Height and integration in proximity networks among Tanzanian Hadza men.

In recent years there has been much interest in investigating the extent to which social status or prestige are related to an individual's degree of integration in social networks. It has been shown that, among hunter-gatherers, social characteristics of an individual based on social status or prestige, such foraging reputation, friendship popularity, and pro-social reputation, can influence the extent to which an individual is embedded in a social network. However, little is known regarding the extent to which height, a physical trait that in Western societies is often associated with social status, is associated in integration in social networks among small-scale hunter gatherers. Here, we investigated the relationship between height and a position an individual occupies in proximity networks among Hadza men (n = 30), hunter-gatherers living in Northern Tanzania. The results of our study show that height is not related to the position an individual maintains in proximity networks. We argue that, in a relatively egalitarian small-scale hunter-gatherer societies such as the Hadza, social interactions driving proximity networks might be influenced by social traits, such as popularity and hunting reputation, rather than physical traits, such as height.

Status does not predict stress among Hadza hunter-gatherer men.

In recent years there has been much research regarding the extent to which social status is related to long-term indices of health. The majority of studies looking at the interplay between social status and health have been conducted in industrialized societies. However, it has been argued that most of human evolution took place in small, mobile and egalitarian hunter-gatherer groups where individuals exhibited very little variation in terms of material wealth or possessions. In this study, we looked at the extent to which two domains of social status, hunting reputation (being perceived as a good hunter) and popularity (being perceived as a friend), are related to physiological stress levels among Hadza men, hunter-gatherers living in Northern Tanzania. The results of our study show that neither hunting reputation nor popularity is associated with stress levels. Overall, our data suggest that, in at least some traditional small-scale societies exhibiting an egalitarian social model, such as the Hadza, the variation in social status measures based on both popularity and hunting reputation does not translate into one of the commonly used indices of wellbeing.

Relationship between proximity and physiological stress levels in hunter-gatherers: The Hadza.

In recent years there has been a great deal of documentation on how social relationships are related to various aspects of human wellbeing. However, until recently most studies investigating the effects of social relationships on wellbeing have applied social network measures to reported social contacts. Recent advances in the application of bio-loggers in biological studies have now made it possible to quantify social relationships based on in-person, rather than self-reported, social interactions. We used GPS-derived in-camp and out-of-camp proximity data to analyse how in-person proximity is related to Hair Cortisol Concentration (HCC) among Hadza hunter-gatherers. Time spent in close proximity to other camp members was associated with higher HCC, especially in women. In contrast, individuals who spent more time in close out-of-camp proximity to their best friend experienced lower HCC. Our study suggests that physiological costs related to group living might be mitigated by in-person interactions with close friends. We also find that the location (i.e., in-camp vs out-of-camp) of proximity to others and self-perceived friends is associated with HCC among the Hadza.

Field-testing olfactory ability to understand human olfactory ecology.

OBJECTIVES: We know little about human olfactory ability in natural settings because current knowledge derives from lab-based studies using nonrepresentative samples of convenience. The primary objective was to use a validated lab tool, the five-item odor identification test, to assess variation in olfactory ability in different environments. METHODS: Using the five-item test, we conducted two repeated measures experiments that assessed participant ability to correctly identify an odor source in different odor environments. We also examined consistency in odor labelling due to documented potential bias from idiosyncrasies in odor terms. RESULTS: We found no variation in olfactory ability due to environment, but this may be due to methodological biases. First, subjective bias results from idiosyncratic differences in participant labelling and researcher coding of answer correctness. Second, better ability to learn odors may provide an advantage to women. Third, reducing positive female learning bias by analyzing consistency in response (regardless of correct odor source identification) results in no sex differences but fails to assess the functional aspect of olfactory ability (naming the correct odor source). Fourth, functional olfactory ability is significantly better in women, especially in food-rich odor environments. CONCLUSIONS: Environment was not a significant factor in olfactory ability in this study but that result may be confounded by methodological biases. We do not recommend odor identification as a field tool. Functional olfactory ability exhibits a sex-based pattern but consistency in recognizing the same odor does not. Food-rich odors may enhance olfactory ability in females. We discuss evolutionary and ecological implications of superior female functional olfactory ability relative to food foraging activity.

