rare morph to have an advantage, a variety of criteria need to be met. First, there needs to be polymorphism present. In addition, the prey cannot be present in equal proportions, since then there would not be a benefit to being able to detect either one. This is related to frequency-dependent predation, where as the predator obtains the greatest advantage from having a search image for the most common type of prey. This causes the most common form of the prey to be the most vulnerable. Changes in prey detection by predators do occur, but the speed in which they occur and the flexibility of a predator's search image depend on the environment. If the frequency of the different prey types continuously changes, the predator may not be able to change its behavior at a rate that will provide an advantage. In these situations, the predators who are able to change their search image rapidly or have a flexible search image are able to survive. In relation to apostatic selection, rapid changes in prey frequencies can decrease the advantage of the rare morph if their predators have a broad search image or are able to rapidly change their search image. However, rapid changes in polymorphism frequencies can also be an advantage to the prey with the rare morph. Since long periods of time are generally required for natural selection to act on predators, the degree of flexibility in their search image may not be able to be changed over a short time frame. Therefore, quickly arising rare morphs are favored by apostatic selection if the predators are not able to change their behavior and search image in a short time frame. Thus, this is a biological process that is victim to evolutionary time delay. Apostatic selection is strongest in environments in which prey with the rare morphism match their background. Behavioural basis of apostatic selection Most of the work done on the behavioural basis of apostatic selection was done by A.B Bond. It has been suggested that in frequency-dependent predation, the number of encounters with the prey shapes the predator's ability to detect prey. This is based on the assumption that when the predator is learning foraging behaviour, it is going to obtain the common form of prey most frequently. Since the predator learns from what is most frequently captured, the most common morph is what is identified as prey.