Abteilung für Verhaltensökologie

The Special Feature “Half a Century of Cultural Evolution” synthesizes existing work in the field of cultural evolution in the context of the development of the field over the last fifty years, addressing its current challenges and building on this work toward a unified science of culture.

The authors of this feature focus on areas where the impact of cultural evolutionary theory has been greatest. The collection collates accounts of the past and visions of the future to provide a solid foundation on which the next fifty years of cultural evolutionary research can be built.

Read article here.  Read press release here.

Human evolution is intricately linked with culture, which permeates almost all facets of human life from health and reproduction, to the environments in which we live. Nevertheless, our understanding of the ways in which stably transmitted, evolutionarily relevant human cultural traits might interact with the human genome is incomplete, and methods to detect such interactions are limited. Here, we describe some rules of cultural transmission which could pertain to both humans and cultural nonhuman animals that could lead to the formation and maintenance of stable associations between cultural and genetic traits. Next, we show that, in the presence of such associations, a process analogous to genetic hitchhiking is possible in gene–culture systems. These could leave signatures in the human genome similar to, and perhaps indistinguishable from, those left by selection on genetic traits. Finally, we model selective interference between cultural and genetic traits. We show that selective interference between a cultural trait under selection and a genetic trait under selection can reduce the efficacy of natural selection in the human genome, both in terms of the probability of fixation of beneficial alleles and the dynamics of selective sweeps. We then show that the efficiency of selection at genetic loci can, however, be increased in the presence of strong cultural transmission biases. This implies that the signatures of gene–culture interactions in genetic data may be complex and wide-ranging in gene–culture coevolutionary systems. Read article here.

Investments in housing influence migration and landscape construction, making them a key component of human–environment interactions. However, the strategic decision-making that builds residential landscapes is an underdeveloped area of research in evolutionary approaches to human behaviour. Our contribution to this literature is a theoretical model and an empirical test of this model using data from Ulaanbaatar, Mongolia. We develop a model of strategic housing decisions using stochastic dynamic programming (SDP) to explore the trade-offs between building, moving and saving over time, finding different trade-offs depending on optimization scenarios and housing costs. Household strategies are then estimated using data on 825 households that settled in the Ger districts of Ulaanbaatar between 1942 and 2020. The Ger districts are areas of self-built housing that feature both mobile dwellings (gers) and immobile houses (bashins). Using approximate Bayesian computation (ABC), we find the parameters of our dynamic programming model that best fit the empirical data. The model is able to capture the time horizon of housing changes and their bi-directionality, showing that moving from a fixed to mobile dwelling can also be an optimal strategy. However, the model underpredicts household persistence in dwelling types. We discuss deviations from model predictions and identify a more detailed exploration of risk and population mixes of strategies as key steps for future research. Read article here.

Across cultures, mothers balance childcare with other labour. Hunter-gatherer mothers face a daily choice of whether to take infants on foraging trips or leave them with caregivers in the settlement, as well as deciding with whom to forage. Yet, it remains unclear how infant presence affects mothers’ mobility and food returns during group foraging. Using GPS, heart rate measurements, and food return data from 348 foraging trips by 22 BaYaka mothers in the Republic of the Congo, we found that mothers go on longer-duration foraging trips when they take infants along, compared to when they leave them behind. Despite this, infant presence does not affect mothers’ mobility, energy expenditure, or food returns. Mothers also go on longer-duration and longer-distance trips during group foraging, compared to foraging alone. However, they have decreased food returns in larger groups with more adults, possibly due to food competition. Nevertheless, BaYaka mothers maintain their energy expenditure and net food returns in general, regardless of infant presence or group dynamics, likely due to their individual foraging strategies and support from group members. Particularly, children in foraging groups increase mothers’ food returns, aligning with women’s reports of children assisting as caregivers. These findings provide insights into how BaYaka mothers accommodate childcare with subsistence activities during group foraging. Read article here.

