Just re-listening to the the series, at chapter 7 part 3 when a team is sent to put trackers on zombies. After repeated exposure to the chloroform, the zeds adapted and the chloroform lost its effect. Maybe I should post this in the theories, but I am wondering, why this is the case that the zeds adapted? What are the limits to their adaptations? Are the varieties of zeds a result of simple natural selection, or other something else?