Evolution was fueled by endosymbiosis, cellular alliances in which one microbe makes a permanent home inside another. For the first time, biologists made it happen in the lab. Endosymbiotic relationships between two microbes, with one living inside the other, underlie cellular complexity across the tree of life. Until now, no one has observed the opening choreography of such a partnership’s formation. Kristina Armitage/Quanta Magazine Introduction Far from being solo operators, most single-celle...