The bullhorn acacia produces soft thorns that don't deter predators, but do make an excellent home for the acacia ant, whose toxic bite deters predators & who will defoliate other trees that shade out the bullhorn acacia.

The two species are co-evolved, so that each benefits (and in fact requires) the other.

So if viruses are real and rapidly evolve, why is there never co-evolution? Why do people get (almost) exactly the same influenza symptoms for a century? Why do ancient plagues supposedly still occur?