UC Santa Barbara

Intermarriage is a primary driver of gene flow and cultural exchange in our species. However, despite strong interest in kinship, exchange and intergroup relations, the potential role of intermarriage has not been systematically studied nor its importance highlighted in the evolutionary social sciences. Core questions to consider include: What drives individuals to marry outside their cultural group? What socioecological conditions may lead to norms favoring marriage within vs. outside one’s cultural group? And what consequences does intermarriage have on interpersonal and intergroup relations? This dissertation addresses the above questions in the context of a multiethnic village located at the intersection of the Amazon and the Andean highlands of Bolivia, where resource access and production strategies vary between indigenous Moseten and first- or second-generation Aymara-Quechua migrants.

First, I find ethnicity is an important factor in the choice of marriage partners and marital stability. Further, intermarriage between Moseten women and Highlander men may be driven by socioeconomic resource exchanges, whereby Moseten women leverage their privileged access to arable land in tribal territory to attract wealthier Highlander men.

Secondly, I leverage a localized crop failure event in 2016-2017 to investigate whether interethnic marriage fulfills a risk management function. Consistent with ethnographic evidence that other forms of exogamy (e.g., intercommunity marriage) help buffer resource shortfalls in high-risk settings, I find that intermarried Moseten-Highlander couples are better able to recover from the economic impacts of crop failure. Their greater resilience is likely due to more diverse production strategies and reliance on remittances from larger extra-community social support networks.

Thirdly, I investigate how the presence of intermarried couples and their progeny, being of mixed ethnicity, affects the community’s social networks, attitudes towards diversity, and the salience of ethnic identities. I find intermarried individuals to be well-integrated into the study community’s networks and act as bridges between different ethnic groups. Although my findings suggest positive effects of intermarriage as a potential accelerator of integration, I find mixed effects on its potential to erode negative attitudes between groups.

In sum, this dissertation suggests that resource exchange and risk buffering may, at least in part, drive intermarriage in multicultural societies where resource access, production strategies and social networks vary between groups. Accordingly, intermarriage may be tolerated and widespread even in contexts where markers of group identity, such as ethnicity, remain important factors in the choice of marriage partners