Strong reciprocity is an effective way to promote cooperation. This is especially true when one not only cooperates with cooperators and defects on defectors (second-party punishment) but even punishes those who defect on others (third-party, “altruistic” punishment). Some suggest we humans have a taste for such altruistic punishment and that this was important in the evolution of human cooperation. To assess this we need to look across a wide range of cultures. As part of a cross-cultural project, I played three (...) experimental economics games with the Hadza, who are hunter-gatherers in Tanzania. The Hadza frequently engaged in second-party punishment but they rarely engaged in third-party punishment. Other small-scale societies engaged in less third-party punishment as well. I suggest third-party punishment only became more important in large, complex societies to solve more pressing collective-action problems. (shrink)

The literature on human mate preferences is vast but most data come from studies on college students in complex societies, who represent a thin slice of cultural variation in an evolutionarily novel environment. Here, I present data on the mate preferences of men and women in a society of hunter-gatherers, the Hadza of Tanzania. Hadza men value fertility in a mate more than women do, and women value intelligence more than men do. Women place great importance on men’s (...) foraging, and both sexes rate character as important. Unlike college students, Hadza men place considerable importance on women being hard-working, and Hadza women cite looks about as often as men do. (shrink)

Cooperative child care among humans, where individuals other than the biological mother (allomothers) provide care, may increase a mother’s fertility and the survivorship of her children. Although the potential benefits to the mother are clear, the motivations for allomothers to provide care are less clear. Here, we evaluate the kin selection allomothering hypothesis using observations on Hadza hunter-gatherers collected in ten camps over 17 months. Our results indicate that related allomothers spend the largest percentage of time holding children. The (...) higher the degree of relatedness among kin, the more time they spend holding, supporting the hypothesis of nepotism as the strongest motivation for providing allomaternal care. Unrelated helpers of all ages also provide a substantial amount of investment, which may be motivated by learning to mother, reciprocity, or coercion. (shrink)

Among hunter-gatherers, the sharing of male and female foods is often assumed to result in virtually the same diet for males and females. Although food sharing is widespread among the hunting and gathering Hadza of Tanzania, women were observed eating significantly more tubers than men. This study investigates the relationship between patterns of dental wear, diet, and extramasticatory use of teeth among the Hadza. Casts of the upper dentitions were made from molds taken from 126 adults and scored (...) according to the Murphy dental attrition scoring system. Females had significantly greater anterior occlusal wear than males when we controlled for age. Males exhibited greater asymmetry in wear, with greater wear on the left side in canines, first premolars, and first molars. We suggest that these sex differences in wear patterns reflect the differences seen in the diet, as well as in the use of teeth as tools. (shrink)

Folk stories featuring prosocial content are ubiquitous across cultures. One explanation for the ubiquity of such stories is that stories teach people about the local socioecology, including norms of prosociality, and stories featuring prosocial content may increase generosity in listeners. We tested this hypothesis in a sample of 185 Hadza hunter-gatherers. We read participants a story in which the main character either swims with another person (control story) or rescues him from drowning (prosocial story). After hearing the story, participants (...) played a dictator game with dried meat sticks and then were given a recall test of facts presented in the story. There was moderate evidence for a small effect of the prosocial story: participants who heard the prosocial story gave an estimated 0.22 [90% HDI: −0.12–0.57] more meat sticks than those who heard the control story. However, the association between generosity and sex, marital status, and region of residence was stronger; men gave more than women, unmarried participants gave more than married participants, and participants living in a region with more exposure to markets gave more than participants living further from markets. There was no evidence that the prosocial story was more easily recalled than the control story. These results provide some support for the hypothesis that prosocial stories can increase prosociality in listeners, though the effect of hearing a single story is small. (shrink)

The Hadza foragers of Tanzania are currently experiencing a nutritional shift that includes the intensification of domesticated cultigens in the diet. Despite these changes, no study, to date, has examined the possible effects of this transition on the food collection behavior of young foragers. Here we present a cross-sectional study on foraging behavior taken from two time points, 2005 and 2017. We compare the number of days foraged and the type and amount of food collected for young foragers, aged (...) 5–14 years, in age- and season-matched samples. Compared with 2005, in 2017 fewer subadults left camp to forage, and overall, they targeted a smaller variety of wild foods, with the noticeable absence of wild honey, figs, and tubers. In addition, participants in 2017 were significantly more likely to have attended school. Despite the increased presence of domesticated plant foods in the diet and increased attendance at school, some young foragers continue to be highly productive in collecting wild, undomesticated foods. Despite the preliminary nature of our results, our findings suggest that the range of wild foods targeted by subadults is decreasing as the amount of domesticated cultigens in the diet increases. These data underscore the importance of studying diet composition and foraging decisions across temporal, nutritional, and ecological landscapes. (shrink)

