Introduction to “Coping with Environmental Risk and Uncertainty: Individual and Cultural Responses”

The papers in this special issue of Human Nature collectively consider societal and individual responses to a wide variety of environmental and social risks. The first paper considers societal level effects of pathogen risk on collectivism and conformity, avoidance of outsiders, and in-group loyalty in a worldwide cross-cultural sample. The second deals with societal-level effects of resource unpredictability on the nature and conduct of warfare in eastern Africa. The third deals with effects of volcanic eruptions and earthquakes and mediating factors on individual perceptions of risk in Mexico and Ecuador. The final paper deals with effects of various types of father absence on women’s reproductive life histories in Bangladesh.     

Life history strategy and human cooperation in economic games

Across five studies using samples from both Japan and United States (N = 2345), we take a multi-method approach to test the prediction from life history theory that a slow, compared to fast, life history strategy promotes investment in cooperative relationships. Studies 1 and 2 examined how different measures as proxies for life history strategy (i.e., Mini-K and High-K Strategy Scale) relate to cooperation in various economic games. Studies 3 to 5 measured early childhood environments (i.e., childhood harshness and unpredictability), manipulated resource scarcity using previously validated methods, and then measured cooperation. Across our studies, we also examined four hypothesized psychological mechanisms that could explain the relation between life history strategy and cooperation: temporal discounting, concern for reputation, social value orientation, and trust in others. Overall, we found no support for the hypothesis that life history strategy predicts cooperation or that early childhood environments interact with current resource scarcity to predict cooperation. Thus, our initial findings imply that life history theory may not account for individual variation in cooperation with unknown others.     

Male social status and its predictors among Garisakang forager-horticulturalists of lowland Papua New Guinea

Social hierarchy exists in all human societies, yet the characteristics important for achieving high social status may differ cross-culturally. Studies among Western industrialized populations often use indices of socioeconomic status (SES) to determine individual social position. Conversely, studies among small-scale societies typically use locally relevant traits. Cross-cultural applicability and the relationships between these two strategies have rarely been investigated. Studies limited to industrialized societies demonstrate that low social status is associated with poor health and elevated levels of chronic stress. It remains unclear, however, if and to what extent this relationship is a recent phenomenon in industrialized Western society or a universal human characteristic that has likely been present throughout much of our recent evolutionary history. In this study, we investigate relationships between various SES and locally relevant measures of male social status, age, body-mass index (BMI), and levels of waking salivary cortisol among relatively egalitarian Garisakang forager-horticulturalists of lowland Papua New Guinea. We employ a photo-ranking method using 32 raters (16 women, 16 men) to evaluate 15 measures of social hierarchy in men (N = 32). These measures target locally relevant traits considered important for male social status (e.g., sociability, hunting skills, fighting ability, and community influence). Using principal component analysis (PCA), we extracted two components labeled as Dominance-Respect and Prosociality-Skills. Models investigating predictors of social status demonstrate that age was significantly and positively related to both Dominance-Respect and Prosociality-Skills while BMI was positively related to only Dominance-Respect. Neither Dominance-Respect nor Prosociality-Skills predicted salivary cortisol levels. However, the SES measure of Income was significantly and positively related to cortisol levels, suggesting that men with higher income experience higher levels of stress. This finding may be explained by increased psychological stress accompanying market integration among the Garisakang or, alternatively, by culturally specific expectations for resource sharing and fear of conflict. These findings emphasize the usefulness of diverse social status measures in anthropological research and stress the need for broadened perspectives regarding the causes and consequences of social status among small-scale populations.     

Patterns of parasitism in insular lizards: effects of body size,condition and resource availability

The spatial distribution of a population of lizards is influenced by the distribution of resources and the individuals’ skills to gain access to them. On several Mediterranean islands with food scarcity and unpredictable resource availability, some resources can be extremely important during some periods of the year, as, e.g., the dead horse arum, Dracunculus muscivorus, on Aire Island, Spain. In this study, we analysed parasite infestation in an endemic lizard, Podarcis lilfordi, in relation to the distribution of D. muscivorus during spring. We found a higher prevalence of parasitism in males from a central area where the plant was significantly more abundant. Also, in this area, males were more abundant and larger than in two areas with lower plant densities. Moreover, overall differences appeared in the intensity of infection, which was higher in individuals from the central area, and we found a relationship between body size and parasite load, with more infected cells in larger individuals. Spatial distribution of individuals due to differential availabilities of D. muscivorus is proposed as an explanation for the observed differences.     

