Mitochondria (the famous powerhouse of the cell) is a symbiotic bacteria that became so entangled with our cell that neither can now live without the other. Sorry to everyone who knows, in some regions this is not common knowledge. Knowing this makes your life immensely better because it's such a cool fact.
Mitochondria is basically a bacteria that got stuck in our cells and found a symbiotic function inside us. Fun fact: the mitochondria has its own DNA and is used in lineage tracking.
The mitochondrion apparently turns out to be a relative of the bacterium that causes typhus. At some point, an intracellular parasite evolved into an intracellular symbiote.
And the first children conceived with 3 parents happened relatively recently. Genetics from traditional mum and dad and another set of mitochondrial DNA from another donor.