Women's subsistence strategies predict fertility across cultures, but context matters.

While it is commonly assumed that farmers have higher, and foragers lower, fertility compared to populations practicing other forms of subsistence, robust supportive evidence is lacking. We tested whether subsistence activities-incorporating market integration-are associated with fertility in 10,250 women from 27 small-scale societies and found considerable variation in fertility. This variation did not align with group-level subsistence typologies. Societies labeled as "farmers" did not have higher fertility than others, while "foragers" did not have lower fertility. However, at the individual level, we found strong evidence that fertility was positively associated with farming and moderate evidence of a negative relationship between foraging and fertility. Markers of market integration were strongly negatively correlated with fertility. Despite strong cross-cultural evidence, these relationships were not consistent in all populations, highlighting the importance of the socioecological context, which likely influences the diverse mechanisms driving the relationship between fertility and subsistence.

Reproductive inequality in humans and other mammals.

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.

Modelling animal network data in R using STRAND.

There have been recent calls for wider application of generative modelling approaches in applied social network analysis. At present, however, it remains difficult for typical end users-for example, field researchers-to implement generative network models, as there is a dearth of openly available software packages that make application of such models as simple as other, permutation-based approaches. Here, we outline the STRAND R package, which provides a suite of generative models for Bayesian analysis of animal social network data that can be implemented using simple, base R syntax. To facilitate ease of use, we provide a tutorial demonstrating how STRAND can be used to model proportion, count or binary network data using stochastic block models, social relation models or a combination of the two modelling frameworks. STRAND facilitates the application of generative network models to a broad range of data found in the animal social networks literature.

Nahua mushroom gatherers use area-restricted search strategies that conform to marginal value theorem predictions.

We develop a method of analysis for testing the marginal value theorem (MVT) in natural settings that does not require an independent definition or mapping of patches. We draw on recent theoretical work on area-restricted search (ARS) that links turning-angle and step-size changes to geographically localized encounter-rates. These models allow us to estimate "giving-up times" using encounter-annotated GPS tracking data. Applied to a case study of Nahua mushroom foragers, these models identify distinct forms of intrapatch and interpatch search behavior, with intrapatch search transitioning to interpatch search after a predictable interval of time since the last encounter with a harvested mushroom. Our empirical estimate of giving-up time coincides with the theoretically optimal giving-up time derived under the MVT in the same environment. The MVT is currently underused in studies of human foraging and settlement patterns, due in large part to the difficulty of identifying discrete resource patches and quantifying their characteristics. Our methods mitigate the need to make such discrete maps of patches and thus have the potential to broaden the scope for empirical evaluations of the MVT and related theory in humans. Beyond studies of naturalistic foraging in humans and other animals, our approach has implications for optimization of search behavior in a range of applied fields where search dynamics must be adapted to shifting patterns of environmental heterogeneity affecting prey density and patchiness.

DieTryin: An R package for data collection, automated data entry, and post-processing of network-structured economic games, social networks, and other roster-based dyadic data.

Researchers studying social networks and inter-personal sentiments in bounded or small-scale communities face a trade-off between the use of roster-based and free-recall/name-generator-based survey tools. Roster-based methods scale poorly with sample size, and can more easily lead to respondent fatigue; however, they generally yield higher quality data that are less susceptible to recall bias and that require less post-processing. Name-generator-based methods, in contrast, scale well with sample size and are less likely to lead to respondent fatigue. However, they may be more sensitive to recall bias, and they entail a large amount of highly error-prone post-processing after data collection in order to link elicited names to unique identifiers. Here, we introduce an R package, DieTryin, that allows for roster-based dyadic data to be collected and entered as rapidly as name-generator-based data; DieTryin can be used to run network-structured economic games, as well as collect and process standard social network data and round-robin Likert-scale peer ratings. DieTryin automates photograph standardization, survey tool compilation, and data entry. We present a complete methodological workflow using DieTryin to teach end-users its full functionality.

The multinomial index: a robust measure of reproductive skew.

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.

Navigating cross-cultural research: methodological and ethical considerations.

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.

Unpacking mating success and testing Bateman's principles in a human population.

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.

A general model of forager search: Adaptive encounter-conditional heuristics outperform Lévy flights in the search for patchily distributed prey.

