The selection of catalysts (the most efficient process of perhaps metabolism and so forth), would most likely be through a direct selection of that specific function that needs to be catalyzed. since as we know that in enzymatic reactions, majority of the reactants are catalyzed via the different combination of the enzyme given at hand (available enzyme). therefore, the selectivity of the catalyst is determined by the synthesis of the enzymes. however, keep in mind that you may also add other factors to higher the activation energy along with the enzymes, this would be by adjusting other factors such as temperature or the pH value perhaps to an optimum value that would be favorable for that reaction. :-)