Earth's forests are continually monitored by both the satellite record and the lived experiences of nearly 2 billion forest-proximate peoples. Generally, the satellite record summarizes production estimates, such as percent tree cover, at regular, relatively coarse scales. Conversely, local perceptions tend to capture changes at irregular and very fine scales. While the utility of both of these sources of information has been widely demonstrated in isolation, little work has explored in what contexts they are expected to correlate or deviate, or how they might be quantitatively integrated. Here, we collect gridded information on community perceived and remotely sensed mangrove cover change across 719 0.5-km grids in Pemba Island, Tanzania. We reveal variation in the association between these two data sources across different wards (shehia) and explore the reasons for this variation using interviews and direct observation. We find that shehia with the greatest alignment between perceived and remotely sensed mangrove change tended to have little planting or natural regeneration of mangrove propagules and large areas of complete cover loss. Alternatively, in shehia with the lowest alignment, we find high levels of natural and/or human-assisted mangrove recolonization and selective harvesting of individual trees and branches. These findings indicate that the alignment between local knowledge and satellite observations of mangrove cover change systematically increases with the scale of change in this system. Finally, we demonstrate a practical workflow for quantitatively leveraging these misalignments by optimizing across both data sources to identify restoration priority areas. Read article here.

Social learning is common in nature, yet cumulative culture (where knowledge and technology increase in complexity and diversity over time) appears restricted to humans. To understand why, we organized a computer tournament in which programmed entries specified when to learn new knowledge and when to refine (i.e. improve) existing knowledge. The tournament revealed a ‘refinement paradox’: refined behavior afforded higher payoffs as individuals converged on a small number of successful behavioral variants, but refining did not generally pay. Paradoxically, entries that refined only in certain conditions did best during behavioral improvement, while simple copying entries thrived when refinement levels were high. Cumulative cultural evolution may be rare in part because sophisticated strategies for improving knowledge and technology are initially advantageous, yet complex culture, once achieved, favors conformity, blind imitation and hyper-credulity. Read article here.

Environments can change suddenly and unpredictably and animals might benefit from being able to flexibly adapt their behavior through learning new associations. Serial (repeated) reversal learning experiments have long been used to investigate differences in behavioral flexibility among individuals and species. In these experiments, individuals initially learn that a reward is associated with a specific cue before the reward is reversed back and forth between cues, forcing individuals to reverse their learned associations. Cues are reliably associated with a reward, but the association between the reward and the cue frequently changes. Here, we apply and expand newly developed Bayesian reinforcement learning models to gain additional insights into how individuals might dynamically modulate their behavioral flexibility if they experience serial reversals. We derive mathematical predictions that, during serial reversal learning experiments, individuals will gain the most rewards if they 1) increase their *rate of updating associations* between cues and the reward to quickly change to a new option after a reversal, and 2) decrease their *sensitivity* to their learned association to explore the alternative option after a reversal. We reanalyzed reversal learning data from 19 wild-caught great-tailed grackles (Quiscalus mexicanus), eight of whom participated in serial reversal learning experiment, and found that these predictions were supported. Their estimated association-updating rate was more than twice as high at the end of the serial reversal learning experiment than at the beginning, and their estimated sensitivities to their learned associations declined by about a third. The changes in behavioral flexibility that grackles showed in their experience of the serial reversals also influenced their behavior in a subsequent experiment, where individuals with more extreme rates or sensitivities solved more options on a multi-option puzzle box. Our findings offer new insights into how individuals react to uncertainty and changes in their environment, in particular, showing how they can modulate their behavioral flexibility inresponse to their past experiences. Read article here.

