I understand that mitochondria was once autonomous before becoming organelles. If this was the case for bacteria, could an animal do the same? Given the right circumstances, could an animal become one with another’s anatomy? Also, is this process reversible; could we turn mitochondria back into their primordial selves?
Some parasites come pretty close: the ones that can only live inside an organism. Certain types of mutual symbionts also come close, so I think it might be possible for that to happen. By now, I think mitochodriae are so modified from their original state that it would take prohibitively long (hundreds of millions of years) to return them to something close.