The Complete Plastid Genome of Lagerstroemia fauriei and Loss of rpl2 Intron from Lagerstroemia (Lythraceae)

Lagerstroemia (crape myrtle) is an important plant genus used in ornamental horticulture in temperate regions worldwide. As such, numerous hybrids have been developed. However, DNA sequence resources and genome information for Lagerstroemia are limited, hindering evolutionary inferences regarding interspecific relationships. We report the complete plastid genome of Lagerstroemia fauriei. To our knowledge, this is the first reported whole plastid genome within Lythraceae. This genome is 152,440 bp in length with 38% GC content and consists of two single-copy regions separated by a pair of 25,793 bp inverted repeats. The large single copy and the small single copy regions span 83,921 bp and 16,933 bp, respectively. The genome contains 129 genes, including 17 located in each inverted repeat. Phylogenetic analysis of genera sampled from Geraniaceae, Myrtaceae, and Onagraceae corroborated the sister relationship between Lythraceae and Onagraceae. The plastid genomes of L. fauriei and several other Lythraceae species lack the rpl2 intron, which indicating an early loss of this intron within the Lythraceae lineage. The plastid genome of L. fauriei provides a much needed genetic resource for further phylogenetic research in Lagerstroemia and Lythraceae. Highly variable markers were identified for application in phylogenetic, barcoding and conservation genetic applications.     

Economic investment by ant colonies in searches for better homes

Organisms should invest more in gathering information when the pay-off from finding a profitable resource is likely to be greater. Here, we ask whether animal societies put more effort in scouting for a new nest when their current one is of low quality. We measured the scouting behaviour of Temnothorax albipennis ant colonies when they inhabit nest-sites with different combinations of desirable attributes. We show that the average probability of an ant scouting decreases significantly with an increase in the quality of the nest in which the colony currently resides. This means that the greater the potential gain from finding a new nest, the more effort a colony puts into gathering information regarding new nest-sites. Our results show, for the first time to our knowledge, the ability of animal societies to respond collectively to the quality of a resource they currently have at their disposal (e.g. current nest-site) and regulate appropriately their information gathering efforts for finding an alternative (e.g. a potentially better nest-site).     

Surplus cost as a life cycle impact indicator for fossil resource scarcity

Purpose

In life cycle impact assessment, various proposals have been made on how to characterise fossil resource scarcity, but they lack appropriateness or completeness. In this paper, we propose a method to assess fossil resource scarcity based on surplus cost, which is the global future cost increase due to marginal fossil resource used in the life cycle of products.

Methods

The marginal cost increase (MCI in US dollars in the year 2008 per kilogram per kilogram produced) is calculated as an intermediate parameter for crude oil, natural gas and coal separately. Its calculations are based on production cost and cumulative future production per production technique or country. The surplus cost (SC in US dollars in the year 2008 per kilogram) is calculated as an indicator for fossil resource scarcity. The SC follows three different societal perspectives used to differentiate the subjective choices regarding discounting and future production scenarios.

Results and discussion

The hierarchist perspective SCs of crude oil, natural gas, and coal are 2.9, 1.5, and 0.033 US$₂₀₀₈/GJ, respectively. The ratios between the indicators of the different types of fossil resources (crude oil/natural gas/coal) are rather constant, except in the egalitarian perspective, where contrastingly no discounting is applied (egalitarian 100:47:21; hierarchist 100:53:1.1; individualist 100:34:0.6). The ratio of the MCIs (100:48:1.0) are similar to the individualist and hierarchist SC ratios.

Conclusions

In all perspectives, coal has a much lower resource scarcity impact factor per gigajoule and crude oil has the highest. In absolute terms of costs per heating value (US dollars in the year 2008 per gigajoule), there are large differences between the SCs for each perspective (egalitarian > hierarchist > individualist).     