We use data collected among Hadza hunter-gatherers between 2005 and 2009 to examine hypotheses about the causes and consequences of men’s foraging and food sharing. We find that Hadza men foraged for a range of food types, including fruit, honey, small animals, and large game. Large game were shared not like common goods, but in ways that significantly advantaged producers’ households. Food sharing and consumption data show that men channeled the foods they produced to their wives, children, and (...) their consanguineal and affinal kin living in other households. On average, single men brought food to camp on 28% of days, married men without children at home on 31% of days, and married men with children at home on 42% of days. Married men brought fruit, the least widely shared resource, to camp significantly more often than single men. A model of the relationship between hunting success and household food consumption indicates that the best hunters provided 3–4 times the amount of food to their families than median or poor hunters. These new data fill important gaps in our knowledge of the subsistence economy of the Hadza and uphold predictions derived from the household and kin provisioning hypotheses. Key evidence and assumptions backing prior claims that Hadza hunting is largely a form of status competition were not replicated in our study. In light of this, family provisioning is a more viable explanation for why good hunters are preferred as husbands and have higher fertility than others. (shrink)

Aspects of human life history and cognition, such as our long childhoods and extensive use of teaching, theoretically evolved to facilitate the acquisition of complex tasks. The present paper empirically examines the relationship between subsistence task difficulty and age of acquisition, rates of teaching, and rates of oblique transmission among Hadza and BaYaka foragers from Tanzania and the Republic of Congo. We further examine cross-cultural variation in how and from whom learning occurred. Learning patterns and community perceptions of task (...) difficulty were assessed through interviews. We found no relationship between task difficulty, age of acquisition, and oblique transmission, and a weak but positive relationship between task difficulty and rates of teaching. While same-sex transmission was normative in both societies, tasks ranked as more difficult were more likely to be transmitted by men among the BaYaka, but not among the Hadza, potentially reflecting cross-cultural differences in the sexual division of subsistence and teaching labor. Further, the BaYaka were more likely to report learning via teaching, and less likely to report learning via observation, than the Hadza, possibly owing to differences in socialization practices. (shrink)

When we have asked Hadza whether married couples should live with the family of the wife (uxorilocally) or the family of the husband (virilocally), we are often told that young couples should spend the first years of a marriage living with the wife’s family, and then later, after a few children have been born, the couple has more freedom—they can continue to reside with the wife’s kin, or else they could join the husband’s kin, or perhaps live in a (...) camp where there are no close kin. In this paper, we address why shifts in kin coresidence patterns may arise in the later years of a marriage, after the birth of children. To do so, we model the inclusive fitness costs that wives might experience from leaving their own kin and joining their husband’s kin as a function of the number of children in their nuclear family. Our model suggests that such shifts should become less costly to wives as their families grow. This simple model may help explain some of the dynamics of postmarital residence among the Hadza and offer insight into the dynamics of multilocal residence, the most prevalent form of postmarital residence among foragers. (shrink)

Cross-cultural sex differences in mobility and harm avoidance have been widely reported, often emphasizing fitness benefits of long-distance travel for males and high costs for females. Data emerging from adults in small-scale societies, however, are challenging the assumption that female mobility is restricted during reproduction. Such findings warrant further exploration of the ontogeny of mobility. Here, using a combination of machine-learning, mixed-effects linear regression, and GIS mapping, we analyze range size, daily distance traveled, and harm avoidance among Hadza foragers (...) during middle childhood and adolescence. Distance traveled increased with age and, while male adolescents had the longest daily ranges, average daily distance traveled by each sex was similar. We found few age- or sex-related patterns in harm-avoidant responses and a high degree of individual variation. When queried on the same issues, children and their parents were often in alignment as to expectations pertaining to harm avoidance, and siblings tended to behave in similar ways. To the extent that sex differences in mobility did emerge, they were associated with ecological differences in physical threats associated with sex-specific foraging behaviors. Further, we found no strong association between harm avoidance and mobility. Young Hadza foragers of both sexes are highly mobile, regardless of how harm avoidant they are. Taken together, our findings indicate that the causal arrows between harm avoidance and mobility must be evaluated in ecologically specific frameworks where cultural expectations of juvenile mobility can be contextualized. (shrink)

