Week 9: Readings

Question 1

Christianity Spread Faster in Small, Politically Structured Societies
(Watts, 2018)

Abstract:
2x hypothesis
measures
Results

Answer 1

Abstract:
• Christianity is the dominant religion in the
Pacific
• This article uses cultural phylogenic
methods to test to opposing hypotheses on
what factors influence the rate of conversion
to Christianity in Pacific cultures across
human history.
• Two hypotheses are Top-Down: driven by
political leadership; Bottom-Down: driven
empowerment of social underclasses.
• They use context whether political
hierarchy, social inequality, and population
size to predict the length of conversion time
across 70 Austolesian cultures. Whilst
controlling for the historical isolation of
cultures, and the year of missionary arrival
and use a phylogenetic generalized least
square methods to estimate the effects of
common ancestry and geographic
proximity of cultures.
• Results:
o Conversion time: typically took less than 30
years.
o Population size: smaller societies were faster
to convert to Christianity than larger
populations (strongest predictor).
o Political Leadership: more socially stratified
societies were faster to convert than non-
stratified societies (supports top-down
hypothesis).
o Social inequality did not reliably affect
conversion times which contradicts the
bottom-down hypothesis which claims that
conversion to Christianity is due to its
egalitarian doctrine empowering social
underclasses.
o The significance of population size and
political structure supports that the rapid
spread of Christianity can be explained by
general dynamics of cultural transmission.

• Top-down hypotheis:
o Political leaders such as Roman Emperor
Constantine the Great played a major role
in Christianity’s success in the Pacific.
o Constantine placed Christians in positions
of power, encouraged conversion among
the population and supported the church
through financial aid.
o Spread through elite minorities.
• Bottom-down hypothesis:
o Argues that Christianity spread because its
relatively egalitarian doctrines appealed to
majority underclasses.
o Suggests that Constantine converted once
Christianity had already become a major
social force and that his support for
Christianity was a strategic move to
appease the masses.
• These effects are difficult to disentangle
from the historical record because both
social inequality and centralized political
control to tended to occur together in early
Christian expansions. Using cultural
phylogeny analysis we can test these two
opposing hypothesis whilst accounting for
the simultaneous effects of social structure
and population size.
o Taken together, this suggests that the rate
of religious change could be slower in
larger and less connected populations
than in smaller and more connected
populations

Definitions:
• Political complexity refers to the number of
levels of political hierarchy in a culture and
provides a measure of the influence of
leaders over a population.
• Political organizations include chiefdoms,
kingdoms and state governments, which all
have the potential to centralize authority
and unite otherwise separate local
communities. It also provides a measure of
how connected the local communities of a
culture are, it can be predicted to facilitate
conversion, as shown by existing literature
on population structure in cultural
evolution.
• Social inequality (also known as social
stratification) refers to inherited differences
in wealth and status within a culture.
Examples of social inequality include the
existence of social elites (nobles with more
resources and power) and subordinate
social classes (slaves). Whilst it involves the
structuring of a population into separate
classes, it doesn’t involve connection
between them (local communities within a
culture).

Hypothesis:
1. Do cultures with greater political
organization are faster to convert to
Christianity, as predicted by top-down
theories of conversion.
2. Do cultures with higher levels of social
inequality are faster to convert, as
predicted by bottom-up theories of
conversion.
3. Are larger populations slower to convert,
as predicted by general processes of
cultural diffusion throughout populations.

Controls:
• Cultural Isolation:
o Cultural isolation refers to the geographic
distance from the nearest neighbouring
society and controls for historical exposure
to different social groups.
• Year of Missionary Arrival:
o The year of missionary arrival refers to the
first year of concerted missionary effort
and is included to control for changes in
the rates of conversion over the three
centuries that missionaries arrived.

