The evolution of human cooperation Apicella, Coren L.; Silk, Joan B.
CB/Current biology,
06/2019, Letnik:
29, Številka:
11
Journal Article
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Darwin viewed cooperation as a perplexing challenge to his theory of natural selection. Natural selection generally favors the evolution of behaviors that enhance the fitness of individuals. ...Cooperative behavior, which increases the fitness of a recipient at the expense of the donor, contradicts this logic. William D. Hamilton helped to solve the puzzle when he showed that cooperation can evolve if cooperators direct benefits selectively to other cooperators (i.e. assortment). Kinship, group selection and the previous behavior of social partners all provide mechanisms for assortment (Figure 1), and kin selection and reciprocal altruism are the foundation of the kinds of cooperative behavior observed in many animals. Humans also bias cooperation in favor of kin and reciprocating partners, but the scope, scale, and variability of human cooperation greatly exceed that of other animals. Here, we introduce derived features of human cooperation in the context in which they originally evolved, and discuss the processes that may have shaped the evolution of our remarkable capacity for cooperation. We argue that culturally-evolved norms that specify how people should behave provide an evolutionarily novel mechanism for assortment, and play an important role in sustaining derived properties of cooperation in human groups.
Coren Apicella and Joan Silk introduce the main factors that have shaped the evolution of the special cooperative capacity of humans.
Social networks show striking structural regularities, and both theory and evidence suggest that networks may have facilitated the development of large-scale cooperation in humans. Here, we ...characterize the social networks of the Hadza, a population of hunter-gatherers in Tanzania. We show that Hadza networks have important properties also seen in modernized social networks, including a skewed degree distribution, degree assortativity, transitivity, reciprocity, geographic decay and homophily. We demonstrate that Hadza camps exhibit high between-group and low within-group variation in public goods game donations. Network ties are also more likely between people who give the same amount, and the similarity in cooperative behaviour extends up to two degrees of separation. Social distance appears to be as important as genetic relatedness and physical proximity in explaining assortativity in cooperation. Our results suggest that certain elements of social network structure may have been present at an early point in human history. Also, early humans may have formed ties with both kin and non-kin, based in part on their tendency to cooperate. Social networks may thus have contributed to the emergence of cooperation.
Widespread cooperation is a defining feature of human societies from hunter-gatherer bands to nation states 1, 2, but explaining its evolution remains a challenge. Although positive assortment of ...cooperators is recognized as a basic requirement for the evolution of cooperation, the mechanisms governing assortment are debated. Moreover, the social structure of modern hunter-gatherers, characterized by high mobility, residential mixing, and low genetic relatedness 3, undermines assortment and adds to the puzzle of how cooperation evolved. Here, we analyze four years of data (2010, 2013, 2014, 2016) tracking residence and levels of cooperation elicited from a public goods game in Hadza hunter-gatherers of Tanzania. Data were collected from 56 camps, comprising 383 unique individuals, 137 of whom we have data for two or more years. Despite significant residential mixing, we observe a robust pattern of assortment that is necessary for cooperation to evolve; in every year, Hadza camps exhibit high between-camp and low within-camp variation in cooperation. We find little evidence that cooperative behavior within individuals is stable over time or that similarity in cooperation between dyads predicts their future cohabitation. Both sets of findings are inconsistent with models that assume stable cooperative and selfish types, including partner choice models. Consistent with social norms, culture, and reciprocity theories, the strongest predictor of an individual’s level of cooperation is the mean cooperation of their current campmates. These findings underscore the adaptive nature of human cooperation—particularly its responsiveness to social contexts—as a feature that is important in generating the assortment necessary for cooperation to evolve.
•Assortment on cooperation is a characteristic feature of hunter-gatherer life•Assortment persists despite substantial migration and residential mixing•No evidence for stable social types or a preference to live with cooperators•Individuals respond in kind to the cooperative behavior of their group members
For cooperation to evolve, cooperators must interact with other cooperators. Smith et al. use panel data from a population of extant hunter-gatherers to show how assortativity in cooperation is maintained.
We report on two experiments investigating whether there is a gender difference in the willingness to compete against oneself (self-competition), similar to what is found when competing against ...others (other-competition). In one laboratory and one online market experiment, involving a total of 1,200 participants, we replicate the gender-gap in willingness to other-compete but find no evidence of a gender difference in the willingness to self-compete. We explore the roles of risk and confidence and suggest that these factors can account for the different findings. Finally, we document that self-competition does no worse than other-competition in terms of performance boosting.
Summary While baseline testosterone has recently been implicated in risk-taking in men, less is known about the effects of changing levels of testosterone on financial risk. Here we attempt to ...influence testosterone in men by having them win or lose money in a chance-based competition against another male opponent. We employ two treatments where we vary the amount of money at stake so that we can directly compare winners to losers who earn the same amount, thereby abstracting from income effects. We find that men who experience a greater increase in bioactive testosterone take on more risk, an association that remains when controlling for whether the participant won the competition. In fact, whether subjects won the competition did not predict future risk. These results suggest that testosterone change, and thus individual differences in testosterone reactivity, rather than the act of winning or losing, influence financial risk-taking.
