MARROW

The first time readers met her, she was a little girl named Sarah, one of the Morlock children living in the tunnels beneath New York. In Cable #15 (1994), by Jeph Loeb and David Brewer, Cable, Domino and the Morlock Thornn performed the Ceremony of Light in the Alley, and young Sarah crossed over from another dimension to greet them. She thanked them, explained that the other Morlocks were still too frightened to return, and went back through the doorway to rejoin her people. She was a child, drawn as a child, in a story published in September 1994.

The doorway led to the Hill, the harsh alternate dimension where Mikhail Rasputin had secretly transported the surviving Morlocks instead of letting them drown. There, under a strict survival-of-the-fittest order, Sarah lived for some ten to fifteen years. Callisto, the former Morlock leader, cared for her like a daughter until her bone powers fully manifested and she was sent up the Hill to fight her way toward the summit. She reached the top as a young adult, took the name Marrow for the jagged bones erupting from her body, and was inducted into Mikhail's elite fighting force, Gene Nation, rising to lead it.

When Marrow finally returned to Earth as Gene Nation's leader, she discovered that only a few years had passed at home, because time moves far faster on the Hill than it does on Earth. Readers saw the result almost immediately: in X-Men: Prime (1995), published barely ten months after her debut, the little girl from Cable #15 was suddenly a grown, scarred, bone-sprouting fighter. No retcon and no clone is needed to explain the jump. She simply grew up somewhere else, at another speed, and came back older than the calendar says she should be.