Drosophila bifurca is a species of fruit fly. Males of this species are known to have the longest sperm cells of any organism on Earth—5.8 cm long when uncoiled, over twenty times the entire body length of the male. Such sperm gigantism is thought to have evolved via a Fisherian runaway process, with a genetic link between sperm length and the length of the female seminal receptacle (sperm-storage organ) length, combined with an increasing competitive advantage of longer sperm as the seminal receptacle evolves to be longer.