Human evolutionary ecology stands to benefit by integrating theory and methods developed in movement ecology, and in turn, to make contributions to the broader field of movement ecology by leveraging our species’ distinct attributes. In this paper, we review data and evolutionary models suggesting that major changes in socio-spatial behaviour accompanied the evolution of language. To illustrate and explore these issues, we present a comparison of GPS measures of the socio-spatial behaviour of Hadza hunter–gatherers of northern Tanzania to those of olive baboons (Papio anubis), a comparatively small-brained primate that is also savanna-adapted. While standard spatial metrics show modest differences, measures of spatial diversity, landscape exploration and spatiotemporal displacement between individuals differ markedly. Groups of Hadza foragers rapidly accumulate a vast, diverse knowledge pool about places and things over the horizon, contrasting with the baboon’s narrower and more homogeneous pool of ecological information. The larger and more complex socio-spatial world illustrated by the Hadza is one where heightened cognitive abilities for spatial and episodic memory, navigation, perspective taking and communication about things beyond the here and now all have clear value. This article is part of the theme issue ‘The spatial–social interface: a theoretical and empirical integration’. Read article here.

For decades, women’s employment has been seen as crucial for achieving greater autonomy and empowerment for women, and for promoting better health and nutrition outcomes for children, particularly in low- and middle-income countries (LMIC). However, numerous empirical studies of the relationship between women’s work and child outcomes have shown mixed results. Our study tests the assumptions of a model that suggests loss of maternal care during working hours may produce negative health outcomes for children. We use longitudinal data collected from traditionally semi-nomadic, boat-dwelling Shodagor families in Matlab, Bangladesh to determine the importance of maternal care as a mechanism influencing the relationship between women’s work and child illness. We use Bayesian linear mixed models to assess the influence of occupation and amount of care on average days of child illness per month, and also to examine the role that allomothers play in buffering against potential negative impacts of lost maternal care on child illness. Results show that children who receive more care from mothers experience fewer days of illness, and that availability of high-quality alloparents mediates the relationship between maternal work and child health. These results indicate that both the care and resources provided by mothers influence children’s biological outcomes. This has important implications for policy and aid interventions in LMIC, which have been developed to capitalize on an assumed positive relationship between maternal work and child health and nutrition. Read article here.

We present the first published ethnographic description of landscape burning by Hadza hunter-gatherers of northern Tanzania and identify environmental, social, and cultural influences on Hadza landscape burning, thereby broadening the ethnographic record of anthropogenic burning practices described for hunter-gatherer communities. We report interview data collected in 2022 and 2023, describing their practices and attitudes regarding the causes and consequences of burning. We provide context by comparing our observations with those recorded for hunting and gathering populations in Africa, Australia, and North America. Hadza landscape burning is generally a solitary and male-dominated activity, contrary to ethnographic accounts of Indigenous landscape burning from North America and Australia. The primary goals stated by Hadza for landscape burning were improved hunting, reduced hazards from dangerous animals, and to reduce the density of livestock. Firsthand observations suggest that landscape burning has decreased over the past 20 years, and this historical trend is supported by interviews. Satellite imagery also suggests an overall decrease in burning activity in the region from 2001 to 2022. Among the Hadza, landscape burning is a culturally influenced and strongly gender-biased activity that is rapidly disappearing. Because burning can radically transform landscapes, these practices often generate or amplify conflicts of interest between groups with different land use strategies. Hadza report serious social conflict with pastoralists over landscape burning, and our study suggests this tension has constrained the practice in the past two decades. Read article here.

Emerging evidence suggests that gender is a defining feature of personhood. Studies show that gender is the primary social category individuals use to perceive humanness and the social category most strongly related to seeing someone—or something—as human. However, the universality of gender’s primacy in social perception and its precedence over other social categories like race and age have been debated. We examined the primacy of gender perception in the Mayangna community of Nicaragua, a population with minimal exposure to Western influences, to test whether the primacy of gender categorization in humanization is more likely to be a culturally specific construct or a cross-cultural and potentially universal phenomenon. Consistent with findings from North American populations [A. E. Martin, M. F. Mason, J. Pers. Soc. Psychol. 123, 292–315 (2022)], the Mayangna ascribed gender to nonhuman objects more strongly than any other social category—including age, race, sexual orientation, disability, and religion—and gender was the only social category that uniquely predicted perceived humanness (i.e., the extent to which a nonhuman entity was seen as “human”). This pattern persisted even in the most isolated subgroup of the sample, who had no exposure to Western culture or media. The present results thus suggest that gender’s primacy in social cognition is a widely generalizable, and potentially universal, phenomenon. Read article here.

