What evolutionary mechanism is often involved when selection favors the co-option of existing structures to create a convergent trait?

Answer

Pre-adaptation.

Convergence frequently occurs through pre-adaptation, where an existing feature originally adapted for one purpose is modified or co-opted by selection to serve a new function, such as early tetrapod limbs being molded into flippers for aquatic life.

What evolutionary mechanism is often involved when selection favors the co-option of existing structures to create a convergent trait?
biologyevolutionselectionconvergencetrait