The Role of Rewards in Motivating Participation in Simple Warfare

In the absence of explicit punitive sanctions, why do individuals voluntarily participate in intergroup warfare when doing so incurs a mortality risk? Here we consider the motivation of individuals for participating in warfare. We hypothesize that in addition to other considerations, individuals are incentivized by the possibility of rewards. We test a prediction of this “cultural rewards war-risk hypothesis” with ethnographic literature on warfare in small-scale societies. We find that a greater number of benefits from warfare is associated with a higher rate of death from conflict. This provides preliminary support for the relationship between rewards and participation in warfare.     

Our better nature: Does resource stress predict beyond-household sharing?

Food sharing and (to a lesser extent) labor sharing play central roles in the evolution of cooperation literature. One popular explanation for sharing beyond the family is that it reduces the likelihood of shortages by pooling risk across households. However, the frequency and scope of sharing have never been systematically documented across nonindustrial societies, and the literature is driven by theoretical models, experimental games, and case studies among a few extensively-studied populations. Here we explore the cross-cultural context, frequency, and scope of food and labor sharing customs in relation to resource stress. Using ethnographic data from a worldwide sample of 98 societies in the Standard Cross-Cultural Sample (SCCS), we test the following hypotheses: 1) customary sharing of food and labor beyond the household are cultural universals, 2) societies subject to more resource stress (including unpredictable food-destroying natural hazards) will share more frequently, and 3) the more frequent the resource stress, the broader the geographic and social scope of sharing customs. Hypotheses 1 and 2 are generally supported and are consistent with the theory that extensive beyond-household sharing is adaptive in societies that are subject to more resource stress. Hypothesis 3 was not supported and, contrary to our predictions, there is suggestive evidence that sharing beyond-relatives may be attenuated when resource stress is high. In light of these findings, we consider how resource stress may constitute an important selection pressure for maintaining extensive cooperation and help to explain the ubiquity of beyond-household sharing.     

Causes of Polygyny: Ecology, Economy, Kinship, and Warfare

We discuss and test competing explanations for polygyny based on household economics, malecentered kin groups, warfare, and environmental characteristics. Data consist of codes for 142 societies from the Standard Cross-Cultural Sample, including new codes for polygyny and environmental characteristics. An explanatory model is tested for the worldwide sample using regression analysis, and then replicated with regional samples. We obtain convergent results with two different measures of polygyny, cultural rules for men's marriages and the percentage of women married polygynously. We conclude that the best predictors of polygyny are fraternal interest groups, warfare for capture of women, absence of constraints on expansion into new lands, and environmental quality and homogeneity.     

Human Lactation, Pair-bonds, and Alloparents

The evolutionary origin of human pair-bonds is uncertain. One hypothesis, supported by data from forgers, suggests that pair-bonds function to provision mothers and dependent offspring during lactation. Similarly, public health data from large-scale industrial societies indicate that single mothers tend to wean their children earlier than do women living with a mate. Here we examine relations between pair-bond stability, alloparenting, and cross-cultural trends in breastfeeding using data from 58 “traditional” societies in the Standard Cross-Cultural Sample (SCCS). Analyses show that stable conjugal relationships were associated with significantly later weaning among the societies in the SCCS. The relationship between pair-bond stability and age at weaning was not mediated by women’s ability to provision themselves or women’s kin support. Availability of alloparental care was also inversely related to age at weaning, and the association was not significantly reduced after controlling for frequency of divorce. This study indicates that among a woman’s kin relationships, a pair-bond with a child’s father is especially supportive of breastfeeding. These cross-cultural findings are further evidence that human pair-bonds may have evolved to support lactation.     

New evidence for diet and niche partitioning in Rudapithecus and Anapithecus from Rudabánya,Hungary

