With reproduction at the heart of the evolution of living organisms, anthropologists have for long wondered how the practice of celibacy could have evolved.
In the new study, published on Wednesday in the journal Proceedings of the Royal Society B, researchers studied the practice in Tibetan Buddhist monasteries in which, until recently, families would send one of their young sons to become a lifelong, celibate monk.
They interviewed over 500 households in 21 villages in the eastern part of the Tibetan plateau, in Gansu province and reconstructed their family genealogies, gathering data on each person’s history and whether any of their family members were monks.
Based on the gathered data, they developed a mathematical model of celibacy to understand the evolutionary costs and benefits associated with the practice.
Researchers say these villages are inhabited by patriarchal Amdo Tibetans who raise herds of yaks and goats, farming small plots of land.
In these communities, wealth is usually passed down the male line. The study found that men with a monk brother were wealthier and owned more yaks.
However, almost no benefits were found for sisters of monks.
“Surprisingly, we also found that men with a monk brother had more children than men with non-celibate brothers,” researchers wrote in The Conversation.
The wives of men with a monk brother also tended to have children at an earlier age.
Those with a monk son also had more grandchildren since their non-celibate sons faced lesser competition within the family for resources.
Since monks cannot own property, the study authors speculate that the practice of parents sending one of their sons to the monastery ended fraternal conflict.
“We show that a minority of sons being celibate can be favoured if this increases their brothers’ reproductive success, but only if the decision is under parental, rather than individual, control,” researchers wrote in the study.
“The practice of sending a son to the monastery, far from being costly to a parent, is therefore in line with a parent’s reproductive interests.”
However, they say while all the men in the village may benefit if one of them becomes a monk, the individual monk’s decision does not further his own genetic fitness.
Researchers believe the framework developed in the study could also be used to understand the evolution of other practices rooted in parental favoritism in other cultural contexts, including infanticide.
They are hoping to apply the model to understand why the frequency of monks and nuns varies across religion and geography.
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