Male intromittent organs are exceedingly diverse, yet we know comparatively very little about female genital diversity. Previously it has been suggested that female genitalia are not very variable, and therefore little effort was dedicated to their study. However, the most direct mechanical interaction between males and females occurs during copulation, and therefore genital coevolution is expected to be widespread. Recent studies that have used more modern morphological and morphometric approaches have found that female genitalia can indeed be quite variable, and female genital adaptations, have been reported in many taxa. These adaptations can be very dramatic, for example in waterfowl, where an evolutionary arms race resulting from sexual conflict over mating has resulted in very obvious morphological changes in female vaginas. Female adaptations can also be subtle and involve physiology and behavior, such as in garter snakes, where females body roll and squeeze their vagina to limit copulation duration and copulatory plug formation. Though studying female genital morphology and function is undeniably challenging, knowledge of female genital morphology and function are absolutely crucial to our understanding of diversity in morphology of the male intromittent organ.