Scientists Re-Create the Conditions That Sparked Complex Life

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.

The original version of this story appeared in Quanta Magazine.

Far from being solo operators, most single-celled microbes are in complex relationships. In the ocean, the soil, and your gut, they might battle and eat each other, exchange DNA, compete for nutrients, or feed on one another’s by-products. Sometimes they get even more intimate: One cell might slip inside another and make itself comfortable. If the conditions are just right, it might stay and be welcomed, sparking a relationship that could last for generations—or billions of years. This phenomenon of one cell living inside another, called endosymbiosis, has fueled the evolution of complex life.

Examples of endosymbiosis are everywhere. Mitochondria, the energy factories in your ...