Indigenous communities in the North American Arctic are characterized by mixed economies that feature hunting, fishing, gathering, and trapping activities—and associated sharing practices—alongside the formal wage economy. The region is also undergoing rapid social, economic, and climate changes, including, in Canada, carbon taxation, which is impacting the cost of fuel used in local food harvesting. Because of the importance of local foods to nutrition, health, and well-being in Arctic Indigenous communities, there is an urgent need to better understand the sensitivity of Arctic food systems to social, economic, and climate changes and to develop plans for mitigating potential adverse effects. Here, we develop a Bayesian model to calculate the substitution value and carbon emissions of market replacements for local food harvests in the Inuvialuit Settlement Region, Canada. Our estimates suggest that under plausible scenarios, replacing locally harvested foods with imported market substitutes would cost over 3.1 million Canadian dollars per year and emit over 1,000 tons of CO₂-equivalent emissions per year, regardless of the shipping scenario. In contrast, we estimate that gasoline inputs to harvesting cost approximately $295,000 and result in 315 to 497 tons of emissions. These results indicate that climate change policies that fail to account for local food production may undermine emissions targets and adversely impact food security and health in Arctic Indigenous communities, who already experience a high cost of living and high rates of food insecurity. Read article here.Read press release here.

This paper examines how BaYaka children from the Congo Basin learn to “walk in the forest” (botamboli na ndima). Specifically, after placing forest walking within historical and ethnographic context, we consider how this practice contributes to BaYaka motor, cognitive, and social development, and thus, to the acquisition of culture. To do so, we draw from our own observations and those of other researchers working throughout the region. We outline four ways in which “walking in the forest” is directly and indirectly socialized: through motion-full caregiving in infancy, play and cooperative foraging in early and middle childhood, and exploration in adolescence. Taking “walking in the forest” as a focal point, we argue that the specific ways in which caregivers enhance learning are grounded in BaYaka subsistence and forest management practices, and that learning to walk in the forest is central to the maintenance of BaYaka social networks and the flow of knowledge in the Congo Basin. Read article here.

Humans cooperate in groups in which mutual monitoring is common, and this provides the possibility of third-party arbitration. Third-party arbitration stabilizes reciprocity in at least two ways: first, when it is accurate, it reduces the frequency of misunderstandings resulting from perception errors, and second, even when it is inaccurate, it provides a public signal that allows pairs to align their expectations about how to behave after errors occur. Here, we describe experiments that test for these two effects. We find that in an iterated, sequential Prisoner’s Dilemma game with errors, players with the highest average payoffs are those who make use of third-party arbitration and who also employ forgiving strategies. The combination of these two behaviours reduces the detrimental effects of errors on reciprocity, resulting in more cooperation. Read article here.

Long-standing questions about human brain evolution may only be resolved through comparisons with close living evolutionary relatives, such as chimpanzees. This applies in particular to structural white matter (WM) connectivity, which continuously expanded throughout evolution. However, due to legal restrictions on chimpanzee research, neuroscience research currently relies largely on data with limited detail or on comparisons with evolutionarily distant monkeys. Here, we present a detailed magnetic resonance imaging resource to study structural WM connectivity in the chimpanzee. This open-access resource contains (1) WM reconstructions of a postmortem chimpanzee brain, using the highest-quality diffusion magnetic resonance imaging data yet acquired from great apes; (2) an optimized and validated method for high-quality fiber orientation reconstructions; and (3) major fiber tract segmentations for cross-species morphological comparisons. This dataset enabled us to identify phylogenetically relevant details of the chimpanzee connectome, and we anticipate that it will substantially contribute to understanding human brain evolution. Read article here.

