Hunter-gatherer genomes reveal diverse demographic trajectories during the rise of farming in Eastern Africa

The fate of hunting and gathering populations following the rise of agriculture and pastoralism remains a topic of debate in the study of human prehistory. Studies of ancient and modern genomes have found that autochthonous groups were largely replaced by expanding farmer populations with varying levels of gene flow, a characterization that is influenced by the almost universal focus on the European Neolithic.^1-5 We sought to understand the demographic impact of an ongoing cultural transition to farming in Southwest Ethiopia, one of the last regions in Africa to experience such shifts.⁶ Importantly, Southwest Ethiopia is home to several of the world's remaining hunter-gatherer groups, including the Chabu people, who are currently transitioning away from their traditional mode of subsistence.⁷ We generated genome-wide data from the Chabu and four neighboring populations, the Majang, Shekkacho, Bench, and Sheko, to characterize their genetic ancestry and estimate their effective population sizes over the last 60 generations. We show that the Chabu are a distinct population closely related to ancient people who occupied Southwest Ethiopia >4,500 years ago. Furthermore, the Chabu are undergoing a severe population bottleneck, which began approximately 1,400 years ago. By analyzing eleven Eastern African populations, we find evidence for divergent demographic trajectories among hunter-gatherer-descendant groups. Our results illustrate that although foragers respond to encroaching agriculture and pastoralism with multiple strategies, including cultural adoption of agropastoralism, gene flow, and economic specialization, they often face population decline.

Gender-Typed and Gender-Segregated Play Among Tanzanian Hadza and Congolese BaYaka Hunter-Gatherer Children and Adolescents

Few data exist on gender-typed and gender-segregated play in hunter-gatherer societies, despite their unique demographic and cultural features which may influence children's gendered play. Using naturalistic observations of Hadza (N = 46, 41% female) and BaYaka (N = 65, 48% female) hunter-gatherer 3- to 18-year-olds from Tanzania and the Republic of Congo, we showed that access to playmates was negatively associated with playing in mixed-gender groups. Young boys did not engage in more rough-and-tumble play than girls, but adolescent boys participated in this type of play more than adolescent girls. Children were also more likely to participate in work-themed play which conformed to gender norms within their society. Findings are discussed within the context of gendered division of labor, child autonomy, and demography.

A genome scan for genes underlying adult body size differences between Central African hunter-gatherers and farmers

The evolutionary and biological bases of the Central African "pygmy" phenotype, a characteristic of rainforest hunter-gatherers defined by reduced body size compared with neighboring farmers, remain largely unknown. Here, we perform a joint investigation in Central African hunter-gatherers and farmers of adult standing height, sitting height, leg length, and body mass index (BMI), considering 358 hunter-gatherers and 169 farmers with genotypes for 153,798 SNPs. In addition to reduced standing heights, hunter-gatherers have shorter sitting heights and leg lengths and higher sitting/standing height ratios than farmers and lower BMI for males. Standing height, sitting height, and leg length are strongly correlated with inferred levels of farmer genetic ancestry, whereas BMI is only weakly correlated, perhaps reflecting greater contributions of non-genetic factors to body weight than to height. Single- and multi-marker association tests identify one region and eight genes associated with hunter-gatherer/farmer status, and 24 genes associated with the height-related traits. Many of these genes have putative functions consistent with roles in determining their associated traits and the pygmy phenotype, and they include three associated with standing height in non-Africans (PRKG1, DSCAM, MAGI2). We find evidence that European height-associated SNPs or variants in linkage disequilibrium with them contribute to standing- and sitting-height determination in Central Africans, but not to the differential status of hunter-gatherers and farmers. These findings provide new insights into the biological basis of the pygmy phenotype, and they highlight the potential of cross-population studies for exploring the genetic basis of phenotypes that vary naturally across populations.

