Linked from
The 15 pages that link to Primary endosymbiosis, each with the reason it gives.
PlastidRelated: This event established the first plastids in eukaryotic lineages.
PlantRelated: It explains the origin of chloroplasts in the lineage containing plants.
GlaucophyteRelated: It explains how glaucophytes acquired plastids from a cyanobacterial ancestor.
Plastid DNABroader topic: This event established the ancestral plastid genome in eukaryotes.