To better understand how vocalisations are used during interactions of multiple individuals, studies are increasingly deploying on-board devices with a microphone on each animal. The resulting recordings are extremely challenging to analyse, since microphone clocks drift non-linearly and record the vocalisations of non-focal individuals as well as noise. Here we address this issue with callsync, an R package designed to align recordings, detect and assign vocalisations to the caller, trace the fundamental frequency, filter out noise and perform basic analysis on the resulting clips. We present a case study where the pipeline is used on a dataset of six captive cockatiels (Nymphicus hollandicus) wearing backpack microphones. Recordings initially had a drift of ~2 min, but were aligned to within ~2 s with our package. Using callsync, we detected and assigned 2101 calls across three multi-hour recording sessions. Two had loud beep markers in the background designed to help the manual alignment process. One contained no obvious markers, in order to demonstrate that markers were not necessary to obtain optimal alignment. We then used a function that traces the fundamental frequency and applied spectrographic cross correlation to show a possible analytical pipeline where vocal similarity is visually assessed. The callsync package can be used to go from raw recordings to a clean dataset of features. The package is designed to be modular and allows users to replace functions as they wish. We also discuss the challenges that might be faced in each step and how the available literature can provide alternatives for each step. Read article here.

Poor oral health is associated with cardiovascular disease and dementia. Potential pathways include sepsis from oral bacteria, systemic inflammation, and nutritional deficiencies. However, in post-industrialized populations, links between oral health and chronic disease may be confounded because the lower socioeconomic exposome (poor diet, pollution, and low physical activity) often entails insufficient dental care. We assessed tooth loss, caries, and damaged teeth, in relation to cardiovascular and brain aging among the Tsimane, a subsistence population living a relatively traditional forager-horticulturalist lifestyle with poor dental health, but minimal cardiovascular disease and dementia. Dental health was assessed by a physician in 739 participants aged 40–92 years with cardiac and brain health measured by chest computed tomography (CT; n = 728) and brain CT (n = 605). A subset of 356 individuals aged 60+ were also assessed for dementia and mild cognitive impairment (n = 33 impaired). Tooth loss was highly prevalent, with 2.2 teeth lost per decade and a 2-fold greater loss in women. The number of teeth with exposed pulp was associated with higher inflammation, as measured by cytokine levels and white blood cell counts, and lower body mass index. Coronary artery calcium and thoracic aortic calcium were not associated with tooth loss or damaged teeth. However, aortic valve calcification and brain tissue loss were higher in those who had more teeth with exposed pulp. Overall, these results suggest that dental health is associated with indicators of chronic diseases in the absence of typical confounds, even in a population with low cardiovascular and dementia risk factors. Read article here.

Tool use is considered a driving force behind the evolution of brain expansion and prolonged juvenile dependency in the hominin lineage. However, it remains rare across animals, possibly due to inherent constraints related to manual dexterity and cognitive abilities. In our study, we investigated the ontogeny of tool use in chimpanzees (Pan troglodytes), a species known for its extensive and flexible tool use behavior. We observed 70 wild chimpanzees across all ages and analyzed 1,460 stick use events filmed in the Taï National Park, Côte d’Ivoire during the chimpanzee attempts to retrieve high-nutrient, but difficult-to-access, foods. We found that chimpanzees increasingly utilized hand grips employing more than 1 independent digit as they matured. Such hand grips emerged at the age of 2, became predominant and fully functional at the age of 6, and ubiquitous at the age of 15, enhancing task accuracy. Adults adjusted their hand grip based on the specific task at hand, favoring power grips for pounding actions and intermediate grips that combine power and precision, for others. Highly protracted development of suitable actions to acquire hidden (i.e., larvae) compared to non-hidden (i.e., nut kernel) food was evident, with adult skill levels achieved only after 15 years, suggesting a pronounced cognitive learning component to task success. The prolonged time required for cognitive assimilation compared to neuromotor control points to selection pressure favoring the retention of learning capacities into adulthood. Read article here.

