What is it about?

The most common preferred marriage practice across cultures is to marry the son or daughter of your parents opposite sex sibling (e.g. your mother's brother or your fathers sister). The reasons why this practice, known as cross cousin marriage, is so widespread is unresolved and is an important puzzle for those interested in understanding the roots of cross cultural variation in human behavior and cultural practices. Results of this paper. An analysis of the reproductive consequences of marriages in the Yanomamö – a tribal society in the Amazon – suggest that this practice may owe it's origin to reproductive conflicts of interest between parents and and competition between brothers for mates.

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Why is it important?

Cultural practices that develop over time as information, abilities, skills and practices that no single individual could ever invent in his or her lifetime seem to emerge as if out of the ether. Cultural practices often arise, however, because they benefitted their practitioners in the past and may continue to do so, even though we may long ago lost any sense of why the practice came about in the first place or how it benefits us today. These results offer insight into the origin of one of the most fundamental and common human cultural practices about who we are allowed to marry and who ultimately benefits from the practices and taboos that have arisen around marriage practices while also offering an answer to one of the oldest questions in anthropology.


I was fortunate enough to do my first post-doctorate after getting my PhD at the University of Missouri with Napoleon Chagnon who spent his career working with and collecting data on the Yanomamö , one of the last large groups of uncontacted peoples in the world. Although, I knew little about cross cultural marriage practices or the Yanomamö when I started, I did know that the data that Nap, who died in 2017, had spent his life collecting was a national treasure and that nobody had or would be able to collect anything like it again. This was a fascinating paper to write and it was a pleasure to have met and worked with Napoleon Chagnon, one of the giants of evolutionary anthropology, if only for a few years.

Dr Robert Francis Lynch
University of Missouri Columbia

Read the Original

This page is a summary of: Cross-cousin marriage among the Yanomamö shows evidence of parent–offspring conflict and mate competition between brothers, Proceedings of the National Academy of Sciences, March 2017, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1618655114.
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