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Critiques of parachute science argue for closer collaborations among local and international scientists. Here, building on such a collaboration, we highlight further challenges when outsiders, typically working through international nongovernmental organizations, fail to respect both the governance framework within which they are working and the realities on the ground. Specifically, we emphasize the importance of observing governance structures, maintaining transparency, and responding flexibly to national and regional priorities (“looking up”), as well as stressing the need to keep a close focus on local cultural context when designing interventions such as educational programs (“looking down”). Addressing the shortcomings for conservation practice contingent on parachute science interventions requires nimble, creative, and respectful actions, which at least in the context of Tanzania, we all still struggle to put into action.

The reduced emissions in deforestation and degradation (REDD+) initiative uses payments for ecosystem services as incentives for developing countries to manage and protect their forests. REDD+ initiatives also prioritize social (and environmental) co-benefits aimed at improving the livelihoods of communities that are dependent on forests. Despite the incorporation of co-benefits into REDD+ goals, carbon sequestration remains the primary metric for which countries can receive payments from REDD+, but after more than 10 years of REDD+, many site-specific programs have failed to complete the carbon verification process. Here, we examine whether the REDD+ social co-benefits alone are sufficient to have slowed deforestation in the absence of carbon payments on Pemba, Tanzania. Using satellite imagery (Landsat archive), we quantified forest cover change for the period before (2001-2010) and after (2010-2018) the launch in 2010-2011 of Pemba island's REDD+ readiness project. We then compared rates of forest cover change between shehia (administrative units) that were part of REDD+ readiness intervention and those that were not, adjusting for confounding variables and the non-random selection of REDD+ shehia with a statistical matching procedure. Despite considerable variation in forest outcomes among shehia, the associated co-benefits with the Pemba REDD+ project had no discernible effect on forest cover change. Likewise, we did not detect an effect of socioecological covariates on forest cover change across all shehia, though island-wide human population growth since 2012 may have played a role. These findings are unsurprising given the failure to secure carbon payments on Pemba and indicate that co-benefits alone are insufficient to reduce deforestation. We conclude that better oversight of all-involved parties is needed to ensure that REDD+ interventions satisfactorily conclude the process of securing a mechanism for carbon payments, if slowing deforestation is to be achieved.

Conservation scientists continue to debate the strengths and weaknesses of REDD+ as an instrument to slow greenhouse gas emissions in the developing world. We propose that general positions on this debate are less helpful than drawing lessons from specific investigations into the features of individual projects that make them successful or not. Here, focusing on a site-specific REDD+ intervention in Pemba, Zanzibar (Tanzania), we examine the circumstances under which REDD+ has a chance of success, teasing out specific features of both REDD+ interventions and the socio-economic and institutional contexts that render REDD+ a potentially valuable complement to community forestry. Additionally, we highlight some unanticipated positive outcomes associated with the design features of REDD+ projects. Our broader goal is to move away from ideologically-driven debate to empirically-based identification of general conditions where REDD+ could work, and to provide policy recommendations.

Phylogenetic analyses increasingly take centre-stage in our understanding of the processes shaping patterns of cultural diversity and cultural evolution over time. Just as biologists explain the origins and maintenance of trait differences among organisms using phylogenetic methods, so anthropologists studying cultural macroevolutionary processes use phylogenetic methods to uncover the history of human populations and the dynamics of culturally transmitted traits. In this paper, we revisit concerns with the validity of these methods. Specifically, we use simulations to reveal how properties of the sample (size, missing data), properties of the tree (shape) and properties of the traits (rate of change, number of variants, transmission mode) might influence the inferences that can be drawn about trait distributions across a given phylogeny and the power to discern alternative histories. Our approach shows that in two example datasets specific combinations of properties of the sample, of the tree and of the trait can lead to potentially high rates of Type I and Type II errors. We offer this simulation tool to help assess the potential impact of this list of persistent perils in future cultural macroevolutionary work. This article is part of the theme issue 'Foundations of cultural evolution'.

