Lots of coevolution. Think about how dependent animals are on plants - not just for food but for oxygen. And plants have coevolved with Cyanobacteria symbionts to the point where we don’t even recognize chloroplasts as independent organisms…jammed into the cell with another co-evolved endosymbiont, the mitochondrIon. Co-evolution with bacterial microbiome partners provides help preventing infections in animals, and bacteria in the digestive tracts of ruminants allows them to digest cellulose.