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Department of Human Behavior, Ecology and Culture

The Department of Human Behavior, Ecology and Culture investigates the role of culture in human evolution and adaptation. The primary goal is to theorize, design, and conduct longitudinal studies of human adaptation and cultural dynamics in ecological context. By integrating cross-cultural fieldwork with mathematical models and advanced quantitative methods, we hope to contribute to the interdisciplinary study of human evolution and human social dynamics.

Please see the Projects and Fieldwork links on the right for much more information.


19 May 2022

Forest income and livelihoods on Pemba: A quantitative ethnography

This paper offers a systematic approach to quantifying the socio-economic role of forests for 'forest-dependent' communities. Focusing on the island of Pemba (Zanzibar, Tanzania), we investigate how forest income contributes to livelihood portfolios, local inequality, and households' insurance against shocks. We also examine how forest income is affected by local institutions and household socio-demographics. We use a series of non-parametric measures in conjunction with multi-level Bayesian models supported by directed acyclic graphs to address these questions. On average, we find that 27% of household income comes from forests, with 83% of that value deriving from fuel products, and that 62% of the total value of forest products are harvested from the agroforestry scrub matrix. At the same time, forest income scales positively with income, forest-dependency scales negatively. Top income earners control ∼ 4 times more forest income than low earners. However, when we consider forestry against other economic sectors, forest income reduces overall income inequality on the island. Despite forests being critical for the poor, we find it offers little insurance against shocks, especially for the vulnerable. In fact, in contrast to expectations, we find that the well-insured are the most likely to increase forest use in response to shocks. Regarding institutions, most forest products come from either government land or land owned by other private individuals, indicating weak tenure institutions on the island. Finally, young, poorly educated male-headed households, which are not integrated into markets, are the most likely to have high forest income. However, female-headed households are generally more dependent due to a lack of alternative income sources. Our results are encouraging as the use of tools from formal causal inference and detailed Bayesian modelling, in conjunction with a quantitative ethnography, build upon previous findings while improving our understanding of local socio-ecological systems. Read article here.

25 April 2022

Expanding the understanding of majority‑bias in children’s social learning

Prior experiments with children across seven different societies have indicated U‑shaped age patterns in the likelihood of copying majority demonstrations. It is unclear which learning strategies underlie the observed responses that create these patterns. Here we broaden the understanding of children’s learning strategies by: (1) exploring social learning patterns among 6–13‑year‑olds (n = 270) from ethnolinguistically varied communities in Vanuatu; (2) comparing these data with those reported from other societies (n = 629), and (3) re‑analysing our and previous data based on a theoretically plausible set of underlying strategies using Bayesian methods. We find higher rates of social learning in children from Vanuatu, a country with high linguistic and cultural diversity. Furthermore, our results provide statistical evidence for modest U‑shaped age patterns for a more clearly delineated majority learning strategy across the current and previously investigated societies, suggesting that the developmental mechanisms structuring majority bias are cross‑culturally highly recurrent and hence a fundamental feature of early human social learning. Read article here.

24 March 2022

Coevolution of relative brain size and life expectancy in parrots

Previous studies have demonstrated a correlation between longevity and brain size in a variety of taxa. Little research has been devoted to understanding this link in parrots; yet parrots are well-known for both their exceptionally long lives and cognitive complexity. We employed a large-scale comparative analysis that investigated the influence of brain size and life-history variables on longevity in parrots. Specifically, we addressed two hypotheses for evolutionary drivers of longevity: the cognitive buffer hypothesis, which proposes that increased cognitive abilities enable longer lifespans, and the expensive brain hypothesis, which holds that increases in life-span are caused by prolonged developmental time of, and increased parental investment in, large-brained offspring. We estimated life expectancy from detailed zoo records for 133 818 individuals across 244 parrot species. Using a principled Bayesian approach that addresses data uncertainty and imputation of missing values, we found a consistent correlation between relative brain size and life expectancy in parrots. This correlation was best explained by a direct effect of relative brain size. Notably, we found no effects of developmental time, clutch size or age at first reproduction. Our results suggest that selection for enhanced cognitive abilities in parrots has in turn promoted longer lifespans. Read article here.

22 February 2022

Effect of Anthropogenic Activities on the Population of Moor Macaques (Macaca maura) in South Sulawesi, Indonesia

Forest loss due to anthropogenic activities is one of the main causes of plant and animal species decline. Studying the species’ population status (i.e., density, abundance, and geographic distribution) on a regular basis is one of the main tools to assess the effect of anthropogenic activities on wildlife, to monitor population dynamics and to intervene with effective conservation strategies when the population of an endangered species declines. On Sulawesi Island, Indonesia, anthropogenic activities, such as agriculture, are decreasing the remaining natural habitats available for several endemic and endangered species. The effect of this forest loss on the threatened moor macaques (Macaca maura) in South Sulawesi is unknown, and data on the population status of this species are needed to design effective conservation strategies. To assess the population status of the moor macaques, we walked linear transects (N = 29, survey effort = 114 km) at six sites between November 2019 and March 2020 to estimate macaque population density and encounter rate. We tested the effect of anthropogenic activities on macaque encounter rate. Our global density estimate (24 individuals/km2) was lower than the overall estimate from the most detailed survey conducted on this species, which covered its whole geographic distribution (36.1 individuals/km 2). However, these results should be interpreted with caution because the previous density estimate falls within the confidence intervals of our estimate. Furthermore, we found regional declines in moor macaque encounter rates in at least two sites compared with previous studies. We found a high presence of anthropogenic activity in the forests inhabited by macaques. Moor macaques were less abundant in open areas with no forest (i.e., clear cuttings) than in forested areas, and in the presence of nonspecies-specific hunting traps (i.e., wire-loop traps). Moreover, moor macaques were more abundant in areas with a higher presence of humans and domestic animals. Overall, our data suggest that the population of this species may be declining in certain regions but further surveys are needed to corroborate whether this is occurring across the entire geographic distribution. Read article here.

1 February 2022

Are the More Flexible Great-Tailed Grackles Also Better at Behavioral Inhibition?

Behavioral flexibility should, theoretically, be positively related to behavioral inhibition because one should need to inhibit a previously learned behavior to change their behavior when the task changes (flexibility). However, several investigations show no or mixed support of this hypothesis, which challenges the assumption that inhibition is involved in making flexible decisions. We tested the hypothesis that flexibility (reversal learning and solution switching on a multi-access box by Logan et al., 2022) is associated with inhibition (go/no go on a touchscreen and detour) by measuring all variables in the same individuals. Because touchscreen experiments had never been conducted in this species, we validated that they are functional for wild-caught grackles who learned to use it and completed go/no go on it. Performance on go/no go and detour tasks did not correlate, indicating they did not measure the same trait. Individuals who were faster to reverse took more time to attempt a new option on the multi-access box and were either faster or slower at go/no go depending on whether one individual, Taquito (accidentally tested beyond 200 trial cap), was included in the GLM. While the relationship between trials to reverse and trials to pass go/no go was strongly influenced by Taquito, the more comprehensive Bayesian flexibility model supported the positive relationship irrespective of whether Taquito was included. Performance on detour did not correlate with either flexibility measure, suggesting that they may measure separate traits. We conclude that flexibility is associated with certain types of inhibition, but not others, in great-tailed grackles. Read article here.

1 February 2022

Investigating Sex Differences in Genetic Relatedness in Great-tailed Grackles in Tempe, Arizona to Infer Potential Sex Biases in Dispersal

In most bird species, females disperse prior to their first breeding attempt, while males remain close to the place they hatched. While explanations for such female bias in natal dispersal have focused on the resource-defense based monogamous mating system that is prevalent in most birds, the factors shaping dispersal decisions are often more complex. Studying species with different social and mating systems can help illuminate the various factors shaping sex biased dispersal. Here, we use genetic approaches to determine whether females and/or males disperse in great-tailed grackles (Quiscalus mexicanus), which have a mating system where the males hold breeding territories that multiple females might choose to place their nest in, but females forage independently of these breeding territories across a wider area. We find that for individuals caught at a single site in Arizona, (i) the average relatedness among all female dyads, but not of males, is higher than average relatedness among other individuals at the site; (ii) that female close relatives are found within shorter distances from each other than pairs of unrelated females, but male close relatives at larger distances than pairs of unrelated males; and (iii) we find a decline in relatedness with increasing spatial distances for females, but not for males. Our findings show that great-tailed grackles offer opportunities to understand how divergent social and mating systems might shape natal philopatry and dispersal, given their reversal of the usual sex-bias in dispersal with females associating with genetic relatives while males are not. Read article here.