(B) Full Model
• Population Size:
o Significantly positively correlated with
conversion times, indicating that larger
populations took longer to convert to
Christianity.
• Political Complexity:
o Was negatively associated with conversion
times, which supports the top-down
hypothesis of Christianity conversion.
• Social Inequality:
o Counter to the bottom-up theories, there
was no reliable support for an association
between conversion time and social
inequality
• Cultural Isolation:
o Significantly negatively predict conversion
times, indicating that more isolated
cultures tended to be faster to convert to
Christianity than less isolated cultures.
• The Year of Missionary Arrival:
o Significantly negatively predicted
conversion times, indicating that societies
in which missionaries arrived more recently
were faster to convert to Christianity.
• The lack of support for phylogenetic and
spatial dependencies is consistent with the
lack of geographic and phylogenetic
clustering evident in the length-of-
conversion-time variable. This suggests
that shared cultural ancestry and
geographically clustered factors had little
effect on the length of conversion time in
Austronesia
(C) Adjusted Model
• Two cultures that took the longest to
convert in this study (Ifuagao and Iban)
lacked any form of political organization
were removed from the model:
o Political complexity was no longer a
significant predictor of conversion times
when these two cultures were removed
from the model. This indicates that the
significant effects of political complexity on
conversion times in our full model may be
due to societies that lack political
organization taking longer to convert,
rather the number of levels of political
hierarchy having a general effect on
conversion times.
o Population size remained a significant
predictor of conversion times even after
societies without political organization
were excluded from our analyses.

In Summary, findings show the importance of population size in cultural transmission, and suggest that political organization, but not social inequality, also played a role in the spread of Christianity. In Austronesian-speaking cultures, the conversion process occurred remarkably rapidly, with the majority of cultures sampled taking less than 30 years to convert. Conversion appears to have occurred mainly through the efforts of foreign missionaries, and cultures’ reactions to missionaries ranged from highly hospitable to violently hostile (faster conversion, 1 year in peaceful missionary contact; slower conversion, 65 years for hostile missionary contact).

o We found only a modest effect size of political complexity on conversion time, and this effect was probably driven by a relatively small number of cultures that lacked political organization within or between communities. This suggests that what is important in our study is whether a culture has political leaders at all, rather than the number of levels of political hierarchy it possesses.

• Population size:
o Strongest predictor of conversion times.
o Population size alone explained almost one-quarter of the variation in conversion times and held across all of our analyses.
o Individual-level data of Western populations show that one of the strongest predictors of whether an individual converts is the number of ties they have to existing converts.
o Christianity can spread by cultural transmission between general community members. Individuals decide whether to convert based on whether those around them have converted = frequency-dependant transmission.
o Frequency-dependant transmission: the probability that any given individual converts is proportional to the frequency of Christianity within the population.
o Non-frequency-dependant transmission: if missionaries simply arrived and broadcasted their message to the entire population, and individuals decided to convert based on their own personal characteristics.
o Frequency-dependent transmission is not necessarily involved if political leaders convert first and then simply impose Christianity on the general population. While Christianity is likely to have spread through a variety of processes, the population size effect we identify may suggest that frequency-dependent processes of cultural transmission played an important role.
o Features of Frequency-Dependant Transmission:
 Frequency-dependent cultural transmission is that it tends to take longer for traits to spread through larger populations than smaller populations.
 A novel trait is seeded to a larger population, it starts off at a lower relative frequency, and so a smaller proportion of the population come into contact with that trait and subsequently adopt it. As the proportion of the population that are converted increases, so too does the average number of ties that individuals have to Christianity, and subsequently how likely they are to convert.
 Christianity is expected to take longer to gain a majority in larger populations than smaller populations, but can rapidly spread once its frequency has increased within the population.
 It can explain the importance of population size in conversion and the spread Christianity gains momentum in larger populations but it depends on Christianity being able to be transmitted between individuals within a population.
 Transmission is facilitated by characteristics of religious beliefs and how they differed from ethnic religious systems:
• Christianity has an universal (rather than ethnocentric) doctrine of a central moralistic high God (rather than a pantheon of deities) and encourages proselytization and fertility, and the claim of exclusive truth.
• Christianity’s remarkable success in the Pacific is its historical link to colonial powers. European colonists did not just bring Christianity with them; they also brought diseases that decimated populations, novel resources and sophisticated weaponry that may all have lent credibility to Christianity.

