FIGURE 1.

Comparison of the ecological-community view (A) and the individual view (B). The blue dashed arrows represent ecological interactions, but not considered from an evolutionary perspective (A), whereas the red arrows represent the evolutionary aspect of these interactions (B). The bacteria stand for hypothetical strains in the cow rumen. In the ecological-community view, herbivory is seen as the result of an ecological interaction, and thus its evolutionary basis does not need to be studied. The individual view, on the contrary, requires studying the evolutionary history of herbivory to unmask the traits of the microbiome that have evolved to make it possible. The red dots in each of the bacterial strains in (B) represent traits that have evolved specifically for herbivory, and thus reveal a hologenomic evolutionary history, being most likely fortuitous benefits (rather than etiological adaptations) of the bacterial strains that bear them.