19 January 2022

Social hierarchies and social networks in humans

Across species, social hierarchies are often governed by dominance relations. In humans, where there are multiple culturally valued axes of distinction, social hierarchies can take a variety of forms and need not rest on dominance relations. Consequently, humans navigate multiple domains of status, i.e. relative standing. Importantly, while these hierarchies may be constructed from dyadic interactions, they are often more fundamentally guided by subjective peer evaluations and group perceptions. Researchers have typically focused on the distinct elements that shape individuals’ relative standing, with some emphasizing individual-level attributes and others outlining emergent macro-level structural outcomes. Here, we synthesize work across the social sciences to suggest that the dynamic interplay between individual-level and meso-level properties of the social networks in which individuals are embedded are crucial for understanding the diverse processes of status differentiation across groups. More specifically, we observe that humans not only navigate multiple social hierarchies at any given time but also simultaneously operate within multiple, overlapping social networks. There are important dynamic feedbacks between social hierarchies and the characteristics of social networks, as the types of social relationships, their structural properties, and the relative position of individuals within them both influence and are influenced by status differentiation.

This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’. Read article here.

1 December 2021

Do the more flexible individuals rely more on causal cognition? Observation versus intervention in causal inference in great-tailed grackles

Behavioral flexibility, the ability to change behavior when circumstances change based on learning from previous experience, is thought to play an important role in a species ability to successfully adapt to new environments and expand its geographic range. It is alternatively or additionally possible that causal cognition, the ability to understand relationships beyond their statistical covariations, could play a significant role in rapid range expansions via the ability to learn faster: causal cognition could lead to making better predictions about outcomes through exerting more control over events. We aim to determine whether great tailed grackles(Quiscalus mexicanus), a species that is rapidly expanding its geographic range, use causal inference and whether this ability relates to their behavioral flexibility (flexibility measured in these individuals by Logan  et al. (2019): reversal learning of a color discrimination and solution switching on a puzzle box). Causal cognition was measured using a touchscreen where individuals learned about the relationships between a star, a tone, a clicking noise, and food. They were then tested on their expectations about which of these causes the food to become available. We found that eight grackles showed no evidence of making causal inferences when given the opportunity to intervene on observed events using a touchscreen apparatus, and that performance on the causal cognition task did not correlate with behavioral flexibility measures. This could indicate that our test was inadequate to assess causal cognition. Because of this, we are unable to speculate about the potential role of causal cognition in a species that is rapidly expanding its geographic range. We suggest  further exploration of this hypothesis using larger sample sizes and multiple test paradigms. Read article here.

30 November 2021

Chimpanzee vowel-like sounds and voice quality suggest formant space expansion through the hominoid lineage

The origins of human speech are obscure; it is still unclear what aspects are unique to our species or shared with our evolutionary cousins, in part due to a lack of a common framework for comparison. We asked what chimpanzee and human vocal production acoustics have in common. We examined visible supra-laryngeal articulators of four major chimpanzee vocalizations (hoos, grunts, barks, screams) and their associated acoustic structures, using techniques from human phonetic and animal communication analysis. Data were collected from wild adult chimpanzees, Taï National Park, Ivory Coast. Both discriminant and principal component classification procedures revealed classification of call types. Discriminating acoustic features include voice quality and formant structure, mirroring phonetic features in human speech. Chimpanzee lip and jaw articulation variables also offered similar discrimination of call types. Formant maps distinguished call types with different vowel-like sounds. Comparing our results with published primate data, humans show less F1 – F2 correlation and further expansion of the vowel space, particularly for [i] sounds. Unlike recent studies suggesting monkeys achieve human vowel space, we conclude from our results that supra-laryngeal articulatory capacities show moderate evolutionary change, with vowel space expansion continuing through hominoid evolution. Studies on more primate species will be required to substantiate this.

This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part II)’.  Read article here.

28 October 2021

Limited Scope for Group Coordination in Stylistic Variations of Kolam Art

In large, complex societies, assorting with others with similar social norms or behaviors can facilitate successful coordination and cooperation. The ability to recognize others with shared norms or behaviors is thus assumed to be under selection. As a medium of communication, human art might reflect fitness-relevant information on shared norms and behaviors of other individuals thus facilitating successful coordination and cooperation. Distinctive styles or patterns of artistic design could signify migration history, different groups with a shared interaction history due to spatial proximity, as well as individual-level expertise and preferences. In addition, cultural boundaries may be even more pronounced in a highly diverse and socially stratified society. In the current study, we focus on a large corpus of an artistic tradition called kolam that is produced by women from Tamil Nadu in South India (N = 3, 139 kolam drawings from 192 women) to test whether stylistic variations in art can be mapped onto caste boundaries, migration and neighborhoods. Since the kolam art system with its sequential drawing decisions can be described by a Markov process, we characterize variation in styles of art due to different facets of an artist's identity and the group affiliations, via hierarchical Bayesian statistical models. Our results reveal that stylistic variations in kolam art only weakly map onto caste boundaries, neighborhoods, and regional origin. In fact, stylistic variations or patterns in art are dominated by artist-level variation and artist expertise. Our results illustrate that although art can be a medium of communication, it is not necessarily marked by group affiliation. Rather, artistic behavior in this context seems to be primarily a behavioral domain within which individuals carve out a unique niche for themselves to differentiate themselves from others. Our findings inform discussions on the evolutionary role of art for group coordination by encouraging researchers to use systematic methods to measure the mapping between specific objects or styles onto groups. Read article here.

1 October 2021

Estimating the reproducibility of social learning research published between 1955 and 2018

Reproducibility is integral to science, but difficult to achieve. Previous research has quantified low rates of data availability and results reproducibility across the biological and behavioural sciences. Here, we surveyed 560 empirical publications, published between 1955 and 2018 in the social learning literature, a research topic that spans animal behaviour, behavioural ecology, cultural evolution and evolutionary psychology. Data were recoverable online or through direct data requests for 30% of this sample. Data recovery declines exponentially with time since publication, halving every 6 years, and up to every 9 years for human experimental data. When data for a publication can be recovered, we estimate a high probability of subsequent data usability (87%), analytical clarity (97%) and agreement of published results with reproduced findings (96%). This corresponds to an overall rate of recovering data and reproducing results of 23%, largely driven by the unavailability or incompleteness of data. We thus outline clear measures to improve the reproducibility of research on the ecology and evolution of social behaviour. Read article here.

30 September 2021

Reproductive consequences of material use in avian nest construction

Birds’ nests represent a rich behavioural ‘fingerprint’, comprising several important decisions—not the least of which is the selection of appropriate material. Material selection in nest-building birds is thought to reflect, in part, builder-birds’ use of the ‘best’ material—in terms of physical properties (e.g., rigidity)—refined across generations. There is, however, little experimental evidence to link the physical properties of nest material to both birds’ nest-building and breeding performance. We examined individual-level material-use consequences for breeding zebra finches by manipulating the kind of material available to laboratory-housed pairs: stiff or flexible same-length string. We show that higher fledgling numbers were related to: (i) fewer pieces used in nest construction by stiff-string builders; and conversely, (ii) more pieces used in nest construction by flexible-string builders. Together, these data suggest that physical differences in nest material can affect avian reproduction (here, the trade-off between nest-construction investment and fledgling success), highlighting the adaptive significance of nest-building birds’ material selectivity. Read article here.

