Interethnic Interaction, Strategic Bargaining Power, and the Dynamics of Cultural Norms
Interethnic Interaction, Strategic Bargaining Power, and the Dynamics of Cultural Norms
A Field Study in an Amazonian Population 0 1 2 3
John Andrew Bunce 0 1 2 3
John Andrew Bunce 0 1 2 3
0 Department of Anthropology, Indiana University , Bloomington, IN , USA
1 Department of Anthropology, University of California , Davis, CA , USA
2 Department of Human Behavior , Ecology, and Culture , Max Planck Institute for Evolutionary Anthropology , Leipzig , Germany
3 Richard McElreath (BS , MA , PhD) is director at the Max Planck Institute for Evolutionary Anthropology in Leipzig and professor in the Department of Anthropology at the University of California, Davis. He studies the role of culture in human evolution , USA
Ethnic groups are universal and unique to human societies. Such groups sometimes have norms of behavior that are adaptively linked to their social and ecological circumstances, and ethnic boundaries may function to protect that variation from erosion by interethnic interaction. However, such interaction is often frequent and voluntary, suggesting that individuals may be able to strategically reduce its costs, allowing adaptive cultural variation to persist in spite of interaction with out-groups with different norms. We examine five mechanisms influencing the dynamics of ethnically distinct cultural norms, each focused on strategic individual-level choices in interethnic interaction: bargaining, interaction-frequency-biased norm adoption, assortment on norms, success-biased interethnic social learning, and childhood socialization. We use Bayesian item response models to analyze patterns of norm variation and interethnic interaction in an ethnically structured Amazonian population. We show that, among indigenous Matsigenka, interethnic education with colonial Mestizos is more strongly associated with Mestizo-typical norms than even extensive interethnic experience in commerce and wage labor is. Using ethnographic observations, we show that all five of the proposed mechanisms of norm adoption may contribute to this effect. However, of these mechanisms, we argue that changes in relative bargaining power are particularly important for ethnic minorities wishing to preserve distinctive norms while engaging in interethnic interaction in domains such as education. If this mechanism
proves applicable in a range of other ethnographic contexts, it would constitute one
cogent explanation for when and why ethnically structured cultural variation can either
persist or erode given frequent, and often mutually beneficial, interethnic interaction.
The extent of human cultural variation is unprecedented in nature, and its evolutionary
origins remain mysterious. Much human cultural variation is structured in symbolically
marked groups (ethnic groups), which are often associated with different suites of
beliefs about what constitutes appropriate behavior in a given context—cultural norms
(Barth 1998; see also Bicchieri 2006)
. Life in such groups may have characterized our
species for 80,000 years or more
(d'Errico et al. 2009; Foley and Lahr 2011)
. The facts
that ethnic groups are nearly universal in human populations at all but the smallest
geographic scales, are absent in all other primates, and are highly dynamic present
important puzzles to evolutionary social scientists: What are the psychological and
cultural processes that make and remake ethnic groups? What role did such processes
play in the adaptive history of humankind?
Evolutionary Models of the Norms and Behaviors of Symbolically Marked
One idea to explain the maintenance of ethnic groups is that assortment on symbolic
markers helps to preserve locally adaptive norms, knowledge, and beliefs from erosion
(Henrich and McElreath 2003; Richerson and Boyd 2005)
. For example,
McElreath et al. (2003)
demonstrate that symbolically marked groups with differences
in norms can arise spontaneously under a minimal set of assumptions: benefits to
interindividual interaction depend on norm coordination, interaction partners are
chosen on the basis of markers, and norms and markers tend to be acquired from locally
successful individuals. Once such marked groups evolve, intragroup coordination
interactions yield greater benefits than interaction between groups. A similar model
Boyd and Richerson (1987)
focuses instead on ecological adaptations rather than
norms, but it also produces symbolically marked groups that protect adaptive, culturally
transmitted behavioral variation from erosion by mixing between residential groups.
Once evolved, ethnic groups in these models have salient, and relatively fixed,
(see also Pagel and Mace 2004)
, and isolating mechanisms attenuate costly
(analogous to reproductive isolating mechanisms in biological
species; e.g., Price 2008)
A shortcoming of these models is that interaction between groups is exogenously
imposed, rather than a result of the strategic decisions of individuals. In these models,
there are no benefits to intergroup over intragroup interaction. In contrast, in nearly all
ethnographic and historically described contexts, people voluntarily engage in at least
some interethnic interaction
(e.g., Wolf 1982)
. Such interaction sometimes entails the
adoption of out-group cultural norms
(Behrens 1992; Kopenawa and Albert 2013;
and is not necessarily viewed by participants as detrimental
. There may be adaptive reasons to interact with other ethnic groups,
and even to adopt culturally transmitted behavior from them. Thus, models that exclude
such benefits miss a potentially important factor affecting cultural dynamics.
One potential resolution to this conflict between models and empirical observation is
that individuals strategically adjust how, and with whom, they interact, in order either to
reduce costs of norm miscoordination or, rather, to preferentially adopt adaptive
behavior from members of other groups. The strategic nature of between-group
interaction could help explain how, in some contexts, ethnic-typical norms can be
maintained for generations despite frequent interethnic interaction
(e.g., the Fur and
Baggara of western Sudan: Haaland 1998)
, while, in other cases, the norms of one
ethnic group are rapidly replaced by those of another
(e.g., assimilation of some
immigrants in the United States: Gans 1979)
. The lack of mechanistic models of these
dynamics represents an important challenge for our understanding of the evolution of
cultural norms in ethnically structured populations. Ultimately we seek a body of
theory that can explain the uniqueness of human ethnic variation among primates,
contribute to an understanding of the dynamics of historical and contemporary ethnic
groups, and enhance the ability of ethnic minority members to reverse or slow the loss
of valued cultural norms, should they wish to.
