Depends on definition of zombies, in the past shamans in the Caribbean would sometimes be hired by people to curse someone. The shaman would poison the victim with a potent pufferfish neurotoxin that would make them catatonic then burry them alive. If the victim survived the ordeal they might escape and try and return to civilization only to be shunned as cursed and forced to wander and survive on their own potentially leading to insanity. Other 'zombies' may have been wandering mentally ill people. Wade Davis was an anthropologist who studied this. I do think there is life outside our planet, the universe is too vast and the probability, given the amount of stars and potentially life sustaining planets, is likely.