The earliest tradition that explains the divergence of Joseph's lineages involves the law of levirate marriage. A woman whose husband died without issue was bound by law to be married to her husband's brother, and the first-born son of such a so-called levirate marriage was reckoned and registered as the son of the deceased brother (Deuteronomy 25:5 sqq.). Sextus Julius Africanus, in his 3rd-century "Epistle to Aristides", reports a tradition that Joseph was born from just such a levirate marriage. According to this report, Joseph's natural father was Jacob son of Matthan, as given in Matthew, while his legal father was Eli son of Melchi ("sic"), as given in Luke.