29 September 2021

APOE4 is associated with elevated blood lipids and lower levels of innate immune biomarkers in a tropical Amerindian subsistence population

In post-industrial settings, apolipoprotein E4 (APOE4) is associated with increased cardiovascular and neurological disease risk. However, the majority of human evolutionary history occurred in environments with higher pathogenic diversity and low cardiovascular risk. We hypothesize that in high-pathogen and energy-limited contexts, the APOE4 allele confers benefits by reducing innate inflammation when uninfected, while maintaining higher lipid levels that buffer costs of immune activation during infection. Among Tsimane forager-farmers of Bolivia (N = 1266, 50% female), APOE4 is associated with 30% lower C-reactive protein, and higher total cholesterol and oxidized LDL. Blood lipids were either not associated, or negatively associated with inflammatory biomarkers, except for associations of oxidized LDL and inflammation which were limited to obese adults. Further, APOE4 carriers maintain higher levels of total and LDL cholesterol at low body mass indices (BMIs). These results suggest that the relationship between APOE4 and lipids may be beneficial for pathogen-driven immune responses and unlikely to increase cardiovascular risk in an active subsistence population. Read article here.

28 August 2021

How small-scale societies achieve large-scale cooperation

For most of our species’ history, humans have lived in relatively small subsistence communities, often called small-scale societies. While these groups lack centralized institutions, they can and often do maintain large-scale cooperation. Here, we explore several mechanisms promoting cooperation in small-scale societies, including (a) the development of social norms that encourage prosocial behavior, (b) reciprocal exchange relationships, (c) reputation that facilitates high-cost cooperation, (d) relational wealth, and (e) risk buffering institutions. We illustrate these with ethnographic and psychological evidence from contemporary small-scale societies. We argue that these mechanisms for cooperation helped past and present small-scale communities adapt to diverse ecological and social niches. Read article here.

2 August 2021

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. Read article here.

14 July 2021

Animal culture research should include avian nest construction

Material culture—that is, group-shared and socially learned object-related behaviour(s)—is a widespread and diverse phenomenon in humans. For dec-ades, researchers have sought to confirm the existence of material culture in non-human animals; however, the main study systems of interest—namely, tool making and/or using non-human primates and corvids—cannot provide such confirmatory evidence: because long-standing ethical and logistical con-straints handicap the collection of necessary experimental data. Synthesizing evidence across decades and disciplines, here, I present a novel framework for (mechanistic, developmental, behavioural, and comparative) study on animal material culture: avian nest construction. Read full article here.

25 June 2021

Explaining Cross-Cultural Variation in Mirror Self-Recognition: New Insights Into the Ontogeny of Objective Self-Awareness

Mirror self-recognition (MSR) is considered to be the benchmark of objective self-awareness—the ability to think about oneself. Cross-cultural research showed that there are systematic differences in toddlers’ MSR abilities between 18 and 24 months. Understanding whether these differences result from systematic variation in early social experiences will help us understand the processes through which objective self-awareness develops. In this study, we examined 57 18- to 22-month-old toddlers (31 girls) and their mothers from two distinct sociocultural contexts: urban Canada (58% of the subsample were Canadian-born native English-speakers) and rural Vanuatu, a small-scale island society located in the South Pacific. We had two main goals: (a) to identify the social-interactional correlates of MSR ability in this cross-cultural sample, and (b) to examine whether differences in passing rates could be attributed to confounding factors. Consistent with previous cross-cultural research, ni-Vanuatu toddlers passed the MSR test at significantly lower rates (7%) compared to their Canadian counterparts (68%). Among a suite of social interactive variables, only mothers’ imitation of their toddlers’ behavior during a free play session predicted MSR in the entire sample and maternal imitation partially mediated the effects of culture on MSR. In addition, low passing rates among ni-Vanuatu toddlers could not be attributed to reasons unrelated to self-development (i.e., motivation to show mark-directed behavior, understanding mirror-correspondence, representational thinking). This suggests that differences in MSR passing rates reflect true differences in self-recognition, and that parental imitation may have an important role in shaping the construction of visual self-knowledge in toddlers. Read full article here.

5 May 2021

Coalitions and conflict: A longitudinal analysis of men’s politics

To negotiate conflict and navigate status hierarchy, individuals in many species form coalitions. We describe inter-personal conflicts and assess theories of coalition formation in a small-scale human society. Based on longitudinal and cross-sectional social network analysis of men in two communities of Tsimane forager–horticulturalists, we find evidence of reciprocity in coalitional support, as well as evi-dence of transitivity: an ally of my ally is likely to become my ally. We find mixed support for coalition formation between individuals who share a common adversary. Coalition formation was also predicted by food- and labour-sharing and especially by kinship. Physically formidable men and men higher in infor-mal status were more likely to provide coalitional support over time; evidence was mixed that they receive more coalitional support. The highest status men are hubs of a dense coalitional support network that indirectly link all men in the community. These findings suggest that male coalition formation is multiply motivated, and in general reveals the political dynamics that structure men’s lives in small, relatively egali-tarian communities. Read article here.

3 May 2021

Children's fingernail cortisol among BaYaka foragers of the Congo Basin: associations with fathers' roles

Children and mothers’ cortisol production in response to family psychosocial conditions, including parenting demands, family resource availability and parental conflict, has been extensively studied in the United States and Europe. Less is known about how such family dynamics relate to family members' cortisol in societies with a strong cultural emphasis on cooperative caregiving. We studied a cumulative indicator of cortisol production, measured from fingernails, among BaYaka forager children (77 samples, n = 48 individuals) and their parents (78 samples, n = 49) in the Congo Basin. Men ranked one another according to locally valued roles for fathers, including providing resources for the family, sharing resources in the community and engaging in less marital conflict. Children had higher cortisol if their parents were ranked as having greater parental conflict, and their fathers were seen as less effective providers and less generous sharers of resources in the community. Children with lower triceps skinfold thickness (an indicator of energetic condition) also had higher cortisol. Parental cortisol was not significantly correlated to men's fathering rankings, including parental conflict. Our results indicate that even in a society in which caregiving is highly cooperative, children's cortisol production was nonetheless correlated to parental conflict as well as variation in locally defined fathering quality.

This article is part of the theme issue ‘Multidisciplinary perspectives on social support and maternal–child health’. Read article here.

8 April 2021

Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei)

Acoustic signals that reliably indicate body size, which usually determines competitive ability, are of particular interest for understanding how animals assess rivals and choose mates. Whereas body size tends to be negatively associated with formant dispersion in animal vocalizations, non-vocal signals have received little attention. Among the most emblematic sounds in the animal kingdom is the chest beat of gorillas, a non-vocal signal that is thought to be important in intra and inter-sexual competition, yet it is unclear whether it reliably indicates body size. We examined the relationship among body size (back breadth), peak frequency, and three temporal characteristics of the chest beat: duration, number of beats and beat rate from sound recordings of wild adult male mountain gorillas. Using linear mixed models, we found that larger males had significantly lower peak frequencies than smaller ones, but we found no consistent relationship between body size and the temporal characteristics measured. Taken together with earlier findings of positive correlations among male body size, dominance rank and reproductive success, we conclude that the gorilla chest beat is an honest signal of competitive ability. These results emphasize the potential of non-vocal signals to convey important information in mammal communication. Read article here.

13 March 2021

A refitting experiment on long bone identification

Refitting is an important analytical tool in archaeology that can yield valuable information on site formation processes and on the range of activities practiced at a site, including tool production, tool curation, and discard behavior, among others. In the present paper, we use refit data from a control assemblage of red deer (Cervus elaphus) long bones to assess problems of specimen identification and representation in an experiment where bones were processed for marrow. Three goals motivated this experiment: (i) to assess how different methods of NISP (number of identified specimens) calculation affect comparisons of the relative abundances of long bone regions, (ii) to evaluate whether long bone shaft regions vary with respect to the probability of identification, and (iii) to ascertain the potential refit rate for a well-preserved and fully-collected sample of faunal specimens. Our results show no statistical differences in terms of patterns of skeletal representation between the two methods of NISP calculation (single vs. multiple NISP counts) that we assessed. Our data also indicate that the shape, particularly the cross-section, of fragments clearly impacts the probability of identification and refitting. Moreover, the refitting experiment reveals that, in ideal conditions, a majority of specimens (>95%) from the NISP sample can be refitted, which leads to largely reconstructed skeletal elements. Thus, the comparatively very low refit rates recorded in archaeological sites, including samples that are well preserved, suggest that the often limited extent of excavations, along with offsite discard and/or extensive sharing of parts, substantially reduce the possibility of finding refits in a faunal sample. Read article here.