Status does not predict stress: Women in an egalitarian hunter-gatherer society.

It is widely believed that there is strong association between physiological stress and an individual's social status in their social hierarchy. This has been claimed for all humans cross-culturally, as well as in non-human animals living in social groups. However, the relationship between stress and social status has not been explored in any egalitarian hunter-gatherer society; it is also under investigated in exclusively female social groups. Most of human evolutionary history was spent in small, mobile foraging bands of hunter-gatherers with little economic differentiation - egalitarian societies. We analysed women's hair cortisol concentration along with two domains of women's social status (foraging reputation and popularity) in an egalitarian hunter-gatherer society, the Hadza. We hypothesized that higher social status would be associated with lower physiological indicators of stress in these women. Surprisingly, we did not find any association between either foraging reputation or popularity and hair cortisol concentration. The results of our study suggest that social status is not a consistent or powerful predictor of physiological stress levels in women in an egalitarian social structure. This challenges the notion that social status has the same basic physiological implications across all demographics and in all human societies.

Early Holocene morphological variation in hunter-gatherer hands and feet.

BACKGROUND: The Windover mortuary pond dates to the Early Archaic period (6,800-5,200 years ago) and constitutes one of the earliest archaeological sites with intact and well-preserved human remains in North America. Unlike many prehistoric egalitarian hunter-gatherers, the Windover people may not have practiced a sex-based division of labor; rather, they may have shared the load. We explore how mobility and subsistence, as reconstructed from archaeological data, influenced hand and foot bone morphology at Windover. METHODS: We took length and width measurements on four carpal bones, four tarsal bones, and load-bearing tarsal areas (calcaneus load arm, trochlea of the talus). We analyzed lateralization using side differences in raw length and width measurements. For other hypothesis testing, we used log transformed length-width ratios to mitigate the confounding effects of sexual dimorphism and trait size variation; we tested between-sex differences in weight-bearing (rear foot) and shock-absorbing (mid foot) tarsal bones and between-sex differences in carpal bones. RESULTS: We identified no significant between-sex differences in rear and midfoot areas, suggesting similar biomechanical stresses. We identified no significant between-sex differences in carpal bones but the test was under-powered due to small sample sizes. Finally, despite widespread behavioral evidence on contemporary populations for human hand and foot lateralization, we found no evidence of either handedness or footedness. DISCUSSION: The lack evidence for footedness was expected due its minimal impact on walking gait but the lack of evidence for handedness was surprising given that ethnographic studies have shown strong handedness in hunter-gatherers during tool and goods manufacture. The reconstructed activity patterns suggested both sexes engaged in heavy load carrying and a shared division of labor. Our results support previous findings-both sexes had stronger weight-bearing bones. Male shock-absorbing bones exhibited a trend towards greater relative width (suggesting greater comparative biomechanical stress) than females which may reflect the typical pattern of male hunter-gatherers engaging in walking greater distances at higher speeds than females. While there were no significant between-sex differences in carpal bones (supporting a shared work load model), females exhibited greater variation in index values, which may reflect a greater variety of and specialization in tasks compared to males. Because carpals and tarsals are so well-preserved at archaeological sites, we had surmised they might be useful proxies for activity in the absence of well-preserved long bones. Tarsals provide a stronger signal of past activity and may be useful in the absence of, or in addition to, preferred bones. Carpals, however, may not be useful as the effect size of biomechanical stress (in this study at least) is low and would require larger samples than may be possible at archaeological sites.

Frequency and developmental timing of linear enamel hypoplasia defects in Early Archaic Texan hunter-gatherers.

