The Origins of Endosymbionts

Leid author Eric Libby believes that this probably has to do with metabolism. Scientists have been wondering if this type of endosymbiont is so awesome, why aren't we seeing it happening today with the many prokaryotic cells that still exist? Leid: Could this new cell survive in a changing environment and not go extinct? And then they looked at evolvability - could you garner enough favorable mutations to adapt)?