Mechanisms of Norm Adoption at Ethnic Boundaries
Previous research on ethnic variation has emphasized links between the adoption of
out-group cultural norms (e.g., assimilation and marginalization), participation in
interethnic interaction (e.g., through social networks), individual personality traits
(e.g., attitude toward the out-group, bicultural efficacy), and the strategic maintenance
or change of ethnic identity
(Berry 1997; LaFromboise et al. 1993; Wimmer 2013)
However, the mechanistic links between interethnic interaction and norm adoption are
often not specified in sufficient detail to facilitate empirical testing. For instance, the
pioneering study of
among minority Spanish-speaking Americans and
Native Americans in a majority Anglo-American town in the southwestern US, found a
strong relationship between interethnic interaction (e.g., in domains such as education,
military service, out-group friendships, employment) and the probability that minority
individuals hold majority-typical norms. From this, it is argued that exposure to
outgroup norms, identification with the out-group, and access to resources controlled by
the out-group all play roles in the adoption of out-group norms. However, the
mechanisms underlying such relationships are not well understood, making it difficult to
distinguish among them with the available data. As an initial step forward, we focus on
five theoretically grounded and previously published mechanisms whose predictions
can be compared using quantitative and ethnographic data at hand. An individual’s
adoption of out-group norms may depend on: (1) differential bargaining power during
interethnic interactions, (2) the relative importance (e.g., relative frequency) of
interethnic coordination interactions; (3) interethnic assortment on coordination norms,
coupled with success-biased social learning among co-ethnics; (4) success-biased
interethnic social learning; and (5) favorable exposure to out-group norms during
childhood socialization. These five mechanisms are neither exhaustive nor mutually
exclusive. However, they make distinct predictions that we can evaluate using
empirical data in order to better understand their roles in the norm dynamics of a
particular ethnically structured population. In the remainder of this section, we sketch
each and provide citations to further discussion.
Norms play an important role in interethnic interactions because many such interactions
have the form of coordination games. In a coordination game, all participants receive a
higher (though not necessarily equal) payoff if they act in concordant rather than
. Consequently, players should seek to interact
with others holding similar norms in the context of interaction
(McElreath et al. 2003)
Many domains of social life, such as commerce, healthcare, education, and marriage
(Nave 2000), can be modeled as coordination games. Interethnic interactions can be
especially challenging because, initially, distributions of norms often differ among
, potentially frustrating attempts at coordination
eighteenth-century Chinese-British commerce: Sahlins 1994)
When two individuals with different norms desire to coordinate, they must negotiate
about whose norm they will use for the interaction. In many contexts of social
coordination, the relevant norms may be deeply held and psychologically costly to
change—for example, norms of fairness, child-rearing, and education. Individuals may
be able to coordinate using norms different from those with which they personally
(e.g., cross-cultural or bicultural competence: Johnson et al. 2006;
LaFromboise et al. 1993)
, but the resulting psychological costs (e.g., cognitive
dissonance: Festinger 1962), among other potential costs, should motivate them to try to
impose their preferred norm on the coordination interaction. Following Ensminger and
(1997; Knight 1992)
, we define an individual’s ability to do this as bargaining
power. Bargaining power is contingent on, among other things, control over the
resources (material or immaterial) that one brings to the coordination interaction, as
well as control over choice of interaction partner. An individual’s ability to impose
coordination norms is reduced if she has less control over (or less-valuable)
coordination resources and if she has less choice about whom she coordinates with
and Knight 1997; Knight 1992)
When there are benefits to interethnic coordination but limited numbers of out-group
coordination partners, members of one ethnic group (e.g., residents) may compete
among themselves to interact with members of the other ethnic group (e.g., visitors).
One way that residents can compete for visitors is to offer to coordinate using
visitortypical, rather than resident-typical, norms. Thus, in a given coordination interaction, a
visitor has greater bargaining power than a resident, all else being equal, because she
can choose from among residents the one most willing to coordinate using her preferred
norm. In the terminology of economics, the visitor has short-side power in a contested
(Bowles and Gintis 1993)
. In this way, where there is interethnic asymmetry
in resource control, intraethnic competition among members of the resource-favored
group tends to decrease any interethnic asymmetry in bargaining power
and Knight 1997)
. The effect of differential bargaining power on norm adoption is
mediated by the frequency and importance of interethnic interactions. The more an
individual engages in subjectively important interactions using particular norms, the
more likely she may be to adopt and internalize those norms, changing her cognition to
align with her behavior
(Barth 1966; Festinger 1962)
. Thus, we predict that the
probability that an individual adopts out-group norms, as opposed to maintaining her
original norms, is a decreasing function of the relative amount of bargaining power she
has in frequent and important interethnic coordination interactions.
Interaction-Frequency-Biased Norm Adoption
Regardless of relative bargaining power, the norms of frequently interacting ethnic
groups would be expected to evolve toward similarity in any domain of interethnic
since both parties would then receive the benefits of
(e.g., market-based interactions: Henrich et al. 2010)
. We predict that, in a given
interaction context, individuals on one side of the interaction should directly adopt the
norm of their most frequent or most important coordination partners, all else being
equal. For instance, given a degree of asymmetry in bargaining power across a range of
interaction contexts, norm adoption by low-power individuals will be most likely in
those domains where interaction is most frequent or most important to them. If
interethnic interactions are important, this mechanism will produce a positive
association between out-group norms and interethnic interaction experience on one side of the
Interethnic Assortment on Norms
If there is preexisting intragroup variation in norms, individuals may preferentially
assort such that those with the most out-group-typical norms engage in the most
interethnic coordination. If there is an added benefit to interethnic over intraethnic
coordination, individuals who have out-group-typical norms in the context of
interaction may attain high prestige. Out-group norms can then spread within a group as
people copy prestigious or successful co-ethnics
(Barth 1966; Henrich and Gil-White
, with the possible result that the norms of one group eventually replace those of
the other. This process can result in a positive association between the amount of
interethnic interaction and the probability of holding out-group-typical norms, an
empirical pattern potentially indistinguishable from that generated by the previous
mechanism of interaction-frequency-biased norm adoption. However, if interethnic
assortment on norms is operating, we expect the probability that an individual initially
engages in interethnic interaction to be higher if she already holds out-group-typical
norms. Without assortment, initial interethnic interaction is expected to be random with
respect to norms.
