For a long time I've just accepted, because it is just what everyone told me, that mitochondria became organelles in the cell when they were "engulfed" by another cell which acted like it's host. This is the endosymbiotic hypothesis.
"The endosymbiotic hypothesis suggests mitochondria were originally prokaryotic cells, capable of implementing oxidative mechanisms that were not possible to eukaryotic cells; they became endosymbionts living inside the eukaryote."
However, recently I looked at the wiki entry on mitochondria and saw there that it lists two main hypothesis, endosymbiotic and autogenous.
"In the autogenous hypothesis, mitochondria were born by splitting off a portion of DNA from the nucleus of the eukaryotic cell at the time of divergence with the prokaryotes; this DNA portion would have been enclosed by membranes, which could not be crossed by proteins."
It also states that, given that mitochondria have some striking similarities to bacteria, the most parsimonious hypothesis for mitochondrial evolution is that of endosymbiosis. (This question here deals with some aspects of multiple-occurence/convergent endosymbiosis).
My questions are;
How strong is the evidence for either of these leading hypotheses (perhaps there is a review article)? Is there evidence that is overwhelmingly in favour of endosymbiosis?
Further, are there any other (plausible) hypotheses to explain the origins of mitochondria (with or without supporting evidence)?