The coconut crab Birgus latro, the largest terrestrial decapod, is under threat in most parts of its geographical range. Its life cycle involves two biomes (restricted terrestrial habitats near the coast, and salt water currents of the tropical Indian and Pacific Oceans). Its dependence on coastal habitat means it is highly vulnerable to the habitat destruction that typically accompanies human population expansion along coastlines. Additionally, it has a slow reproductive rate and can reach large adult body sizes that, together with its slow movement when on land, make it highly susceptible to overharvesting. We studied the distribution and population changes of coconut crabs at 15 island sites in coastal Tanzania on the western edge of the species' geographical range. Our aim was to provide the data required for reassessment of the extinction risk status of this species, which, despite indications of sharp declines in many places, is currently categorized on the IUCN Red List as Data Deficient. Pemba Island, Zanzibar, in Tanzania, is an important refuge for B. latro but subpopulations are fragmented and exploited by children and fishers. We discovered that larger subpopulations are found in the presence of crops and farther away from people, whereas the largest adult coconut crabs are found on more remote island reserves and where crabs are not exploited. Remoteness and protection still offer hope for this species but there are also opportunities for protection through local communities capitalizing on tourist revenue, a conservation solution that could be applied more generally across the species' range.

What happens when conservation interventions ostensibly fail? We outline a REDD+ intervention on Zanzibar, Tanzania which is adapting to a failure to implement carbon compensation payments and to the increased global price of cloves. Using a mix of quantitative and qualitative methods we provide preliminary evidence that well-managed shehia (wards) with registered Community Forestry Management Agreements (CoFMAs) are slowing their rates of deforestation. We also find an increase in the number of shehia with CoFMAs despite the absence of carbon payments. Using this island-wide case study we make inferences about the mechanisms whereby institutional expansion has occurred in ways consistent with cultural evolutionary dynamics of institutional change. We draw lessons for planning and practice that may help with the design of future conservation interventions and with bolstering the morale and effectiveness of disappointed partners.

Inequality or skew in reproductive success (RS) is common across many animal species and is of long-standing interest to the study of social evolution. However, the measurement of inequality in RS in natural populations has been challenging because existing quantitative measures are highly sensitive to variation in group/sample size, mean RS, and age-structure. This makes comparisons across multiple groups and/or species vulnerable to statistical artefacts and hinders empirical and theoretical progress. Here, we present a new measure of reproductive skew, the multinomial index, M, that is unaffected by many of the structural biases affecting existing indices. M is analytically related to Nonacs' binomial index, B, and comparably accounts for heterogeneity in age across individuals; in addition, M allows for the possibility of diminishing or even highly nonlinear RS returns to age. Unlike B, however, M is not biased by differences in sample/group size. To demonstrate the value of our index for cross-population comparisons, we conduct a reanalysis of male reproductive skew in 31 primate species. We show that a previously reported negative effect of group size on mating skew was an artefact of structural biases in existing skew measures, which inevitably decline with group size; this bias disappears when using M. Applying phylogenetically controlled, mixed-effects models to the same dataset, we identify key similarities and differences in the inferred within- and between-species predictors of reproductive skew across metrics. Finally, we provide an R package, SkewCalc, to estimate M from empirical data.

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour.

Female-biased kinship (FBK) arises in numerous species and in diverse human cultures, suggesting deep evolutionary roots to female-oriented social structures. The significance of FBK has been debated for centuries in human studies, where it has often been described as difficult to explain. At the same time, studies of FBK in non-human animals point to its apparent benefits for longevity, social complexity and reproduction. Are female-biased social systems evolutionarily stable and under what circumstances? What are the causes and consequences of FBK? The purpose of this theme issue is to consolidate efforts towards understanding the evolutionary significance and stability of FBK in humans and other mammals. The issue includes broad theoretical and empirical reviews as well as specific case studies addressing the social and ecological correlates of FBK across taxa, time and space. It leverages a comparative approach to test existing hypotheses and presents novel arguments that aim to expand our understanding of how males and females negotiate kinship across diverse contexts in ways that lead to the expression of female biases in kinship behaviour and social structure. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.

