moreover, it provides the first meta-analytic estimate of the effect of competition outcome on testosterone concentrations in women. Results from a meta-analysis involving 60 effect sizes and > 2500 participants indicated that winners of a competition demonstrated a larger increase in testosterone concentrations relative to losers (D = 0.20)—an effect that was highly heterogeneous. This ‘winner-loser’ effect was most robust in studies conducted outside the lab (e.g., in sport venues) (D = 0.43); for studies conducted in the lab, the effect of competition outcome on testosterone reactivity patterns was relatively weak (D = 0.08), and only found in studies of men (D = 0.15; in women: D = − 0.04). Further, the 'winner-loser' effect was stronger among studies in which pre-competition testosterone was sampled earlier than (D = 0.38, after trim and fill correction) rather than within (D = 0.09) 10 min of the start of the competition. Therefore, these results also provide important insight regarding study design and methodology, and will be a valuable resource for researchers conducting subsequent studies on the 'winner loser' effect.     

The spatial scale of competition from recruits on an older cohort in Atlantic salmon

Competitive effects of younger cohorts on older ones are frequently assumed to be negligible in species where older, larger individuals dominate in pairwise behavioural interactions. Here, we provide field estimates of such competition by recruits on an older age class in Atlantic salmon (Salmo salar), a species where observational studies have documented strong body size advantages which should favour older individuals in direct interactions. By creating realistic levels of spatial variation in the density of underyearling (YOY) recruits over a 1-km stretch of a stream, and obtaining accurate measurements of individual growth rates of overyearlings (parr) from capture–mark–recapture data on a fine spatial scale, we demonstrate that high YOY density can substantially decrease parr growth. Models integrating multiple spatial scales indicated that parr were influenced by YOY density within 16 m. The preferred model suggested parr daily mass increase to be reduced by 39% when increasing YOY density from 0.0 to 1.0 m⁻², which is well within the range of naturally occurring densities. Reduced juvenile growth rates will in general be expected to reduce juvenile survival (via increased length of exposure to freshwater mortality) and increase generation times (via increased age at seaward migrations). Thus, increased recruitment can significantly affect the performance of older cohorts, with important implications for population dynamics. Our results highlight that, even for the wide range of organisms that rely on defendable resources, the direction of competition among age classes cannot be assumed a priori or be inferred from behavioural observations alone.     

Facilitation, competition, and vegetation patchiness: from scale free distribution to patterns

A new technique for the modeling of perennial vegetation patchiness in the arid/semiarid climatic zone is suggested. Incorporating the stochasticity that affects life history of seedlings and the deterministic dynamics of soil moisture and biomass, this model is flexible enough to yield qualitatively different forms of spatial organization. In the facilitation-dominated regime, scale free distribution of patch sizes is observed, in correspondence with recent field studies. In the competition controlled case, on the other hand, power-law statistics is valid up to a cutoff, and an intrinsic length scale appears.     

Land use and drought interactively affect interspecific competition and species diversity at the local scale in a semiarid steppe ecosystem

Few studies have considered interactive effects of grazing and drought on species composition and the relative contribution of species to total biomass, although it is important to understand the short-term dynamics and community succession in grazed ecosystems. We monitored species diversity and relative biomass contribution at one site protected from grazing since 1979 (UG79), and at winter grazing (WG) and heavily grazed (HG) sites. Continuous heavy grazing resulted in lower plant height and more but small individuals (tillers or stolons). Drought significantly reduced total plant density on all sites. Grazing affected species diversity more than drought. Species richness at site UG79 was significantly higher than at sites WG and HG, while drought only tended to reduce species diversity. Drought stress and grazing disturbance interactively controlled species competition and functional groups. Both perennial grasses and forbs had greater contribution to total biomass at site UG79, and perennial grasses contributed more than 97% of total biomass at site WG. The contribution to total biomass of annual forbs and semi-shrubs significantly increased at site HG after two dry years. The significant decrease in Potentilla acaulis and a substantial increase in annual species at this site indicate that the perennial vegetation of this ecosystem is in great danger of extinction under conditions of prolonged drought.     

A regional analysis of weather mediated competition between a parasitoid and a coccinellid predator of oleander scale

The regulation of an asexual population of the oleander scale [Aspidiotus nerii Bouchè (Hemiptera: Diaspididae)] on California bay tree [Umbellularia californica (Hopk. & Arn.) Nut.] by two natural enemies; an idiobiont, ectoparasitoid Aphytis chilensis Howard (Hymenoptera: Aphelinidae) and a coccinellid predator (Rhysobius lophanthae (Blaisd.) (Coleoptera: Coccinellidae), was examined using a general weather-driven, tri-trophic, physiologically based age-mass structured demographic model. The model is of intermediate complexity and was parameterized using extensive laboratory data and field observations from Albany, CA. Temperature-dependent physiological indices were estimated from the laboratory data and used to scale per capita growth, fecundity and survivorship rates from maximal values in a time varying environment. The tri-trophic model was integrated in a GIS (geographic information system) and the species dynamics examined across years and across the ecological zones of California. Field data and simulation results suggested the coccinellid predator was the most important regulating agent of oleander scale in the mild climate of Albany. However, multiple linear regression analysis of simulation data across all ecological zones of California shows that the parasitoid A. chilensis is the most important agent in suppressing oleander scale densities in warmer climates, while the predator R. lophanthae increases scale density an average of 9.7% across all regions.     

Secretion of the cell surface lipoprotein pullulanase in Escherichia coli. Cooperation or competition between the specific secretion pathway and the lipoprotein sorting pathway.

The fatty acid-acylated enzyme pullulanase is normally found in either of two locations in Escherichia coli, depending on whether or not the producing strains also express the genes specifically required for the second step in pullulanase secretion. When they are expressed, the enzyme is localized to the cell surface, while in their absence, it is directed to an unidentified location in the cell envelope which, upon lysis, forms vesicles whose density is intermediate between those of outer and cytoplasmic membrane vesicles. In order to test the role of the putative lipoprotein sorting signal, Asp2, in pullulanase sorting and secretion, the structural gene (pulA) was subjected to site-directed mutagenesis. Replacement of the Asp2 residue by Asn, Glu, or Ser caused the enzyme to fractionate with outer membrane-derived vesicles rather than with intermediate density vesicles from E. coli cells devoid of pullulanase secretion genes. A pronounced secretion defect was observed in a two-step secretion assay in which the first (sec gene-dependent) and second (pul gene-dependent) secretion steps were uncoupled. We propose that the Asp residue increases the efficiency of pullulanase secretion by allowing the enzyme to be initially sorted to a region of the cell envelope wherein most of the pullulase-specific secretion factors are located.