The spotted hyena's reproductive system is extremely unusual in that that externally there seems to be no difference between males and females. Specifically, a female hyena's genitals resemble a male's to the point that unless a hyena is suckling cubs (and is therefore female), it is not possible for the untrained observer to tell the two sexes apart. More specifically:

• The labia (vaginal lips) of the female hyena have grown together and are backed with pads of fat, making them look like a male's scrotum;
• The clitoris of the female hyena has hypertrophied (that is, grown over-sized) to the point it looks like a male's penis, and a large one at that;
• Through muscle control, the female hyena can extend and make rigid her clitoris, mimicking a male's erect penis.
• A urogenital canal runs down the center of the clitoris through which the female urinates, like the male. It is also through this canal that the female takes the male's penis during sex, and through which her cubs pass at birth.

While there are visual cues wildlife biologists working in the field use to sex hyenas-for example, the female's clitoris is thick and terminates in a rounded and blunt tip while the male's penis is thin and terminates in a sharp and wedge-shaped tip-experience and training are required to employ them with any degree of success, and even the most experienced researchers will make an incorrect call at times.

The female hyena's mimicry of male sexual organs has severe consequences for the sexual and reproductive life of the spotted hyena:

1. Sex is difficult for spotted hyenas because of this strange anatomy. With the vagina closed off by the pseudo-scrotum, the male must fumble to find the tip of her clitoris. To assist the male, the female can fully retract her clitoris and even widen the opening of her urogenital canal, but it is still several centimeters forward and above where the vagina would be, and on her underside, not her rump. The male must maintain the longest and hardest erection he can to achieve insertion-and that through blind fumbling. Worse, once entry is achieved, in addition to having his penis as far forward as possible, he must point it upwards in order to thrust.
2. If sex is bad for the male, birth is worse for the female and potential cubs. The birth of the first cub will tear the clitoris, causing an injury that takes weeks to heal-provided it doesn't kill the mother. Estimates of death from first childbirth run about 10%. The injury and scar widen the birth canal, so subsequent births are easier, but there is still a high rate of death from asphyxiation for cubs at birth when labor times are long.

Why hyenas have such a strange and hazardous reproductive system is unknown. It is thought that some it conferred some evolutionary advantage to the species, but what that advantage is or might have been is currently a subject of debate among scholars studying the spotted hyena.