jueves, 18 de febrero de 2016

Anthropology: Hand of the gods in human civilization


In the modern world, we rely on governments, courts and the police to deter and punish those who would otherwise undermine social cooperation. But how did human societies achieve and sustain cooperation before these institutions existed? One possibility is religion: under the watchful gaze of supernatural agents, people modify their behaviour in an effort to avoid the wrath of the gods. In this issue, Purzycki et al.1 (page 327) report a cross-cultural field-study finding that people are consistently more willing to give money to strangers of the same religion if the donor believes in a god that is moralizing (concerned about good and bad behaviour), knowledgeable (aware of one's thoughts and actions) and punishing (able to exact harm).
Pioneering anthropologists, such as Émile Durkheim and Bronisław Malinowski in the early twentieth century, have long argued that supernatural beliefs offer a powerful way to build materially cooperative societies. But in the thriving new field of evolutionary religious studies, researchers are drawing on evolutionary theory to explore how religious beliefs can bring adaptive advantages — that is, contribute to an individual's survival or reproductive success. Although major debates remain2, one theory that has gathered momentum is that a belief in supernatural punishment for violating social norms may be adaptive3(Fig. 1).
Figure 1: Weighing of the heart.
Weighing of the heart.
This papyrus manuscript, a detail from the ancient Egyptian 'Book of the Dead' called Papyrus of Ani, depicts a scene in which the dead Ani's heart is weighed against a feather, representing Maat, goddess of truth and justice. At the top of the scene are the great Egyptian gods, ready to pronounce judgment on whether Ani should be granted entrance to the afterlife or banished to the underworld.
The Trustees of the British Museum
How could this idea apply to cooperation? Deterring oneself from the pursuit of self-interest because of the risk of punishment from a watchful supernatural eye would seem to reduce an individual's evolutionary fitness, and should thus be eliminated by natural selection. However, even if such beliefs are false and costly, they may have generated net benefits: to individuals, by steering them away from selfish behaviour that risked retaliation in increasingly transparent and gossiping human societies; and/or to groups, by increasing the performance of the group as a whole in competition with other groups4, 5.
But what evidence do we have for such a theory? Empirical evidence that supernatural beliefs promote cooperation is mounting, but has tended to rely on qualitative, society-level or proxy measures of beliefs. Study participants have also typically been university students in developed nations, thus omitting the small-scale societies most relevant to the evolutionary problem at hand: how human groups achieved cooperation and made the transition from small to large societies in the first place. Perhaps the most important lacuna is that previous studies have not rigorously addressed whether the beliefs of the recipients of cooperative acts changes people's generosity towards them.
Purzycki and colleagues' study addresses many of these issues by using controlled experimental games among participants from eight small-scale societies around the world and tying the results to explicit measures of individuals' beliefs. Participants played a simple but clever game (designed to subtly reveal preferences), in which they allocated coins between a distant co-religionist (people who were members of the same religion, but who lived geographically far away) and either themselves or a local co-religionist. The researchers found that the more subjects rated their god as moralistic, knowledgeable and punishing, the more money they gave to distant strangers adhering to the same religion. Notably, belief in rewards from the god could not account for the results — supernatural punishment seemed responsible.
Because the study is correlational, one worry is that some unexamined variable could account for the results — perhaps certain people are disposed to both kindness to strangers and belief in punitive gods, for example. However, Purzycki et al. show that allocations increased for moralistic gods that were punishing and knowledgeable, but not for more locally relevant supernatural agents that were also punishing and knowledgeable. Hence, general conceptions of supernatural agents cannot alone explain the results. Rather, it is moralistic, 'big' gods that seem to stimulate generosity towards distant co-religionists6.
The authors did not conduct experiments to assess allocations to oneself versus a local co-religionist, nor experiments involving non-religious recipients, so we don't know whether local supernatural agents might promote cooperation between individuals within the local community, as other work has found7, or whether any kind of god promotes cooperation with strangers of another, or no, religion. Purzycki et al. focused on cooperation with co-religionists beyond the local community, and thus the expansion of human society from small to large groups. But future studies of the role of local gods are needed to improve our understanding of the evolutionary origins of religion (before there were big groups or big gods), and of whether and how religion brings adaptive advantages to individuals8.
It is worth emphasizing that the subjects in this experiment were not cooperative with random strangers, only with strangers that shared the same god. We therefore still face the challenge of understanding the promotion of cooperation and trust among members of different religions. Purzycki and colleagues' finding that sharing the same god is key to cooperation suggests that this may be an even harder nut to crack. In fact, one of the most compelling explanations for why individuals may help the group at their own expense is that it aids survival in an environment of inter-group competition. Whenever the threat of exploitation or warfare is present, the best protection is larger and more-cohesive societies, which are better able to deter or defeat rivals. Religion's positive role in reducing self-interest and promoting cooperation may therefore reflect the costs of competition as much as the benefits of generosity9.
Religion is arguably the most powerful mechanism that societies have found to bind people together in common purpose. From ancient civilizations, to the spread of Christianity, to today's Islamist terrorist groups, religion has motivated not only the subordination of self-interest for the wider group, but even martyrdom in the name of a god. We are still grappling to understand, from a scientific perspective, why and under what circumstances humans sacrifice their own welfare for the benefit of distant others10. But there is little doubt about the power of religion to promote allegiance to one's god and group. Purzycki and colleagues' study offers the most explicit evidence yet that belief in supernatural punishment has been instrumental in boosting cooperation in human societies. A large part of the success of human civilizations may have lain in the hands of the gods, whether or not they are real.

