The claim that brother adelphos here means cousin anepsios is a theoretical contention the invention of which is credited to Jerome and dates back no earlier than  CE     Not only does Jerome fail to cite any support for his newborn hypothesis but in later writings he wavers in his opinions and even expresses misgivings about his cousin theory J B Lightfoot states that St Jerome pleaded no traditional authority for his theory and that therefore the evidence in its favour is to be sought in Scripture alone I have examined the scriptural evidence and the    combination of difficulties    more than counterbalances these secondary arguments in its favour and in fact must lead to its rejectionSt Pauls Epistle to the Galatians London  p