The sex lives of male marine iguanas on the Galápagos Islands can be extremely trying. Females mate only once per season, with one male, so the competition among males is intense. Typically, copulating males are disturbed by one to four rivals. If the mating male is large, the disturbances rarely result in a separation before ejaculation. But almost a third of all small male lizards are torn away from their mate before they finish. Martin Wikelski, a zoologist at the University of Washington, has found that these abused males have evolved a unique reproductive strategy: at the sight of a female, they freeze in copulatory poses and ejaculate. The ejaculate from this masturbation is stored in a pouch near the base of the tail and remains viable for more than a day. The male then darts after a female--either the same one that excited it or a different one-- bites her on the neck, and inserts the stored ejaculate before beginning a new round of copulation. If a big male drags him off before the crucial moment, the prepared semen of the smaller male has already been deposited and the larger lizard won’t get to mate. I guess natural selection just selected for those that somehow get excited when females pass by, says Wikelski, It gives a signal to the brain that something’s going on, makes the animal really excited and leads to pre-ejaculation.