09 March 2021

How can evolutionary and biological anthropologists engage broader audiences?


With our diverse training, theoretical and empirical toolkits, and rich data, evolutionary and biological anthropologists (EBAs) have much to contribute to research and policy decisions about climate change and other pressing social issues. However, we remain largely absent from these critical, ongoing efforts. Here, we draw on the literature and our own experiences to make recommendations for how EBAs can engage broader audiences, including the communities with whom we collaborate, a more diverse population of students, researchers in other disciplines and the development sector, policymakers, and the general public. These recommendations include: (1) playing to our strength in longitudinal, place-based research, (2) collaborating more broadly, (3) engaging in greater public communication of science, (4) aligning our work with open-science practices to the extent possible, and (5) increasing diversity of our field and teams through intentional action, outreach, training, and mentorship.


We EBAs need to put ourselves out there: research and engagement are complementary, not opposed to each other. With the resources and workable examples we provide here, we hope to spur more EBAs to action. Read article here.

1 March 2021

Entropy trade-offs in artistic design: A case study of Tamil kolam

From an evolutionary perspective, art presents many puzzles. Humans invest substantial effort in generating apparently useless displays that include artworks. These vary greatly from ordinary to intricate. From the perspective of signalling theory, these investments in highly complex artistic designs can reflect information about individuals and their social standing. Using a large corpus of kolam art from South India (N = 3139 kolam from 192 women), we test a number of hypotheses about the ways in which social stratification and individual differences affect the complexity of artistic designs. Consistent with evolutionary signalling theories of constrained optimisation, we find that kolam art tends to occupy a ‘sweet spot’ at which artistic complexity, as measured by Shannon information entropy, remains relatively constant from small to large drawings. This stability is maintained through an observable, apparently unconscious trade-off between two standard information-theoretic measures: richness and evenness. Although these drawings arise in a highly stratified, caste-based society, we do not find strong evidence that artistic complexity is influenced by the caste boundaries of Indian society. Rather, the trade-off is likely due to individual-level aesthetic preferences and differences in skill, dedication and time, as well as the fundamental constraints of human cognition and memory. Read article here.

1 March 2021

The Potential to Infer the Historical Pattern of Cultural Macroevolution

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. Read full article here.

23 February 2021

Taking charge and stepping in: Individuals who punish are rewarded with prestige and dominance

A hallmark of human societies is the scale at which we cooperate with many others, even when they are not closely genetically related to us. One proposed mechanism that helps explain why we cooperate is punishment; cooperation may pay and proliferate if those who free ride on the cooperation of others are punished. Yet this ‘solu-tion’ raises another puzzle of its own: Who will bear the costs of punishing? While the deterrence of free‐riders via punishment serves collective interests, presumably any single individual—who has no direct incentive to punish—is better off letting others pay the costs of punishment. However, emerging theory and evidence indicate that, while punishment may at times be a costly act, certain individuals are better able to ‘afford’ to pay the price of punishment and are often consequentially rewarded with fitness‐enhancing reputation benefits. Synthesizing across these latest lines of research, we propose a novel frame-work that considers how high status individuals—that is, individuals with greater prestige or dominance—enjoy lower punishment costs. These individuals are thus more willing to punish, and through their punitive action can in turn reap reputational rewards by further gaining more prestige or dominance. These reputational gains, which work in concert to promote the social success of punishers, recoup the costs of punishing. Together, these lines of work suggest that while punishment is often assumed to be altruistic, it need not always depend on altruism, and mo-tivations to punish may at times be self‐interested and driven (whether consciously or unconsciously) by reputa-tional benefits. Read article here.

19 February 2021

Using touchscreen equipped operant chambers to study animal cognition. Benefits, limitations, and advice

Operant chambers are small enclosures used to test animal behavior and cognition. While traditionally reliant on simple technologies for presenting stimuli (e.g., lights and sounds) and recording responses made to basic manipulanda (e.g., levers and buttons), an increas-ing number of researchers are beginning to use Touchscreen-equipped Operant Chambers (TOCs). These TOCs have obvious advantages, namely by allowing researchers to present a near infinite number of visual stimuli as well as increased flexibility in the types of responses that can be made and recorded. We trained wild-caught adult and juvenile great-tailed grackles (Quiscalus mexicanus) to complete experiments using a TOC. We learned much from these efforts, and outline the advantages and disadvantages of our protocols. Our training data are summarized to quantify the variables that might influence participation and success, and we discuss important modifications to facilitate animal engagement and participation in various tasks. Finally, we provide a “training guide” for creating experiments using PsychoPy, a free and open-source software that was incredibly useful during these endeavors. This article, therefore, should serve as a resource to those interested in switch-ing to or maintaining a TOC, or who similarly wish to use a TOC to test the cognitive abilities of non-model species or wild-caught individuals. Read full article here.

16 February 2021

Very Low Prevalence and Incidence of Atrial Fibrillation among Bolivian Forager-Farmers

Background: Atrial fibrillation is the most common arrhythmia in post-industrialized populations. Older age, hypertension, obesity, chronic inflammation, and diabetes are significant atrial fibrillation risk factors, suggesting that modern urban environments may promote atrial fibrillation.

Objective: Here we assess atrial fibrillation prevalence and incidence among tropical horticulturalists of the Bolivian Amazon with high levels of physical activity, a lean diet, and minimal coronary atherosclerosis, but also high infectious disease burden and associated inflammation.

Methods: Between 2005–2019, 1314 Tsimane aged 40–94 years (52% female) and 534 Moseten Amerindians aged 40–89 years (50% female) underwent resting 12-lead electrocardiograms to assess atrial fibrillation prevalence. For atrial fibrillation incidence assessment, 1059 (81% of original sample) Tsimane and 310 Moseten (58%) underwent additional ECGs (mean time to follow up 7.0, 1.8 years, respectively).

Findings:Only one (male) of 1314 Tsimane (0.076%) and one (male) of 534 Moseten (0.187%) demonstrated atrial fibrillation at baseline. There was one new (female) Tsimane case in 7395 risk years for the 1059 participants with >1 ECG (incidence rate = 0.14 per 1,000 risk years). No new cases were detected among Moseten, based on 542 risk years.

Conclusion: Tsimane and Moseten show the lowest levels of atrial fibrillation ever reported, 1/20 to ~1/6 of rates in high-income countries. These findings provide additional evidence that a subsistence lifestyle with high levels of physical activity, and a diet low in processed carbohydrates and fat is cardioprotective, despite frequent infection-induced inflammation. Findings suggest that atrial fibrillation is a modifiable lifestyle disease rather than an inevitable feature of cardiovascular aging. Read article here.

9 February 2021

Manipulative and Technological Skills Do Not Require a Slow Life History

A recent developmental study reveals that—at least in primates—a slow life history might be a prerequisite for skilled manipulation and technological behavior. This supposition, however, demands critical evaluation because other taxa with a much shorter lifespan also exhibit dexterous object handling and material technology. By examining object-handling and nest-building data from, respectively, mice and birds, we show that a slow life history does not govern the evolution of manipulative and technological ability. More generally, we highlight the need for a comparative, cross-taxa approach to understand drivers—such as differences in life history, ecology, task complexity, and brain size—of seemingly sophisticated behavior. Read article here.

20 January 2021

Demonstrating the Utility of Egocentric Relational Event Modeling Using Focal Follow Data from Congolese BaYaka Children and Adolescents Engaging in Work and Play

Temporal aspects of child and adolescent time allocation in diverse cultural settings have been difficult to model using conventional statistical techniques. A new statistical approach, Egocentric Relational Event Modelling (EREM), allows for the simultaneous modelling of activity frequency, duration, and sequencing. Here, EREM is applied to a focal follow dataset of Congolese BaYaka forager child and adolescent play and work activities. Results show that, as children age, they engage in less frequent and extended play bouts and more frequent and extended work bouts. Bout frequency and duration were a more sensitive measure for early sex differences than overall time allocation. Sequential patterns of work and play suggest that these activities have short-term energetic trade-offs. This article demonstrates that EREM can reveal stable and variable patterns in child development.