Moralistic gods, supernatural punishment and the expansion of human sociality


Since the origins of agriculture, the scale of human cooperation and societal complexity has dramatically expanded1, 2. This fact challenges standard evolutionary explanations of prosociality because well-studied mechanisms of cooperation based on genetic relatedness, reciprocity and partner choice falter as people increasingly engage in fleeting transactions with genetically unrelated strangers in large anonymous groups. To explain this rapid expansion of prosociality, researchers have proposed several mechanisms3, 4. Here we focus on one key hypothesis: cognitive representations of gods as increasingly knowledgeable and punitive, and who sanction violators of interpersonal social norms, foster and sustain the expansion of cooperation, trust and fairness towards co-religionist strangers5, 6, 7, 8. We tested this hypothesis using extensive ethnographic interviews and two behavioural games designed to measure impartial rule-following among people (n = 591, observations = 35,400) from eight diverse communities from around the world: (1) inland Tanna, Vanuatu; (2) coastal Tanna, Vanuatu; (3) Yasawa, Fiji; (4) Lovu, Fiji; (5) Pesqueiro, Brazil; (6) Pointe aux Piments, Mauritius; (7) the Tyva Republic (Siberia), Russia; and (8) Hadzaland, Tanzania. Participants reported adherence to a wide array of world religious traditions including Christianity, Hinduism and Buddhism, as well as notably diverse local traditions, including animism and ancestor worship. Holding a range of relevant variables constant, the higher participants rated their moralistic gods as punitive and knowledgeable about human thoughts and actions, the more coins they allocated to geographically distant co-religionist strangers relative to both themselves and local co-religionists. Our results support the hypothesis that beliefs in moralistic, punitive and knowing gods increase impartial behaviour towards distant co-religionists, and therefore can contribute to the expansion of prosociality.

At a glance

Figures

View all figures
left
  1. The random allocation game.
    Figure 1
  2. Allocations to distant co-religionists increase as a function of moralistic gods’ punishment.
    Figure 2
  3. Log odds ratios with 95% confidence interval plots of the influence of key variables on the odds that a coin goes into the cup for the distant co-religionist.
    Figure 3
  4. Map of the eight field site locations.
    Extended Data Fig. 1
  5. Proportion of sample listing moral and virtue items for moralistic and local gods’ dislikes and likes by site.
    Extended Data Fig. 2
  6. Mean moralistic and local gods’ knowledge and punishment scales by site.
    Extended Data Fig. 3
  7. Plot of differences between size of actual allocations and allocations from binomially distributed sample of the same size.
    Extended Data Fig. 4
  8. Per cent of sample by allocation amount to distant cup in local co-religionist (grey) and self games (black) as compared to binomial distribution (white).
    Extended Data Fig. 5
right