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. We estimate these correlations for 38 wealth measures, including somatic and relational wealth, from 15 populations ranging from hunter-gatherers to small-scale farmers. Although small sample sizes limit our statistical power, we find no evidence of ubiquitous male bias, at least as inferred from comparing parent-son and parent-daughter correlations. Rather we find wide variation in signatures of sex bias, with evidence of both son and daughter-biased transmission. Further, we introduce a model that helps pinpoint the conditions under which simple mid-point parent-offspring wealth correlations can reveal information about sex-biased parental investment. Our findings are relevant to the study of female-biased kinship by revealing just how little normative descriptors of kinship systems, such as patrilineal inheritance, capture intergenerational correlations in wealth, and how variable parent-son and parent-daughter correlations can be. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.

Human marriage systems, characterized by long-term partnerships and extended windows of parental care, differ from the mating systems of pulsed or seasonally breeding non-human animals in which Bateman's principles were originally tested. These features, paradigmatic of but not unique to humans, complicate the accurate measurement of mating success in evaluating Bateman's three principles. Here, we unpack the concept of mating success into distinct components: number of partners, number of years partnered, the timing of partnerships, and the quality of partners. Drawing on longitudinal records of marriage and reproduction collected in a natural-fertility East African population over a 20-year period, we test and compare various models of the relationship between mating success and reproductive success (RS), and show that an accurate assessment of male and female reproductive behaviour requires consideration of all major components of mating success. Furthermore, we demonstrate that while Bateman's third principle holds when mating success is defined in terms of years married, women's fitness increases whereas men's fitness decreases from an increase in the number of marriage partners, holding constant the total effective duration of marriages. We discuss these findings in terms of the distinct, sex-specific pathways through which RS can be optimized, and comment on the contribution of this approach to the broader study of sexual selection.

Nuclear family structures are often thought to be essential for the well-being of children. Divorce, the loss of either biological parent, the presence of step-parents, and the practice of polygynous marriage have all been claimed to negatively impact child well-being. However, empirical research on these topics has been limited by the routine use of cross-regional and cross-sectional databases. Cross-regional data render research vulnerable to the ecological inference fallacy, and cross-sectional data prevent assessment of age-specific impacts of time-varying family-structure variables. When longitudinal data are available, they tend to be drawn from Western/urban contexts. Detailed data on family structure and children's well-being are rarely collected in more marginalized communities. In many rural and traditional communities, nonnuclear family structures are indeed prevalent and viewed as socially permissible--and, as such, may have different impacts on children's well-being than in Western contexts. Here, we draw on a detailed, longitudinal dataset from a 20-y prospective study in rural Tanzania, where polygyny and serial monogamy are common. We analyze survival outcomes for 3,693 children born between 1931 and 2014, growth outcomes for 881 children born between 1976 and 2014, and educational outcomes for 1,370 children born between 1976 and 2014. Our analyses indicate that monogamous marriage is not consistently associated with better outcomes for children--contrary to some popular and public health perspectives on human family structure. [ABSTRACT FROM AUTHOR]

African lions are a significant threat to pastoralists, triggering both retaliatory and nonretaliatory killings that represent a high-profile example of human-wildlife conflict. In the present article, we report on a grassroots campaign to reduce such conflict by shifting agropastoralists' attitudes toward lion killing and the central role of bylaws in its apparent success. Insofar as all of East Africa's principal protected areas still harboring lions are surrounded by pastoralist populations, the vast majority of which persecute lions, this novel strategy is of considerable wide-scale and practical significance. We report on an estimated 59%-69% reduction in the number of lions killed since the implementation of bylaws and use our experiences to highlight the need for fresh dialog among project managers, conservation organizations, and their funders in crafting appropriate conservation success metrics. In the context of human-wildlife conflict, changes in peoples' norms and attitudes are of greater significance over the long term than simplistic tabulations of the number of individuals saved.

