Fig. 7.

The endosymbiotic theory of the origin of mitochondria and chloroplasts. Mitochondria arose from engulfed bacteria that were initially taken in and digested for their nutrients. During evolution, the ingested bacteria developed a symbiotic relationship with the host cell and evolved into mitochondria. Likewise, photosynthetic bacteria were also taken in as food but eventually evolved to form chloroplasts. Since, the ingested bacteria (which formed both mitochondria and chloroplasts) produced melatonin, we proposed this function was retained such that in current day animals and plants, both mitochondria and chloroplasts retain the ability to produce melatonin. Emerging evidence supports this assumption.

Reprinted with permission from Manchester et al. [13]