Where did mitochondria come from?

Mitochondria are a fascinating organelle, which we, as humans, rely on for so much. They are where the electron transport chain occurs, where ADP is converted to ATP with the high-energy bond we utilise everywhere in the body. But what if I told you those mitochondria may not be a truly eukaryotic organelle?

Mitochondria can divide independent of their host; this is because they have their own genome. No other organelle, in humans anyway, can do this. Even more interesting is that if you look at the mitochondrial DNA it is frighteningly similar to some bacterial DNA from which it is thought to derive from.

So where did it come from?

The truth is that nobody really knows, although there are some theories. The  endosymbiosis hypothesis suggests that the function of mitochondria was beneficial to humans and the human host was also beneficial to the mitochondrion. 

If this is an evolutionary process, what is next?

Whilst I can't answer that, I can suggest following on from the endosymbiosis hypothesis. Further research has proven that not all of the mitochondrial proteins required for ATP synthesis are present in the mitochondrial genome; these proteins have relocated to the cell's genome. What I would suggest is that perhaps, over a long period of time, more and more of the once-mitochondrial proteins will relocate to the cell's genome until one day the cell can produce all of the proteins required for the mitochondria's function.