Autonomy, Equality, and Teaching among Aka Foragers and Ngandu Farmers of the Congo Basin

The significance of teaching to the evolution of human culture is under debate. We contribute to the discussion by using a quantitative, cross-cultural comparative approach to investigate the role of teaching in the lives of children in two small-scale societies: Aka foragers and Ngandu farmers of the Central African Republic. Focal follows with behavior coding were used to record social learning experiences of children aged 4 to 16 during daily life. "Teaching" was coded based on a functional definition from evolutionary biology. Frequencies, contexts, and subtypes of teaching as well as the identity of teachers were analyzed. Teaching was rare compared to observational learning, although both forms of social learning were negatively correlated with age. Children received teaching from a variety of individuals, and they also engaged in teaching. Several teaching types were observed, including instruction, negative feedback, and commands. Statistical differences in the distribution of teaching types and the identity of teachers corresponded with contrasting forager vs. farmer foundational cultural schema. For example, Aka children received less instruction, which empirically limits autonomous learning, and were as likely to receive instruction and negative feedback from other children as they were from adults. Commands, however, exhibited a different pattern suggesting a more complex role for this teaching type. Although consistent with claims that teaching is relatively rare in small-scale societies, this evidence supports the conclusion that teaching is a universal, early emerging cognitive ability in humans. However, culture (e.g., values for autonomy and egalitarianism) structures the nature of teaching.

Providing Care and Facing Death: Nursing During Ebola Outbreaks in Central Africa

Few studies have focused on describing the experiences of health care workers during rapid killing epidemics. In this article, the views and experiences of nurses during three outbreaks of Ebola hemorrhagic fever (EHF) in Central Africa are examined. These three outbreaks occurred in Kikwit, Democratic Republic of Congo (DRC, 1995); Gulu, Uganda (2000-2001); and Republic of Congo (ROC, 2003). Open-ended and semistructured interviews with individuals and small groups were conducted during the outbreaks in Uganda and ROC; data from DRC are extracted from published sources. Three key themes emerged from the interviews: (a) lack of protective gear, basic equipment, and other resources necessary to provide care, especially during the early phases of the outbreaks; (b) stigmatization by family, coworkers, and community; and (c) exceptional commitment to the nursing profession in a context where the lives of the health care workers were in jeopardy.

Teaching in hunter-gatherer infancy

A debate exists as to whether teaching is part of human nature and central to understanding culture or whether it is a recent invention of Western, Educated, Industrial, Rich, Democratic cultures. Some social-cultural anthropologists and cultural psychologists indicate teaching is rare in small-scale cultures while cognitive psychologists and evolutionary biologists indicate it is universal and key to understanding human culture. This study addresses the following questions: Does teaching of infants exist in hunter-gatherers? If teaching occurs in infancy, what skills or knowledge is transmitted by this process, how often does it occur and who is teaching? The study focuses on late infancy because cognitive psychologists indicate that one form of teaching, called natural pedagogy, emerges at this age. Videotapes of Aka hunter-gatherer infants were used to evaluate whether or not teaching exists among Aka hunter-gatherers of central Africa. The study finds evidence of multiple forms of teaching, including natural pedagogy, that are used to enhance learning of a variety of skills and knowledge.

Cultural variation in the use of overimitation by the Aka and Ngandu of the Congo Basin

Studies in Western cultures have observed that both children and adults tend to overimitate, copying causally irrelevant actions in the presence of clear causal information. Investigation of this feature in non-Western groups has found little difference cross-culturally in the frequency or manner with which individuals overimitate. However, each of the non-Western populations studied thus far has a history of close interaction with Western cultures, such that they are now far removed from life in a hunter-gatherer or other small-scale culture. To investigate overimitation in a context of limited Western cultural influences, we conducted a study with the Aka hunter-gatherers and neighboring Ngandu horticulturalists of the Congo Basin rainforest in the southern Central African Republic. Aka children, Ngandu children, and Aka adults were presented with a reward retrieval task similar to those performed in previous studies, involving a demonstrated sequence of causally relevant and irrelevant actions. Aka children were found not to overimitate as expected, instead displaying one of the lowest rates of overimitation seen under similar conditions. Aka children copied fewer irrelevant actions than Aka adults, used a lower proportion of irrelevant actions than Ngandu children and Aka adults, and had less copying fidelity than Aka adults. Measures from Ngandu children were intermediate between the two Aka groups. Of the participants that succeeded in retrieving the reward, 60% of Aka children used emulation rather than imitation, compared to 15% of Ngandu children, 11% of Aka adults, and 0% of Western children of similar age. From these results, we conclude that cross-cultural variation exists in the use of overimitation during childhood. Further study is needed under a more diverse representation of cultural and socioeconomic groups in order to investigate the cognitive underpinnings of overimitation and its possible influences on social learning and the biological and cultural evolution of our species.