Most people name the myriad colors in the environment using between two and about a dozen color terms 1, with great variation within and between languages 2. Investigators generally agree that color ...lexicons evolve from fewer terms to more terms, as technology advances and color communication becomes increasingly important 3. However, little is understood about the color naming systems at the least technologically advanced end of the continuum. The Hadza people of Tanzania are nomadic hunter-gatherers who live a subsistence lifestyle that was common before the advent of agriculture (see Supplemental Experimental Procedures, section I; 4), suggesting that the Hadzane language should be at an early stage of color lexicon evolution. When Hadza, Somali, and US informants named 23 color samples, Hadza informants named only the black, white, and red samples with perfect consensus. Otherwise, they used low-consensus terms or responded “don’t know.” However, even low-consensus color terms grouped test colors into lexical categories that aligned with those found in other world languages 5. Furthermore, information-theoretic analysis showed that color communication efficiency within the Hadza, Somali, and US language communities falls on the same continuum as other world languages. Thus, the structure of color categories is in place in Hadzane, even though words for many of the categories are not in general use. These results suggest that even very simple color lexicons include precursors of many color categories but that these categories are initially represented in a diverse and distributed fashion.
•Hadza hunter-gatherers use high-consensus color terms for black, white, and red•Other Hadza color terms are low consensus, and “don’t know” is commonly used•Each Hadza names his/her own subset of the color categories of world languages•A complete color lexicon is distributed across the Hadzane-speaking community
Lindsey et al. show that color naming by Hadza hunter-gatherers, while individually idiosyncratic, is remarkably structured across the language community: Hadza share few color terms and often respond “don’t know” when naming colors. Yet collectively, Hadzane color terms represent most color categories found in English and other world languages.
Humans and many non-human primates exhibit large sexual dimorphisms in vocalizations and vocal anatomy. In humans, same-sex competitors and potential mates attend to acoustic features of male ...vocalizations, but vocal masculinity especially increases perceptions of physical prowess. Yet, the information content of male vocalizations remains obscure. We therefore examined relationships between sexually dimorphic acoustic properties and men's threat potential. We first introduce a new measure of the structure of vocal formant frequencies, ‘formant position’ (Pf), which we show is more sexually dimorphic and more strongly related to height than is the most widely used measure of formant structure, ‘formant dispersion’, in both a US sample and a sample of Hadza foragers from Tanzania. We also show large sexual dimorphisms in the mean fundamental frequency (F0) and the within-utterance standard deviation in F0 (F0 − s.d.) in both samples. We then explore relationships between these acoustic parameters and men's body size, strength, testosterone and physical aggressiveness. Each acoustic parameter was related to at least one measure of male threat potential. The most dimorphic parameters, F0 and Pf, were most strongly related to body size in both samples. In the US sample, F0 predicted testosterone levels, Pf predicted upper body strength and F0 − s.d. predicted physical aggressiveness.
The emergence of large-scale cooperation during the Holocene remains a central problem in the evolutionary literature. One hypothesis points to culturally evolved beliefs in punishing, ...interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant co-religionists. Furthermore, another hypothesis points to such mechanisms being constrained to the religious ingroup, possibly at the expense of religious outgroups. To test these hypotheses, we administered two behavioural experiments and a set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, and wage labourers, practicing Buddhism, Christianity, and Hinduism, but also forms of animism and ancestor worship. Using the Random Allocation Game (RAG) and the Dictator Game (DG) in which individuals allocated money between themselves, local and geographically distant co-religionists, and religious outgroups, we found that higher ratings of gods as monitoring and punishing predicted decreased local favouritism (RAGs) and increased resource-sharing with distant co-religionists (DGs). The effects of punishing and monitoring gods on outgroup allocations revealed between-site variability, suggesting that in the absence of intergroup hostility, moralizing gods may be implicated in cooperative behaviour toward outgroups. These results provide support for the hypothesis that beliefs in monitoring and punitive gods help expand the circle of sustainable social interaction, and open questions about the treatment of religious outgroups.
Many animals both display and assess multiple signals. Two prominently studied traits are symmetry and sexual dimorphism, which, for many animals, are proposed cues to heritable fitness benefits. ...These traits are associated with other potential benefits, such as fertility. In humans, the face has been extensively studied in terms of attractiveness. Faces have the potential to be advertisements of mate quality and both symmetry and sexual dimorphism have been linked to the attractiveness of human face shape.
Here we show that measurements of symmetry and sexual dimorphism from faces are related in humans, both in Europeans and African hunter-gatherers, and in a non-human primate. Using human judges, symmetry measurements were also related to perceived sexual dimorphism. In all samples, symmetric males had more masculine facial proportions and symmetric females had more feminine facial proportions.
Our findings support the claim that sexual dimorphism and symmetry in faces are signals advertising quality by providing evidence that there must be a biological mechanism linking the two traits during development. Such data also suggests that the signalling properties of faces are universal across human populations and are potentially phylogenetically old in primates.
Humans are motivated to compete for access to valuable social partners, which is a function of their willingness to share and ability to generate resources. However, relative preferences for each ...trait should be responsive to socioecological conditions. Here, we test the flexibility of partner choice psychology among Hadza hunter-gatherers of Tanzania. Ninety-two Hadza ranked their campmates on generosity and foraging ability and then shared resources with those campmates. We found Hadza with greater exposure to other cultures shared more with campmates ranked higher on generosity, whereas Hadza with lower exposure showed a smaller preference for sharing with generous campmates. This moderating effect was specific to generosity-regardless of exposure, Hadza showed only a small preference for sharing with better foragers. We argue this difference in preferences is due to high exposure Hadza having more experience cooperating with others in the absence of strong norms of sharing, and thus are exposed to greater variance in willingness to cooperate among potential partners increasing the benefits of choosing partners based on generosity. As such, participants place a greater emphasis on choosing more generous partners, highlighting the flexibility of partner preferences.
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