You now know that natural seleqtion aims at evolving adaptations of organisms in response to environmental changes in the inanimate world. Also many adaptations arise due to interaction with or as a response to the presence of other organisms in the environment. So far we discussed the evolution of such interactions and adaptations between closely related species which wore or less occupy the same level in the food chain. Such interspecific interactions may also occur between organisms at different lkvels in the food chain. The evolution of adaptations in response to such interactions has been largely responsible for the development of various associations be it commensalism, mutalism, parasitism or predation. For instance, the claws, teeth, speed etc., found in carnivores are adaptations evolved in response to the kind of prey species which makes up their diet. Similarly, the toxins, protective coloration I and chemical warfare devices are the adaptations evolved by the prey species to escape from the evil designs of the predator. Also selection is able to maintain and adjust the rate of reproduction of the prey species to that of predators. In short, interspecific relationships are a direct result of the coordination of the evolution of ecologically related species by the natural selection process. Very interestingly, of the two species that are involved in the evolution of such relationships, each one acts as the mutual agent of selection for the other. It is this process that is known as coevolution. In this section, we shall be analysing prey-predator, plant-herbivore and host-parasite relationships as coevolutionary processes.