Success-Biased Interethnic Social Learning
An individual’s decision to adopt the norms of another ethnic group may be based on
the relative perceived success or prestige of individuals in the other ethnic group
relative to that of those in her own group. When there is a causal link between a
socially learned norm and group-level success (e.g., when group benefits depend, in a
non-additive manner, on the frequency of the norm among its constituents), the
selective imitation of successful groups can be operationalized as cultural group
(Henrich 2004; Richerson et al. 2016)
. This may occur with or without direct
interaction between individuals in the two groups, as long as the norms of the
successful or prestigious group are known to individuals in the other. Thus,
successbiased interethnic social learning of norms need not depend on the benefits or costs to
individuals of interethnic coordination interactions. Boyd and Richerson (2002)
showed that, under a range of conditions, this mechanism can result in the spread of
individually costly group-beneficial norms among ethnic groups, and it may explain the
spread of early Christian norms of mutual aid
(reviewed in Richerson and Boyd 2005)
However, such success-biased social learning is easily generalized to any norm that
people wish to copy, whether or not the norm itself entails group benefits. One type of
evidence for this mechanism would come from an observation that the norms typical of
a successful or prestigious ethnic group are directly copied by individuals in other
ethnic groups, regardless of those individuals’ personal interethnic interaction
experience in the social contexts in which such norms apply. Note that the principal difference
between this mechanism and the previous mechanism of interethnic assortment on
norms is that, here, the targets of success-biased social learning tend to be individuals in
the out-group rather than co-ethnics with out-group-typical norms.
Socialization is the process by which children are taught the norms of the society
or ethnic group in which they live. Although some norms may correspond to a
near-universal genetic predisposition
(e.g., mating aversion for very close kin: van
den Berghe 1983)
, it is likely that, on average, children are not born with a strong
predisposition one way or the other toward most norms responsible for ethnic
variation in our species. The cultural pluripotency of young children is most
apparent in situations of cross-cultural fostering, where children readily adopt
norms very different from those of their biological parents
Richerson and Boyd 2005)
, and in societies undergoing rapid social and economic
change—for instance, where norms covary with birth cohort
(reviewed in Chen
and French 2008)
. Children have evolved high receptivity to learning whichever
norms are used to socialize them (Legare and Nielsen 2015) since this facilitates
access to the benefits associated with integration into the society where they
expect to grow up
(Chen and French 2008; Ochs and Izquierdo 2009)
The purpose of norms, by definition, is to restrict the range of available behavioral
choices in a given decision context, at times eliminating choices that might otherwise
seem desirable (e.g., a norm against cheating). In order to function, a norm must be
reasonably inflexible given contextual variation in the behavior to which it applies (e.g.,
cheating on an exam versus cheating in sports). However, this same quality of
inflexibility may make norms, once learned, relatively resistant to change later in life,
even when there may be benefits to doing so
(e.g., norms of circumcision learned prior
to immigration into a non-circumcising host society: Morison et al. 2004)
. For this
reason, a child socialized using an in-group norm may become progressively more
resistant to subsequent adoption of a conflicting out-group norm. It may also be the
case that children pass through a developmental window (perhaps prior to adolescence)
in which they are cognitively more receptive to the adoption of cultural norms
et al. 2011; but see Chudek et al. 2015)
. If either norm inflexibility or a developmental
norm-adoption window occur (or if both occur), we predict that, on average over a
broad range of ages, the earlier in the socialization process (e.g., the younger) an
individual is favorably exposed to out-group norms through interethnic interaction, the
more likely she is to adopt norms of the other ethnic group.
Overview of the Present Study
Incorporating the mechanisms described above, we develop and evaluate hypotheses
for why interethnic interaction variably results in persistence or erosion of cultural
norm differences. We do so using ethnographic data on interethnic interaction and norm
adoption decisions in a relatively remote population in Amazonian Peru, where a
salient ethnic boundary exists between indigenous Matsigenka and neighboring
colonist Mestizos. Matsigenka live in a community legally protected from incursion by
Mestizos, and with very little exposure to mass media. Matsigenka-Mestizo interaction
is almost entirely constrained to the domains of commerce, wage labor, and education,
and such interethnic interaction nearly always requires Matsigenka to leave their
community and travel to Mestizo towns. Hence, the circumstances of interethnic
interaction are highly asymmetric and limited to specific memorable contexts. This
allows us to abstract away from the full complexity of interethnic frontiers and collect
individual-level data on both norms and histories of interethnic interaction that address
hypothetical mechanisms for the persistence or erosion of norm differences.
We find that Matsigenka who interact voluntarily, and even frequently, with
Mestizos in the contexts of labor and commerce show little evidence of change
towards Mestizo-typical norms, whereas those who attended Mestizo schools
are more likely to hold Mestizo-typical norms as adults. A number of
mechanisms likely contribute to this empirical pattern. However, using ethnographic
data we argue that, in particular, the differential bargaining power of each
ethnic group in each domain of interaction provides both a theoretically cogent
and an empirically accurate explanation that extends existing evolutionary
models of the cultural dynamics of ethnic groups in human societies.
