Endosymbiotic theory of mitochondrial origin

The endosymbiotic theory of mitochondrial origin is an endosymbiotic theory that has been proposed to explain the evolutionary origin of the mitochondrion, an organelle found in most eukaryotic cells. The theory briefly states the following: mitochondria are evolutionary descended from endosymbionts in the eukaryotic cells that were independent living organisms (bacteria). The symbiotic relationship was as follows: the endosymbionts performed aerobic respiration for the cell, and in turn, the cell gave them food and sustenance.

The theory was proposed by the biologist Lynn Margulis and is also termed the Lynn Margulis hypothesis.