Endosymbiotic hypothesis

The hypothesis used to explain the origin of certain cellular organelles, specifically mitochondria and chloroplasts. Early in the course of terrestrial life, all cells were prokayrotes. It is hypothesized that at some point, endophagocytosis occurred whereby one bacteria "hijacked" the energy producing potential of another by engulfing a respiring or photosynthesizing bacteria. Mitochondria and chloroplasts are the only organelles to contain their own DNA (other than the nucleus, which contains the DNA for the entire cell) and their DNA is well-conserved enough that they appear to be nearly separate organisms. DNA and RNA analyses have borne out much of this hypothesis. Further evidence supporting mitochondria and chloroplasts being endosymbionts lies in the fact that both organelles have plasma membrane bound spaces inside of their outer membranes, something no other organelle possesses.

Alternate hypotheses are that eukaryotic and prokaryotic cells were simply designed as they are. This is, of course, neither testable nor falsifiable. Creationists cite the perceived lack of evidence of the hypothesis. Most valid complaints of the hypothesis will offer opposing, falsifiable analysis.