Digital photographs taken under controlled conditions were used to examine the incidence of linear enamel hypoplasia defects (LEHs) in burials from the Buckeye Knoll archaeological site (41VT98 Victoria county, Texas), which spans the Early to Late Archaic Period (ca. 2,500-6,500 BP uncorrected radiocarbon). The majority (68 of 74 burials) date to the Texas Early Archaic, including one extremely early burial dated to 8,500 BP. The photogrammetric data collection method also results in an archive for Buckeye Knoll, a significant rare Archaic period collection that has been repatriated and reinterred. We analyzed the incidence and developmental timing of LEHs in permanent canines. Fifty-nine percent of permanent canines (n = 54) had at least one defect. There were no significant differences in LEH frequency between the maxillary and mandibular canines (U = 640.5, n1 = 37, n2 = 43, p = .110). The sample studied (n = 92 permanent canines) had an overall mean of 0.93 LEH defect per tooth, with a median of one defect, and a mode of zero defects. Average age at first insult was 3.92 (median = 4.00, range = 2.5-5.4) and the mean age of all insults per individual was 4.18 years old (range = 2.5-5.67). Age at first insult is consistent with onset of weaning stress-the weaning age range for hunter-gatherer societies is 1-4.5. Having an earlier age of first insult was associated with having more LEHs (n = 54, rho = -0.381, p = 0.005).

Honey, Hadza, hunter-gatherers, and human evolution.

Honey is the most energy dense food in nature. It is therefore not surprising that, where it exists, honey is an important food for almost all hunter-gatherers. Here we describe and analyze widespread honey collecting among foragers and show that where it is absent, in arctic and subarctic habitats, honey bees are also rare to absent. Second, we focus on one hunter-gatherer society, the Hadza of Tanzania. Hadza men and women both rank honey as their favorite food. Hadza acquire seven types of honey. Hadza women usually acquire honey that is close to the ground while men often climb tall baobab trees to raid the largest bee hives with stinging bees. Honey accounts for a substantial proportion of the kilocalories in the Hadza diet, especially that of Hadza men. Cross-cultural forager data reveal that in most hunter-gatherers, men acquire more honey than women but often, as with the Hadza, women do acquire some. Virtually all warm-climate foragers consume honey. Our closest living relatives, the great apes, take honey when they can. We suggest that honey has been part of the diet of our ancestors dating back to at least the earliest hominins. The earliest hominins, however, would have surely been less capable of acquiring as much honey as more recent, fully modern human hunter-gatherers. We discuss reasons for thinking our early ancestors would have acquired less honey than foragers ethnographically described, yet still significantly more than our great ape relatives.

Hunter-gatherers have less famine than agriculturalists.

The idea that hunter-gatherer societies experience more frequent famine than societies with other modes of subsistence is pervasive in the literature on human evolution. This idea underpins, for example, the 'thrifty genotype hypothesis'. This hypothesis proposes that our hunter-gatherer ancestors were adapted to frequent famines, and that these once adaptive 'thrifty genotypes' are now responsible for the current obesity epidemic. The suggestion that hunter-gatherers are more prone to famine also underlies the widespread assumption that these societies live in marginal habitats. Despite the ubiquity of references to 'feast and famine' in the literature describing our hunter-gatherer ancestors, it has rarely been tested whether hunter-gatherers suffer from more famine than other societies. Here, we analyse famine frequency and severity in a large cross-cultural database, in order to explore relationships between subsistence and famine risk. This is the first study to report that, if we control for habitat quality, hunter-gatherers actually had significantly less--not more--famine than other subsistence modes. This finding challenges some of the assumptions underlying for models of the evolution of the human diet, as well as our understanding of the recent epidemic of obesity and type 2 diabetes mellitus.

The human operational sex ratio: effects of marriage, concealed ovulation, and menopause on mate competition.

