All multicellular creatures interact with bacteria, but some have taken the relationship to another level with highly specialized structures that house, feed, and exploit the tiny organisms.
Evolution needn’t make improbable leaps to facilitate transitions into uncharted biological territory. Adapting new uses for existing structures works just fine.
Neanderthal extinction; eradicating polio; virus takes down massive algal bloom; receptor behind the hummingbird’s sweet tooth; legal threat for PubPeer; price tag of scientific fraud