Color in living organisms can be formed two ways: pigmentation or anatomical structure. Structural colors arise from the physical interaction of light with biological nanostructures. A wide range of organisms possess this ability, but the biological mechanisms underlying the process have been poorly understood.

It’s been more than 50 years since scientists discovered that the single-celled organism Tetrahymena thermophila has seven sexes. But in all that time, they’ve never known how each cell’s sex, or “mating type,” is determined.