The ratio of index- and ring-finger lengths is thought to be related to prenatal androgen exposure, and in many, though not all, populations, men have a lower average digit ratio than do women. In many studies an inverse relationship has been observed, among both men and women, between 2D:4D ratio and measures of athletic ability. It has been further suggested that, in hunter-gatherer populations, 2D:4D ratio might also be negatively correlated with hunting ability, itself assumed to be contingent on athleticism. (...) This hypothesis has been tested using endurance running performance among runners from a Western, educated, and industrialized population as a proximate measure of hunting ability. However, it has not previously been tested among actual hunter-gatherers using more ecologically valid measures of hunting ability and success. The current study addresses this question among Tanzanian Hadza hunter-gatherers. I employ a novel method of assessing hunting reputation that, unlike previous methods, allows granular distinctions to be made between hunters at all levels of perceived ability. I find no statistically significant relationship between digit ratio and either hunting reputation or two important hunting skills. I confirm that Hadza men have higher mean 2D:4D ratios than men in many Western populations. I discuss the notion that 2D:4D ratio may be the consequence of an allometric scaling relationship between relative and absolute finger lengths. Although it is difficult to draw clear conclusions from these results, the current study provides no support for the theorized relationship between 2D:4D ratio and hunting skill. (shrink)

The ratio of index- and ring-finger lengths is thought to be related to prenatal androgen exposure, and in many, though not all, populations, men have a lower average digit ratio than do women. In many studies an inverse relationship has been observed, among both men and women, between 2D:4D ratio and measures of athletic ability. It has been further suggested that, in hunter-gatherer populations, 2D:4D ratio might also be negatively correlated with hunting ability, itself assumed to be contingent on athleticism. (...) This hypothesis has been tested using endurance running performance among runners from a Western, educated, and industrialized population as a proximate measure of hunting ability. However, it has not previously been tested among actual hunter-gatherers using more ecologically valid measures of hunting ability and success. The current study addresses this question among Tanzanian Hadza hunter-gatherers. I employ a novel method of assessing hunting reputation that, unlike previous methods, allows granular distinctions to be made between hunters at all levels of perceived ability. I find no statistically significant relationship between digit ratio and either hunting reputation or two important hunting skills. I confirm that Hadza men have higher mean 2D:4D ratios than men in many Western populations. I discuss the notion that 2D:4D ratio may be the consequence of an allometric scaling relationship between relative and absolute finger lengths. Although it is difficult to draw clear conclusions from these results, the current study provides no support for the theorized relationship between 2D:4D ratio and hunting skill. (shrink)

A correction to this paper has been published: https://doi.org/10.1007/s12110-021-09403-x.

Helping behavior is likely to have evolved to increase summary chances for survival of an individual and their group. Nevertheless, populations differ significantly in their eagerness to help, and still little is known about populational and inter-individual determinants of these differences. Previous studies indicated that economic and physiological factors might influence helping behavior. The aim of the present study was to investigate the effects of approach to resource management of a society (immediate-return economy vs. delayed-return economy), prenatal androgenization (based on (...) second-to-fourth digit ratio), and physical strength (based on hand grip strength) on helping behavior towards others. Helping was assessed in terms of both general eagerness to help and differential helping towards: (1) kin, (2) other group members indiscriminately, (3) friends, and (4) those from whom help was obtained in the past. Based on data collected in two small-scale societies, we found that people in the egalitarian immediate-return society (the Hadza hunter-gatherers of Tanzania) engaged in helping behavior significantly more often than representatives of a more stratified delayed-return economy (Yali horticulturalists of Papua). Additionally, our results revealed that physical strength was a significant predictor of helping behavior in women but not in men. We discuss our findings in the light of the adaptive value of helping behavior. (shrink)

