What is specific or pair-wise coevolution?

• A. The evolution of a trait in one species in response to a trait in another species, which originally evolved in response to the first.
• B. Co-evolution that involves many species across ecosystems.
• C. The evolution of multiple traits within a single species without interspecific interaction.
• D. The random drift of traits in isolated populations.

Answer: (A)

Pairwise coevolution is about reciprocal evolutionary changes between two interacting species. The idea in the statement fits this well: a trait in one species evolves in response to a trait in the other, and that second trait had originally evolved in response to the first. This back-and-forth adaptation is the classic image of two species shaping each other’s evolution, like predator and prey or host and parasite where each lineage continually counters the other. It’s different from diffuse coevolution, which involves many species, and from evolution of multiple traits within a single species without interspecific interaction, or from random genetic drift. A familiar example is one species evolving stronger toxins and the other evolving greater resistance, in a continual arms race.