Dyadic inter-group cooperation in shotgun hunting activities in a Congo Basin village.

Understanding the dynamics of inter-group cooperation in human adaptation has been the subject of recent empirical and theoretical studies in evolutionary anthropology, beginning to fill gaps in our knowledge of how interactions across political, economic and social domains can - and often do - lead to stable, large-scale cooperation. Here we investigate dyadic intergroup cooperation in shotgun hunting in the Republic of the Congo. In the Congo Basin, inter-group cooperation between foragers and farmers is at the centre of an exchange system maintained by traditional norms and institutions such as fictive kinship. Here, we focused on what factors predict cooperative shotgun hunting exchanges between BaYaka and Yambe. We conducted structured interviews with 48 BaYaka hunters and 18 Yambe men who organise hunts in a village along the Motaba River. We used Bayesian multilevel regression models to investigate the influence of Yambe and BaYaka attributes on probability of dyadic cooperation. We found that BaYaka men's reputations as skilled hunters and their family size each predicted cooperation in shotgun hunting, whereas there was no effect of Yambe attributes (status, wealth, family size). We discuss the results in terms of evolutionary models of men as hunters and inter-group cooperation, as well as biodiversity conservation implications.

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

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

Music production and its role in coalition signaling during foraging contexts in a hunter-gatherer society.

Music is a cultural activity universally present in all human societies. Several hypotheses have been formulated to understand the possible origins of music and the reasons for its emergence. Here, we test two hypotheses: (1) the coalition signaling hypothesis which posits that music could have emerged as a tool to signal cooperative intent and signal strength of alliances and (2) music as a strategy to deter potential predators. In addition, we further explore the link between tactile cues and the propensity of mothers to sing toward infants. For this, we investigated the singing behaviors of hunter-gatherer mothers during daily foraging trips among the Mbendjele BaYaka in the Republic of the Congo. Although singing is a significant component of their daily activities, such as when walking in the forest or collecting food sources, studies on human music production in hunter-gatherer societies are mostly conducted during their ritual ceremonies. In this study, we collected foraging and singing behavioral data of mothers by using focal follows of five BaYaka women during their foraging trips in the forest. In accordance with our predictions for the coalition signaling hypothesis, women were more likely to sing when present in large groups, especially when group members were less familiar. However, predictions of the predation deterrence hypothesis were not supported as the interaction between group size and distance from the village did not have a significant effect on the likelihood of singing. The latter may be due to limited variation in predation risk in the foraging areas, because of the intense bush meat trade, and hence, future studies should include foraging areas with higher densities of wild animals. Lastly, we found that mothers were more likely to sing when they were carrying infants compared to when infants were close, but carried by others, supporting the prediction that touch plays an important prerequisite role in musical interaction between the mother and child. Our study provides important insight into the role of music as a tool in displaying the intent between or within groups to strengthen potentially conflict-free alliances during joint foraging activities.

Intergroup Cooperation in Shotgun Hunting Among BaYaka Foragers and Yambe Farmers from the Republic of the Congo.

Whereas many evolutionary models emphasize within-group cooperation or between-group competition in explaining human large-scale cooperation, recent work highlights a critical role for intergroup cooperation in human adaptation. Here we investigate intergroup cooperation in the domain of shotgun hunting in northern Republic of the Congo. In the Congo Basin broadly, forest foragers maintain relationships with neighboring farmers based on systems of exchange regulated by norms and institutions such as fictive kinship. In this study, we examine how relationships between Yambe farmers and BaYaka foragers support stable intergroup cooperation in the domain of shotgun hunting. In the study village, shotgun hunting is based on a specialization-based exchange wherein Yambe farmers contribute shotguns and access to markets to buy cartridges and sell meat while BaYaka foragers contribute their specialized forest knowledge and skill. To understand how costs and benefits are distributed, we conducted structured interviews with 77 BaYaka hunters and 15 Yambe gun owners and accompanied hunters on nine hunting trips. We found that hunts are organized in a conventional manner within a fictive kinship structure, consistent with the presence of intercultural mechanisms to stabilize cooperation. However, because bushmeat demand is high, gun owners can gain significant cash profit, while compensating hunters only with cigarettes, alcohol, and a traditional hunter's portion of meat. To level payoffs, hunters strategically hide kills or cartridges from gun owners to feed their own families. Our results illustrate how each group prioritizes different currencies (e.g., cash, meat, family, intergroup relations) and provide insights into how intergroup cooperation is stabilized in this setting. The example of this long-standing intergroup cooperative system is discussed in terms of its contemporary entwinement with logging, the bushmeat trade, and growing market intersection.

