Biology

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 cells, were once free-living bacteria. Photosynthetic plants owe their sun-spun sugars to the chloroplast, which was also originally an independent organism. Many insects get essential nutrients from bacteria that live inside them. And last year researchers discovered the “nitroplast,”(opens a new tab) an endosymbiont that helps some algae process nitrogen.