Allomaternal nursing in humans

Few studies exist of allomaternal nursing in humans. It is relatively common among some cultures, such as the Aka and Efé hunter-gatherers of the Congo Basin, but it does not occur in other foragers such as the !Kung and Hadza of Southern and East Africa. This paper utilizes focal follow observations of Aka and Efé infants, interviews with Aka mothers, ethnographic reports from researchers working with hunter-gatherers, and a survey of the eHRAF cultures to try to answer the following questions: how often does allomaternal nursing occur, who provides it, and under what contexts does it take place? The study indicates that it occurs in many cultures (93% of cultures with data) but that it is normative in relatively few cultures; biological kin, especially grandmothers, frequently provide allomaternal nursing and that infant age, mother's condition, and culture (e.g., cultural models about if and when women other than the mother can nurse an infant or colostrum taboos) impact the nature and frequency of allomaternal nursing. The empirical results of this exploratory study are discussed in the context of existing hypotheses used to explain allomaternal nursing.

Ontogeny of prosocial behavior across diverse societies

Humans are an exceptionally cooperative species, but there is substantial variation in the extent of cooperation across societies. Understanding the sources of this variability may provide insights about the forces that sustain cooperation. We examined the ontogeny of prosocial behavior by studying 326 children 3-14 y of age and 120 adults from six societies (age distributions varied across societies). These six societies span a wide range of extant human variation in culture, geography, and subsistence strategies, including foragers, herders, horticulturalists, and urban dwellers across the Americas, Oceania, and Africa. When delivering benefits to others was personally costly, rates of prosocial behavior dropped across all six societies as children approached middle childhood and then rates of prosociality diverged as children tracked toward the behavior of adults in their own societies. When prosocial acts did not require personal sacrifice, prosocial responses increased steadily as children matured with little variation in behavior across societies. Our results are consistent with theories emphasizing the importance of acquired cultural norms in shaping costly forms of cooperation and creating cross-cultural diversity.

A biocultural approach to breastfeeding interactions in Central Africa

Anthropologists have long recognized that breastfeeding involves much more than feeding; it entails intimate social interactions between infants or children and their mothers. However, breastfeeding has predominantly been studied with respect to structural features (frequency, timing) as well as nutritional and health aspects of infant feeding. Thus, in this study we complement previous anthropological studies by examining social interactions that occur during breastfeeding among the Aka and Bofi foragers and Ngandu and Bofi farmers at various ages (three to four months, nine to ten months, toddlers). Further, we use an integrated biocultural perspective to explore how patterns of breastfeeding and social interactions can be shaped by economic constraints, cultural values, and children's development. Overall, our findings illustrate how biological and cultural factors interact and provide useful explanations of variations in breastfeeding structure and social interactions more so than either perspective alone.

Social learning among Congo Basin hunter-gatherers

This paper explores childhood social learning among Aka and Bofi hunter-gatherers in Central Africa. Existing literature suggests that hunter-gatherer social learning is primarily vertical (parent-to-child) and that teaching is rare. We use behavioural observations, open-ended and semi-structured interviews, and informal and anecdotal observations to examine the modes (e.g. vertical versus horizontal/oblique) and processes (e.g. teaching versus observation and imitation) of cultural transmission. Cultural and demographic contexts of social learning associated with the modes and processes of cultural transmission are described. Hunter-gatherer social learning occurred early, was relatively rapid, primarily vertical under age 5 and oblique and horizontal between the ages of 6 and 12. Pedagogy and other forms of teaching existed as early as 12 months of age, but were relatively infrequent by comparison to other processes of social learning such as observation and imitation.

Medical anthropology and Ebola in Congo: cultural models and humanistic care

Seldom have medical anthropologists been involved in efforts to control high mortality diseases such as Ebola hemorrhagic fever (EHF) This paper describes the results of two distinct but complementary interventions during the first phases of an outbreak in the Republic of Congo in 2003. The first approach emphasized understanding local peoples cultural models and political-economic explanations for the disease while the second approach focused on providing more humanitarian care of patients by identifying and incorporating local beliefs and practices into patient care and response efforts.

Cultural contexts of Ebola in northern Uganda

Technical guidelines for the control of Ebola hemorrhagic fever (EHF) indicate that understanding local views and responses to an outbreak is essential. However, few studies with such information exist. Thus, we used qualitative and quantitative methods to determine how local residents of Gulu, Uganda, viewed and responded to the 2000–2001 outbreak of EHF. Results indicated that Acholi people used at least three explanatory models to explain and respond to the outbreak; indigenous epidemic control measures were often implemented and consistent with those being promoted by healthcare workers; and some cultural practices amplified the outbreak (e.g., burial practices). However, most persons were willing to modify and work with national and international healthcare workers.

