Coevolution is the evolution of two or more species that reciprocally influence each other’s adaptations.
The process occurs when natural selection acting on one species changes the selective pressures experienced by another. For example, flowering plants may evolve structures that improve pollination by particular insects, while those insects evolve body parts or behaviours that help them reach the plants’ nectar. Each species can therefore shape the other’s evolutionary trajectory over many generations.
Coevolution does not mean that species consciously adapt for one another, nor does every evolutionary change in interacting species qualify. Scientists look for evidence that changes in one lineage are linked to changes in another. Predator–prey arms races are a familiar example: prey may evolve better defences, while predators evolve improved ways to overcome them. Parasites and hosts can produce similarly reciprocal adaptations.
The idea has roots in Charles Darwin’s discussions of plant–insect relationships, including his work on orchids. It is commonly confused with convergent evolution, in which unrelated species independently develop similar traits because they face similar environmental pressures. Divergent evolution instead describes related populations becoming increasingly different.