Menopause is puzzling because life-history theory predicts there should be no selection for outliving one’s reproductive capacity. Adaptive explanations of menopause offered thus far turn on women’s long-term investment in offspring and grandoffspring, all variations on the grandmother hypothesis. Here, I offer a very different explanation. The patriarch hypothesis proposes that once males became capable of maintaining high status and reproductive access beyond their peak physical condition, selection favored the extension of maximum life span in males. Because the relevant genes (...) were not on the Y chromosome, life span increased in females as well. However, the female reproductive span was constrained by the depletion of viable oocytes, which resulted in menopause. (shrink)

Humans have a much longer juvenile period (weaning to first reproduction, 14 or more years) than their closest relatives (chimpanzees, 8 years). Three explanations are prominent in the literature. (a) Humans need the extra time to learn their complex subsistence techniques. (b) Among mammals, since length of the juvenile period bears a constant relationship to adult lifespan, the human juvenile period is just as expected. We therefore only need to explain the elongated adult lifespan, which can be explained by the (...) opportunity for older individuals to increase their fitness by providing for grandchildren. (c) The recent model by Kaplan and colleagues suggests that longevity and investment in "embodied capital" will coevolve, and that the need to learn subsistence technology contributed to selection for our extended lifespan.We report experiments designed to test the first explanation: human subsistence technology takes many years to learn, and spending more time learning it gives reproductive benefits that outweight lost time. Taking away some of this time should lead to deficits in efficiency. We paid Hadza foragers to participate in tests of important subsistence skills. We compared efficiency of males and females at digging tubers. They differ greatly in time spent practicing digging but show no difference in efficiency. Children who lost "bush experience" by spending years in boarding school performed no worse at digging tubers or target archery than those who had spent their entire lives in the bush. Climbing baobab trees, an important and dangerous skill, showed no change with age among those who attempted it. We could show no effects of practice time.These findings do not support what we label "the practice theory," but we discuss ways in which the theory could be defended; for example, some as-yet-untested skill may be greatly impaired by loss of a few years of the juvenile period. Our data also show that it is not safe to assume that increases in skill with age are entirely due to learning or practice; they may instead be due to increases in size and strength. (shrink)

Anecdotal evidence from many hunter-gatherer societies suggests that successful hunters experience higher prestige and greater reproductive success. Detailed quantitative data on these patterns are now available for five widely dispersed cases (Ache, Hadza, !Kung, Lamalera, and Meriam) and indicate that better hunters exhibit higher age-corrected reproductive success than other men in their social group. Leading explanations to account for this pattern are: (1) direct provisioning of hunters’ wives and offspring, (2) dyadic reciprocity, (3) indirect reciprocity, (4) costly signaling, and (...) (5) phenotypic correlation. I examine the qualitative and quantitative evidence bearing on these explanations and conclude that although none can be definitively rejected, extensive and apparently unconditional sharing of large game somewhat weakens the first three explanations. The costly signaling explanation has support in some cases, although the exact nature of the benefits gained from mating or allying with or deferring to better hunters needs further study. (shrink)

The ratio of index- and ring-finger lengths is thought to be related to prenatal androgen exposure, and in many, though not all, populations, men have a lower average digit ratio than do women. In many studies an inverse relationship has been observed, among both men and women, between 2D:4D ratio and measures of athletic ability. It has been further suggested that, in hunter-gatherer populations, 2D:4D ratio might also be negatively correlated with hunting ability, itself assumed to be contingent on athleticism. (...) This hypothesis has been tested using endurance running performance among runners from a Western, educated, and industrialized population as a proximate measure of hunting ability. However, it has not previously been tested among actual hunter-gatherers using more ecologically valid measures of hunting ability and success. The current study addresses this question among Tanzanian Hadza hunter-gatherers. I employ a novel method of assessing hunting reputation that, unlike previous methods, allows granular distinctions to be made between hunters at all levels of perceived ability. I find no statistically significant relationship between digit ratio and either hunting reputation or two important hunting skills. I confirm that Hadza men have higher mean 2D:4D ratios than men in many Western populations. I discuss the notion that 2D:4D ratio may be the consequence of an allometric scaling relationship between relative and absolute finger lengths. Although it is difficult to draw clear conclusions from these results, the current study provides no support for the theorized relationship between 2D:4D ratio and hunting skill. (shrink)