With apologies, an incorrect author list was given in the article. An additional author, Chris von Rueden, (Jepson School of Leadership Studies, University of Richmond) also contributed to this work. Author Ryan Schacht's affiliation was out-of-date. His correct affiliation is: Department of Anthropology, East Carolina University.

Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

Internal or within-state migration is common in Africa and elsewhere and has environmental and social consequences that are often poorly understood. We conducted a national-scale study tracking the movements of agropastoralists in Tanzania and documented the extent of associated environmental changes. The data were drawn from interviews with government officials in 80 rural districts covering the majority of land area across the country. According to interviewees, recent settlement is associated with forest clearing, overgrazing, and landscape burning. Conflicts such as lion killing and forced evictions of settlers often occur. Our interview data uncover limited capacity and lack of coordination among different levels of government to deal with these challenges. The novelty of our study is in its ability to draw on reports from ground-level administrators and to aggregate this information in order to both describe the impacts of rural migration over a large area and inform appropriate policy action from national-level decision-makers.

Conservation strategies to protect biodiversity and support household livelihoods face numerous challenges. Across the tropics, efforts focus on balancing trade-offs in local communities near the borders of protected areas. Devolving rights and control over certain resources to communities is increasingly considered necessary, but decades of attempts have yielded limited success and few lessons on how such interventions could be successful in improving livelihoods. We investigated a key feature of household well-being, the experience of food insecurity, in villages across Tanzania's northern wildlife tourist circuit. Using a sample of 2,499 primarily livestock-keeping households we compared food insecurity in villages participating in the country's principal community-based conservation strategy with nearby control areas. We tested whether community-based projects could offset the central costs experienced by households near strictly protected areas (i.e. frequent human-wildlife conflict and restricted access to resources). We found substantial heterogeneity in outcomes associated with the presence of community-based conservation projects across multiple project sites. Although households in project villages experienced more frequent conflict with wildlife and received few provisioned benefits, there is evidence that these households may have been buffered to some degree against negative effects of wildlife conflict. We interpret our results in light of qualitative institutional factors that may explain various project outcomes. Tanzania, like many areas of conservation importance, contains threatened biodiversity alongside areas of extreme poverty. Our analyses highlight the need to examine more precisely the complex and locally specific mechanisms by which interventions do or do not benefit wildlife and local communities.

Evolutionary ecological models of human fertility predict that: (1) parents will bias investment toward the sex with the highest fitness prospects in a particular socio-ecological context; (2) fertility is subject to quantity–quality trade-offs; and (3) fertility decisions will be sensitive to both predictable and stochastic mortality risk and the relative fitness value of differently sized sib-sets (the variance compensation hypothesis). We test these predictions using demographic records from the Agta, an indigenous population from the Philippines, who, as a result of disruption by loggers, miners, and settlers, are undergoing a demographic and social/ecological transition from foragers to peasant laborers. Leveraging the spatial and temporal variation in the Agta Demographic Database, we conduct an analysis of Agta life-history traits across this transition. Specifically, we compare the Casiguran Agta (CA) with the more isolated peninsular San Ildefonso Agta (SIA) sub-population from before (phase 1) and after (phase 2) encroachment. We find: (1) evidence of a decline in overall survival from phase 1 to phase 2, coupled with increased parental investment in first-born daughters compared to first-born sons in the CA population, and increased parental investment in sons versus daughters in the SIA population; (2) evidence of a moderate quantity–quality trade-off in CA and SIA fertility in phase 1; and (3) support for predictions of the variance compensation hypothesis as a driver of the lowered relative fertility in the CA. Our customized methods, comparative framework, and simultaneous focus on fertility and mortality allow us to show how heterogeneity in mortality and fertility are linked to life history trade-offs and environmental context in a manner consistent with the predictions of evolutionary ecological models.