Question 2

Ritual Human Sacrifice Promoted and Sustained the Evolution of Stratified Societies
(Watts, 2016)

Abstract:

Answer 2

Abstract:
• There is evidence of human sacrifice is found across human history in early human civilisations.
• Use of cultural phylogeny models (Bayesian( to test the social control hypothesis to explain why human sacrifice (religious rituals) have evolved in 93 traditional Australasian cultures which are geographically and socially diverse cultures.
• The social control hypothesis proposes that human sacrifice legitimizes political authority and social class systems, functioning to stabilize such social stratification.
• Support for the social control hypothesis is largely confined to historical anecdotes rather than empirical evidence.
• He current study found strong support that human sacrifice stabilises social stratification once stratification has arisen and promotes a shift to strictly inherited class systems.

• According to the social control hypothesis, human sacrifice legitimizes class-based power distinctions by combining displays of ultimate authority (the taking of a life with supernatural justifications that sanctify authority as divinely ordained).

Method:
• We test the social control hypothesis with a Bayesian phylogenetic analysis of 93 traditional Austronesian cultures from the Pulotu database.
• Phylogenetic methods enable us to account for the common ancestry of cultures, test for patterns of coevolution, and infer the direction of causality based on the order that traits evolve in.
• Reasons or occasions for human sacrifice in these societies included the breach of taboo or custom, the funeral of an important chief, and the consecration of a newly built house or boat.
• Sacrificial victims were typically of low social status, such as slaves, and the instigators were of high social status, such as priests and chief.
• The methods of sacrifice included burning, drowning, strangulation, bludgeoning, burial, being crushed under a newly built canoe, being cut to pieces, as well as being rolled off the roof of a house and then decapitated.
• For each culture in our sample, we recorded:
o The presence or absence of human sacrifice.
o Level of social stratification (differences in wealth and status):
 No social stratification (egalitarianism)
 Moderate social stratification (inherited differences in wealth and social position with the potential for status change within a generation)
 High social stratification (inherited difference in wealth and social position with little or no possibility of status change within a generation)
• The social control hypothesis predicts that human sacrifice:
1. Co-evolves with social stratification,
2. Increases the chance of a culture gaining social stratification, and
3. Reduces the chance of a culture losing social stratification once stratification has arisen.
• We perform two series of analyses,:
o The first to test the effects of human sacrifice on the evolution of social stratification in general, and
o The second to test the effects of human sacrifice on the evolution of high social stratification

Results:

Descriptive:
• Evidence of human sacrifice was observed in 40 of the 93 cultures sampled (43%)
• Human sacrifice was practiced in 5 of the 20 egalitarian societies (25%),
• 17 of the 46 moderately stratified societies (37%),
• 18 of the 27 highly stratified societies (67%) sampled

Analysis 1:
• In our first series of analyses:
• We grouped moderate and high stratification together, referred to hereafter as ‘social stratification’.
• To test for the co-evolution of human sacrifice and social stratification, we compared the posterior distribution of models in which human sacrifice and social stratification evolve independently of one another with models in which the two traits co-evolve such that the probability of a change in one trait is dependent on the value of the other trait.This indicates that human sacrifice co-evolved with social stratification.
• We then performed two additional constrained analyses to test whether human sacrifice functioned to drive and stabilize the evolution of social stratification, as the social control hypothesis predicts. In the first constrained analysis, cultures with and without human sacrifice were forced to have an equal chance of losing social stratification (rates e and g in Fig. 1c were set to be equal). This indicates that human sacrifice affects the rate at which cultures lose social stratification. The unconstrained dependent model shows that cultures with human sacrifice were less likely to lose social stratification than were cultures that lacked human sacrifice (in Fig. 1c rate e is higher than rate g)
• Together these results indicate that human sacrifice functioned to stabilize social stratification once it had arisen, but did not affect whether egalitarian cultures gained social stratification (in Fig. 1c, rate e is higher than rate g).

