Which statement best defines coevolution?

• A. Evolution occurs only within a single species.
• B. Two species evolve in response to each other over time.
• C. Coevolution means one species causes the extinction of the other.
• D. Evolution happens only due to abiotic factors.

Answer: (B)

Coevolution is when two species influence each other’s evolution over time through their interactions. When one species develops a new trait, it changes the selective pressures on its partner, and that partner responds with its own adaptations, leading to a cycle of reciprocal changes. A classic example is flowering plants and their pollinators: plants evolve traits like bright colors and nectar rewards to attract pollinators, while pollinators evolve features that let them access the nectar more efficiently. Predator and prey pairs also show this back-and-forth evolution, with each side gaining improvements that push the other to adapt again. This idea stands apart from evolution happening in just one species, or evolution driven only by nonliving factors, or the notion that one species must drive the other to extinction.