Girls in early childhood increase food returns of nursing women during subsistence activities of the BaYaka in the Republic of Congo.

Nursing mothers face an energetic trade-off between infant care and work. Under pooled energy budgets, this trade-off can be reduced by assistance in food acquisition and infant care tasks from non-maternal carers. Across cultures, children also often provide infant care. Yet the question of who helps nursing mothers during foraging has been understudied, especially the role of children. Using focal follow data from 140 subsistence expeditions by BaYaka women in the Republic of Congo, we investigated how potential support from carers increased mothers' foraging productivity. We found that the number of girls in early childhood (ages 4-7 years) in subsistence groups increased food returns of nursing women with infants (kcal collected per minute). This effect was stronger than that of other adult women, and older girls in middle childhood (ages 8-13 years) and adolescence (ages 14-19 years). Child helpers were not necessarily genetically related to nursing women. Our results suggest that it is young girls who provide infant care while nursing mothers are acquiring food-by holding, monitoring and playing with infants-and, thus, that they also contribute to the energy pool of the community during women's subsistence activities. Our study highlights the critical role of children as carers from early childhood.

Effects of thermal aging on the electronic and structural properties of Pt-Pd and toluene oxidation activity.

Catalytic oxidation is a feasible method for remediating volatile organic compounds (VOCs), due to its lower energy consumption and mineralization of VOCs into H2O and CO2. Noble metal-based catalysts are preferred for the catalytic oxidation of VOCs because of their superior activity, but they are usually deactivated by thermal aging which sinters the metal particles. Here, we report that Pt-Pd/Al2O3 thermally aged at 700-900 °C in air showed enhanced catalytic activity for toluene oxidation in humid conditions. There were electronic and structural changes in the thermally aged Pt-Pd/Al2O3, as confirmed by numerous analyses. Both Pt and Pd existed in a metallic rather than oxidized state without additional reduction steps. The noble metal particles were assembled to form Pt-Pd alloy, in the form of isolated Pd atoms surrounded by Pt atoms. This specific alloy structure was found to be crucial to the observed enhancement in catalytic toluene oxidation at low temperature.

Social ties in the Congo Basin: insights into tropical forest adaptation from BaYaka and their neighbours.

Investigating past and present human adaptation to the Congo Basin tropical forest can shed light on how climate and ecosystem variability have shaped human evolution. Here, we first review and synthesize genetic, palaeoclimatological, linguistic and historical data on the peopling of the Congo Basin. While forest fragmentation led to the increased genetic and geographical divergence of forest foragers, these groups maintained long-distance connectivity. The eventual expansion of Bantu speakers into the Congo Basin provided new opportunities for forging inter-group links, as evidenced by linguistic shifts and historical accounts. Building from our ethnographic work in the northern Republic of the Congo, we show how these inter-group links between forest forager communities as well as trade relationships with neighbouring farmers facilitate adaptation to ecoregions through knowledge exchange. While researchers tend to emphasize forager-farmer interactions that began in the Iron Age, we argue that foragers' cultivation of relational wealth with groups across the region played a major role in the initial occupation of the Congo Basin and, consequently, in cultural evolution among the ancestors of contemporary peoples. This article is part of the theme issue 'Tropical forests in the deep human past'.

Do Javan gibbons (Hylobates moloch) use fruiting synchrony as a foraging strategy?

Tropical rainforests are characterized by a high diversity of plant species. Each plant species presents with differential phenological patterns in fruit production. In some species, all individual trees produce fruit simultaneously within clustered periods; whereas in others, each individual tree fruits at irregular time intervals. By observing this pattern, some primate species use the presence of fruits in one tree as a cue to find fruit in other trees of the same synchronously fruiting tree species. Here, we investigated whether the highly frugivorous Javan gibbons (Hylobates moloch) in Gunung Halimun-Salak National Park in Indonesia have knowledge of synchronous characteristics of fruiting trees and whether they can further distinguish fruit species with different synchrony levels, that is, tree species with highly synchronous fruiting patterns versus tree species with less synchronous fruiting patterns. Across 12 months we collected biweekly phenological data on 250 trees from 10 fruit species and observed Javan gibbons' visits to those species. We found that a fruit discovery in the beginning of fruiting seasons triggered gibbons to visit trees of the same fruit species. However, gibbons' visit rates did not differ between highly synchronous and asynchronous species. Our results suggest that Javan gibbons have knowledge of synchronous characteristics of fruiting trees in general, but they do not differentiate highly synchronous versus asynchronous fruit species. We speculate that Javan gibbons, who live in relatively small ranges with very low tree density of preferred fruit species, are likely able to track and remember fruiting states of individual trees without needing to distinguish fruit species with different synchrony levels. Moreover, gibbons may make little benefit of distinguishing highly synchronous versus asynchronous fruit species, probably due to gibbons' heavy use of asynchronous figs. Our study provides an insight into how gibbon's foraging strategies may have been shaped in response to their ecological environment.

