As revealed in the first issue of X-Men: PhoenixWarsong, the sisters are grown from ova cells harvested from telepath and then villain Emma Frost while she lay comatose after a Sentinel attack that killed her students, the original Hellions, and are only five of many cloned daughters. The remaining hundreds (if not thousands) of clones reside within incubation chambers inside a hidden underground laboratory at The World, a complex housing the Weapon Plus (living beings designed to serve as weapons) program. They were created by Dr. John Sublime to be powerful weapons able to kill every mutant by combining their telepathic abilities. The Cuckoos were designated Weapon XIV.
