Every individual in this whip-tailed lizard population is female - genetically the same female. Every time they lay eggs, a clutch of new female clones is born. The lizards live in the deserts of Arizona and New Mexico, and must be perfectly adapted to their surroundings. As a result, they don’t want their good genes diluted by the involvement of males. The females have opted to hang on to their favourable genes and have driven the males to extinction. But the ghost of the male haunts their life nevertheless. Near laying, all the virgins need the stimulation which a male would provide to make them ovulate. With none around, the role is played by a female. In every sense she apes being a male. Driven by a surge of the male hormone testosterone, she temporarily forsakes her true gender - and goes through the motions of copulating.