All Other Factors Being Equal, Which Scenario is Least Likely

Question

All other factors being equal, which scenario is least likely to involve coevolution?
A) An obligate positive interaction in which one party lives inside the other
B) An obligate positive interaction in which the two parties are closely related
C) An obligate positive interaction in which the two parties are from different kingdoms
D) A facultative interaction in which the two parties are from different kingdoms

Accepted Answer

Coevolution is less likely in facultative interactions because the relationship is not essential for the survival of either party, reducing the selective pressure for reciprocal evolutionary changes.