Proximity or closeness in degree of kinship is one of the ways to determine succession based on genealogy.

It has been at loggerheads with primogeniture in numerous medieval succession disputes. Primogeniture is the common tradition of inheritance by the first-born of the entirety of a parents wealth, estate or office; or in the absence of children, by collateral relatives, in order of seniority of the collateral line. ...

Feudal custom accorded quite a strong value to this claim.

Examples:

In 1361, the Duchy of Burgundy would have gone to Charles II of Navarre according to primogeniture, but went to John II of France according to degree of kinship. Charles II of Navarre was grandson and heir to Margaret of Burgundy, eldest daughter of Duke Robert II of Burgundy. John II of France was son and heir to Joan of Burgundy, second daughter of Duke Robert II of Burgundy. John was first cousin of Philip's father, whereas Charles was son of a first cousin of Philip's father, i.e a second cousin himself. Charles' mother Joan had died already 1349. John was thus one degree closer to Dukes of Burgundy than the primogeniture heir Charles. Charles II (1332–1387), called Charles the Bad, was King of Navarre 1349–1387 and Count of Évreux 1343–1387. ... Robert II of Burgundy (1248–March 21, 1306) was duke of Burgundy between 1272 and 1306. ... John II the Good (French: Jean II le Bon) (April 16, 1319 – April 8, 1364), was King of France 1350–1364, Duke of Normandy and Count of Anjou and Maine 1332–1350, Count of Poitiers 1344–1350, and Duke of Guienne 1345–1350. ...

Earlier, Mary of Antioch claimed the throne of Jerusalem in 1269. She was the daughter of Prince Bohemond IV of Antioch and Tripoli (d 1233) and his second wife Melisend of Cyprus (who died after 1249). Melisend was the youngest daughter of King Amaury I of Cyprus and his third wife Queen Isabella of Jerusalem. Since Mary was, at the time of the death of Conradin, the only living grandchild of Queen Isabella, she claimed the throne on basis of proximity in kinship to Conradin and to the Kings of Jerusalem. However, the Haute Cour of Kingdom awarded the succession to a heir of Melisend's elder sister, though he was a great-grandson of Isabella. Maria of Antioch pretended to the throne of Jerusalem from 1269 to 1277. ... Bohemund IV of Antioch (d. ... Isabella of Jerusalem (c. ... Portrait of Conradin from the Codex Manesse (Folio 7r). ...

Philip V of France became king by its force in 1316. Philip V the Tall (French: Philippe V le Long) (1293 - January 3, 1322) was King of France from 1316 to 1322, a member of the Capetian dynasty. ...

Robert Bruce of Annandale claimed the crown of Scotland using that argument (and his grandson and namesake managed to wrest Scotland to himself, later). Robert Bruce a. ...