How a lot of eukaryotic organelles (not just the mitochondria) came from cells eating bacteria and holding onto it instead of digesting it. Cells don’t have consciousness and can’t just “decide” to not digest something because it’s useful to have around, it was probably the digestion mechanism not working properly, which normally would have decreased the cell’s fitness, but in a few rare occurrences the thing it didn’t digest was so useful it greatly increased the cell’s fitness.
How a lot of eukaryotic organelles (not just the mitochondria) came from cells eating bacteria and holding onto it instead of digesting it. Cells don’t have consciousness and can’t just “decide” to not digest something because it’s useful to have around, it was probably the digestion mechanism not working properly, which normally would have decreased the cell’s fitness, but in a few rare occurrences the thing it didn’t digest was so useful it greatly increased the cell’s fitness.