Figure 2

Two stages of proposed origin of eukaryotes. A) Pre-specialization close association. Three species closely associating because of respiratory energetic benefit, but maintaining independent nutrient uptake, respiration, DNA, RNA, and protein functions. B) Later stage in which cells have specialized to perform certain life functions (i.e., are obligate symbionts: left cell, protein factory; right cell, DNA repository/RNA factory; bottom cell, respirer), in which cell wall expression is regulated (and would be absent during symbiotic portions of existence, dashed outer large circles), but before internalization of any entity and while each still produces separate offspring. “H⁺ DNA” and “H⁺ RNA” represent the genetic material and abilities the respiratory symbiont maintains. In both panels small double-circled entities with outward pointing arrows represent offspring.