Board Thread:Theories and Speculation/@comment-25319479-20171101152711/@comment-1512913-20171108131631

Well, in case Asura having Wood Release is canon, then Hashirama's Wood Release would have origins in Asura as his ancestor, or Hashirama being Asura's incarnate or both. Perhaps it just skips generations.

One thing to consider... Maybe there might have been other Wood Release users before Hashirama in the Senju Clan, they just weren't Asura's incarnates, thus their Wood Release usage was much weaker than Hashirama's or even Yamato's AND if that's true, there might have been Senju children with Wood Release who simply got murdered before they could manifest it, as was ordinary during the warring states era.