Monks relax sibling competition over parental resources in Tibetan populations

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.