ctothel t1_irdn77l wrote

If I understand your question, mitochondria are probably responsible for us existing at all. The partnership between our cells and theirs granted the energy required to become multi-cellular, and to start increasing the size of the genome.

It takes energy to copy a gene, and more genes require more energy. Oxygen is much more efficient energy source for cells than the alternatives.

There’s also a theory that having a separate set of genes that handled energy means the host cell didn’t need to worry about that bit, which allowed both us and our “powerhouse” to adapt more quickly and effectively to our environment.


ctothel t1_ir9pzms wrote

It doesn’t really make sense to look at a species that’s alive today and think of it as the last common ancestor of two branches, because that species has been changing as well (even if not very much).

Plus, given we don’t have chloroplasts but the Euglena does, it might be safe to assume it split off the branch that would eventually form plants after we did. Unless we once had chloroplasts but got rid of them, but I haven’t heard that theory.

But it seems as though the Euglena split off quite early, yes.


ctothel t1_ir9kdyg wrote

To be clear, mitochondria were once separate organisms, which had evolved to process oxygen for their energy.

Our single-called ancestors probably got energy from hydrogen, or from fermentation, but one of them engulfed a mitochondria (actually, an ancestor of what we call mitochondria) and was then able to use the energy produced by it.

When that cell divided, the mitochondria divided too, going along for the ride. This line of symbiotic cells was very successful, and is the ancestor of all plants and animals.

The exact same thing happened on a sub branch of this line, but with the cell also incorporating a kind of photosynthetic bacteria we now call chloroplasts. This sub branch evolved into plants.

Both chloroplasts and mitochondria have their own separate DNA that has nothing to do with ours. They are literally separate organisms that make up part of our cells.