We present formal evolutionary models for the origins and persistence of the practice of Female Genital Modification (FGMo). We then test the implications of these models using normative cross-cultural data on FGMo in Africa and Bayesian phylogenetic methods that explicitly model adaptive evolution. Empirical evidence provides some support for the findings of our evolutionary models that the de novo origins of the FGMo practice should be associated with social stratification, and that social stratification should place selective pressures on the adoption of FGMo; these results, however, are tempered by the finding that FGMo has arisen in many cultures that have no social stratification, and that forces operating orthogonally to stratification appear to play a more important role in the cross-cultural distribution of FGMo. To explain these cases, one must consider cultural evolutionary explanations in conjunction with behavioral ecological ones. We conclude with a discussion of the implications of our study for policies designed to end the practice of FGMo.

The idea that trade-offs between offspring quantity and quality shape reproductive behaviour has long been central to economic perspectives on fertility. It also has a parallel and richer theoretical foundation in evolutionary ecology. We review the application of the quantity-quality trade-off concept to human reproduction, emphasizing distinctions between clutch size and lifetime fertility, and the wider set of forces contributing to fertility variation in iteroparous and sexually reproducing species like our own. We then argue that in settings approximating human evolutionary history, several factors limit costly sibling competition. Consequently, while the optimization of quantity-quality trade-offs undoubtedly shaped the evolution of human physiology setting the upper limits of reproduction, we argue it plays a modest role in accounting for socio-ecological and individual variation in fertility. Only upon entering the demographic transition can fertility limitation be clearly interpreted as strategically orientated to advancing offspring quality via increased parental investment per child, with low fertility increasing descendant socio-economic success, although not reproductive success. We conclude that existing economic and evolutionary literature has often overemphasized the centrality of quantity-quality trade-offs to human fertility variation and advocate for the development of more holistic frameworks encompassing alternative life-history trade-offs and the evolved mechanisms guiding their resolution.

Evolutionary and economic models of the demographic transition argue that economic development incentivizes low-fertility, high-investment parental strategies, and that such strategies emerge first in relatively wealthy families within populations undergoing 'modernization'. However, most research focuses on fertility reduction rather than shifting parental investment, and few studies consider how parental decisions regarding educational investment vary in relation to alternative rural livelihoods. Using data from 19 villages and 1,719 children (7-19 years), we investigate the effects of diversifying livelihoods, wealth and child characteristics on multiple measures of educational investment in rural Tanzania. Children in (predominantly Maasai) pastoralist households were the least likely to attend school, while neighboring farmers and business owners invested more in education. Household wealth, as measured by asset ownership, was also independently positively associated with educational investment for all livelihood types. These results are consistent with lower opportunity costs and greater perceived economic pay-offs to education for relatively labor market-integrated and wealthy households. However, among pastoralists wealth held in livestock was not associated with educational investment. This result may reflect elevated opportunity costs related to the child labor demands of livestock herding. We find a marginal female advantage in education, which is surprising because qualitative research and numerous development projects in the region emphasize the disadvantages facing girls. We also find suggestive evidence of a later-born disadvantage (i.e. borderline statistically significant) consistent with the predicted consequences of sequential household resource dilution. Female advantage and later-born disadvantage were particularly evident in the wealthiest households. Greater reliability in the returns to education for wealthy households may favor preferential treatment of children with higher perceived long-term payoffs, while equal but lower-level investment in all children in relatively poor families may reflect a bet-hedging strategy. We discuss our results in light of parental investment theory and the wider literature on the demographic transition.

