Editing Pathogen transmission (section)

===Mixed-mode transmission===

Many microbial symbionts, including [[Gut flora#Acquisition of gut flora in human infants|human microbiota]], can be transmitted both vertically and horizontally. Mixed-mode transmission can allow symbionts to have the "best of both worlds" – they can vertically infect host offspring when host density is low, and horizontally infect diverse additional hosts when a number of additional hosts are available. Mixed-mode transmission make the outcome (degree of harm or benefit) of the relationship more difficult to predict, because the [[Fitness (biology)|evolutionary success]] of the symbiont is sometimes but not always tied to the success of the host.<ref name="auto"/>