In most animal species the close approach of one individual to another is an aggressive action. Yet, for reproductive purposes such a male-female approach must be made. Thus complicated behavior patterns have evolved from a combination of submissive gestures and ritualized displacement activities, to appease the sexual partner. In many cases these rituals also involve the development of morphological display characters. Mating rituals may also serve as an isolating mechanism to ensure that mating is with another member of the same species.