Better-than-chance prediction of cooperative behaviour from first and second impressions.

Could cooperation among strangers be facilitated by adaptations that use sparse information to accurately predict cooperative behaviour? We hypothesise that predictions are influenced by beliefs, descriptions, appearance and behavioural history available for first and second impressions. We also hypothesise that predictions improve when more information is available. We conducted a two-part study.

Development of a graphical resilience framework to understand a coupled human-natural system in a remote arid highland of Baja California Sur.

Unlabelled: Hydrological systems are important to society as water resources and effective management requires an understanding of how water and humans influence each other. To describe human-water connections it is necessary to bridge social and natural sciences. To this end, we construct an interdisciplinary graphical framework for evaluating potential human-water system resilience, which is a tool to show the spatial and temporal response to system change of both human and natural systems.

Geochemistry and Provenance of Springs in a Baja California Sur Mountain Catchment.

Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured-dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity.

Age-Appropriate Wisdom? : Ethnobiological Knowledge Ontogeny in Pastoralist Mexican Choyeros.

We investigate whether age profiles of ethnobiological knowledge development are consistent with predictions derived from life history theory about the timing of productivity and reproduction. Life history models predict complementary knowledge profiles developing across the lifespan for women and men as they experience changes in embodied capital and the needs of dependent offspring. We evaluate these predictions using an ethnobiological knowledge assessment tool developed for an off-grid pastoralist population known as Choyeros, from Baja California Sur, Mexico.

The role of dispersal and school attendance on reproductive dynamics in small, dispersed populations: Choyeros of Baja California Sur, Mexico.

Individuals from small populations face challenges to initiating reproduction because stochastic demographic processes create local mate scarcity. In response, flexible dispersal patterns that facilitate the movement of individuals across groups have been argued to reduce mate search costs and inbreeding depression. Furthermore, factors that aggregate dispersed peoples, such as rural schools, could lower mate search costs through expansion of mating markets.

Marriage dynamics in old Lower California: ecological constraints and reproductive value in an arid peninsular frontier.

It is commonly expected that natural selection will favor earlier reproduction, yet ecological constraints can force people to delay marriage. Furthermore, humans demonstrate sex-specific preferences in marriage partners - with grooms normally a few years older than their brides; however, the age at which individuals marry can influence the spousal age gap. We investigate factors influencing age at first marriage and age difference at marriage using nineteenth-century historical demographic data from Baja California Sur, Mexico.

Kinship ties across the lifespan in human communities.

A hypothesis for the evolution of long post-reproductive lifespans in the human lineage involves asymmetries in relatedness between young immigrant females and the older females in their new groups. In these circumstances, inter-generational reproductive conflicts between younger and older females are predicted to resolve in favour of the younger females, who realize fewer inclusive fitness benefits from ceding reproduction to others. This conceptual model anticipates that immigrants to a community initially have few kin ties to others in the group, gradually showing greater relatedness to group members as they have descendants who remain with them in the group.

Differences between sons and daughters in the intergenerational transmission of wealth.

Persistent interest lies in gender inequality, especially with regard to the favouring of sons over daughters. Economists are concerned with how privilege is transmitted across generations, and anthropologists have long studied sex-biased inheritance norms. There has, however, been no focused cross-cultural investigation of how parent-offspring correlations in wealth vary by offspring sex.

Experimental tests of the tolerated theft and risk-reduction theories of resource exchange.

Here we report the results of an experiment that tests the reciprocal risk reduction and 'tolerated theft' or taking hypotheses for why the human species is unique in having extensive exchange of resources among non-kin. We designed an experiment to determine whether, in response to variance of resource acquisition, people exchange food resources via taking or, alternatively, form reciprocal relationships based on giving. In the experiment, subjects forage individually, experience variation in resource acquisition, and then consume either by actions in which resources are taken from, or moved to, others in a group environment.

Information transmission and the oral tradition: Evidence of a late-life service niche for Tsimane Amerindians.

Storytelling can affect wellbeing and fitness by transmitting information and reinforcing cultural codes of conduct. Despite their potential importance, the development and timing of storytelling skills, and the transmission of story knowledge have received minimal attention in studies of subsistence societies that more often focus on food production skills. Here we examine how storytelling and patterns of information transmission among Tsimane forager-horticulturalists are predicted by the changing age profiles of storytellers' abilities and accumulated experience.

Skill ontogeny among Tsimane forager-horticulturalists.

Objectives: We investigate whether age profiles of Tsimane forager-horticulturalists' reported skill development are consistent with predictions derived from life history theory about the timing of productivity and reproduction. Previous studies of forager skill development have often focused on a few abilities (e.g.

Regulatory adaptations for delivering information: The case of confession.

Prior to, or concurrent with, the encoding of concepts into speech, the individual faces decisions about whether, what, when, how, and with whom to communicate. Compared to the existing wealth of linguistic knowledge however, we know little of the mechanisms that govern the delivery and accrual of information. Here we focus on a fundamental issue of communication: The decision to deliver information.

Predictable and predictive emotions: explaining cheap signals and trust re-extension.

Despite normative predictions from economics and biology, unrelated strangers will often develop the trust necessary to reap gains from one-shot economic exchange opportunities. This appears to be especially true when declared intentions and emotions can be cheaply communicated. Perhaps even more puzzling to economists and biologists is the observation that anonymous and unrelated individuals, known to have breached trust, often make effective use of cheap signals, such as promises and apologies, to encourage trust re-extension.

Functional Disability and Social Conflict Increase Risk of Depression in Older Adulthood Among Bolivian Forager-Farmers.

Objectives: To present an explanatory framework for depression in older adulthood in a small-scale society. We propose that depression is a consequence of functional disability, which can reduce subsistence productivity and resource transfers within and across generations. Social conflict can also disrupt resource flows and should be associated with depression.

Risk and the evolution of human exchange.

Compared with other species, exchange among non-kin is a hallmark of human sociality in both the breadth of individuals and total resources involved. One hypothesis is that extensive exchange evolved to buffer the risks associated with hominid dietary specialization on calorie dense, large packages, especially from hunting. 'Lucky' individuals share food with 'unlucky' individuals with the expectation of reciprocity when roles are reversed.

Intergenerational wealth transmission and the dynamics of inequality in small-scale societies.

Small-scale human societies range from foraging bands with a strong egalitarian ethos to more economically stratified agrarian and pastoral societies. We explain this variation in inequality using a dynamic model in which a population's long-run steady-state level of inequality depends on the extent to which its most important forms of wealth are transmitted within families across generations. We estimate the degree of intergenerational transmission of three different types of wealth (material, embodied, and relational), as well as the extent of wealth inequality in 21 historical and contemporary populations.

Culture sometimes matters: intra-cultural variation in pro-social behavior among Tsimane Amerindians.

Agent-centered models usually consider only individual-level variables in calculations of economic costs and benefits. There has been little consideration of social or cultural history on shaping payoffs in ways that impact decisions. To examine the role of local expectations on economic behavior, we explore whether village affiliation accounts for the variation in Dictator Game offers among the Tsimane of the Bolivian Amazon independently of other factors that could confound such an effect.