"These are all lifestyles that exist in bacteria anyway. ...Photosynthesis obviously. The only eukaryotic lifestyle that does not exist at all in bacteria is ... the ability to engulf other cells, to grow around them. That's never been found yet in bacteria. It seems to require... a lot of energy, a large complicated system capable of changing shape and moving around. ...For whatever reasons it never evolved. I would say the reason was that you need mitochondria to get that large and complex in the first place."