Board Thread:Naruto Discussions/@comment-25573196-20141023231527/@comment-418162-20141024023546

Kohametasuka19's explanation makes the most sense. The manga simply says the Uzumaki and Senju share an ancestor and most likely that ancestor is Ashura through maybe some second son of his or possibly even a daughter since in Japanese culture when a clan is formed sometimes a man of a lesser clan takes the clan name of his wife of a more prestigious clan so that their children continue the more prestigious clan's name. It's kinda funny actually cause the Senju and Uchiha are related the same way, sharing of a common ancestor (Hagoromo). This just made me realize Sasuke and Naruto are distantly related.