What is required to scientifically identify the process of coevolution?

Answer

Demonstrating reciprocal selective pressure where A influences B and B influences A.

To confirm coevolution, researchers must prove that the selective agent influences the evolution of the selected species, and that the resulting evolutionary changes in the selected species impose a new selection pressure back onto the original agent.

What is required to scientifically identify the process of coevolution?
speciesEcologyEcosysteminteractioncoevolution