Observational studies of children’s time allocation demonstrate that age, sex, family circumstance, and culture influence activity budgets (Blurton Jones 1972; Bock and Johnson 2004; Gosso 2010; Munroe et al. 1984; Whiting and Whiting 1975). However, temporal aspects of behavior have been difficult to model using conventional statistical techniques. Here, we demonstrate the applicability of the Egocentric Relational Event Model (EREM) using a focal follow dataset of BaYaka child and adolescent play and work activities (Butts 2008; Marcum and Butts 2015). While EREM is not the only statistical framework to accommodate sequential data, it is unique in the flexibility with which it can simultaneously model the probability and duration of multiple events. Read article here.

20 January 2021

Socialization, Autonomy, and Cooperation: Insights from Task Assignment Among the Egalitarian BaYaka

Across diverse societies, task assignment is a socialization practice that gradually builds children's instrumental skills and integrates them into the flow of daily activities in their community. However, psychosocial tensions can arise when cooperation is demanded from children. Through their compliance or noncompliance, they learn cultural norms and values related to autonomy and obligations to others. Here, we investigate task assignment among BaYaka foragers of the Republic of the Congo, among whom individual autonomy is a foundational cultural schema. Our analysis is based on systematic observations, participant observation, and informal interviews with adults about their perspectives on children's learning and noncompliance, as well as their own learning experiences growing up. We find that children are assigned fewer tasks as they age. However, children's rate of noncompliance remains steady across childhood, indicating an early internalization of a core value for autonomy. Despite demonstrating some frustration with children's noncompliance, adults endorse their autonomy and remember task assignment being critical to their own learning as children. We argue that cross-cultural variation in children's compliance with task assignments must be understood within a larger framework of socialization as constituted by many integrated and bidirectional processes embedded in a social, ecological, and cultural context. Read article here.

15 January 2021

Local convergence of behavior across species

Behavior is a way for organisms to respond flexibly to the environmental conditions they encounter. Our own species occurs in a variety of habits, sharing these with a large number of other species, but it remains unclear to what degree a shared environment constrains behavior. Here, we show that foraging human populations and non-human mammal and bird species who live in a given environment show high levels of similarity in their foraging, reproductive, and social behavior. Our findings suggest that local conditions may select for similar behaviors in both humans and non-human animals. Read full article here.

7 January 2021

Human behavioral ecology and niche construction

We examine the relationship between niche construction theory (NCT) and human behavioral ecology (HBE), two branches of evolutionary science that are important sources of theory in archeology. We distinguish between formal models of niche con-struction as an evolutionary process, and uses of niche construction to refer to a kind of human behavior. Formal models from NCT examine how environmental modifica-tion can change the selection pressures that organisms face. In contrast, formal models from HBE predict behavior assuming people behave adaptively in their local setting, and can be used to predict when and why people engage in niche construction. We emphasize that HBE as a field is much broader than foraging theory and can incorpo-rate social and cultural influences on decision-making. We demonstrate how these approaches can be formally incorporated in a multi-inheritance framework for evolu-tionary research, and argue that archeologists can best contribute to evolutionary the-ory by building and testing models that flexibly incorporate HBE and NCT elements. Read article here.

28 November 2020

Want climate-change adaptation? Evolutionary theory can help

The idea of adaptation, in which an organism or population becomes better suited to its environment, is used in a variety of disciplines. Originating in evolutionary biology, adaptation has been a central theme in biological anthropology and human ecology. More recently, the study of adaptation in the context of climate change has become an important topic of research in the social sciences. While there are clearly commonalities in the different uses of the concept of adaptation in these fields, there are also substantial differences. We describe these differences and suggest that the study of climate-change adaptation could benefit from a re-integration with biological and evolutionary conceptions of human adaptation. This integration would allow us to employ the substantial theoretical tools of evolutionary biology and anthropology to understand what promotes or impedes adaptation. The evolutionary perspective on adaptation focuses on diversity because diversity drives adaptive evolution. Population structures are also critical in facilitating or preventing adaptation to local environmental conditions. This suggests that climate-change adaptation should focus on the sources of innovation and social structures that nurture innovations and allow them to spread. Truly innovative ideas are likely to arise on the periphery of cohesive social groups and spread inward. The evolutionary perspective also suggests that we pay careful attention to correlated traits, which can distort adaptive trajectories, as well as to the importance of risk management in adaptations to variable or uncertain environments. Finally, we suggest that climate-change adaptation could benefit from a broader study of how local groups adapt to their dynamic environments, a process we call “autochthonous adaptation.” Read article here.

7 November 2020

“All the problems in the community are multifaceted and related to each other”: Inuit concerns in an era of climate change


Human dimensions of climate change research in the Arctic often proposes ways for local communities to adapt to changes to their environment, foregrounding problems posed by climate change while treating social, political, and economic factors as background conditions. We explore the relevance of this research paradigm for Inuit by examining how Inuit from Kangiqsujuaq present and discuss the major issues facing their community.


We thematically code and analyze the responses of 107 Inuit to three free-response questions about the problems facing their community and the best things about their community. The data were collected as part of a questionnaire for a project focused on food security and food sharing conducted in Kangiqsujuaq, Nunavik, in 2013 to 2014.


Few respondents mentioned issues relating to climate change among the most pressing problems faced by their community. Rather, a suite of interconnected social and economic issues, particularly substance abuse and the cost of living, emerged as the main concerns of Kangiqsujuarmiut. However, the environment was a central theme in respondents' favorite thing about their community.


In light of the concerns identified by Inuit, we argue that much research on climate change makes incorrect a priori assumptions and consequently fails to capture aspects of Arctic socioecological systems that are essential for how Inuit are responding to climate change. An inductive, open-ended approach can help produce research more relevant to communities. Read article here.

13 August 2020

Comparing Social Network Structures Generated through Sociometric and Ethnographic Methods

Social connections between individuals are often an important source of information for both quantitative and qualitative anthropological research. Here, we seek to understand the relative strengths and weaknesses of sociometric and ethnographic representations of social connections. We do this by comparing network data collected using a sociometric technique (a name generator) with a network drawn by project ethnographers representing their understanding of social structure in the study population. We find many similarities in the two networks, but they offer somewhat different perspectives into the local social structure. Although the ethnographic network is shaped by the ethnographers’ deeper knowledge of a subset of network members, individuals with high degree (but not betweenness) in the sociometric network are generally present in the ethnographic network. The ethnographers’ interpretation of the factors that lead to high degree centrality in the network is broadly accurate. However, the sociometric network is characterized by a high level of transitivity not seen in the ethnographic network. We consider the importance of the differences we observe for ethnographic practice. Read full article here.

28 July 2020

Fatherhood, egalitarianism, and child health in two small-scale societies in the Republic of the Congo

Objectives: The study goals were to (a) characterize the cultural model of fatherhood among the BaYaka, a community of egalitarian foragers in the Republic of the Congo; (b) test if BaYaka fathers' quality in relation to the cultural model predicts their children's energetic status; and (c) compare the variance in BaYaka children's energetic status to that of children of neighboring Bondongo fisher-farmers, among whom there is less cooperative caregiving, less resource sharing, and greater social inequality.
Methods: We used informal interviews to establirmal interviews to establish the cultural model of fatherhood, which we used to build a peer ranking task to quantify father quality. Children's energetic status was assessed by measuring height, weight, and triceps skinfold thickness. We then tested for associations between father quality scores derived from the ranking task and children's energetic status using ordinary least squares regression. Equality of variance tests were used to compare BaYaka and Bondongo children's energetic statuses.
Results: The BaYaka described fathers as responsible for acquiring resources and maintaining marital harmony, welcoming others to the community and sharing well with them, and teaching their children about the forest. Agreement on men's quality in these domains was high, but father quality did not significantly predict children's energetic status. BaYaka children had lower variance in energetic status overall compared to Bondongo children.
Conclusions: We suggest that the core BaYaka values and practices that maintain egalitarian social relations and distribution of resources help buffer children's health and well-being from variation in their fathers' qualities in culturally valued domains. Read fullarticle here.

