 Different approaches also exist regarding allowing "second-generation" descendants of heroes or villains, full-grown over 18 years after an event (for example, Hulkling, other members of the Young Avengers, the Runaways, and the Secret Warriors), whereas other books, such as "Young Allies" use the inherent contradiction to debunk similar claims.If a past storyline wherein a direct depiction of a then-current president or similar is referred to in a later era, it tends to become updated accordingly, sometimes with an "in-joke" acknowledgment.A more recent explanation was given by Galactus to the Ultimates, namely that some important events - for instance, the creation of the Fantastic Four or the Avengers - have a 'gravity' all their own and warp time around them, causing the timeline to subtly change to accommodate this.