Furthermore, we suggest that changes in bargaining power in the context of
intercultural education may contribute to the maintenance of cultural norms valued by
This paper employs multilevel Bayesian item-response models to analyze
patterns of individual-level variation in cultural norms. This framework is
consistent with, and meaningfully advances, quantitative anthropological approaches to
(e.g., cultural consensus and consonance: Dressler et al. 2005;
Oravecz et al. 2014, 2015; Romney et al. 1986)
. These models treat norm
variation as directly unobservable, but nevertheless inferable from patterns of
behavior (e.g., responses to interview questions), and make no assumptions about
the correctness or incorrectness of any norm or behavior. We provide a script
sufficient to repeat and extend our analysis so that other researchers can engage
with these models and adapt them to other contexts.
The study was conducted among residents of the Matsigenka native community of
Tayakome (adult population: 79), located inside Manu National Park, in the department
of Madre de Dios, in the lowland Amazonian region of southeastern Peru, and in the
Mestizo towns of Boca Manu (adult population: ~80) and Atalaya (adult population:
~65), located just outside the boundary of the park, in the departments of Madre de
Dios and Cusco, respectively (Fig. 1).
Tayakome residents practice swidden horticulture, fishing, and hunting. Most
Matsigenka understand basic Spanish but prefer to interact in their own language.
Some travel outside the park and live among Mestizos for weeks to months working as
wage-laborers (32%), or to attend Mestizo-run schools (20%). Shorter excursions are
occasionally made to purchase items (e.g., pots, flashlights) in Mestizo general stores.
There is a government health post in Tayakome, though most adult Matsigenka interact
little with the Mestizo technician. The primary school in Tayakome is staffed by
externally trained Matsigenka teachers. Nearly all interethnic interaction with Mestizos
occurs in the three domains of commerce, wage labor, and education, and takes place in
Mestizo towns. There is very little Matsigenka-Mestizo intermarriage or domestic
interaction. Most Mestizos are colonists from the Andean highlands who usually
interact with each other in Spanish. They are not permitted to enter the national park
without a government permit. Residents of Boca Manu and Atalaya tend small general
stores and restaurants, build wooden boats, grow plantains for the market, log the
surrounding forest, and/or work in tourism for the park. Further details of the study
communities can be found in ESM A.1, as well as in
Shepard et al. (2010)
Isenrich and Nieto Degregori (2003).
JAB lived in Boca Manu for approximately three months (September and November
2012, January 2014), Atalaya for two months (December 2012 and February 2014),
and Tayakome for 13 months (January–December 2013, March 2014). Over several
rounds of semi-structured interviews, he recorded interviewees’ life history and
recollections of personal intra- and interethnic interaction experience, emphasizing the
domains of commerce, wage labor, and education. He then designed a set of fourteen
vignette questions (Table 1) for the purpose of learning about specific norms in eight
contexts of social coordination (commerce, wage labor, education, spousal relations,
parent-offspring relations, inheritance, healthcare, and religion) and administered these
questions privately to 74 (94%) residents of Tayakome (including the Mestizo health
technician), 45 (56%) residents of Boca Manu, and 42 (65%) residents of Atalaya, all of
whom had been previously interviewed regarding life history and interethnic
interaction experience. Further description of data collection methodology, as well as
translations of vignette questions are provided in ESM A.2.
The norms measured by the vignette questions may covary, such that knowing how an
individual answered one question gives you information about how she answered
another question, and, in the ideal case, about how she answered all of the other
questions. If true, then people’s responses to the fourteen vignettes can be represented
by a smaller number of latent dimensions, and, ideally, by a single latent dimension. We
use Item Response Theory (IRT) models
(Bafumi et al. 2005; Fox 2010; Jackman
2001; Schacht and Grote 2015)
in a Bayesian framework (McElreath 2016) to show
that, for this study, the vignette responses of each interviewee are well represented by a
single dimension. This latent dimension constitutes a convenient way to compare
individuals on the basis of all fourteen measured norms simultaneously. It does not
necessarily represent a unitary, overarching belief held by actual people (e.g., a
metanorm). For instance, it may be that the fourteen measured norms are functionally
independent but happen to covary within this sample of people. However, for ease of
exposition below, we will refer to the latent dimension as representing a meta-norm. We
interpret the negative pole of the dimensional axis as a meta-norm prioritizing
respectful autonomy, while the positive pole represents a meta-norm prioritizing practical
a See ESM A.2 for an explanation of the cultural context of drunkenness in Matsigenka society, which will
differ from that of most readers
interdependence. See ESM A.2 for the relation between individual vignette questions and
interpretation of the latent dimension. Note, however, that the conclusions below do not depend
on interpretation of this constructed dimension. The location on the latent axis of individual j (and
thus a continuous measure of j’s meta-norm) is represented by the parameter αj. We model αj as
a linear function of a population-mean intercept (b0), an individual-level random effect (bindiv[j],
zero-centered offset from b0 for each individual j), and various combinations of hypothesized
predictors, including ethnicity, and interethnic commerce, wage labor, and education experience:
α j ¼ b0 þ bindiv½ j þ b1x1½ j …; for j ¼ 1; …; J
where J is the number of interviewees. An example fixed effect predictor, b1x1[j], is
the product of the coefficient for ethnicity and the binary ethnicity indicator for
To construct an IRT model, we follow
Bafumi et al. (2005)
by embedding the linear function
αj within a logistic function. This allows us to simultaneously evaluate properties of each
individual and each vignette question with respect to the latent dimension. The probability that
the response y of a particular interviewee j to a particular vignette question k is the practical
interdependence response (column four of Table 1), Pr(yjk = interdependence), is given by a
logistic function (inverse logit) ranging between zero and one:
Pr yjk ¼ 1
¼ logit−1 γk α j−βk
where practical interdependence and respectful autonomy responses are represented by
1 and 0, respectively. The domain (x axis) of this logistic function is the latent
dimension. The slope at the function’s inflection point, γk, is the degree to which an
affirmative versus negative response to question k discriminates among individuals
holding the meta-norm for respectful autonomy versus practical interdependence. The
location of the inflection point on the latent axis, βk, is the degree to which a person
must hold the meta-norm for practical interdependence in order for the model to predict
that she give the interdependence-associated response to question k. See ESM
Figure B1 for illustrations.