25 June 2020

The life history of human foraging: Cross-cultural and individual variation

Human adaptation depends on the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring hunters’ increases and declines of skill from approximately 23,000 hunting records generated by more than 1800 indi-viduals at 40 locations. The data reveal an average age of peak productivity between 30 and 35 years of age, although high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more on heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the coevolution of human life history and cultural adaptation. Read full article here.

22 June 2020

Competing forces of withdrawal and disease avoidance in the risk networks of people who inject drugs

We analyze a network of needle-sharing ties among 117 people who inject drugs (PWID) in rural Puerto Rico, using exponential random graph modeling to examine whether network members engage in partner restriction to lower their risk of contracting HIV or hepatitis C (HCV), or in informed altruism to prevent others from contracting these infections. Although sharing of used syringes is a significant risk factor for transmission of these diseases among PWID, we find limited evidence for partner restriction or informed altruism in the network of reported needle-sharing ties. We find however that sharing of needles is strongly reciprocal, and individuals with higher injection frequency are more likely to have injected with a used needle. Drawing on our ethnographic work, we discuss how the network structures we observe may relate to a decision-making rationale focused on avoiding withdrawal sickness, which leads to risk-taking behaviors in this poor, rural context where economic considerations often lead PWID to cooperate in the acquisition and use of drugs. Read full text here.

2 April 2020

Market integration reduces kin density in women’s ego-networks in rural Poland

It is widely assumed that as populations become more market integrated the ‘inner circles’ of people’s social networks become less densely connected and family-oriented. This ‘loosening’ of kin networks may fundamentally alter the social dynamics of reproduction, facilitating demographic transitions to low fertility. Few data exist to test this hypothesis. Previous research in urbanized populations has not explicitly measured kin density in ego-networks, nor assessed how market integration influences network structure at different levels of aggregation. Here I analyze the ego-networks of ~2000 women in 22 rural Polish communities transitioning from subsistence farming to market-dependence. I compare how egonetwork size, density and kin density co-vary with household and community-level market integration. Market integration is associated with less kin-dense networks, but not necessarily less dense ones, and is unrelated to network size. Declining kin density during economic transitions may be a critical mechanism for the broader cultural transmission of low fertility values. Read full article here.

10 February 2020

Field evidence for two paths to cross-cultural competence: implications for cultural dynamics

Interaction between members of culturally distinct (ethnic) groups is an important driver of the evolutionary dynamics of human culture, yet relevant mechanisms remain underexplored. For example, cultural loss resulting from integration with culturally distinct immigrants or colonial majority populations remains a topic whose political salience exceeds our understanding of mechanisms that may drive or impede it. For such dynamics, one mediating factor is the ability to interact successfully across cultural boundaries (cross-cultural competence). However, measurement difficulties often hinder its investigation. Here, simple field methods in a uniquely suited Amazonian population and Bayesian item–response theory models are used to derive the first experience-level measure of cross-cultural competence, as well as evidence for two developmental paths: cross-cultural competence may emerge as a side effect of adopting out-group cultural norms, or it may be acquired while maintaining in-group norms. Ethnographic evidence suggests that the path taken is a likely consequence of power differences in inter- vs intra-group interaction. The former path, paralleling language extinction, may lead to cultural loss; the latter to cultural sustainability. Recognition of such path-dependent effects is vital to theory of cultural dynamics in humans and perhaps other species, and to effective policy promoting cultural diversity and constructive inter-ethnic interaction. Read full article here.

1 February 2020

Who teaches children to forage? Exploring the primacy of child-to-child teaching among Hadza and BaYaka Hunter-Gatherers of Tanzania and Congo

Teaching is cross-culturally widespread but few studies have considered children as teachers as well as learners. This is surprising, since forager children spend much of their time playing and foraging in child-only groups, and thus, have access to many potential child teachers. Using the Social Relations Model, we examined the prevalence
of child-to-child teaching using focal follow data from 35 Hadza and 38 BaYaka 3- to 18-year-olds. We investigated the effect of age, sex and kinship on the teaching of subsistence skills. We found that child-to-child teaching was more frequent than adult-child teaching. Additionally, children taught more with age, teaching was more likely to occur within same-sex versus opposite-sex dyads, and close kin were more likely to teach than non-kin. The Hadza and BaYaka also showed distinct learning patterns; teaching was more likely to occur between sibling dyads among the Hadza than among the BaYaka, and a multistage learning model where younger children learn from peers, and older children from adults, was evident for the BaYaka, but not for the Hadza. We attribute these differences to subsistence and settlement patterns. These findings highlight the role of children in the intergenerational transmission of subsistence skills. Read full text here.

10 December 2019

Challenges of Learning to Escape Evolutionary Traps

Many animals respond well behaviorally to stimuli associated with human-induced rapid environmental change (HIREC), such as novel predators or food sources. Yet others make errors and succumb to evolutionary traps: approaching or even preferring low quality, dangerous or toxic options, avoiding beneficial stimuli, or wasting resources responding to stimuli with neutral payoffs. A common expectation is that learning should help animals adjust to HIREC; however, learning is not always expected or even favored in many scenarios that expose animals to ecological and evolutionary traps. We propose a conceptual framework that aims to explain variation in when learning can help animals avoid and escape traps caused by HIREC. We first clarify why learning to correct two main types of errors (avoiding beneficial options and approaching detrimental options) might be difficult (limited by constraints). We then identify and discuss several key behavioral mechanisms (adaptive sampling, generalization, habituation, reversal learning) that can be targeted to help animals learn to avoid traps. Finally, we discuss how individual differences in neophobia/neophilia and personality relate to learning in the context of HIREC traps, and offer some general guidance for disarming traps. Given how devastating traps can be for animal populations, any breakthrough in mitigating trap outcomes via learning could make the difference in developing effective solutions. Read full article here.

5 December 2019

Cultural linkage: the influence of package transmission on cultural dynamics

Many cultural traits are not transmitted independently, but together as a package. This can happen because, for example, media may store information together making it more likely to be transmitted together, or through cognitive mechanisms such as causal reasoning. Evolutionary biology suggests that physical linkage of genes (being on the same chromosome) allows neutral and maladaptive genes to spread by hitchhiking on adaptive genes, while the pairwise difference between neutral genes is unaffected. Whether packaging may lead to similar dynamics in cultural evolution is unclear. To understand the effect of cultural packages on cultural evolutionary dynamics, we built an agent-based simulation that allows links to form and break between cultural traits. During transmission, one trait and others that are directly or indirectly connected to it are transmitted together in a package. We compare variation in cultural traits between different rates of link formation and breakage and find that an intermediate frequency of links can lower cultural diversity, which can be misinterpreted as a signature of payoff bias or conformity. Further, cultural hitchhiking can occur when links are common. Read full article here.

11 November 2019

Lions, Bylaws, and Conservation Metrics

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. Read full article here.

15 August 2019

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, ... Read full article here.

23 July 2019

Patterns of paternal investment predict cross-cultural variation in jealous response

Long-lasting, romantic partnerships are a universal feature of human societies, but almost as ubiquitous is the risk of instability when one partner strays. Jealous response to the threat of infidelity is well studied, but most empirical work on the topic has focused on a proposed sex difference in the type of jealousy (sexual or emotional) that men and women find most upsetting, rather than on how jealous response varies1,2. This stems in part from the predominance of studies using student samples from industrialized populations, which represent a relatively homogenous group in terms of age, life history stage and social norms3,4. To better understand variation in jealous response, we conducted a 2-part study in 11 populations (1,048 individuals). In line with previous work, we find a robust sex difference in the classic forced-choice jealousy task. However, we also show substantial variation in jealous response across populations. Read full article here.

27 June 2019

Counter-Culture: Does Social Learning Help or Hinder Adaptive Response to Human-Induced Rapid Environmental Change?