Main

Among the other factors2, 3, 4, 7 that influence the emergence of human ultrasociality and complex societies, the diffusion of explicit beliefs in increasingly moralistic, punitive and knowledgeable gods may have played a crucial role6, 7. People may trust in, cooperate with and interact fairly within wider social circles, partly because they believe that knowing gods will punish them if they do not. Additionally, through increased frequency and consistency in belief and behaviour sets, commitments to the same gods coordinate people’s expectations about social interactions5, 6, 7, 8, 9. Moreover, the social radius within which people are willing to engage in behaviours that benefit others at a cost to themselves may enlarge as gods’ powers to monitor and punish increase10. To account for the emergence of these patterns, some evolutionary approaches to religion have theorized that cultural evolution may have harnessed and exploited aspects of our evolved psychology, such as mentalizing abilities, dualistic tendencies and sensitivity to norm compliance, to gradually assemble configurations of supernatural beliefs that promote greater cooperation and trust within expanding groups, leading to greater success in intergroup competition. Of course, given that cultural evolution can produce self-reinforcing stable patterns of beliefs and practices, these supernatural agent concepts may also have been individually favoured within groups due to mechanisms related to signalling, reputation and punishment5, 6, 7, 8, 9, 11, 12. Over time, these deities spread culturally and came to dominate the modern world religions like Christianity, Islam and Hinduism. Such traditions eventually came to account for a large proportion of the world’s population6, 7, 13, 14 (see Supplementary Information section S1). Here we directly test one specific hypothesis: conceptions of moralistic and punitive gods that know people’s thoughts and behaviours promote impartiality towards distant co-religionists, and as a result contribute to the expansion of sociality.
At the societal level, several lines of converging evidence are consistent with this hypothesis. For example, after controlling for key correlates, analyses of cross-cultural data sets show that larger and more politically complex societies tend to have more supernatural punishment and moralistic deities5, 15, and historical analyses in one geographic region show that precursors to supernatural punishment beliefs precede social complexity16. However, this data derives from qualitative ethnographies of entire societies; a more focused, direct and systematic cross-cultural assessment of what individuals think their gods care about, and whether or not people explicitly or implicitly view their gods as concerned with norms of interpersonal social behaviour (termed here as ‘morality’17, 18; see Supplementary Information section S4.2) has only recently begun18, 19, 20. Analyses of cross-national databases (for example, the World Values Survey) reveal positive relationships between beliefs in hell, beliefs in gods’ power to punish, and various self-reported prosocial behaviours21, 22. Although valuable, these lines of research primarily rely on survey questions not specifically designed to address the research question we are interested in. Moreover, they rely on samples drawn broadly from nation states, thus excluding small-scale societies that are crucial for assessing questions about the expansion of prosociality.
At the individual level, two types of behavioural studies are also consistent with this hypothesis, but each has crucial limitations. First, laboratory experiments show that exposure to religious reminders increases generosity and decreases cheating among religious believers23, 24, 25. However, as is the case for most psychological experiments, the vast majority of these studies rely on Western, Christian-majority samples, limiting their generalizability26. Second, in one field study27 across 15 diverse societies of foragers, pastoralists and horticulturalists, adherence to Christianity or Islam predicted greater fairness in economic games relative to adherence to local/traditional religions. This study, however, lacked precise measures for our theoretically important components of beliefs about gods’ minds—punishment, knowledge and moralism. Moreover, these studies did not consider the religious affiliation of the anonymous recipients of players’ monetary decisions. It is therefore unclear whether these findings explain the expansion of prosociality specifically towards geographically distant co-religionists.
Addressing these limitations, we combined two behavioural experiments with detailed ethnographic interviews to assess whether participants who report that their moralistic gods are punishing and more knowledgeable about human thought and behaviour are more likely to impartially allocate money to anonymous, geographically distant co-religionists over both themselves and their local community6, 7. In five of the sites, we also tested whether religious priming associated with moralistic gods had effects on gameplay, but these had no overall effect (see Supplementary Information sections S2.2.2 and S6.2.
