The "false penis", which is actually a fusion of the clitoris and labia of the vagina, seems to be used in dominance displays and to indicate aggression and willingness to fight. Female hyenas dominate over males in many cases, and they behave in the way that male wolves do when establishing pack heirarchy: they often "mount" subordinate animals, and an "erection" indicates they are confident of being able to take on a challenger in a fight. Their rather unique genitalia, and the accompanying high levels of "male" hormones, is probably very much connected to their social order and dominance structure. As with wolves, usually only the dominant one or two hyenas in a pack breed in a year. Levels of testosterone are connected to dominance and aggression; and it is likely that the most "male-like" of the females were traditionally the ones that fought their way to the top of the pack, and thus bred. Over the generations this would have selected females closer and closer to the male model, until they became more "male" than the males. This said, it is not without cost. The first pups a hyena female has have to rip the psuedo-penis open in order to be born; these pups are almost invariably suffocated during the process, and it is not unknown for the hyena mother herself to sustain too much trauma and die of it.