Human-induced rapid environmental change (HIREC) poses threats to a variety of species, and if or how it changes phenotypes is a question of central importance bridging evolutionary ecology and conservation management. Social learning is one type of phenotypic plasticity that can shape organismal responses to HIREC; it allows organisms to acquire phenotypes on a timescale that closely tracks environmental change while minimizing the costs of individual learning. A common assumption in behavioral ecology, is that social learning is generally an adaptive way to cope with HIREC by facilitating the rapid spread of innovative responses to change. While this can be true, social learning can also be maladaptive. It may hinder the spread of adaptive behavior by causing a carryover of old, no longer adaptive behaviors that slow the response to HIREC or even promote the spread of maladaptive behaviors. Here, we present a conceptual framework outlining how an organism's evolutionary history can shape cognitive mechanisms, social behavior, and population composition, which in turn affect how an organism responds to HIREC. Read full article here.

12 June 2019

Hidden Markov Models Reveal Tactical Adjustment of Temporally Clustered Courtship Displays in Response to the Behaviors of a Robotic Female

We present a statistical approach—a custom-built hidden Markov model (HMM)—that is broadly applicable to the analysis of temporally clustered display events, as found in many animals, including
birds, orthopterans, and anurans. This HMM can simultaneously estimate both the expected lengths of each animal’s display bouts and their within-bout display rates. We highlight the HMM’s ability to estimate changes in animals’ display effort over time and across different social contexts, using data from male greater sage grouse (Centrocercus urophasianus). Male display effort was modeled across three sites in two experimental treatments (robotic female simulating interested or uninterested behavior) and in the presence or absence of live females. Across contexts, we show that sage grouse males primarily adjust their bout lengths rather than their within-bout display rates. Males’ responses to female behavior were correlated with male mating success: males with more matings showed high display persistence regardless of female behavior, whilemales with fewer matings
tended to invest selectively in females that were already showing interest in mating. Additionally, males with higher mating success responded more to the presence of a female than males with fewer
matings did. We conclude with suggestions for adapting our HMM approach for use in other animal systems. Read the full article.

15 May 2019

Rapid environmental change in games: complications and counter- intuitive outcomes

Human-induced rapid environmental change (HIREC) has recently led to alterations in the fitness and behavior of many organisms. Game theory is an important tool of behavioral ecology for analyzing evolutionary situations involving multiple individuals. However, game theory bypasses the details by which behavioral phenotypes are determined, taking the functional perspective straight from expected payoffs to predicted frequencies of behaviors. In contrast with optimization approaches, we identify that to use existing game theoretic models to predict HIREC effects, additional mechanistic details (or assumptions) will often be required. We illustrate this in relation to the hawk-dove game by showing that three different mechanisms, each of which support the same ESS prior to HIREC (fixed polymorphism, probabilistic choice, or cue dependency), can have a substantial effect on behavior (and success) following HIREC. Read the full article.

02 May 2019

Machine behaviour

Machines powered by artificial intelligence increasingly mediate our social, cultural, economic and political interactions. Understanding the behaviour of artificial intelligence systems is essential to our ability to control their actions, reap their benefits and minimize their harms. Here we argue that this necessitates a broad scientific research agenda to study machine behaviour that incorporates and expands upon the discipline of computer science and includes insights from across the sciences. We first outline a set of questions that are fundamental to this emerging field and then explore the technical, legal and institutional constraints on the study of machine behaviour. Read the full article.

06 March 2019

Moralizing gods, impartiality and religious parochialism across 15 societies

The emergence of large-scale cooperation during the Holocene remains a central problem in the evolutionary literature. One hypothesis points to culturally evolved beliefs in punishing, interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant coreligionists. Furthermore, another hypothesis points to such mechanisms being constrained to the religious ingroup, possibly at the expense of religious outgroups. To test these hypotheses, we administered two behavioural experiments and a set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, and wage labourers, practicing Buddhism, Christianity, and Hinduism, but also forms of animism and ancestor worship. Read the full article.

01 February 2019

Identity fusion, outgroup relations, and sacrifice: A cross-cultural test

Identity fusion theory has become a popular psychological explanation of costly self-sacrifice. It posits that while maintaining one’s own individual identity, a deep affinity with one’s group can contribute to sacrifice for that group. We test this and related hypotheses using a behavioral economic experiment designed to detect biased, self-interested favoritism among eight different populations ranging from foragers and horticulturalists to the fully market-integrated. We find that while individuals favor themselves on average, those with higher ingroup fusion sacrifice more money to other members of their ingroup who are unable to reciprocate. We also find that positive outgroup relations has a similar effect. Additionally, we assess a recently-posited interaction between ingroup and outgroup relations and show no consistent effect at the individual or sub-sample levels. Read the full article.

29 January 2019

War increases religiosity

Does the experience of war increase people’s religiosity? Much evidence supports the idea that particular religious beliefs and ritual forms can galvanize social solidarity and motivate in-group cooperation, thus facilitating a wide range of cooperative behaviours including—but not limited to—peaceful resistance and collective aggression. However, little work has focused on whether violent conflict, in turn, might fuel greater religious participation. Here, we analyse survey data from 1,709 individuals in three post-conflict societies—Uganda,  Sierra Leone and Tajikistan. The nature of these conflicts allows us to infer, and statistically verify, that individuals were quasirandomly afflicted with different intensities of war experience—thus potentially providing a natural experiment. We then show that those with greater exposure to these wars were more likely to participate in Christian or Muslim religious groups and rituals, even several years after the conflict. Read the full article.

24 October 2018

Higher fundamental frequency in bonobos is explained by larynx morphology

Acoustic signals, shaped by natural and sexual selection, reveal ecological and social selection pressures. Examining acoustic signals together with morphology can be particularly revealing. But this approach has rarely been applied to primates, where clues to the evolutionary trajectory of human communication may be found. Across vertebrate species, there is a close relationship between body size and acoustic parameters, such as formant dispersion and fundamental frequency (f0). Deviations from this acoustic allometry usually produce calls with a lower f0 than expected for a given body size, often due to morphological adaptations in the larynx or vocal tract. An unusual example of an obvious mismatch between fundamental frequency and body size is found in the two closest living relatives of humans, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Read the full article.

16 October 2018

The evolution of bequeathal in stable habitats

Adults sometimes disperse, while philopatric offspring inherit the natal site, a pattern known as bequeathal. Despite a decades‐old empirical literature, little theoretical work has explored when natural selection may favor bequeathal. We present a simple mathematical model of the evolution of bequeathal in a stable environment, under both global and local dispersal. We find that natural selection favors bequeathal when adults are competitively advantaged over juveniles, baseline mortality is high, the environment is unsaturated, and when juveniles experience high dispersal mortality. However, frequently bequeathal may not evolve, because the fitness cost for the adult is too large relative to inclusive fitness benefits. Read the full article.

04 September 2018

Habitual stone-tool-aided extractive foraging in white-faced capuchins, Cebus capucinus

Habitual reliance on tool use is a marked behavioural difference between wild robust (genus Sapajus) and gracile (genus Cebus) capuchin monkeys. Despite being well studied and having a rich repertoire of social and extractive foraging traditions, Cebus sp. rarely use tools and have never been observed using stone tools. By contrast, habitual tool use by Sapajus is widespread. We review theory and discuss factors which might explain these differences in patterns of tool use between Cebus and Sapajus. We then report the first case of habitual stone tool use in a gracile capuchin: a population of whitefaced capuchins (Cebus capucinus imitator) in Coiba National Park, Panama who habitually rely on hammerstone and anvil tool use to access structurally protected food items in coastal areas including Terminalia catappa seeds, hermit crabs, marine snails, terrestrial crabs and other items. Read the full article.

18 July 2018

Greater wealth inequality, less polygyny: rethinking the polygyny threshold model

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. Read the full article.

16 July 2018

Complex Dynamics From Simple Cognition: The Primary Ratchet Effect in Animal Culture

It is often observed that human culture, unlike most other animal culture, is cumulative: Human technology and behavior is more complex than any individual could invent in their own lifetime. Cumulative culture is often explained by appeal to a combination of highfidelity social learning and innovation, the “ratchet effect.” What is often overlooked is that both human and other animal cultures are supported by a more primary ratchet effect that retains and increases the prevalence of adaptive behavior. This primary ratchet can arise without appeal to specialized cognitive adaptations and is plausibly more widespread in animal societies. We use a simple model to highlight how simple forms of contingent social learning can create the primary ratchet effect, dramatically increasing the prevalence of adaptive, hard-to-invent behavior. Read the full article.