To check the robustness of results to the effects of different predictors, we fit a series
of 19 models varying in the fixed effect predictors included in the linear function for αj.
Parameter estimation for each model was accomplished with RStan
, running four Hamiltonian Monte Carlo chains in parallel until
convergence was suggested by a high effective number of samples (>500) and R^ estimates of
. This entailed 4000 samples per chain, half of which were
warm-up. We compared model fit with WAIC
. Data and statistical
analysis scripts in R
(R Core Team 2014)
implementing RStan are available from
Further explanation and priors for model parameters are provided in ESM A.3.
Associations between Norms and Interethnic Experience
Figure 2 shows that, for all fourteen vignette questions, a larger proportion of
Matsigenka than Mestizos gave responses corresponding to practical interdependence.
These raw proportions suggest an overall ethnic difference in the distributions of the
norms applied by the interviewees to answer the questions, and they demonstrate the
utility of the interview instrument to distinguish between these two ethnic groups. See
ESM C.1 for further discussion of this result. In all nineteen IRT models, posterior
estimates of the discrimination parameters (γk) for all vignette questions are non-zero
(ESM Figures B1 and B2). This indicates that all questions can reasonably distinguish
among individuals along a single latent axis
, which, as described
above, we interpret as representing an individual’s meta-norm for practical
interdependence versus respectful autonomy.
Next we turn to individual norm differences among Matsigenka and examine the
extent to which such differences are predicted by interethnic interaction experience.
Figure 3 plots the locations of all 161 interviewees on the latent (meta-norm) axis. As
expected, there is marked separation by ethnicity, with Matsigenka tending toward the
positive pole for practical interdependence and Mestizos tending toward the negative
pole for respectful autonomy. However, it is apparent that a number of Matsigenka
individuals have axis locations very similar to those of average Mestizos, suggesting
that they hold the Mestizo-typical meta-norm for respectful autonomy. The right three
columns of Fig. 3 demonstrate that these Matsigenka with the Mestizo-typical norm
tend to have interethnic commerce, wage labor, and education experience. In contrast,
Matsigenka with the more Matsigenka-typical norm for practical interdependence may
have interethnic commerce and wage labor experience, but almost none have education
experience with Mestizos.
The same effect is seen in Fig. 4, plotting counterfactual contrasts of posterior
predictions from the best-fitting model (m19 in ESM Table B1, with 33% of model
Fig. 3 Mean posterior probability estimates for the locations (αj) of all 161 interviewees on the latent axis, as
predicted by an IRT model with a random effect for individual and no predictors (model m1 in ESM
Table B1). Plotted in columns from left to right are: all Mestizos, all Matsigenka, only Matsigenka who have
commerce experience with Mestizos (w/ Com), only Matsigenka who have wage labor experience with
Mestizos (w/ Lab), and only Matsigenka who have education experience with Mestizos (w/ Edu). Horizontal
lines are drawn at the mean of each column. Within columns, points are jittered on the x-axis for clarity
Matsi w/o exp − Mest w/ com
Matsi w/o exp − Mest w/ lab
Matsi w/o exp − Mest w/ edu
Matsi w/o exp − w/ com
Matsi w/o exp − w/ lab
Matsi w/o exp − w/ edu
Matsi w/ com − Mest w/ com
Matsi w/ lab − Mest w/ lab
Matsi w/ edu − Mest w/ edu
Contrast on Latent Axis
weight). The model predicts that Matsigenka who have never engaged in commerce,
wage labor, or education interactions with Mestizos have the Matsigenka-typical
metanorm of practical interdependence, which differs from the Mestizo-typical meta-norm
of respectful autonomy (Fig. 4a). Similarly, Matsigenka with commerce and wage labor
experience tend to hold the norm of practical interdependence like those of other
Matsigenka (Fig. 4b), but unlike the norm of most Mestizos (Fig. 4c). In contrast,
Matsigenka who went to school with Mestizos tend to hold the norm of respectful
autonomy like most Mestizos (Fig. 4c), and unlike the norm typical of their fellow
Matsigenka (Fig. 4b) (further details of analysis in ESM B).
An exploratory model including sex and categorical age predictors achieved 7% of
model weight, although the coefficients of each of these predictors could not be
distinguished from zero (m12 in ESM Table B1). Furthermore, coefficient estimates
for ethnicity and the interethnic experience predictors were not distinguishable from
those of the best-fitting model, above. This gives us confidence that inclusion of sex
and age in the model has little effect on the results. Coefficient estimates for all models
are provided in ESM Table B1.
There is ethnographic evidence that Matsigenka have less bargaining power in the
domain of interethnic education than they do in interethnic wage labor and
commerce. This coincides with the result above that Matsigenka with interethnic
education experience are more likely to hold Mestizo-typical norms than are
Matsigenka with interethnic labor and commerce experience. In the context of a
strict boarding school environment, Matsigenka children usually do not control
their presence or absence in classrooms, nor the time they must allocate to studying,
which constitute their contributions to coordination in the domain of education.
Additionally, students usually cannot choose their coordination partners—in other
words, the Mestizo teachers and caretakers with whom they interact. By leveraging
their physical strength and institutional authority to adjust punishments and
incentives, teachers can thus compel students to coordinate using Mestizo norms, which
many students likely adopt and internalize. Mestizo-run secondary schools are
attractive to many Matsigenka parents and children, and they generally function
near maximum capacity. Thus, competition among Mestizo-run schools for
Matsigenka students is largely absent.