We tested these predictions with a sample of 591 participants (310 females; observations = 35,400; Table 1 and Extended Data Fig. 1) from eight diverse communities, including hunter-gatherers, horticulturalists, herders and farmers, as well as fully market-integrated populations engaged in wage labour or operating small businesses. The participants adhere to a variety of world religious traditions including Christianity, Hinduism and Buddhism, and report beliefs in an immense range of local supernatural agents, including spirit-masters, saints, ancestors, animistic beings, anthropomorphic celestial deities, garden spirits, and ghosts (Supplementary Information section S3).
Table 1: Site descriptive statistics
To measure favouritism towards oneself and local community under maximally anonymous conditions, we modified the random allocation game9, 28, 29. In this game (Fig. 1), participants play in private with 30 coins, two cups and a fair die with three sides of one colour and three sides of another colour. In the experiment, the participant’s job is to allocate each coin to one of the two cups. First, they mentally choose one of the cups and then roll the die. If one coloured side comes up, players are instructed to put the coin into the cup they mentally chose. If the die comes up the other colour, people are instructed to put the coin into the opposite cup from the one they chose. Of course, as cup selection occurs only mentally, participants can overrule the die in favour of one of the cups without anyone else observing their decision. If people play by the rules and thereby allocate the coins impartially, the mean number of coins in each cup should be 15, and the distribution around this average will be binomial. This allows us to test for systematic deviations from this distribution (Supplementary Information section S2.2).
Figure 1: The random allocation game.
The random allocation game.
a, b, Generic game setup (a) and variants used in present work (b).
Participants played two counterbalanced games for a total of 60 coin allocations per person (Fig. 1). In one game, the local co-religionist game, participants chose between a cup assigned to an unspecified anonymous co-religionist from their local community and a cup assigned to an anonymous co-religionist living in a geographically distant community that does not regularly interact with the player’s community. In the other game, the self game, participants chose between a cup for themselves and a cup for another anonymous distant co-religionist. In order to control for any effects of ethnicity30 and nationality, both local and distant co-religionists were of the same ethnic group and nationality as the participant.
Participants understood that money put into the cups would be given to the people they represented, including themselves, and we actually distributed allocations to participants and randomly selected people described by the cups (that is, there was no deception). After gameplay, we asked each participant a battery of questions, including a series of counterbalanced questions about two locally relevant deities (Supplementary Information section S2).
To assess the gods’ relative moral concern, we conducted preliminary ethnographic interviews in each site to identify the most moralistic deities (that is, ‘moralistic gods’), as well as locally salient, relatively less moralistic, ‘local gods’ or spirits. We verified the degree to which gods care about morality with a free-list task asking about gods’ concerns19 and scales created to measure how important participants claim punishing theft, murder and deceit are to these supernatural beings. We measured gods’ punishment and knowledge, using the mean of two, two-item, easy-to-understand scales with dichotomous responses. The target gods associated with games were rated significantly more moralistic, knowledgeable and punitive than local gods (see Extended Data Figs 2 and 3; Supplementary Information section S4). We also aggregated gods’ punishment and knowledge scores by averaging all four dichotomous responses, labelled ‘punishment–knowledge combined’ in Table 2. These measures are our key theoretical predictors for game allocations.
Table 2: Log odds ratios for predicting allocations to distant co-religionists with 95% confidence intervals from our main binomial logistic regression models
Figure 2 displays the effect of punishment for moralizing gods, without any controls, and reveals the impact of “I don’t know” answers which were otherwise excluded from our analyses below. When people report not knowing if a god punishes, they put considerably fewer coins in the cups for distant co-religionists in both games (local co-religionist game: M = 12.97, s.d. = 4.33; self game: M = 12.50, s.d. = 4.15) than those who consistently report that their god punishes (local co-religionist game: M = 14.58, s.d. = 3.24; self game: M  = 14.53, s.d. = 3.31). One way to estimate the magnitude of these effects is to calculate the quotient of deviations from the ideal impartial allocation of 15. Compared to those who don’t know, claiming the moralizing god punishes increases allocations towards distant co-religionists in the self game by a factor of 4.8 and in the local co-religionist game by a factor of 5.3. Extended Data Figs 4 and 5 detail the overall allocation distributions for both games.