Analysis 2:
• In our second series of analyses:
• we used the same approach to test whether human sacrifice co-evolves with high social stratification specifically. In this series, we grouped egalitarian and moderately stratified societies together (Fig. 1d).
• We found strong support for the models in the dependent analyses over the models in the independent analyses (BF=6.04), indicating that human sacrifice has co-evolved with high social stratification.
• To test the prediction that human sacrifice functions to stabilize and drive high social stratification, we performed the same sequence of constrained analyses as previously described for social stratification in general.
• In the first constrained analysis, cultures with and without human sacrifice were forced to have an equal chance of losing high social stratification. Results indicate that the presence of human sacrifice is not associated with a change in the rate at which highly stratified cultures become less stratified.
• The second analysis was constrained so that cultures with and without human sacrifice were forced to have an equal chance of gaining high social stratification (rates b and d in Fig. 1e are equal). The results indicate that human sacrifice increased the rate at which cultures with human sacrifice gain high social stratification, but did not function to stabilize high social stratification once it had arisen (in Fig. 1e, rate d is higher than rate b).
• Taken together,
o our results provide strong evidence for the claim that human sacrifice played a powerful role in the construction and maintenance of stratified societies.
o Though human sacrifice was practiced in the majority of highly stratified societies in our sample, it was scarce in egalitarian societies, and we find that its effect depended on the level of stratification.
o Specifically, human sacrifice substantially increased the chances of high social stratification arising and prevented the loss of social stratification once it had arisen, yet was not found to increase social stratification in egalitarian societies.
o This is consistent with historical accounts that speculate that in order for human sacrifice to be exploited by social elites, there must first be social elites to exploit it.
o In our ancestral reconstructions Proto-Austronesian culture is inferred to have had some level of social stratification (Extended Fig. 1), but not high social stratification (Fig. 2), and the most common changes inferred across our trees were the loss of social stratification in general, and the gain in high social stratification. We caution that the lack of support we find for human sacrifice sustaining high social stratification may be due to high social stratification having been rarely lost in the history of Austronesian cultures.
• Experimental research indicates that while social inequality may foster group decision-making and efficiency, power hierarchies become unstable when they lack sanctioning status. In Austronesian cultures human sacrifice was used to punish taboo violations, demoralise underclasses, mark class boundaries, and instil fear of social elites— proving a wide range of potential mechanisms for maintaining and building social control.
• Throughout human history the practice of human sacrifice was often used by social elites as a display of power, intended to instil fear of the secular and supernatural consequences of transgressing ruling authority. While there are many factors that help build and sustain social stratification, human sacrifice may be a particularly effective means of maintaining and building social control because it minimizes the potential of retaliation by eliminating the victim, and shifts the agent believed to be ultimately responsible to the realm of the supernatural.
• Religion has long been proposed to play a functional role in society, and is commonly claimed to underpin morality. Recent evolutionary theories of religion have focused on the potential of pro-social and moral religious beliefs to increase cooperation. Our findings suggest that religious rituals also played a darker role in the evolution of modern complex societies. In traditional Austronesian cultures there was substantial religious and political overlap, and ritualised human sacrifice may have been co-opted by elites as a divinely sanctioned means of social control.
• The approach adopted in this paper demonstrates the way causal hypotheses about major transitions in human social organization can be tested by combining computational models and language phylogenies with a wealth of cultural and historical data.
• Unpalatable as it might be, our results suggest that ritual killing helped humans transition from the small egalitarian groups of our ancestors, to the large stratified societies we live in today.

Question 3

Broad Supernatural Punishment but not Moralizing High Gods Precede the Evolution of Political Complexity in Austronesia
(Watts, 2015)

Answer 3

Abstract:
• Supernatural belief presents an explanatory challenge to evolutionary theorists— it is both costly and prevalent.
• Functional explanations claim that the imagined threat of supernatural punishment can suppress selfishness and enhance cooperation. Specifically, ‘moralizing high gods’ have been argued to reduce free-riding in large social groups, enabling believers to build the kind of complex societies that define modern humanity.
• Previous cross-cultural studies claiming to support the Moralizing High God hypothesis rely on correlational analyses only and do not correct for the statistical non-independence of sampled cultures.
• Here we use a Bayesian phylogenetic approach with a sample of 96 Austronesian cultures to test the MHG hypothesis as well as an alternative supernatural punishment hypothesis that allows punishment by a broad range of moralizing agents.
• We find evidence that broad supernatural punishment drives political complexity, whereas Moralizing High Gods follow political complexity.
• We suggest that the concept of MHGs diffused as part of a suite of traits arising from cultural exchange between complex societies.
• Our results show the power of phylogenetic methods to address long-standing debates about the origins and functions of religion in human society.