In contrast, for both wage labor and commerce, Matsigenka control valued
resources for coordination: their labor and their money, respectively. Because
laborers and customers are usually in demand, Mestizos compete among
themselves to interact with Matsigenka, who can often choose to work for or buy
from those Mestizos most willing to coordinate using Matsigenka-typical norms.
For instance, Matsigenka wage laborers usually have the option of changing
employers if Mestizos try to impose Mestizo-typical norms either inside or
outside of the context of labor. As a Mestizo from Atalaya who routinely
contracted Matsigenka field hands stated,
[Matsigenka] work well, but I let them work in their own way, because their
world is different. A type of person like us [Mestizos] already knows how this
kind of work is. [We] work until late, [and are] more demanding. But a Machi,
when you bring him [to the agricultural field], you let him work in his own way.
If he wants to leave, then we leave. If he wants to go for a little while because he
is tired, I let him . . . If I say something to them, like demanding that they do
something, they get angry and they leave you, just like that. They’re not even
interested in the money.
Thus, relative to education, there may be less incentive for Matsigenka to adopt
Mestizotypical norms during interaction in domains such as wage labor and commerce, where
Matsigenka have greater bargaining power (additional examples in ESM C.2).
Interaction-Frequency-Biased Norm Adoption
It seems likely that Matsigenka directly adopt Mestizo-typical norms as a result of interethnic
coordination interactions. For instance, describing Matsigenka boarding school students in Boca
Manu, who also engage extensively in commerce and wage labor on weekends, one Mestizo
When they first come, they have many problems, and they are used to not
working. That is one of their customs. And when they come here they have to
change their way of thinking. They have to see how to get ahead. It’s a struggle
for them. He who does the most, is the most ambitious, obtains the best things.
They see that among themselves, and they change.
There is evidence of a positive relationship between the frequency of interethnic
interaction and the probability of holding out-group norms. Relative to Matsigenka
with interethnic wage labor and commerce experience, Matsigenka who went to school
with Mestizos tend to have the most Mestizo-like norms and also the most lifetime
interethnic interaction experience. For instance, of the 16 Matsigenka who attended
Mestizo-run schools, 14 also have interethnic wage labor experience, which is often
quite extensive. Thus, Matsigenka with interethnic education experience tend to have
more years of interaction experience with Mestizos in the combined domains of
education and labor (~12 years, on average) than do Matsigenka wage laborers who
did not attend a Mestizo-run school (~ 4 years, on average). It is thus likely that the total
amount of interaction experience with Mestizos, regardless of domain, is positively
associated with Mestizo-like norms among Matsigenka.
However, it is also likely that education has a unique effect on out-group norm
adoption, independent of the frequency or amount of time spent in interaction. Two
Matsigenka interviewees did not go to Mestizo-run schools but have approximately
15 years of wage labor experience, living and working for more than half of each year
with Mestizos outside of Tayakome. Despite this extensive interethnic experience,
these individuals tend to have more Matsigenka-typical norms (larger αj) than do the
nine Matsigenka who each have combined education and labor experience with
Mestizos totaling approximately 10 to 15 years (ESM Figure C1). This anecdotal
evidence suggests that, on average, accounting for the total amount of interethnic
experience, interethnic education is more strongly associated with Mestizo-like norms
than is wage labor alone.
Interethnic Assortment on Norms
There is ethnographic evidence for a moderate degree of assortment on norms in
interethnic interaction. Matsigenka children with the most Mestizo-like norms may
be preferentially selected for, and retained in, Mestizo boarding schools. For instance,
two of the three Mestizo boarding secondary schools currently attended by Tayakome
children require matriculation interviews, including a cursory evaluation of norms (e.g.,
readiness to shake hands and return a greeting in Spanish). Additionally, several
Matsigenka students have been expelled from these two schools for failure to conform
to Mestizo norms of acceptable students (e.g., obedient and nulliparous). In contrast,
one of the three boarding schools attended by Tayakome students does not require
matriculation interviews and has not, to our knowledge, expelled students. Thus, at this
school, initial assortment on norms is not enforced from the Mestizo side of the
interethnic interaction. Similarly, in informal conversations in Tayakome, several
Matsigenka with very Matsigenka-typical norms (high αj) expressed a strong desire,
and detailed future plans, to engage in wage labor interactions with Mestizos (ESM
Figure C1). Thus, assortment on norms may occur in some contexts of interethnic
education, but it may be weak or absent for many other Matsigenka-Mestizo
In order for interethnic assortment on norms to affect norm dynamics, the
norms of Matsigenka with Mestizo-typical norms should be preferentially
copied by their fellow Matsigenka (i.e., success- or prestige-biased intra-ethnic
social learning). Although we did not explicitly investigate such a preference
in the present study, we note its plausibility. For example, the mother of a
Mestizo-educated Matsigenka man in Tayakome told JAB that she stopped
wearing a traditional Matsigenka nose ring (koriki) at the insistence of her
son, whom she esteems, and who had apparently adopted a Mestizo norm for
the inappropriateness of such ornaments.
Success-Biased Interethnic Social Learning
As shown above, the probability of holding Mestizo-typical norms is contingent
on the type of interethnic interaction experience of Matsigenka individuals (i.e.,
commerce or labor versus education). This is contrary to the expectation under
success-biased social learning, assuming Matsigenka regard Mestizos as
successful or prestigious, and assuming all Matsigenka regardless of interethnic
experience are aware of Mestizo-typical norms. Although Mestizos do control access to
desired manufactured goods, JAB’s ethnographic observations suggest that most
Matsigenka may not generally regard the Mestizos of Boca Manu and Atalaya as
more prestigious than they are. For instance, a Matsigenka with extensive
experience working on a Mestizo-owned tourist boat in Atalaya viewed Mestizos as
inferior workers, stating,
Mestizos are a little lazy. Matsigenka surpass them in work. As crew members,
sometimes [the boss] tells us to wash the boat. The Mestizo doesn’t wash; he just
stays watching. The Matsigenka washes everything.