Leadership is an active area of research in both the biological and social sciences. This review provides a transdisciplinary synthesis of biological and social-science views of leadership from an evolutionary perspective, and examines patterns of leadership in a set of small-scale human and non-human mammalian societies. We review empirical and theoretical work on leadership in four domains: movement, food acquisition, within-group conflict mediation, and between-group interactions. We categorize patterns of variation in leadership in five dimensions: distribution (across individuals), emergence (achieved versus inherited), power, relative payoff to leadership, and generality (across domains). We find that human leadership exhibits commonalities with and differences from the broader mammalian pattern, raising interesting theoretical and empirical issues.

Polygyny is cross-culturally common and a topic of considerable academic and policy interest, often deemed a harmful cultural practice serving the interests of men contrary to those of women and children. Supporting this view, large-scale studies of national African demographic surveys consistently demonstrate that poor child health outcomes are concentrated in polygynous households. Negative population-level associations between polygyny and well-being have also been reported, consistent with the hypothesis that modern transitions to socially imposed monogamy are driven by cultural group selection. We challenge the consensus view that polygyny is harmful, drawing on multilevel data from 56 ethnically diverse Tanzanian villages. We first demonstrate the vulnerability of aggregated data to confounding between ecological and individual determinants of health; while across villages polygyny is associated with poor child health and low food security, such relationships are absent or reversed within villages, particularly when children and fathers are coresident. We then provide data indicating that the costs of sharing a husband are offset by greater wealth (land and livestock) of polygynous households. These results are consistent with models of polygyny based on female choice. Finally, we show that village-level negative associations between polygyny prevalence, food security, and child health are fully accounted for by underlying differences in ecological vulnerability (rainfall) and socioeconomic marginalization (access to education). We highlight the need for improved, culturally sensitive measurement tools and appropriate scales of analysis in studies of polygyny and other purportedly harmful practices and discuss the relevance of our results to theoretical accounts of marriage and contemporary population policy.

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

A recent discussion debates the extent of human in-migration around protected areas (PAs) in the tropics. One proposed argument is that rural migrants move to bordering areas to access conservation outreach benefits. A counter proposal maintains that PAs have largely negative effects on local populations and that outreach initiatives even if successful present insufficient benefits to drive in-migration. Using data from Tanzania, we examined merits of statistical tests and spatial methods used previously to evaluate migration near PAs and applied hierarchical modeling with appropriate controls for demographic and geographic factors to advance the debate. Areas bordering national parks in Tanzania did not have elevated rates of in-migration. Low baseline population density and high vegetation productivity with low interannual variation rather than conservation outreach explained observed migration patterns. More generally we argue that to produce results of conservation policy significance, analyses must be conducted at appropriate scales, and we caution against use of demographic data without appropriate controls when drawing conclusions about migration dynamics.

There is a strong intuitive expectation in both popular lore and conventional evolutionary thinking that more males lead to more violence. Here, we untangle the logic behind this widely held notion with a specific focus on humans. We first review the relation between the intensity of sexual selection in human populations and the adult sex ratio (ASR), and find that it is more in line with recent reformulations of sexual selection theory than with conventional models. We then turn directly to the patterning of violence across human societies in relation to the sex ratio. Although the 'more men, more violence' expectation is not met, it is clear that the patterning of violence is undertheorized and we offer recommendations for steps forward.

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The incidence of HIV infection in rural African youth remains high despite widespread knowledge of the disease within the region and increasing funds allocated to programs aimed at its prevention and treatment. This suggests that program efficacy requires a more nuanced understanding of the profiles of the most at-risk individuals. To evaluate the explanatory power of novel psychographic variables in relation to high-risk sexual behaviors, we conducted a survey to assess the effects of psychographic factors, both behavioral and attitudinal, controlling for standard predictors in 546 youth (12-26 years of age) across 8 villages in northern Tanzania. Indicators of high-risk sexual behavior included HIV testing, sexual history (i.e., virgin/non-virgin), age of first sexual activity, condom use, and number of lifetime sexual partners. Predictors in the statistical models included standard demographic variables, patterns of media consumption, HIV awareness, and six new psychographic features identified via factor analyses: personal vanity, family-building values, ambition for higher education, town recreation, perceived parental strictness, and spending preferences. In a series of hierarchical regression analyses, we find that models including psychographic factors contribute significant additional explanatory information when compared to models including only demographic and other conventional predictors. We propose that the psychographic approach used here, in so far as it identifies individual characteristics, aspirations, aspects of personal life style and spending preferences, can be used to target appropriate communities of youth within villages for leading and receiving outreach, and to build communities of like-minded youth who support new patterns of sexual behavior.

