Clan, social group claiming descent from a common ancestor. Clans have existed all over the world, from primitive societies to the famous Highland clans of Scotland (said to have originated in the 11th century). Some clans have expressed their unity in the symbol of the totem (an object, animal, or plant revered as the ancestor of the group). Most, but not all clans, are exogamous, requiring marriage outside of the clan (marriage within being regarded as incest). Several clans may organize into a larger social structure known as phratry.