If interethnic differences in prestige or perceived success are small,
successbiased social learning will be weak. On the other hand, it may also be the case
that many of the norms represented by the vignette questions are difficult for
Matsigenka to observe, or hear about, without extensive experience living among
Mestizos. However, once a Matsigenka learns of such norms, she may adopt
them via success-biased social learning even if she never employs such norms in
her personal interactions with Mestizos. There is some limited evidence for this
type of learning. Among the twenty Matsigenka with four or more years of
combined interethnic education and wage labor experience, approximately half
held a Mestizo-typical (respectful autonomy) norm concerning inheritance
(Question 7, 11/20 interviewees), compared with only 15% (9/59) among Matsigenka
with less-extensive interethnic experience. This occurred despite the fact that
only four Matsigenka interviewees have had the opportunity to coordinate with
Mestizos in the context of inheritance (two have children with a Mestizo, and
two have one Mestizo parent). Thus, success-biased social learning may occur to
a limited extent among Matsigenka with extensive interethnic interaction
There is an association between early age of interethnic socialization and the
probability of holding out-group-typical norms. Matsigenka interviewees who engaged in
interethnic interaction at the earliest ages were those who attended Mestizo-run schools.
These included five students who attended just interethnic primary school (when aged
approximately 6–12), five who just attended interethnic secondary school (when aged
approximately 13–17) or beyond, and six who attended both interethnic primary and
secondary schools. As shown above, for Matsigenka, interethnic education has the
strongest association with Mestizo-typical norms. Socialization of children to a broad
range of Mestizo norms, including those outside of academics, appears to be one goal
of Mestizo-run education. For instance, a Mestizo staff member at one boarding school
attended by Tayakome children explained:
In the boarding school there are rules. . . . [What] we’re doing here is simply the
way to put away dishes, [to] put things in order, [to go about] cleaning, [to] have a
clean room, [to] have everything in order, [to] live with beauty and honor.
No Matsigenka engaged in interethnic wage labor or commerce as a young child
without also attending Mestizo schools. Thus, in this sample, the effect of early age
of out-group socialization on norm adoption cannot be distinguished from that of other
aspects of interethnic education experience.
Our objective was to investigate the mechanisms by which individuals adopt out-group
norms, potentially leading to cultural dynamics in ethnically structured populations. We
have shown quantitatively that indigenous Matsigenka who attended Mestizo-run
schools tend to hold more Mestizo-typical norms across a range of social contexts,
relative to Matsigenka with only wage labor and commerce experience with Mestizos.
Cross-sectional data of this type cannot be used directly as evidence that interethnic
interaction, such as education, causes cultural change
(see also Graves 1967)
we have leveraged our ethnographic observations to show that the observed pattern is
likely due to all five of the mechanisms we identified as potentially influencing
individual adoption of out-group cultural norms: bargaining,
interaction-frequencybiased norm adoption, interethnic assortment on norms, success-biased interethnic
social learning, and childhood socialization. Below we argue that, of these mechanisms,
bargaining is particularly important in this ethnographic context and may also explain
why interethnic education can be such a potent driver of cultural dynamics in other
ethnic groups engaging with colonial powers. However, first we address limitations and
strengths of our methodology and analysis.
Limitations and Strengths of the Study
This study systematically examined norms, but not the behaviors to which they apply.
Norms and behavior may correspond
(e.g., Atran et al. 2002)
, though they need not. Of
particular importance are cases of bicultural competence
(LaFromboise et al. 1993)
which an individual may modify her behavior according to the norms of the ethnic
group in which she finds herself. In this study we assume that each individual holds a
single norm with respect to each vignette question (or a single meta-norm applicable to
each question), and that this norm is reflected in each response. Under this assumption,
if the behavior of a biculturally competent individual changes with ethnic context, it
may therefore periodically deviate from the norms that she personally holds. It is
possible that, rather than reflecting individually held norms, vignette responses of a
biculturally competent individual reflect behavioral decisions corresponding to the
ethnic context that she imagines while listening to each vignette (which are mostly
designed to be neutral with regard to Matsigenka and Mestizo ethnic context). This
study is limited by the assumption that any such imagined context is one in which the
subjectively appropriate behavior corresponds to the norms that the interviewee
We employed Bayesian item-response models to analyze individual-level responses
to a range of questions about norms. Although similar in underlying mathematical form
to the widely used cultural consensus model framework
(Romney et al. 1986)
models are more flexible, and, most importantly, facilitate direct estimation of the
effects of predictors on latent outcome variables in hierarchically structured data
(Schacht and Grote 2015; Oravecz et al. 2014)
. An important goal of this study is to
assess between-group variation and explain within-group variation in a variety of
norms, apparent in Fig. 2. The IRT models allow us to represent this norm variation
in a lower-dimensional space, where effects of the hypothesized predictor variables can
be meaningfully estimated and understood. We expect this analytical strategy to prove
particularly useful for anthropological interview data in any context where the
researcher employs a battery of questions to investigate and explain individual-level variation in
cognitive states (e.g., norms, preferences, beliefs) that cannot be directly observed. We
encourage other researchers to explore our analysis scripts (https://github.
com/jabunce/bunce-mcelreath-HN-2016-matsigenka-norms) and modify them to suit
Bargaining Power Interacts with Other Mechanisms
The low bargaining power of Matsigenka children in Mestizo-run schools interacts with
other identified mechanisms of norm adoption. For instance, the fact that
Mestizoeducated Matsigenka have more lifetime interethnic interactions than Matsigenka
without such experience may contribute to their adoption of Mestizo-typical norms
over the course of their lives. However, it also seems likely that Mestizo-typical norms
learned in school facilitate subsequent interethnic coordination in domains such as
commerce and wage labor. After graduating, Mestizo-educated Matsigenka may
selfassort into commerce and wage-labor coordination interactions with Mestizos, domains
in which subsequent norm adoption may occur, though at comparatively lower rates
owing to the increased bargaining power of Matsigenka. Thus, adoption of
Mestizotypical norms by Matsigenka students with low bargaining power may facilitate
subsequent interaction-frequency-biased norm adoption.
