I tend towards the argument that one of the greatest filters in the universe was how a single cell organism some how took in another cell organism and instead of consuming it the organism integrated it, hence our mitochondria. That leap in evolution we found took billions of years AFTER life emerged on earth when life itself we see almost took off as soon as it was possible on this planet. But that leap from single cell to multicellular life I think is a rare thing in the universe. Like why didn’t that single cell organism just consume that other single cell organism like it did for BILLIONS of years but instead integrate it where it would start making energy for them.,(reply>), Natural selection