Probably the most feasible cause of the outbreak is a lab experiment gone wrong. Think about every disease disaster movie you've ever seen, it all stems from a shaky-handed scientist spilling a misty formula, or someone leaving a door unlocked to allow immense hordes of apes to roam wild and free. It would be a cliched cause, but what if it did happen? Some fans have even suggested that it could be linked to real-world disease, an 'in search of the cure, they created a monster' scenario. The CDC storyline was not explored for long enough looking at the entire run of the show, but there could easily have been a leak or contamination which escaped into the world, thus causing the downfall of mankind, right?