Among mammals, male-male competition for sexual access to females frequently involves fighting. Larger body size gives males an advantage in fighting, which explains why males tend to be larger than females in many species, including anthropoid primates. Mitani et al. derived a formula to measure the operational sex ratio (OSR) to reflect the degree of male-male competition using the number of reproductively available males to females who are cycling and capable of conceiving. The OSR should predict the degree of sexual dimorphism in body mass-at least if male-male competition involves much fighting or threatening. Here, we use hunter-gatherer demographic data and the Mitani et al. formula to calculate the human OSR. We show that humans have a much lower degree of body mass sexual dimorphism than is predicted by our OSR. We suggest this is because human competition rarely involves fighting. In human hunter-gatherer societies, differences in the ages of marriage have an impact on competition in that the age of males at first marriage is younger when there is a lower percentage of married men with two or more wives, and older when there is a higher percentage of married men with two or more wives. We discuss the implications of this for females, along with the effects of two key life history traits that influence the OSR, concealed ovulation and menopause. While menopause decreases the number of reproductively available females to males and thus increases male-male competition, concealed ovulation decreases male-male competition. Finally, we discuss the importance of mostly monogamous mate bonds in human evolution.

Sex differences in Hadza dental wear patterns : a preliminary report.

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.

Sex differences in Hadza eating frequency by food type.

OBJECTIVES: We investigate sex differences in frequencies of adults eating in a foraging population-the Hadza of Tanzania. METHODS: We use eating frequency data from instantaneous scan observations of the Hadza, to see to how much sharing of foods taken back to camp compensates for the targeting of different foods by each sex while out foraging. RESULTS: Eating in camp differs by sex in terms of overall eating frequency, as well as in terms of diet composition (frequencies of eating each food type). We also control for sex-differences in time spent in camp and still find sex-differences in eating frequencies-women are observed eating significantly more frequently than men. There are also sex-differences in the eating frequencies of particular food types both with and without controlling for presence in camp. Finally, we use data on acquisition of each food type by sex and find that both sexes are more frequently observed eating women's foods in camp than men's foods. CONCLUSIONS: At least in the case of the Hadza, we see pronounced sex differences in the in-camp diet. Hadza men are eating a higher quality diet than are women, but women are able to eat far more frequently, and spend less time foraging than men. It is not yet clear whether a regular caloric intake of lower quality foods would be more beneficial for maintaining fecundity than a more variable diet consisting of higher quality foods.

The 'spiteful' origins of human cooperation.

We analyse generosity, second-party ('spiteful') punishment (2PP), and third-party ('altruistic') punishment (3PP) in a cross-cultural experimental economics project. We show that smaller societies are less generous in the Dictator Game but no less prone to 2PP in the Ultimatum Game. We might assume people everywhere would be more willing to punish someone who hurt them directly (2PP) than someone who hurt an anonymous third person (3PP). While this is true of small societies, people in large societies are actually more likely to engage in 3PP than 2PP. Strong reciprocity, including generous offers and 3PP, exists mostly in large, complex societies that face numerous challenging collective action problems. We argue that 'spiteful' 2PP, motivated by the basic emotion of anger, is more universal than 3PP and sufficient to explain the origins of human cooperation.

More 'altruistic' punishment in larger societies.

If individuals will cooperate with cooperators, and punish non-cooperators even at a cost to themselves, then this strong reciprocity could minimize the cheating that undermines cooperation. Based upon numerous economic experiments, some have proposed that human cooperation is explained by strong reciprocity and norm enforcement. Second-party punishment is when you punish someone who defected on you; third-party punishment is when you punish someone who defected on someone else. Third-party punishment is an effective way to enforce the norms of strong reciprocity and promote cooperation. Here we present new results that expand on a previous report from a large cross-cultural project. This project has already shown that there is considerable cross-cultural variation in punishment and cooperation. Here we test the hypothesis that population size (and complexity) predicts the level of third-party punishment. Our results show that people in larger, more complex societies engage in significantly more third-party punishment than people in small-scale societies.