Introduction:
• Religion is a hallmark of our species.
• Today the most successful world religions worship moralizing high gods (MHGs: powerful supreme creator gods who monitor and enforce moral codes).
• MHG hypotheses:
o Powerful animistic gods, specifically MHGs, owing to their ability to reliably and automatically punish all transgressions. It is widely claimed that beliefs in supernatural punishment increase cooperation and play a functional role in the evolution of complex societies.
• Alternative Hypothesis: Broad Supernatural Punishment (BSP)
o Broad range of supernatural punishment found throughout ethnic and world religions (including localized ancestral spirits, inanimate processes like karma and MHGs).
• Previous cross-cultural studies have found a correlation between MHGs and a range of measures of social complexity which supports both the BSP and MHG hypotheses. However, these studies are problematic for two reasons.
o First, traditional analyses of cross-cultural data do not incorporate enough information about the cultural evolution of human societies to be able to test the hypothesis.
 Cultures are related and not statistically independent (Galton’s Problem) and standard correlational do not account for this (i.e., common ancestry making sample non-independent and potentially creating spurious correlations).
 Despite attempting to select only distantly related cultures, the samples used in previous comparative studies of MHGs are known to be non-independent.
o Second, these studies are unable to distinguish the direction of causal relationship.
 Previous studies have assumed that a link between high gods and political complexity arises from the effect of the belief on political structure.
 Yet the direction of causation could be reversed (i.e., complex societies might be more likely to gain MHG concepts).
 Only an approach that explicitly incorporates phylogenetic information is able to both address Galton’s problem and determine the temporal sequence in which MHGs and political complexity emerged.
• Phylogenetic methods have revolutionized the biological sciences and have recently been used to make inferences about cultural evolution.

Hypothesis:
• Here we use a phylogenetic method to first test whether beliefs in MHGs and BSP coevolve with political complexity.
• Then we test if such beliefs:
o (i) facilitate the evolution of political complexity and
o (ii) stabilize political complexity once it has arisen.
• Only recently has the availability of robust language phylogenies made it possible to trace the evolutionary pathways of cultural traits, enabling us to evaluate causal connections between the evolution of supernatural concepts and the evolution of political complexity.
• To test whether beliefs in either BSP or MHGs have coevolved with political complexity we fitted independent and dependent models of trait evolution onto language phylogenies:
o Under dependent models the probability of a change in one trait depends on the state of the other trait. For example, the probability of a culture gaining political complexity can differ between cultures with a MHG and cultures without one.
o Under independent models the probability of a change in one trait is independent of the state of the other, supernatural beliefs and political complexity evolve independently.
• Functional hypotheses predict that:
o (i) the dependent model will fit best,
o (ii) beliefs in BSP and MHGs will facilitate the evolution of political complexity and that
o (iii) such beliefs will sustain political complexity once it has arisen

Material and Methods:
• Cultures are the unit of analysis as our hypotheses concern the features and evolutionary patterns at this level, not at the level of individuals within a culture.
• In order to minimize the effects of cultural borrowing, cultures have been coded based on the earliest available ethnographic records. Cases of known borrowing from Abrahamic religions were excluded
• For political complexity, cultures were coded as low if they had no more than one level of jurisdictional hierarchy beyond the local community (acephalous societies and simple chiefdoms), or high if they had two or more levels of jurisdictional hierarchy beyond the local community (complex chiefdoms and states).
• For a MHG to be coded as present in a culture there must be the concept of a god who:
o (i) created or governs the cosmos,
o (ii) is active in human affairs and
o (iii) is specifically supportive of human morality
• For BSP to be coded as present in a culture there must be the concept of a supernatural agent or process that reliably monitors and punishes selfish actions, and this concept must:
o (i) be widely advocated within the community,
o (ii) involve punishment of a broad range of selfish behaviours and
o (iii) apply to a wide range of community members

Phylogenetic trees
• We used a sample of 4000 trees from a Bayesian analysis of Austronesian languages. The population history inferred from these trees fits very well with both what is known from archaeology about the sequence and timing of the Austronesian expansion in the Pacific as well as current genetic data. The original 400 cultures used to construct the tree were pruned down to the 96 cultures with the richest ethnographic records.

