In a group of bark lice, a penis has evolved twice — in the females. In their nutrient-scarce environment, 'seminal gifts' are an incentive for females to force mating, leading to the co-evolution of female penises and male vaginas.
In a group of bark lice, a penis has evolved twice — in the females. In their nutrient-scarce environment, 'seminal gifts' are an incentive for females to force mating, leading to the co-evolution of female penises and male vaginas.