The low bargaining power of Matsigenka students may cause feelings of inferiority.
In a boarding school environment, Matsigenka children may view Mestizo teachers and
peers as more prestigious and successful, thereby facilitating success-biased social
learning of Mestizo norms unrelated to those that Matsigenka actually use to interact
with Mestizos. In contrast, in domains such as wage labor, the higher bargaining power
of Matsigenka may reduce feelings of inferiority and thereby reduce the success-biased
adoption of such norms. Thus, bargaining power may interact with success-biased
interethnic social learning.
Finally, the young age of Matsigenka students may contribute to their susceptibility
to adoption of Mestizo-typical norms. However, consistent with JAB’s observations,
Ochs and Izquierdo (2009)
argue that Matsigenka children as young as six years old
have already learned important Matsigenka-typical norms, such as sharing, hard work,
and intragroup harmony. Simple exposure to alternative Mestizo-typical norms would
not necessarily induce these children to change the norms they have already learned.
Thus, in addition to early exposure, the potent effect of interethnic education on norms
is likely also due to the fact that children are easier to physically manage and
strategically isolate from elder co-ethnics (e.g., in a boarding school), such that their
control over coordination resources and choice of adult coordination partners is
constrained, thereby reducing bargaining power. In summary, the low bargaining power
of Matsigenka students likely plays an important role in norm adoption, despite the fact
that other identified mechanisms may operate concurrently.
Education, Bargaining Power, and Cultural Change
The potency of education as a driver of cultural change has long been recognized and
exploited by colonial powers attempting to eradicate the cultural norms of indigenous
peoples (e.g., to “develop” or “civilize” them), including Native South Americans
, Native North Americans
(Parliament of Canada 1985; Trennert
, and Indians under British colonial rule (Seth 2007). The contemporary
movement for intercultural bilingual education attempts to combat this legacy. One strategy
is to introduce non-Western students to desired Western academic knowledge using the
pedagogical norms of the students’ own society, and to require local community
oversight of, and participation in, students’ education
(Aikman 2003; Trapnell 2003)
Only local communities themselves can judge the appropriateness of such an
educational program. However, we note that several elements of this approach may, in effect,
increase the relative bargaining power of indigenous students and parents in
educational coordination with out-group teachers: for example, community choice of teachers
(hiring and firing power), students learn from both co-ethnics and out-group members,
attendance is voluntary. Thus, if such a program is effective in transcending the
historical paradigm of colonial education by reducing the loss of valued
ethnictypical cultural norms, an increase in relative bargaining power may be an important
part of the explanation.
We argue that differential bargaining power is likely to be one powerful driver of
cultural dynamics in contexts of interethnic interaction, and it is at least partially
responsible for the pattern among Matsigenka that out-group cultural norms strongly
co-vary with interethnic education experience. Bargaining power can vary by domain
of interethnic interaction (e.g., education versus wage labor), affecting the costs and
benefits accruing to individuals of such interactions. Consequently, even when norm
distributions differ across an ethnic boundary, as they do here, interethnic interaction
does not invariably entail miscoordination costs for all participants
et al. 2003)
, and it does not always lead to the erosion of ethnic-typical cultural
variation. Similarly, although ethnic communities may have compelling reasons to
curtail it, the adoption of out-group norms, when it does occur, should not be viewed
as invariably costly. Rather, to advance theory of cultural change in ethnically
structured populations, interethnic norm adoption decisions can be more productively
investigated as resulting from the interaction of several mechanisms, including strategic
choice of benefit-seeking individuals in contexts of low bargaining power. Future work
in this and other ethnographic settings should incorporate longitudinal data on
individual norm development and look for situations affording natural experimental control
over interethnic interaction experience, in order to more effectively distinguish among
the predictions of the five mechanisms of norm adoption identified here.
Acknowledgments Open access funding was provided by the Max Planck Society. We thank the residents
of Tayakome, Boca Manu, and Atalaya for their participation. For help with fieldwork and data analysis we
thank Caissa Revilla, Cecilio Huamantupa and family, Rosa Maria Chigueti, Napoleon and Lila Oyeyoyeyo,
Berta Chura, Mircia Metaki, Veronica Chavez, Cesar Flores, Fortunato Rayan, and staff of the Cocha Cashu
Biological Station, Patricia Alvarez, Cecilia Carrasco, Miriam Minaya, Oscar and Natalia Revilla, Gonzalo
Lugon, Rainforest Flow, SERNANP Cusco, Oscar Espinosa and the Pontificia Universidad Católica del Perú,
Mark Grote, and Lynne Isbell. Ronny Barr assisted in the design of Fig. 1. Anne Pisor, Cody Ross, Bret
Beheim, Cristina Moya, and staff in the Department of Human Behavior, Ecology, and Culture at the Max
Planck Institute for Evolutionary Anthropology, as well as Doug Yu and two anonymous reviewers, provided
valuable comments and insightful criticism on earlier versions of this manuscript. Funding was provided by
the U.S. National Science Foundation (BCS 1227152) to JAB. All work was conducted under University of
California, Davis IRB 226284-2.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International
License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
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link to the Creative Commons license, and indicate if changes were made.
John Bunce is a postdoctoral fellow in the Department of Human Behavior, Ecology, and Culture at the Max
Planck Institute for Evolutionary Anthropology. He studies cultural change at ethnic boundaries using both
theoretical mathematical models and ethnographic fieldwork in Amazonian Peru. For his Ph.D. at the
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