Using natural travel paths to infer and compare primate cognition in the wild.

Within comparative psychology, the evolution of animal cognition is typically studied either by comparing indirect measures of cognitive abilities (e.g., relative brain size) across many species or by conducting batteries of decision-making experiments among (typically) a few captive species. Here, we propose a third, complementary approach: inferring and comparing cognitive abilities through observational field records of natural information gradients and the associated variation in decision-making outcomes, using the ranging behavior of wild animals. To demonstrate the feasibility of our proposal, we present the results of a global survey assessing the availability of long-term ranging data sets from wild primates and the willingness of primatologists to share such data. We explore three ways in which such ranging data, with or without the associated behavioral and ecological data often collected by primatologists, might be used to infer and compare spatial cognition. Finally, we suggest how ecological complexity may be best incorporated into comparative analyses.

Travel linearity and speed of human foragers and chimpanzees during their daily search for food in tropical rainforests.

To understand the evolutionary roots of human spatial cognition, researchers have compared spatial abilities of humans and one of our closest living relatives, the chimpanzee (Pan troglodytes). However, how humans and chimpanzees compare in solving spatial tasks during real-world foraging is unclear to date, as measuring such spatial abilities in natural habitats is challenging. Here we compared spatial movement patterns of the Mbendjele BaYaka people and the Taï chimpanzees during their daily search for food in rainforests. We measured linearity and speed during off-trail travels toward out-of-sight locations as proxies for spatial knowledge. We found similarly high levels of linearity in individuals of Mbendjele foragers and Taï chimpanzees. However, human foragers and chimpanzees clearly differed in their reactions to group size and familiarity with the foraging areas. Mbendjele foragers increased travel linearity with increasing familiarity and group size, without obvious changes in speed. This pattern was reversed in Taï chimpanzees. We suggest that these differences between Mbendjele foragers and Taï chimpanzees reflect their different ranging styles, such as life-time range size and trail use. This result highlights the impact of socio-ecological settings on comparing spatial movement patterns. Our study provides a first step toward comparing long-range spatial movement patterns of two closely-related species in their natural environments.

Sun, age and test location affect spatial orientation in human foragers in rainforests.

The ability to know the direction of food sources is important for the foraging success of hunter-gatherers, especially in rainforests where dense vegetation limits visual detection distances. Besides sex and age, prior experience with the environment and the use of environmental cues are known to influence orientation abilities of humans. Among environmental cues, the position of the sun in the sky is important for orientation of diurnal animal species. However, whether or to what extent humans use the sun is largely unknown. Here, we investigated orientation abilities of the Mbendjele BaYaka people in the Republic of Congo, by conducting pointing tests (Nparticipants = 54, age: 6-76 years) in different locations in the rainforest. The Mbendjele were overall highly accurate at pointing to out-of-sight targets (median error: 6°). Pointing accuracy increased with age, but sex did not affect accuracy. Crucially, sun visibility increased pointing accuracy in young participants, especially when they were far from the camp. However, this effect became less apparent in older participants who exhibited high pointing accuracy, also when the sun was not visible. This study extends our understandings of orientation abilities of human foragers and provides the first behavioural evidence for sun compass use in humans.

Size-Controlled Synthesis of Copper Oxide Particles on Reduced Graphene Oxide for Lithium-Ion Battery Anode Applications.

Copper oxide/reduced graphene oxide (rGO) hybrids have been successfully synthesized by attaching copper ions onto the functional groups of GO by means of a solution process, which causes precipitation and agglomeration of copper oxides during subsequent thermal reduction of the GO. The resulting copper oxide/rGO hybrid exhibited improved electrochemical performance compared to monolithic CuO, which is presumed to be due to rGO acting as a mechanical support that buffers the volume change in copper oxides that occurs as a result of the conversion reaction during charge/discharge cycling. Furthermore, it was found that the size of the copper oxide particles can be optimized by adjusting the annealing time, with a hybrid annealed for 30 min achieving a reversible capacity of 544 mA h g(-1) and an initial coulombic efficiency of 62.7%.