The Maasai of northern Tanzania, a semi-nomadic ethnic group predominantly reliant on pastoralism, face a number of challenges anticipated to have negative impacts on child health, including marginalisation, vulnerabilities to drought, substandard service provision and on-going land grabbing conflicts. Yet, stemming from a lack of appropriate national survey data, no large-scale comparative study of Maasai child health has been conducted. Savannas Forever Tanzania surveyed the health of over 3500 children from 56 villages in northern Tanzania between 2009 and 2011. The major ethnic groups sampled were the Maasai, Sukuma, Rangi, and the Meru. Using multilevel regression we compare each ethnic group on the basis of (i) measurements of child health, including anthropometric indicators of nutritional status and self-reported incidence of disease; and (ii) important proximate determinants of child health, including food insecurity, diet, breastfeeding behaviour and vaccination coverage. We then (iii) contrast households among the Maasai by the extent to which subsistence is reliant on livestock herding. Measures of both child nutritional status and disease confirm that the Maasai are substantially disadvantaged compared to neighbouring ethnic groups, Meru are relatively advantaged, and Rangi and Sukuma intermediate in most comparisons. However, Maasai children were less likely to report malaria and worm infections. Food insecurity was high throughout the study site, but particularly severe for the Maasai, and reflected in lower dietary intake of carbohydrate-rich staple foods, and fruits and vegetables. Breastfeeding was extended in the Maasai, despite higher reported consumption of cow's milk, a potential weaning food. Vaccination coverage was lowest in Maasai and Sukuma. Maasai who rely primarily on livestock herding showed signs of further disadvantage compared to Maasai relying primarily on agriculture. We discuss the potential ecological, socioeconomic, demographic and cultural factors responsible for these differences and the implications for population health research and policy.

Livingstone's second mission site on the shore of Lake Malawi suffers very high rates of consequential lightning strikes. Comprehensive interviewing of victims and their relatives in seven Traditional Authorities in Nkhata Bay District, Malawi revealed that the annual rate of consequential strikes was 419/million, more than six times higher than that in other developing countries; the rate of deaths from lightning was 84/million/year, 5.4 times greater than the highest ever recorded. These remarkable figures reveal that lightning constitutes a significant stochastic source of mortality with potential life history consequences, but it should not deflect attention away from the more prominent causes of mortality in this rural area.

Evolutionary studies of human behavior have emphasized the importance of kin selection in explaining social institutions and fitness outcomes. Our relatives can nevertheless be competitors as well as sources of altruism. This is particularly likely when there is local competition over resources, where conflict can lead to strife among nondispersing relatives, reducing or even negating the effects of relatedness on promoting altruism. Here, I present demographic data on a land-limited human population, utilizing large within-population variation in land ownership to determine the interactions between local resource competition and the benefits of kin in enhancing child survival, a key component of fitness in this population. As predicted, wealth affects the extent of kin altruism, in that paternal relatives (specifically father's brothers) appear to buffer young children from mortality much more effectively in rich than in poor households. This interaction effect is interpreted as evidence that the extent of nepotism among humans depends critically on resource availability. Further unanticipated evidence that maternal kin play a role in buffering children from mortality in situations where paternal kin control few resources speaks to the important role that specific local circumstance plays in shaping kin contributions to child welfare. (C) 2007 Elsevier Inc. All rights reserved.