Experts discovered that female penises evolved twice in a group of female bark lice, the female bark lice received the male gifts in their nutrient deprived environment. Through it, the females are forced to mate, which leads to the development of male vaginas and female penises.

Based on the study at Hokkaido University performed by Professor Kazunori Yoshizawa, South America’s Neotragla bark lice and South Africa’s Afrotrogla bark lice have both evolved functional penises in their females.

The Neotragla females did not have anchoring spines, which are usually found in other species. Researchers said that this may be caused by the group’s dry environment, which did not encourage rivals. The spines were not needed because the mating was not usually disturbed at all.

The hypothesis links specific environments, penile evolution, and selection pressures. Yoshizawa also said that the study of female penises may bring light to the development of the male penises.