Grand Unifying Guesses/Gene Carriers

Every badass in fiction is related - they all carry the Badass Gene.
The Badass Gene is activated by a need to kick some serious ass, and manifests in increased strength, reflexes, combat skills, courage, and ability to keep fighting despite severe injuries. See the Badass page for a list of known carriers.
 * A carrier may go through their entire life without manifesting. This is how non-badasses have badass children.
 * The Badass Gene can also result from mutation, caused by exposure to radiation. This is why people who work in science labs, go into space, or live in post-apocalyptic environments, are more likely to display the Badass Gene.
 * Any program to create super-soldiers that involves a screening process to pick out qualified candidates will only select those with the Badass Gene.
 * By the 41st Millenium, natural selection has killed off every human being that does not carry the Badass Gene.
 * The universe of Dune is actually the future of the Warhammer 40K universe - after the discovery of Arrakis, humanity successfully got the Tau, Tyranids, Orks etc hooked on spice to such a degree that they became completely apathetic junkies and were easily slaughtered. Humanity itself started taking the spice after successfully purging the galaxy of all non-humans and re-organised into the Great Houses. The Bene Gesserits' actual aim of producing a Kwisatch Haderach was to produce a man so badass he would shake humanity out of its apathy and prepare it for battle against the Necrons - robots can't get addicted to drugs, can they?
 * The Les Enfentes Terribles project's true aim was to isolate and harness the Badass gene by conducting experiments with the DNA of the most Badass person alive, Big Boss.
 * Big Boss eventually goes on to become the God-Emperor of Mankind, meaning that all Space Marines carry his geneseed.
 * Soldiers wishing to join the Orbital Drop Shock Troopers are screened for this gene as well.
 * The first known carrier of the Badass Gene was Beowulf; he may be the Badass from which all others are descended.
 * Slayers automatically get this activated when they are activated, and becoming a vampire also activates it.

All Chosen One figures are descended from Jesus and Mary Magdalene (or analogous individuals).
Jesus's mother Mary could only supply Him 23 chromosomes, meaning that the other 23 must have come from God. Assuming that he had offspring with Mary Magdalene, His descendents probably would have carried DNA sequences that did not exist before Jesus was conceived.
 * When these genes are active, the carrier becomes a full-fledged Messiah.
 * All four Pevensie children carry the Messiah genes, making Aslan guilty of nepotism.