Phylogenetic comparative method
• We use Bayesian phylogenetic reversible-jump Markov chain Monte Carlo (RJMCMC) analyses in the program BayesTraits to calculate the posterior distributions of dependent and independent models of trait evolution.
• We compared the likelihood of the models found within each analysis by calculating a Bayes factor from their marginal likelihoods.
• Following Kass & Raftery, a Bayes factor of 0– 3 is interpreted as indicating no support for one model over the other, while a Bayes factor of 3 – 10 is taken as substantial support and a Bayes factor of over 10 is taken as very strong support.

Results:
• We found 22 instances of high political complexity throughout historically and geographically distant regions of Austronesia. Ancestral state reconstruction indicates that high levels of political complexity are likely to have independently evolved numerous times throughout the history of Austronesia.
• This result corroborates lexical and archaeological evidence indicating that proto-Austronesian culture distinguished rank based on gender, birth order, age and genealogy, but lacked political stratification beyond the local community.
• We found evidence of beliefs in BSP in 37 of the cultures sampled, however beliefs in MHGs were present in only six cultures. Considerable differences also exist in the geographical distribution of supernatural concepts. Notably, beliefs in BSP were found across an expansive range of Austronesian cultures (figure 2A), while beliefs in MHGs tended to be clustered predominantly in Southeast Asia (figure 1A). These Southeast Asian cultures are Bontok, Toba Batak, Manggarai and Tagbanua.
• The two exceptions to this trend were the MHGs Andriamanitra of the Merina and Makemake of Rapanui [31,32]. Both these cultures represent geographical outliers. The geographical grouping of beliefs in MHGs in Southeast Asia raises the possibility of common descent. However, ancestral state reconstruction indicates that all six instances of MHGs have arisen both independently and relatively recently (figure 1A).
• Testing for the coevolution of MHGs and political complexity, we find that the models of the RJMCMC-dependent analysis than those of the independent analysis Of the six cultures with MHGs, three were politically complex, indicating that the evolution of these two traits is not necessarily strictly coupled. However, given the relative rarity of both MHGs and complex societies in Austronesia, this correlation is sufficient to drive support for dependent models of evolution.
• We then tested whether beliefs in MHGs precede and stabilize political complexity by running two additional constrained-dependent analyses:
o In the first analysis, high levels of political complexity must be gained before MHGs. The resulting models fitted better than both the independent models and the unconstrained-dependent models, though the difference was only substantial with the former. This finding is consistent with our analysis of the unconstrained dependent model in which seven of the 10 most frequently sampled model strings did not allow political complexity to be gained before MHGs.
o In the second constrained analysis we forced cultures with and without MHGs to have the same chances of losing complexity. The resulting models were more likely than the independent model and slightly more likely than the unrestricted-dependent model though not substantially so. Taken together these findings indicate that MHGs did not drive or sustain the evolution of political complexity in indigenous Austronesia.
• We then tested the general claim that beliefs in BSP play a functional role in the evolution of political complexity. We found support for dependent analysis over the independent analysis:
o In this model seven of the eight transition rates were inferred to be equal cultures without BSP did not gain political complexity but all other transition rates were equal.
• We then ran two restricted-dependent analysis to test whether beliefs in BSP precedes and stabilizes political complexity:
o In the first analysis we constrained the model so that beliefs in BSP needed to occur before the evolution of political complexity. The resulting models were substantially more likely than the independent model, and slightly more likely than the unrestricted-dependent model.
o In the second restricted analysis cultures with and without beliefs in BSP were equally likely to lose political complexity.
o These restricted models indicate that beliefs in BSP facilitate political complexity, but cultures with beliefs in BSP are just as likely to lose complexity as cultures without BSP.