A theoretical and applied literature has suggested that foragers search using Lévy flights, since Lévy flights can maximize the efficiency of search in the absence of information on the location of randomly distributed prey. Foragers, however, often have available to them at least some information about the distribution of prey, gained either through evolved mechanisms, experience and memory, or social transmission of information. As such, we might expect selection for heuristics that make use of such information to further improve the efficiency of random search. Here we present a general model of random search behavior that includes as special cases: area-restricted search, correlated random walks, Brownian search, and Lévy flights. This generative model allows foragers to adjust search parameters based on encounter-conditional and other heuristics. Using a simulation model, we demonstrate the efficiency gains of these search heuristics, and illustrate the resulting differences in the distributions of step-size and heading angle change they imply, relative to Lévy flights. We conclude by presenting a statistical model that can be fit to empirical data and a set of testable, quantitative predictions that contrast our model of adaptive search with the Lévy flight foraging hypothesis.

A hierarchical bayesian analysis of parasite prevalence and sociocultural outcomes: The role of structural racism and sanitation infrastructure.

OBJECTIVES: We conduct a revaluation of the Thornhill and Fincher research project on parasites using finely-resolved geographic data on parasite prevalence, individual-level sociocultural data, and multilevel Bayesian modeling. In contrast to the evolutionary psychological mechanisms linking parasites to human behavior and cultural characteristics proposed by Thornhill and Fincher, we offer an alternative hypothesis that structural racism and differential access to sanitation systems drive both variation in parasite prevalence and differential behaviors and cultural characteristics. METHODS: We adopt a Bayesian framework to estimate parasite prevalence rates in 51 districts in eight Latin American countries using the disease status of 170,220 individuals tested for infection with the intestinal roundworm Ascaris lumbricoides (Hürlimann et al., []: PLoS Negl Trop Dis 5:e1404). We then use district-level estimates of parasite prevalence and individual-level social data from 5,558 individuals in the same 51 districts (Latinobarómetro, 2008) to assess claims of causal associations between parasite prevalence and sociocultural characteristics. RESULTS: We find, contrary to Thornhill and Fincher, that parasite prevalence is positively associated with preferences for democracy, negatively associated with preferences for collectivism, and not associated with violent crime rates or gender inequality. A positive association between parasite prevalence and religiosity, as in Fincher and Thornhill (: Behav Brain Sci 35:61-79), and a negative association between parasite prevalence and achieved education, as predicted by Eppig et al. (: Proc R S B: Biol Sci 277:3801-3808), become negative and unreliable when reasonable controls are included in the model. We find support for all predictions derived from our hypothesis linking structural racism to both parasite prevalence and cultural outcomes. CONCLUSIONS: We conclude that best practices in biocultural modeling require examining more than one hypothesis, retaining individual-level data and its associated variance whenever possible, and adopting multilevel techniques suited to the structuring of the data.

Cultural group selection plays an essential role in explaining human cooperation: A sketch of the evidence.

Human cooperation is highly unusual. We live in large groups composed mostly of non-relatives. Evolutionists have proposed a number of explanations for this pattern, including cultural group selection and extensions of more general processes such as reciprocity, kin selection, and multi-level selection acting on genes. Evolutionary processes are consilient; they affect several different empirical domains, such as patterns of behavior and the proximal drivers of that behavior. In this target article, we sketch the evidence from five domains that bear on the explanatory adequacy of cultural group selection and competing hypotheses to explain human cooperation. Does cultural transmission constitute an inheritance system that can evolve in a Darwinian fashion? Are the norms that underpin institutions among the cultural traits so transmitted? Do we observe sufficient variation at the level of groups of considerable size for group selection to be a plausible process? Do human groups compete, and do success and failure in competition depend upon cultural variation? Do we observe adaptations for cooperation in humans that most plausibly arose by cultural group selection? If the answer to one of these questions is "no," then we must look to other hypotheses. We present evidence, including quantitative evidence, that the answer to all of the questions is "yes" and argue that we must take the cultural group selection hypothesis seriously. If culturally transmitted systems of rules (institutions) that limit individual deviance organize cooperation in human societies, then it is not clear that any extant alternative to cultural group selection can be a complete explanation.

Cultural group selection follows Darwin's classic syllogism for the operation of selection.

The main objective of our target article was to sketch the empirical case for the importance of selection at the level of groups on cultural variation. Such variation is massive in humans, but modest or absent in other species. Group selection processes acting on this variation is a framework for developing explanations of the unusual level of cooperation between non-relatives found in our species. Our case for cultural group selection (CGS) followed Darwin's classic syllogism regarding natural selection: If variation exists at the level of groups, if this variation is heritable, and if it plays a role in the success or failure of competing groups, then selection will operate at the level of groups. We outlined the relevant domains where such evidence can be sought and characterized the main conclusions of work in those domains. Most commentators agree that CGS plays some role in human evolution, although some were considerably more skeptical. Some contributed additional empirical cases. Some raised issues of the scope of CGS explanations versus competing ones.