Rudabánya is rare among Eurasian Miocene fossil primate localities in preserving both a hominid and pliopithecoid, and as such provides the unique opportunity to reconstruct the nature of sympatry and niche partitioning in these taxa. Rudapithecus and Anapithecus have similar locomotor and positional behavior and overlapping body mass ranges. While prior analyses of molar occlusal anatomy and microwear identify Rudapithecus as a soft-object frugivore, reconstructing the dietary behavior of Anapithecus has been more problematic. This taxon has been interpreted to be more folivorous by some, and more frugivorous by others. Here, we use high-resolution polynomial curve fitting (HR-PCF) to quantify and evaluate the mesiodistal and cervico-incisal curvatures of the incisor crowns of Rudapithecus and Anapithecus to identify diet-specific morphological variation in these taxa. Results are consistent with the interpretation that Anapithecus and Rudapithecus were primarily frugivorous and had diets that included similar resource types. However, Anapithecus may have consumed greater amounts of foliage, similar to extant mixed folivore–frugivores (i.e., Gorilla gorilla gorilla, Symphalangus syndactylus), while Rudapithecus generated elevated compressive loads in the incisor region consistent with a specialized role for the anterior dentition in food processing (i.e., removal of tough protective fruit pericarps). We interpret these findings in light of the paleoecology at Rudabánya and conclude that, if these taxa were indeed sympatric, Anapithecus may have used additional leaf consumption as a seasonal fallback resource to avoid direct competition with Rudapithecus. Conversely, Rudapithecus may have relied on less preferred and harder fruiting resources as a seasonal fallback resource during periods of fruit scarcity.     

Loss of estrus in human evolution: Too many answers,too few questions

Models addressing the importance of “loss of estrus” in human evolution assume that, as part of a general trend among higher primates, endogenous hormonal fluctuations have less influence on human female sexuality than cognitive and socioenvironmental factors. The diversity of reproductive patterns among primate species is not satisfactorily explained as the outcome of evolutionary trends along dimensions such as brain enlargement, behavioral flexibility, or relative independence of behavior from physiology. Rather, the role of hormones and other factors must be viewed in the context of species' life history and ecological constraints. Human studies on the relationship between the menstrual cycle and sexual behavior have been limited to Western women in industrialized societies, which may not reveal evolved behavioral-physiological patterns. Furthermore, available studies have yielded inconsistent results. No single pattern emerges that can be said to characterize the human female, and no conclusion can be reached regarding the relationship between cyclic hormonal fluctuations and sexual behavior and, thus, whether human ovulation is concealed. Future studies are needed that are methodologically improved and systematically document the interaction among ecological, subsistence, social, and physiological variables.     

Exploring the components, asymmetry and distribution of relationship quality in wild Barbary macaques (Macaca sylvanus)

Social relationships between group members are a key feature of many animal societies. The quality of social relationships has been described by three main components: value, compatibility and security, based on the benefits, tenure and stability of social exchanges. We aimed to analyse whether this three component structure could be used to describe the quality of social relationships in wild Barbary macaques (Macaca sylvanus). Moreover, we examined whether relationship quality was affected by the sex, age and rank differences between social partners, and investigated the asymmetric nature of social relationships. We collected over 1,900 hours of focal data on seven behavioural variables measuring relationship quality, and used principal component analysis to investigate how these variables clustered together. We found that relationship quality in wild Barbary macaques can be described by a three component structure that represents the value, compatibility and security of a relationship. Female-female dyads had more valuable relationships and same-age dyads more compatible relationships than any other dyad. Rank difference had no effect on the quality of a social relationship. Finally, we found a high degree of asymmetry in how members of a dyad exchange social behaviour. We argue that the asymmetry of social relationships should be taken into account when exploring the pattern and function of social behaviour in animal societies.     

The appropriate response of Spanish Gitanos: short-run orientation beyond current socio-economic status

Humans differ greatly in their tendency to discount future events, but the reasons underlying such inter-individual differences remain poorly understood. Based on the evolutionary framework of Life History Theory, influential models predict that the extent to which individuals discount the future should be influenced by socio-ecological factors such as mortality risk, environmental predictability and resource scarcity. However, little empirical work has been conducted to compare the discounting behavior of human groups facing different socio-ecological conditions. In a lab-in-the-field economic experiment, we compared the delay discounting of a sample of Romani people from Southern Spain (Gitanos) with that of their non-Romani neighbors (i.e., the majority Spanish population). The Romani-Gitano population constitutes the main ethnic minority in all of Europe today and is characterized by lower socio-economic status (SES), lower life expectancy and poorer health than the majority, along with a historical experience of discrimination and persecution. According to those Life History Theory models, Gitanos will tend to adopt “faster” life history strategies (e.g., earlier marriage and reproduction) as an adaptation to such ecological conditions and, therefore, should discount the future more heavily than the majority. Our results support this prediction, even after controlling for the individuals' current SES (income and education). Moreover, group-level differences explain a large share of the individual-level differences. Our data suggest that human inter-group discrimination might shape group members' time preferences through its impact on the environmental harshness and unpredictability conditions they face.     