Discussion:
• The results presented here cast doubt on the widely held view that MHGs facilitate the emergence of political complexity.
• Although beliefs in MHGs do coevolve with political complexity, beliefs follow rather than drive political complexity.
• Instead, we find that beliefs in BSP facilitate the evolution of political complexity, though neither MHGs nor BSP sustains political complexity once it has arisen.
• The punishing agents that fall under BSP tend to be anthropomophic beings such as the spirits of deceased ancestors and our results suggest that it is these kinds of supernatural punishers that have facilitated the evolution of political complexity in Austronesia. However, ancestral spirits are suboptimal supernatural punishers as they generally have restricted abilities to know about and influence the world, are only important to their own lineage and are biased to favour this lineage. Ancestral spirits may be suited to facilitating cooperation within small scale lineage based groups, but fail to maintain cooperation in larger more complex societies in which there are multiple lineages. While this explains why BSP is found to facilitate but not sustain political complexity, it does not account for why MHGs are not found to drive or sustain political complexity, despite claims that MHGs are the ultimate form of supernatural punishment.
• An alternative explanation for the coevolution of BSP and political complexity is that beliefs in ancestral spirits are a common source of supernatural punishment, which are used to make claims of political authority. An example of a culture in which geneology was used to justify political leadership is Hawaii, where the ancestors of chiefs were elevated to the place of gods and provided chiefs with both authority and supernatural power in the form of mana [35]. The extent to which beliefs in ancestral spirits facilitate political complexity by increasing cooperation, as opposed to motivating claims of political authority, needs to be tested in future research.
• Previous cross-cultural support for both the MHG and BSP hypotheses has relied on the MHG variable coded in the EA and SCCS and there are three reasons our findings differ from previous studies:
o First, previous research has relied on standard correlational techniques that are unable to get at the direction of causality.
o Second, previous research has not fully taken into account the phylogenetic history of cultures. When cultural fission occurs, such as when a group splits off to inhabit a new island, the resulting cultures retain many of their ancestral traits. Supernatural beliefs and level of political complexity are no exception By making inferences based on phylogenetic trees, we were able to infer independent evolutionary events [12], rather than relying on potentially spurious correlations.
o Third reason our results differ from previous studies is that our coding eliminated cases of MHGs that were clearly attributable to contact with Abrahamic religions. External influence potentially confounds the correlations previously found between political complexity and beliefs in MHGs. The scarcity of indigenous MHGs in the Standard Cross-Cultural Sample suggests that the frequency of these gods in indigenous Austronesian cultures is representative of patterns globally. Here we have systematically coded for the states of cultures prior to Abrahamic influence. By excluding clear cases of conversion to Abrahamic religions from our dataset we have controlled for the most prominent form of religious borrowing in Austronesia. In linguistics a subtle form of borrowing, known as calquing, occurs where foreign concepts are adopted using native vocabulary. A similar process may have occurred in the religious beliefs of some Austronesian societies, where the concept of a MHG was borrowed under the name of an existing deity due to contact with Muslim traders. Four out of the six cultures with MHGs in out sample are located in the Southeast Asian cultures where early Muslim trade occurred.
• High complexity societies may have been more likely to have contact with Muslim traders because they had greater resource surpluses to trade. Thus, instead of a direct causal connection between beliefs in MHGs and political complexity, we suggest that the relationship reflects the increased opportunity for more complex societies to have borrowed the concept of a MHG.
• The last decade has seen a substantial growth in the contribution of evolutionary theory to these debates. Despite an appreciation of comparative methods in the study of religion, we know of only one other study that uses an explicit computational phylogenetic approach.
• In contrast to a range of functionalist theories of supernatural punishment, and claims from previous comparative non-phylogenetic studies, our results indicate that beliefs in neither MHGs nor BSP sustains political complexity. While beliefs in BSP may play a role in the emergence of political complexity, beliefs in high gods did not drive the evolution of big societies. The fact that highly complex societies such as the ancient Greeks and Romans did not have MHGs either raises the possibility that this finding may be quite general.
• This work shows a new way forward for historical and comparative research in the humanities— a rigorous scientific way of testing functionalist hypotheses using comparative phylogenetic methods.