Culture and early infancy among central African foragers and farmers

Everyday infant experiences among the Aka hunter-gatherers and the neighboring Ngandu farmers were observed and compared. Twenty Aka and 21 Ngandu 3- to 4-month-olds and 20 Aka and 20 Ngandu 9- to 10-month-olds were observed for 3 hr on each of 4 days so that all 12 daylight hr were covered. The Aka infants were more likely to be held, fed, and asleep or drowsy, whereas Ngandu infants were more likely to be alone and to fuss or cry, smile, vocalize, or play. The amount of crying, soothing, feeding, and sleeping declined over time in both groups. Distal social interaction increased over time among the Ngandu but not among the Aka. Despite striking cultural differences on many variables, however, functional context systematically affected the relative prominence of the infants' behavior in both cultural groups.

Culture and early infancy among central African foragers and farmers

Everyday infant experiences among the Aka hunter-gatherers and the neighboring Ngandu farmers were observed and compared. Twenty Aka and 21 Ngandu 3- to 4-month-olds and 20 Aka and 20 Ngandu 9- to 10-month-olds were observed for 3 hr on each of 4 days so that all 12 daylight hr were covered. The Aka infants were more likely to be held, fed, and asleep or drowsy, whereas Ngandu infants were more likely to be alone and to fuss or cry, smile, vocalize, or play. The amount of crying, soothing, feeding, and sleeping declined over time in both groups. Distal social interaction increased over time among the Ngandu but not among the Aka. Despite striking cultural differences on many variables, however, functional context systematically affected the relative prominence of the infants' behavior in both cultural groups.

Anthropological contributions to a community-based schistosomiasis control project in northern Cameroun

This paper describes how anthropological contributions and extensive cooperation between tropical medicine and medical anthropology researchers contributed to a successful community-based cost recovery schistosomiasis control project in northern Cameroun. The project led to increased knowledge about urinary schistosomiasis by local people, significant decreases in prevalence and intensity of the disease, and increased utilization of primary health care centers.

Ivermectin distribution and the cultural context of forest onchocerciasis in South Province, Cameroon

This investigation examined the cultural context of forest onchocerciasis in several communities in the Dja-Lobo Division of southern Cameroon. The study sought to elucidate behaviors that would enhance or diminish health status relative to forest onchocerciasis and other filarial infections, and to make culturally sensitive and appropriate recommendations regarding the development of health education materials and the long-term sustainability of the ivermectin distribution program in Dja-Lobo. The study consisted of two sequential components; the first was a qualitative study of a few severely affected villages and the second was a quantitative study of 212 randomly selected heads of households from eight villages. The Boulou and Baka peoples in these communities defined general filariasis (minak) as small worms under the skin, identified flies as important transmitters of the illness, and indicated that blindness and other skin and ocular problems were a consequence of the illness. Illness of the Dja (referring to an illness found near the Dja River) was another illness that was closely linked to onchocerciasis; local people indicated it was transmitted by the black flies found near the Dja River, resulting in severe itching and leopard skin. These and other cultural-behavioral data on filariasis were used to implement a health education and distribution program.

Community-based approach to schistosomiasis control

With few exceptions, efforts to control schistosomiasis have relied upon ongoing community cooperation with "outsiders' rather than creating within the community the capacity and means for carrying out ongoing disease control measures with minimal external support. Offered as a useful model is a program in Kaele subdivision, Extreme North Province, Cameroon designed to establish and integrate within the primary health care (PHC) system the control of urinary schistosomiasis, hyperendemic in the region. At the community level, and with minimal dependence upon external resources, culturally appropriate and effective health education was instituted, the capacity to diagnose and treat schistosomiasis was created, diagnosis and drug therapy (praziquantel) was made available conveniently and at low cost, and, on a very limited basis, snails were controlled. Efforts were made to build upon and strengthen existing community structures and institutions rather than create new ones. The impact of the interventions was measured in terms of changes in knowledge and behavior, prevalence and intensity of infection, utilization of health services, and the ability to finance the control activities within the context of a generalized cost recovery system. Program successes and failures are discussed, as well as lessons learned and their implications.