Sit-and-wait versus active-search hunting: A behavioral ecological model of optimal search mode.

Drawing on Skellam׳s (1958) work on sampling animal populations using transects, we derive a behavioral ecological model of the choice between sit-and-wait and active-search hunting. Using simple, biologically based assumptions about the characteristics of predator and prey, we show how an empirically definable parameter space favoring active-search hunting expands as: (1) the average rate of movement of prey decreases, or (2) the energetic costs of hunter locomotion decline. The same parameter space narrows as: (3) prey skittishness increases as a function of a hunter׳s velocity, or (4) prey become less detectable as a function of a hunter׳s velocity. Under either search tactic, encounter rate increases as a function of increasing prey velocity and increasing detection zone radius. Additionally, we investigate the roles of habitat heterogeneity and spatial auto-correlation or grouping of prey on the optimal search mode of a hunter, finding that habitat heterogeneity has the potential to complicate application of the model to some empirical examples, while the effects of prey grouping lead to relatively similar model outcomes. As predicted by the model, the introduction of the horse to the Great Plains and the introduction of the snowmobile to Arctic foraging communities decreased the metabolic costs of active-search and led to a change in normative hunting strategies that favored active-search in place of sit-and-wait hunting.

Comparison of sampling strategies for monitoring water quality in mesoscale Canadian Prairie watersheds.

The Canadian Prairies are subject to cold winter dynamics, spring snowmelt runoff, and summer storms; a process variability that makes it difficult to identify an adequate sampling strategy for capturing representative water quality data. Hence, our research objective was to compare multiple water quality sampling strategies for Prairie watersheds and rank them based on operational and statistical criteria. The focus was on the Catfish Creek Watershed (Manitoba, Canada), which drains into the hypereutrophic Lake Winnipeg. Water samples were collected every 7 h during the 2013 open-water season and notably analyzed for nitrate and orthophosphate. The original high-frequency dataset (7 h) was then deconstructed into lower-frequency datasets to mimic strategies involving sample collection on a daily, weekly, bi-weekly, monthly, and seasonal basis. A comparison and decision matrix was also built to assess the ability of the lower-frequency datasets to retain the statistical properties of the original (7 h) dataset. Results indicate that nutrient concentrations vary significantly over short timescales and are affected by both sampling time (day versus night) and water level fluctuations. The decision matrix revealed that seasonal sampling is sufficient when the goal is only to capture mean water quality conditions; however, sub-daily to daily sampling is required for accurate process signal representation. While we acknowledge that sampling programs designed by researchers and public agencies are often driven by different goals, we found daily sampling to be the most parsimonious strategy for the study watershed and suggest that it would help to better quantify nutrient loads to Lake Winnipeg.

An empirical comparison of short tandem repeats (STRs) and single nucleotide polymorphisms (SNPs) for relatedness estimation in Chinese rhesus macaques (Macaca mulatta).

We compare the effectiveness of short tandem repeat (STR) and single nucleotide polymorphism (SNP) genotypes for estimating pairwise relatedness, using molecular data and pedigree records from a captive Chinese rhesus macaque population at the California National Primate Research Center. We find that a panel of 81 SNPs is as effective at estimating first-order kin relationships as a panel of 14 highly polymorphic STRs. We note, however, that the selected STRs provide more precise predictions of relatedness than the selected SNPs, and may be preferred in contexts that require the discrimination of kin related more distantly than first-order relatives. Additionally, we compare the performance of three commonly used relatedness estimation algorithms, and find that the Wang [2002] algorithm outperforms other algorithms when analyzing STR data, while the Queller & Goodnight [1989] algorithm outperforms other algorithms when analyzing SNP data. Future research is needed to address the number of SNPs required to reach the discriminatory power of a standard STR panel in relatedness estimation for primate colony management.

Identifying human-rhesus macaque gene orthologs using heterospecific SNP probes.

We genotyped a Chinese and an Indian-origin rhesus macaque using the Affymetrix Genome-Wide Human SNP Array 6.0 and cataloged 85,473 uniquely mapping heterospecific SNPs. These SNPs were assigned to rhesus chromosomes according to their probe sequence alignments as displayed in the human and rhesus reference sequences. The conserved gene order (synteny) revealed by heterospecific SNP maps is in concordance with that of the published human and rhesus macaque genomes. Using these SNPs' original human rs numbers, we identified 12,328 genes annotated in humans that are associated with these SNPs, 3674 of which were found in at least one of the two rhesus macaques studied. Due to their density, the heterospecific SNPs allow fine-grained comparisons, including approximate boundaries of intra- and extra-chromosomal rearrangements involving gene orthologs, which can be used to distinguish rhesus macaque chromosomes from human chromosomes.

