Coevolution refers to the process where two or more species modify each other's evolution via natural selection. Darwin mentioned how insects and flowering plants could coevolve by reciprocal evolutionary modifications. Coevolution has firstly been associated with mutualism between species including, for example, birds and flowering plants. However, coevolution may also involve host-parasite relationships, such as associations involving parasitic organisms and their sexually reproducing hosts. Finally, there are situations where coevolution involves both parasitism and mutualism (i.e., antagonistic coevolution).