06 June 2018

Resolution of apparent paradoxes in the race-specific frequency of use-of-force by police

Analyses of racial disparities in police use-of-force against unarmed individuals are central to public policy interventions; however, recent studies have come to apparently paradoxical findings concerning the existence and form of such disparities. Although anti-black racial disparities in U.S. police shootings have been consistently documented at the population level, new work has suggested that racial disparities in encounter-conditional use of lethal force by police are reversed relative to expectations, with police being more likely to: (1) shoot white relative to black individuals, and (2) use non-lethal as opposed to lethal force on black relative to white individuals. Encounter- and use-of-force-conditional results, however, can be misleading if the rates with which police encounter and use non-lethal force vary across officers and depend on suspect race. We find that all currently described empirical patterns in the structuring of police use-of-force—including the “reversed” racial disparities in encounter-conditional use of lethal force—are explainable under a generative model in which there are consistent and systemic biases against black individuals. Read the full article.

25 May 2018

Social complexity and kinship in animal societies

Studies of eusocial invertebrates regard complex societies as those where there is a clear division of labour and extensive cooperation between breeders and helpers. In contrast, studies of social mammals identify complex societies as those where differentiated social relationships influence access to resources and reproductive opportunities. We show here that, while traits associated with social complexity of the first kind occur in social mammals that live in groups composed of close relatives, traits associated with the complexity of social relationships occur where average kinship between female group members is low. Read the full article.

24 May 2018

Sizing up human brain evolution

An innovative computational analysis of factors that might have influenced human brain evolution suggests that ecological, rather than social, factors had a key role in the evolution of large, rapidly developing brains. Read the full article.

03 April 2018

The Evolution of Covert Signaling

Human sociality depends upon the benefits of mutual aid and extensive communication. However, diverse norms and preferences complicate mutual aid, and ambiguity in meaning hinders communication. Here we demonstrate that these two problems can work together to enhance cooperation through the strategic use of deliberately ambiguous signals: covert signaling. Covert signaling is the transmission of information that is accurately received by its intended audience but obscured when perceived by others. Such signals may allow coordination and enhanced cooperation while also avoiding the alienation or hostile reactions of individuals with different preferences. Read the full article.

08 March 2018

Material security, life history, and moralistic religions: A cross-cultural examination

Researchers have recently proposed that “moralistic” religions—those with moral doctrines, moralistic supernatural punishment, and lower emphasis on ritual—emerged as an effect of greater wealth and material security. One interpretation appeals to life history theory, predicting that individuals with “slow life history” strategies will be more attracted to moralistic traditions as a means to judge those with “fast life history” strategies. As we had reservations about the validity of this application of life history theory, we tested these predictions with a data set consisting of 592 individuals from eight diverse societies. Read the full article.

12 February 2018

Generative inference for cultural evolution

Dr Anne Kandler and her co-author Dr Adam Powell have published a review paper on methods for inferring cultural evolutionary mechanisms from data. One of the major challenges in cultural evolution is to understand why and how various forms of social learning are used in human populations, both now and in the past. The authors demonstrate the applicability and utility of generative inference approaches to the field of cultural evolution. The framework advocated uses observed population-level frequency data directly to establish the likely presence or absence of particular hypothesized learning strategies. Read the full article.

11 January 2018

Evolutionary dynamics of the cryptocurrency market

New work from Dr Anne Kandler and colleagues sheds light on the cultural evolutionary dynamics of cryptocurrencies. Kandler and colleagues consider the history of 1469 cryptocurrencies introduced between April 2013 and May 2017. They reveal that, while new cryptocurrencies appear and disappear continuously and their market capitalization is increasing (super-)exponentially, several statistical properties of the market have been stable for years. These include the number of active cryptocurrencies, market share distribution and the turnover of cryptocurrencies. Adopting an ecological perspective, they show that the so-called neutral model of evolution is able to reproduce a number of key empirical observations. Read the full article.

11 January 2018

Inferring processes of cultural transmission: the critical role of rare variants in distinguishing neutrality from novelty biases

Neutral evolution assumes that there are no selective forces distinguishing different variants in a population. Many studies have sought to assess whether neutrality can provide a good description of different episodes of cultural change. One approach has been to test whether neutral predictions are consistent with observed progeny distributions, recording the number of variants that have produced a given number of new instances within a specified time interval: a classic example is the distribution of baby names. New work from HBEC scientist Dr Anne Kandler and colleague Dr James O'Dwyer shows that these distributions consist of two phases: a power-law phase followed by an exponential cut-off for variants with very large numbers of progeny. They show that analyses based on only the most popular variants, as is often the case in studies of cultural evolution, can provide misleading evidence. While neutrality provides a plausible description of progeny distributions of abundant variants, rare variants deviate from neutrality. Read the full article.

19 October 2017

Friendliness is more important in a new friend than which group she belongs to

Despite the global headlines emphasizing division and conflict, humans actually have a long history of forming friendships across group boundaries. But which criteria do they use for picking friends from a different group? In collaboration with three populations of horticulturalists in Bolivia, researchers of the Max Planck Institute for Evolutionary Anthropology and the University of California Santa Barbara found that we use very similar criteria when choosing friends from among in-group and out-group strangers – individual cooperative qualities are most important in both cases. Only when it comes to dividing limited resources, qualities associated with a group can affect partner preference. Full press release. Access the paper.

06 September 2017

Inferring individual-level processes from population-level patterns in cultural evolution

Dr Anne Kandler has published a new analysis of the potential for inferring learning mechanisms from population-level data. Patterns of cultural change depend upon individual-level strategies. Inferring these strategies from data is complicated by the paucity of individual-level data. Researchers commonly attempt to infer strategies instead of available population-level data. Kandler and her co-authors show that such data are useful in limited, but valuable, ways. These results represent a substantial advance and refine thinking about both the limits and potential of using aggregate data to infer individual processes.

26 August 2017

Multinomial analysis of behavior: statistical methods

Jeremy Koster and Richard McElreath have published a new statistical framework for analyzing behavioral data, applying the technique to human data from Koster's field site. The method accepts the multinomial nature of behavior data and also accounts for repeated observations. It is also capable of revealing individual-level trade-offs across behaviors, allowing for models that reveal the extent to which individuals who regularly engage in one behavior also exhibit relatively more or less of another behavior. These models can potentially be applied to a broad class of statistical analyses by behavioral ecologists, focusing on other polytomous response variables, such as behavior, habitat choice, or emotional states.

21 August 2017

Interethnic Interaction, Strategic Bargaining Power, and the Dynamics of Cultural Norms

New publication by Dr John Bunce, Interethnic Interaction, Strategic Bargaining Power, and the Dynamics of Cultural Norms.

Dr Bunce addresses processes of ethnic boundary maintenance and change, using ethnographic data from his fieldwork in lowland Amazonia, in combination with Bayesian models of normative behavior. Code and data.

24 July 2017

Conformity does not perpetuate suboptimal traditions in a wild population of songbirds

New analysis published on a collaboration between HBEC and the Edward Grey Institute at Oxford: Conformity does not perpetuate suboptimal traditions in a wild population of songbirds. Conformist learning can be adaptive, but it may be maladaptive when environments change. Using a field experiment, the researchers document the social learning strategies that allow a wild population to adapt to environmental change. A mix of conformity and innovation is found in the analysis and demonstrated in theory to be broadly adaptive. Code and data.

07 June 2017

Pay-off-biased social learning underlies the diffusion of novel extractive foraging traditions in a wild primate

New analysis of social learning in a wild primate, by Brendan Barrett, Richard McElreath, and Susan Perry. Using field experiments, they document the spread of behavioral traditions and analyze the learning strategies that may account for the spread. The analysis suggests that payoff-biased social learning strongly influences behavior. Data and code

31 May 2017

Seminar: A Life History of Human Foraging in 39 Societies

Seminar (YouTube), presented by Richard McElreath at Aarhus University. This seminar presents progress on a large meta-analysis of foraging records from 39 human samples.