A suggestion to give wild critters mutations within their own branches or (a smaller chance of mutations within) a similar one.
As the zombies evolve because of ‘blob’, the wolves, the mooses, the ants, the wasps, are all stagnant. The player evolves, by getting better gear and better skills, and even with bionics and forced mutations of their own.
So, if wild animals slowly ‘evolved’ and fortified their own traits they would become better attackers, or withstand more attacks, or have their night vison improved, or become more aggressive, or even more amicible to other factions.