The spotted hyena (Crocuta crocuta) has long been the subject of confusion and folklore due to the remarkable appearance of the female’s external reproductive anatomy. Observers speculated that the species was capable of sex change or possessed the organs of both sexes simultaneously. The unique morphology of the female’s genitalia closely resembles that of the male, challenging traditional understanding of mammalian sexual dimorphism. This scientific puzzle involves a complex interaction of hormones and anatomy, making the female hyena a biological outlier.
Defining Hermaphroditism and the Hyena Answer
The question of whether hyenas are hermaphrodites is answered simply: no. True hermaphroditism describes an organism that possesses both functional male and female reproductive organs, producing both sperm and eggs. This phenomenon is common among invertebrates, such as snails and earthworms.
The female spotted hyena is physiologically female, possessing fully functional ovaries that produce only eggs. They are gonochoric, meaning they are distinctly one sex or the other. The confusion stems entirely from the external appearance of the female’s urogenital structures, which mimic the male’s anatomy.
The Female Pseudo-Penis and Pseudo-Scrotum
The female’s highly modified clitoris, known as the pseudo-penis, is the anatomical feature responsible for the species’ reputation. This structure is significantly elongated and is almost indistinguishable from the male’s penis, capable of full erection during social displays and dominance rituals. The pseudo-penis is traversed by the urogenital canal, a tube through which the female must urinate, copulate, and give birth.
The labia are fused to form a sac-like structure that closely resembles a scrotum, known as the pseudo-scrotum. This formation contains fatty and connective tissue, completing the illusion of male genitalia. The female hyena lacks an external vaginal opening.
The physical resemblance is so close that sexing a spotted hyena in the field is nearly impossible. The female’s phallus is about 90% the length of the male’s, demonstrating a high degree of masculinization. Mating is awkward, requiring the male to execute a specific, submissive maneuver to align his penis with the female’s retractable pseudo-penis.
Hormonal Basis for Female Masculinization
The female hyena’s unique anatomy develops due to exposure to high levels of male hormones during gestation. Female spotted hyena fetuses are exposed to concentrations of androgens, such as androstenedione and testosterone, comparable to those found in males. This hormonal environment drives the masculinization of the external genitalia.
The elevated androgens originate from a complex biological cascade involving both maternal and placental hormone production. Unlike in other mammals, the hyena placenta is highly active, converting precursor hormones into potent androgens. Furthermore, the hyena’s Sex Hormone-Binding Globulin (SHBG) results in lower concentrations in the bloodstream.
Lower SHBG means more biologically active, unbound androgens influence the developing female fetus, leading to changes in the clitoris and labia. This hormonal exposure is also linked to the female’s social dominance, as adult females are physically larger and more aggressive than males. The masculinization of the genitalia is a byproduct of the selective pressure for highly aggressive, dominant females.
Reproductive Challenges Caused by Unique Anatomy
The trade-off for the female hyena’s social dominance is a difficult reproductive process. Since the female must mate and give birth through the narrow pseudo-penis, copulation requires her full cooperation, which prevents forced mating. The most significant consequence, however, is the difficulty of parturition.
The urogenital canal is narrow, measuring as little as one inch in diameter. Hyena cubs are large relative to the mother’s weight, making the birth process traumatic. During the first birth, the rigid tissue of the clitoris must tear open to allow the cubs to pass through.
This tearing can result in severe blood loss, infection, and a high mortality rate for first-time mothers, estimated around 20%. Cub mortality in first litters can reach 60% due to suffocation in the narrow birth canal, imposing a costly reproductive burden despite the tissue healing for subsequent births.