In the unpredictable Anthropocene, a particularly pressing open question is how certain species invade urban environments. Sex-biased dispersal and learning arguably influence movement ecology, but their joint influence remains unexplored empirically, and might vary by space and time. We assayed reinforcement learning in wild-caught, temporarily captive core-, middle-, or edge-range great-tailed grackles—a bird species undergoing urban-tracking rapid range expansion, led by dispersing males. We show, across populations, both sexes initially perform similarly when learning stimulus-reward pairings, but, when reward contingencies reverse, male—versus female—grackles finish ‘relearning’ faster, making fewer choice-option switches. How do male grackles do this? Bayesian cognitive modelling revealed male grackles’ choice behaviour is governed more strongly by the ‘weight’ of relative differences in recent foraging payoffs—i.e., they show more pronounced risk-sensitive learning. Confirming this mechanism, agent-based forward simulations of reinforcement learning—where we simulate ‘birds’ based on empirical estimates of our grackles’ reinforcement learning—replicate our sex-difference behavioural data. Finally, evolutionary modelling revealed natural selection should favour risk-sensitive learning in hypothesised urban-like environments: stable but stochastic settings. Together, these results imply risk-sensitive learning is a winning strategy for urban-invasion leaders, underscoring the potential for life history and cognition to shape invasion success in human-modified environments. Read article here.  Read press release here.

Book description: Human behavioral ecology (HBE) applies the principles of evolutionary theory and optimisation to the study of human behavioural and cultural diversity. Among other things, HBE attempts to explain variation in behaviour as adaptive solutions to the competing life-history demands of growth, development, reproduction, parental care, and mate acquisition. This book is a comprehensive introduction to the theoretical orientation and specific findings of HBE. It consolidates the insights of evolution and human behaviour into a single volume that reflects the current state and future of the field. It brings together leading scholars from across the evolutionary social sciences to provide a comprehensive and thought-provoking review of the state of the topic. Throughout, the authors explain the latest developments in theory and highlight critical debates in the literature, while also engaging readers with ethnographic insights and field-based studies that remain at the core of human behavioral ecology. More information on the CUP website.

Quantifying the distance between cultural groups has received substantial recent interest. A key innovation, borrowed from population genetics, is the calculation of cultural FST (CFST) statistics on datasets of human culture. Measuring the variance between groups as a fraction of total variance, FST is theoretically important in additive models of cooperation. Consistent with this, recent empirical work has confirmed that high values of pairwise CFST (measuring cultural distance) strongly predict unwillingness to cooperate with strangers in coordination vignettes. As applications for CFST increase, however, there is greater need to understand its meaning in naturalistic situations beyond additive cooperation. Focusing on games with both positive and negative frequency dependence and high-diversity, mixed equilibria, we derive a simple relationship between FST and the evolution of group-beneficial traits across a broad spectrum of social interactions. Contrary to standard assumptions, this model shows why FST can have both positive and negative marginal effects on the spread of group-beneficial traits under certain realistic conditions. These results provide broader theoretical direction for empirical applications of CFST in the evolutionary study of culture. Read article here.

With commons encompassing approximately 65% of Earth’s surface and vast tracts of the ocean, a critical challenge for sustainability involves establishing effective institutions for governing these common-pool resources (CPR). While examples of successful governance exist, the circumstances and mechanisms behind their development have often faded from historical records and memories. Drawing on ethnographic work, we introduce a generic evolutionary multigroup modelling framework that examines the emergence, stability and temporal dynamics of collective property rights. Our research reveals a fundamental insight: when intergroup conflicts over resources exist, establishing and enforcing ‘access rights’ becomes an essential prerequisite for evolving sustainable ‘use rights’. These access rights, in turn, enable cultural group selection and facilitate the evolution of sustainable use rights through the imitation of successful groups. Moreover, we identify four crucial aspects within these systems: (1) seizures in CPR systems create individual-level incentives to enforce use and access rights; (2) support for collective property rights is frequency dependent and prone to oscillations; (3) the maximum sustainable yield (MSY) is a tipping point that alters the interplay between individual and group-level selection pressures; (4) success-biased social learning (imitation) of out-group members plays a vital role in spreading sustainable institutions and preventing the tragedy of the commons. Read article here.  Read press release here.

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