Surnames do not perfectly indicate ethnicity due to the fact that modern surnames in English are generally patrilineal, meaning the family inherits the name from the father and excludes the mother's line of descent. Surnames are also sometimes adopted by ethnic minorities to assimilate, or changed through marriage.
A person's surname and ancestry may not match due to name changes or intermarriage with other ethnicities. Many surnames in English are poor indicators of ethnic origin in their possessors, such as with the actress Rashida Jones, whose surname is neither African nor Jewish in origin despite descent from a Jewish-American mother and an African-American father.
Family names in Germanic and Romance-influenced languages are often occupations, such as "Smith" or "Mason," or else refer to descent from an ancestor, such as "McClellan" or "Jackson." Reference to a place of residence or origin is also common, as in "Scott" or "Danjou"
Place-based names determine ethnicity based on the country of origin, region or province of origin, geographic features or estates. Common prefixes for place-based surnames are “from” are “de” in French, “van” in Dutch and “von” in German.
Many Old English surnames denote both ethnicity and occupation, such as the obvious “Baker” or “Miller,” or “Barker” the word for a leather tanner, “Cooper” for a barrel maker, or "Wainwright" for a wagon maker.
Some common patronymic prefixes are “O-” for an Irish surname, “Bar-” or “Ben-” for a Hebrew surname, and “Ibn-” for Arabic surnames. Many last names change over time. The original spelling of a last name gives clues to its ethnicity, for example, the German “Mueller” becomes “Miller” in the United States.
Learning to differentiate languages by ear or by eye is the surest way to determine the original language of a family name. Even then, ethnic family names may go through a process of acculturation in which the surname changes to fit the culture of the family member's current residence by translating the meaning of the family name or adjusting spelling and pronunciation for speakers of the local language and dialect.
Despite patrilineal inheritance of family names in English, family names are not patronyms that change each generation, as in Russian-naming conventions.