That evolved into Marquess. The eldest son also bears one of his father's subsidiary titles. Earls The word Earl is from the Anglo-Saxon magnate known as an ealdorman who was a local ruler. Many former Prime Ministers were made earls when they left office. Until the 17th century an earl was invested by the Sovereign with the sword he wore at his waist - hence the term 'a belted earl'.
Some Scottish earldoms pass through the female line.
The present Earl of Mar is a woman. Daughters are styled Lady. Such designations are not courtesy titles but ancient and honorable designations. Recently, the title has been used to reward distinguished people who deserve more than a barony to get them into the House of Lords. Even if a Viscount has s secondary title of baron, it is not used by his heir.