DOI: 10.5061/dryad.p2ngf1vss
title: Monks relax sibling competition over parental resources in Tibetan populations

description: Why parents in some societies induce some of their sons to become
 religious celibates is an evolutionary puzzle. Some have speculated that
 this might be associated with brother competition for family resources.
 However, the behavioral ecology of monks and the possible links with
 competition between brothers remains unexplored. Here, we use demographic
 data from Amdo Tibetan agropastoralists in western China to evaluate what
 factors determine the probability of becoming a monk and explore the
 possible association between wealth and having a monk brother. We found
 that boys with at least one older brother are more likely to be induced by
 their parents to become celibate monks. Patrilocal heads of household, who
 inherit parental property, are more likely to be first-born sons, whereas
 men who marry uxorilocally, that is they move to their wife’s household,
 are generally second or later born sons. Moreover, we find that men with
 at least one monk brother are wealthier than men who only have
 non-celibate brothers. Together, these results suggest that sending a son
 to the monastery is way for parents to decrease competition between
 brothers over family resources. Harsh and resource-limited environments,
 like the one we consider, can lead to the emergence of communal
 households, including polyandrous families, which used to be common in
 Tibetan areas. Directing one son to become a religious celibate offers a
 potentially effective solution to brother competition in our population.
description: Socio-demographic data were collected in 2017 in a county
 in Gansu province, China. The study was approved by the School of Life
 Sciences, Lanzhou University, and the Research Ethics Committee of UCL
 (0449/003). We collected detailed
 sociodemographic data from 530 households in 21 natural villages in a
 county in Gansu province. Natural villages are clusters of houses that do
 not necessarily correspond to the larger administrative villages
 recognised by the local government. The households reported on a total of
 3591 living people (1702 women and 1889 men). In each household, one adult
 man or woman was interviewed and asked about the age, sex, marital status,
 socioeconomic status and profession of all household members, including
 whether any members in the household were monks or nuns. In some cases, we
 were not able to obtain sibling information, because some people were
 absent at the time of the interview and the main interviewee could not
 recall this information. Interviews were conducted with the help of local
 translators, one adult man and one adult woman. Female interviewees were
 generally interviewed by a woman assistant. Participants were briefed
 regarding data anonymisation in the local language. Participants were
 briefed about the anonymity of our methods and data in local languages
 before giving consent. Informed consent was obtained from all
 participants.
description: Analyses reported
 in this article can be reproduced using this data. Notice that we reduced
 the number of covariates for the analyses in Tables 1-2 and have not
 included data for the analysis in Tables 3-4 to protect the identity of
 the participants.