Figure 2: Allocations to distant co-religionists increase as a function of moralistic gods’ punishment.
Allocations to distant co-religionists increase as a function of moralistic gods’ punishment.
Punishment indices are mean values of a two-item scale (see Supplementary Information section S2.3.2). Error bars represent bootstrapped (1,000 replications) 95% confidence intervals of the mean. Histogram labels are sample sizes per category. Note that among the 32 individuals who responded “I don’t know” to the questions pertaining to moralistic gods’ punishment, 17 were Hadza and 15 were inland Tannese.
We explored this relationship in more detail by regressing the number of coins allocated to the distant co-religionist cup on a host of variables for each game in a large set of binomial regressions (Extended Data Table 1 and Supplementary Information section S6). Table 2 shows a subset of the key predictors for the models with the largest set of control variables, including a number of economic and demographic variables such as education, material insecurity, number of children and field site fixed effects. Using sites as fixed effects allows us to remove the variation between our sites, so the results in Table 2 only capture the differences among individuals within sites. Based on previous work9, 29, we suspected that material insecurity and number of children would increase self and local favouritism, and therefore we include both in our model (Supplementary Information section S2.3.1). To affirm the robustness of these analyses, we estimated many alternative models, formulated mixed models, and used both alternative standard error estimates and different approaches to modelling the error (Supplementary Information section S5.4). Across a wide range of specifications and models including a host of variables (for example, divine rewards, emotional closeness to distant co-religionists, among others), both moralistic gods’ punishment and knowledge, as well as our aggregate punishment–knowledge variable, are reliably associated with less bias against distant co-religionists (Supplementary Tables S5–S9).
We checked whether the effects of moralistic gods’ punishment and knowledge were indeed specific to powerful, moralizing gods. We added local gods’ punishment and knowledge to the models presented in Table 2. Figure 3 shows the odds ratios and confidence intervals for these coefficients. Although neither the punishing powers nor knowledge of these local deities had any association with the allocations, the odds ratios for our key predictors pertaining to moralistic gods actually increased. These overall findings are correlational and should be interpreted with caution and in combination with other evidence, also considering that religious priming did not reveal consistent effects. However, these patterns reduce concerns that omitted third variables might account for the correlations we observe. A third variable, in addition to correlating with allocations, would have to correlate only with the punishing and knowing character of moralistic and knowledgeable gods, but not with those same attributes in local gods or with the tendency of either type of deity to reward people.
Figure 3: Log odds ratios with 95% confidence interval plots of the influence of key variables on the odds that a coin goes into the cup for the distant co-religionist.
Log odds ratios with 95% confidence interval plots of the influence of key variables on the odds that a coin goes into the cup for the distant co-religionist.
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 ≤ 0.001, **P ≤ 0.01; *P ≤ 0.05; ‡P ≤ 0.15). The x axis is on a logarithmic scale. Both models include other controls (n  = 390). Local co-religionist and self results include sites as fixed effects. Note that Indo-Fijians are not included in these models due to the lack of data for local gods. See Supplementary Tables S5 and S6 for full models (models 2FE are presented here). These results build on previous findings and have important implications for understanding the evolution of the wide-ranging cooperation found in large-scale societies. Moreover, when people are more inclined to behave impartially towards others, they are more likely to share beliefs and behaviours that foster the development of larger-scale cooperative institutions, trade, markets and alliances with strangers. This helps to partly explain two phenomena: the evolution of large and complex human societies and the religious features of societies with greater social complexity that are heavily populated by such gods6, 7. In addition to some forms of religious rituals and non-religious norms and institutions, such as courts, markets and police, the present results point to the role that commitment to knowledgeable, moralistic and punitive gods plays in solidifying the social bonds that create broader imagined communities11, 12, 31.

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