How do Meat Scarcity and Bushmeat Commodification Influence Sharing and Giving among Forest Foragers? A View from the Central African Republic

Meat sharing is a societal norm among hunter-gatherer societies that provisions families and supports social networks. Meat is also a valued resource central to traditional barter exchange. Ethnographic research often cites prey scarcity and commodification as two factors reducing traditional meat transactions among indigenous Central African foragers. We present quantitative data based on ethnographic observations of foragers in the Central African Republic that show that neither scarcity nor commodification eliminates sharing. The bushmeat market is associated with changes in village demographic structure that limits the distribution of meat among extended kin. Although cash generated from the sale of forest products reduces the need for inter-ethnic barter, gift giving and exchange maintain these important relationships. Our data show the persistence of traditional meat transactions and identify potential changes in demographic structure as a less obvious outcome of the bushmeat trade that can have extended consequences for forager populations.     

Phylogeny of Veronica in the Southern and Northern Hemispheres based on plastid,nuclear ribosomal and nuclear low-copy DNA

The cosmopolitan and ecologically diverse genus Veronica with approximately 450 species is the largest genus of the newly circumscribed Plantaginaceae. Previous analyses of Veronica DNA sequences were in stark contrast to traditional systematics. However, analyses did not allow many inferences regarding the relationship between major groups identified, hindering further analysis of diversification and evolutionary trends in the genus. To resolve the backbone relationships of Veronica, we added sequences from additional plastid DNA regions to existing data and analyzed matching data sets for 78 taxa and more than 5000 aligned characters from nuclear ribosomal DNA and plastid DNA regions. The results provide the best resolved and supported estimate of relationships among major groups in the Northern (Veronica s. str.) and Southern Hemisphere (hebes). We present new informal names for the five main species groups within the Southern Hemisphere sect. Hebe. Furthermore, in two instances we provide morphological and karyological characters supporting these relationships. Finally, we present the first evidence from nuclear low-copy CYCLOIDEA2-region to compare results from the plastid genome with the nuclear genome.     

Conifer Stored Resources and Resistance to a Fungus Associated with the Spruce Bark Beetle Ips typographus

Bark beetles and associated fungi are among the greatest natural threats to conifers worldwide. Conifers have potent defenses, but resistance to beetles and fungal pathogens may be reduced if tree stored resources are consumed by fungi rather than used for tree defense. Here, we assessed the relationship between tree stored resources and resistance to Ceratocystis polonica, a phytopathogenic fungus vectored by the spruce bark beetle Ips typographus. We measured phloem and sapwood nitrogen, non-structural carbohydrates (NSC), and lipids before and after trees were attacked by I. typographus (vectoring C. polonica) or artificially inoculated with C. polonica alone. Tree resistance was assessed by measuring phloem lesions and the proportion of necrotic phloem around the tree''s circumference following attack or inoculation. While initial resource concentrations were unrelated to tree resistance to C. polonica, over time, phloem NSC and sapwood lipids declined in the trees inoculated with C. polonica. Greater resource declines correlated with less resistant trees (trees with larger lesions or more necrotic phloem), suggesting that resource depletion may be caused by fungal consumption rather than tree resistance. Ips typographus may then benefit indirectly from reduced tree defenses caused by fungal resource uptake. Our research on tree stored resources represents a novel way of understanding bark beetle-fungal-conifer interactions.     

Androgen Receptor Gene Polymorphism,Aggression, and Reproduction in Tanzanian Foragers and Pastoralists

The androgen receptor (AR) gene polymorphism in humans is linked to aggression and may also be linked to reproduction. Here we report associations between AR gene polymorphism and aggression and reproduction in two small-scale societies in northern Tanzania (Africa)—the Hadza (monogamous foragers) and the Datoga (polygynous pastoralists). We secured self-reports of aggression and assessed genetic polymorphism of the number of CAG repeats for the AR gene for 210 Hadza men and 229 Datoga men (aged 17–70 years). We conducted structural equation modeling to identify links between AR gene polymorphism, aggression, and number of children born, and included age and ethnicity as covariates. Fewer AR CAG repeats predicted greater aggression, and Datoga men reported more aggression than did Hadza men. In addition, aggression mediated the identified negative relationship between CAG repeats and number of children born.