In the Firefly universe, there are a group of monstrous, man-eating madmen known as the Reavers.
There are many myths spinning around their origin, one of the most prevalent being that they traveled to the end of universe and went mad after staring into the nothingness.
During one Firefly episode, the crew discovers a stranded vessel that was attacked by Reavers. Onboard they find slaughtered people, while one of them apparently was forced by the Reavers to watch the whole thing. I am not certain I remember that part right, but Raynolds explains that that is how they recruit new "members" (by turning them crazy).
However, in the movie Serenity it is explained that the Reaver state is a side effect of a drug meant to calm the population of the planet Miranda.
To me that seems to contradict the explanation presented before. I find it hard to believe they can mimic the results of the drug by driving someone mad "manually".
So how do the Reavers actually grow in numbers? Do they recruit new members by turning them mad? Do they reproduce the old fashioned way? Or do they not recruit at all and all the Reavers we see are actually original inhabitants of Miranda?