The endo-symbiotic theory was given by Lynn Margilus in 1967 which explained the origin of complex eukaryote from simple prokaryotes.
The endosymbiotic theory stated that a eukaryote became complex after the ingestion of prokaryotic cells which became permanent which proved useful to each other.
The presence of mitochondria is evidence supporting the endosymbiosis which is thought to have evolved from a prokaryotic chemosynthetic bacteria in past.
