The children, born using IVF that replaces a mother's damaged mitochondrial DNA with a donor's, show no signs of disease.

Mitochondria are responsible for producing and providing energy to our bodies, especially in organs such as the heart, brain, and muscles, which require high-energy production. These organs ...

On the other hand, if evidence was found for a way that a simple archaeal cell could acquire an endosymbiont, that would make the “mitochondria early” hypothesis more plausible.

Scientists believe that mitochondria evolved from an ancient collaboration that came about when cells with nuclei engulfed oxygen-dependent simple cells that lacked a nucleus.

This paper finds that healthy mitochondrial complexes can be delivered to the livers of living rats through simple intravenous injection. The team harvested mitochondria from mouse specimens.

So, the function of the mitochondrial remnant remains unclear at this point. But it is possible to speculate how this ended up being the only known animal species without functioning mitochondria.