 Of particular note is the revelation that the male-typical sexual behaviors which parthenogenetic females display turn out to be under the control of the postovulatory surge of progesterone rather than androgen, which the parthenogens do not produce.This discovery in the parthenogenetic lizard led Dr. Crews to extend his work to genetically-modified mice and rats, demonstrating that progesterone is not a “female-specific” hormone but plays a critical role in sexual behavior in males.Indeed, Crews demonstrated that androgen and progesterone synergize in males to control copulatory behavior much as estrogen and progesterone synergize in females to facilitate sexual receptivity.