Marriage with aunts and uncles (avunculate marriage) is legal in several countries. The term "avunculate" comes from the Latin "avunculus," the maternal uncle. Sibling marriage and avunculate marriage is prohibited, while cousin marriage is legal. Because of this avunculate marriage, Margaret's mother was nearly thirty years younger than her father. Avunculate marriage was the preferred type of union in some pre-modern societies. Franz Boas categorized various avunculate arrangements based on the location of residence in 1922.