Women's subsistence networks scaffold cultural transmission among BaYaka foragers in the Congo Basin.

In hunter-gatherer societies, women's subsistence activities are crucial for food provisioning and children's social learning but are understudied relative to men's activities. To understand the structure of women's foraging networks, we present 230 days of focal-follow data in a BaYaka community. To analyze these data, we develop a stochastic blockmodel for repeat observations with uneven sampling. We find that women's subsistence networks are characterized by cooperation between kin, gender homophily, and mixed age-group composition. During early childhood, individuals preferentially coforage with adult kin, but those in middle childhood and adolescence are likely to coforage with nonkin peers, providing opportunities for horizontal learning. By quantifying the probability of coforaging ties across age classes and relatedness levels, our findings provide insights into the scope for social learning during women's subsistence activities in a real-world foraging population and provide ground-truth values for key parameters used in formal models of cumulative culture.

Cross-cousin marriage among Tsimane forager-horticulturalists during demographic transition and market integration.

Although still prevalent in many human societies, the practice of cousin marriage has precipitously declined in populations undergoing rapid demographic and socioeconomic change. However, it is still unclear whether changes in the structure of the marriage pool or changes in the fitness-relevant consequences of cousin marriage more strongly influence the frequency of cousin marriage. Here, we use genealogical data collected by the Tsimane Health and Life History Project to show that there is a small but measurable decline in the frequency of first cross-cousin marriage since the mid-twentieth century. Such changes are linked to concomitant changes in the pool of potential spouses in recent decades. We find only very modest differences in fitness-relevant demographic measures between first cousin and non-cousin marriages. These differences have been diminishing as the Tsimane have become more market integrated. The factors that influence preferences for cousin marriage appear to be less prevalent now than in the past, but cultural inertia might slow the pace of change in marriage norms. Overall, our findings suggest that cultural changes in marriage practices reflect underlying societal changes that shape the pool of potential spouses.

Reliable network inference from unreliable data: A tutorial on latent network modeling using STRAND.

Social network analysis provides an important framework for studying the causes, consequences, and structure of social ties. However, standard self-report measures-for example, as collected through the popular "name-generator" method-do not provide an impartial representation of such ties, be they transfers, interactions, or social relationships. At best, they represent perceptions filtered through the cognitive biases of respondents. Individuals may, for example, report transfers that did not really occur, or forget to mention transfers that really did. The propensity to make such reporting inaccuracies is both an individual-level and item-level characteristic-variable across members of any given group. Past research has highlighted that many network-level properties are highly sensitive to such reporting inaccuracies. However, there remains a dearth of easily deployed statistical tools that account for such biases. To address this issue, we provide a latent network model that allows researchers to jointly estimate parameters measuring both reporting biases and a latent, underlying social network. Building upon past research, we conduct several simulation experiments in which network data are subject to various reporting biases, and find that these reporting biases strongly impact fundamental network properties. These impacts are not adequately remedied using the most frequently deployed approaches for network reconstruction in the social sciences (i.e., treating either the union or the intersection of double-sampled data as the true network), but are appropriately resolved through the use of our latent network models. To make implementation of our models easier for end-users, we provide a fully documented R package, STRAND, and include a tutorial illustrating its functionality when applied to empirical food/money sharing data from a rural Colombian population. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Fitness consequences of cousin marriage: a life-history assessment in two populations.

Cousin marriage, a spousal union between close kin, occurs at high frequencies in many parts of the world. The rates of cousin marriage in humans are concordant with empirical studies that challenge the traditionally held view that reproduction with kin is generally avoided in animals. Similarly, some theoretical models in animal behaviour show that inbreeding avoidance is more constrained than previously thought. Such studies highlight the importance of quantifying the costs and benefits of reproduction among close kin over the whole life-course. Here, we use genealogical data from two human populations with high frequencies of cousin marriage (the Dogon from Mali, and the Ancien Régime nobility from Europe) to estimate these potential costs and benefits. We compare age-specific fertility and survival curves, as well as the projected growth rates, of subpopulations of each marriage type. Fitness costs of cousin marriage are present in terms of reduced child survival (in both populations), while benefits exist as increased fertility for men (in the Dogon) and for women (in the Ancien Régime nobility). We also find some differences in the projected growth rates of lineages as a function of marriage type. Finally, we discuss the trade-offs that might shape marriage decisions in different ecological conditions.