The incest taboo is one of the most widespread of all cultural taboos , both in present and in past societies. In most cases, the parents did not have the option to marry to remove that status, as incestuous marriages were, and are, normally also prohibited. A common justification for prohibiting incest is avoiding inbreeding : a collection of genetic disorders suffered by the children of parents with a close genetic relationship. In some societies, such as those of Ancient Egypt , brother—sister, father—daughter, mother—son, cousin—cousin, aunt—nephew, uncle—niece, and other combinations of relations within a royal family were married as a means of perpetuating the royal lineage. However, sexual relations with a first-degree relative meaning a parent or sibling are almost universally forbidden. The English word incest is derived from the Latin incestus , which has a general meaning of "impure, unchaste".