Cross-cousin marriages among the Yanomamo found to benefit grandparents

Phys.org has an article about the Yanomami tribe in the Amazon rainforest on the border between Venezuela and Brazil:

Cross-cousin marriage is where cousins from opposite sex siblings are wedded, generally as part of an arrangement between the parents of the cousins, who are, of course, siblings. As the researchers note, it is more common than parallel cousin marriages in cultures around the globe, though it is not known why. In South America, a group of indigenous people called the Yanomamö live in over 200 villages, which adds up to approximately 35,000 people. Researchers have studied them to learn more about their culture, which includes arranged marriages. The researchers with this effort were interested in cross-cousin or consanguineous marriage, and what benefits it might provide.